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Gastrointestinal Neuroendocrine Tumors and The Carcinoid Syndrome

ABSTRACT

 

Neuroendocrine neoplasms originating from the gut are increasingly diagnosed as a result of the rise in radiological and endoscopic procedures, improved pathological classification, and likely an increase in true incidence. The diffuse neuroendocrine gastrointestinal system can trigger cancer formation into a wide variety of neoplasm subtypes, ranging from well-differentiated tumors to poorly differentiated carcinomas. All gastrointestinal neuroendocrine neoplasms have the potential to metastasize and ultimately impair patient survival. In recent years, changes have occurred in the pathophysiological understanding, nomenclature, pathological grading, molecular imaging, and management options for these neuroendocrine neoplasms. This chapter will focus on well-differentiated neuroendocrine tumors of gastrointestinal origin, which find their origin at separate primary locations, all characterized by their specific clinical behavior. A minority of patients suffer from hormonal syndromes due to the secretion of peptides or amines from the neuroendocrine tumor. The carcinoid syndrome is the quintessential hormonal syndrome in gastrointestinal neuroendocrine tumors, particularly those of midgut origin. Patients suffering from the carcinoid syndrome have a reduced survival and quality of life, due to debilitating symptoms of flushing and diarrhea as well as fibrotic complications. We provide an overview of the background of gastrointestinal neuroendocrine tumors as well as the carcinoid syndrome and discuss the diagnostic pathways as well as treatment possibilities for patients presenting with this disease.

 

INTRODUCTION

 

Enteroendocrine cells constitute approximately 1-2% of all cells within the gastrointestinal tract. Quite similarly, neuroendocrine neoplasms (NEN) of the digestive tract form 1-2% of all malignancies in this organ system. When grouped together with pancreatic NEN (panNEN), gastroenteropancreatic (GEP) NEN are the second most common malignancy in the gut, surpassing esophagus, gastric, and pancreatic carcinomas in incidence rates (1). These tumors can arise anywhere along the primitive gut, but are most commonly detected in the small intestine or rectum. Based on histology, NENs are grouped into well-differentiated neuroendocrine tumors (NET) and poorly differentiated neuroendocrine carcinomas (NEC) (2). The former group was previously termed carcinoid tumors, based on the original observation by Siegfried Obendorfer (1876-1944) in 1907 that NETs of the small bowel displayed “carcinoma-like” or “carcinoid” features (3). As this term has led to the common misconception that carcinoid tumors are benign or always indolent, current correct nomenclature of this gastrointestinal malignancy solely uses the term NEN.

 

This chapter focuses on the clinical features, diagnosis, and management of the different well-differentiated NET along the gastrointestinal tract. The reader is referred to chapter “Diffuse hormonal systems” for lung NEN (4), where well-differentiated tumors are still termed typical or atypical carcinoids, and to chapter “Pathophysiology and treatment of pancreatic neuroendocrine tumors” for panNEN (5).

 

EPIDEMIOLOGY

 

NEN are historically considered a rare cancer type with an incidence of all subtypes combined of 5-10 per 100,000 persons per year (6). Two registry studies have shown that the incidence of NEN is rising several fold over the last decades. In the United States of America, NEN incidence increased 6.4-fold from 1.09 to 6.98 per 100,000 population per year between 1973 and 2012 (7), while in the United Kingdom rates rose 3.7-fold from 2.35 to 8.61 per 100,000 population per year between 1995 and 2018 (8). Within the GEP subtypes, small intestinal, pancreatic, and rectal NEN are most prevalent and have seen the clearest rising incidence rates. Part of the increased detection rate is caused by the rise in the absolute number of endoscopy procedures and radiological imaging, shifting the diagnosis more often towards incidentalomas. On the other hand, increased awareness among pathologists and improved classification likely also plays a role. The striking rise of NEN incidence compared to the stable incidence of all other malignant neoplasms in recent decades (7, 8) might suggest that a currently unknown epigenetic or environmental risk factor could stimulate NEN carcinogenesis.

 

The combination of increased detection as well as improved survival leads to an overall increase in NEN prevalence. The recent epidemiological data in the United Kingdom (8) suggest that NEN should not be considered a rare form of cancer anymore, as it comprised the 10th most prevalent cancer.

 

PATHOPHYSIOLOGY

 

Much is unknown about the pathogenesis of gastrointestinal NET (9). Besides the driver function of gastrin in two subtypes of gastric NET (see below), the causative factors for NET formation in the gut remain elusive. Genetic mutations have been identified as driving carcinogenesis across a wide array of malignancies, but – even in late, advanced stages of disease – NET remains among the tumor types with the lowest amount of tumor mutational burden or driver mutations (10). Contrarily, NEC show a high tumor mutational burden with gene mutations in well-known oncogenes or tumor suppressor genes, such as TP53, KRAS, RB1 (11). Dedicated studies of small intestinal NET genotypes with next generation sequencing have failed to detect prevalent mutations. The most commonly mutated gene in small intestinal NET, CDKN1B encoding cyclin-dependent kinase inhibitor p27, was found to be mutated in 10% of cases (12). Germline mutation in CDKN1B also cause the rare endocrine tumor syndrome multiple endocrine neoplasia type 4 (MEN4), which predisposes to the occurrence of gastric, duodenal, and pancreatic NET among other tumor types (13). Whole genome sequencing of synchronous multifocal small intestinal NET also failed to detect common genetic drivers, but instead observed clonal independency of tumors within individuals (14). No clear driver mutations have been identified for the other subtypes of gastrointestinal NET as well. Multiple endocrine neoplasia type 1 (MEN1) is besides primary hyperparathyroidism and pituitary NET primarily associated with the occurrence of pancreatic, bronchial, and thymic NET (15). However, duodenal NET can also arise within the context of MEN1 and these have a predilection to secrete gastrin, leading to gastrinoma or Zollinger-Ellison syndrome. This in turn stimulates secondary gastric NET formation (16). A genome-wide association study of 405 patients compared to more than 600,000 control subjects in two cohorts revealed an association between the occurrence of small intestinal NET and single nucleotide polymorphisms in 6 genes (17). The most interesting locus was of a missense mutation in the intestinal stem cell factor LGR5, suggesting a role for aberrant cellular differentiation in the development of small intestinal NET. Contrary to DNA mutations, chromosomal aberrations are prevalent in gastrointestinal NET. For small intestinal NET copy number variations have been frequently detected. The most prominent observed change is loss of chromosome 18 in up to 70% of cases, followed by losses in chromosomes 9, 11 and 16 and gains in chromosomes 4, 5, 14 and 20 (18). Whether these changes have a causative role in the development of small intestinal NET is currently unknown.

 

Due to the lack of obvious DNA changes contributing to NET pathogenesis, studies have investigated the role of epigenetics, e.g. changes to the chromatin that affect gene transcription without changing the DNA code (19). In the largest study to date in 97 patients with small intestinal NET, integrated genetic, epigenetic, and transcriptomic analysis detected 3 molecular subtypes, that differed in their survival outcome (20). DNA methylation analysis found that small intestinal NET were highly epigenetically dysregulated. The prognostically favorable molecular subgroup was associated with loss of chromosome 18, while another subgroup displayed no copy numbers alterations. NET in the molecular subgroup with inferior survival outcome displayed multiple copy number variations.

 

Because of the link between enteroendocrine cells and the bowel content, there have been speculations on carcinogenic factors in the bowel content. This could include but is not limited to dietary factors, microbial species, and microplastics. Further research is needed before a clear role can be identified for these factors.

 

COMMON FEATURES

 

NET of the gastrointestinal tract share many features owing to their collective origin from enteroendocrine cells. Originally described as APUD (amine precursor uptake and decarboxylation) tumors or APUDomas by Anthony Pearse (1916-2003) these neoplasms retain the potential to produce and secrete several hormonal substances in the form of amines and peptides (3, 21). These secretagogues are stored in intracellular dense-core secretory granules, which are released upon fusion with the plasma membrane. Gastrointestinal NET, like other types of NET, express markers specific for their neuroendocrine phenotype. The two most prevalent markers, synaptophysin and chromogranin A, form the basis for a immunohistochemical diagnosis of a NEN cell (22).

 

Stage

 

Similar to other cancers, NET are staged according to the TNM classification, which signifies key therapeutic and prognostic information (2), Table 1. Whereas stage I and II indicate local disease confined to the presence of the primary tumor (T1-4 N0 M0), stage III signifies the presence of regional spread to lymph node metastases (T1-4 N1 M0). Distant metastases (T1-4 N0-1 M1) are classified as stage IV disease.

 

Table 1. TNM staging of gastrointestinal neuroendocrine neoplasms according to the 8th edition of the AJCC Cancer Staging Manual (2018)

 

Stomach

Duodenum

Small intestine

Appendix

Colon and rectum

Tx

Primary tumor cannot be assessed

T0

No evidence of primary tumor

T1

Invades the lamina propria or submucosa and is ≤ 1 cm in size

Invades the lamina propria or submucosa or confined within the sphincter of Oddi and is ≤ 1 cm in size

Invades the lamina propria or submucosa and is ≤ 1 cm in size

Tumor ≤ 2 cm in size

Invades the lamina propria or submucosa and is ≤ 2 cm in size

  T1a

 

 

 

 

Tumor ≤ 1 cm in size

  T1b

 

 

 

 

Tumor > 1 and ≤ 2 cm in size

T2

Invades the muscularis propria or is > 1 cm in size

Tumor > 2 but ≤ 4 cm in size

Invades the muscularis propria or is > 2 cm in size

T3

Invades into the subserosa

Growth into the pancreas or peripancreatic adipose tissue

Invades into the subserosa

Tumor > 4 cm in size or invades into the subserosa or mesoappendix

Invades into the subserosa

T4

Invades into the (visceral) peritoneum or adjacent organs or structures

Nx

Regional lymph nodes cannot be assessed

N0

No regional lymph node metastasis has occurred

N1

Regional lymph node metastasis

Regional lymph node metastasis in < 12 nodes

Regional lymph node metastasis

 

N2

 

 

Large mesenteric masses (> 2 cm) or extensive nodal deposits (≥ 12)

 

 

 

 

M0

No distant metastasis

M1

Distant metastasis

M1a

Metastasis confined to liver

M1b

Metastasis in at least one extrahepatic site (e.g., lung, ovary, nonregional lymph node, peritoneum, bone)

M1c

Both hepatic and extrahepatic metastasis

 

 

 

 

 

 

 

 

Stage I

T1 N0 M0

 

Stage II

T2-3 N0 M0

 

 

Stage IIA

 

 

 

 

T2 N0 M0

Stage IIB

 

 

 

 

T3 N0 M0

Stage III

Any T N1 M0 or T4 N0 M0

 

 

Stage IIIA

 

 

 

 

 T4 N0 M0

Stage IIIB

 

 

 

 

Any T N1 M0

Stage IV

Any T any N M1

 

Grade

 

The biological behavior of the individual NEN is classified according to the tumor grade. NEN can display a wide array of biological behavior from generally very indolent taking years to significantly grow (e.g., appendix NET) to very aggressive inevitably leading to death (small cell lung NEC) (23). In order to predict prognosis and guide management all gastrointestinal NEN should be examined histologically for differentiation (well versus poorly differentiated), mitotic index (per 10 HPF), and ki67 index. The latter encompasses staining of the nuclear proliferation marker ki67 by the MIB1 antibody. Different grading cut-offs have been used in the past (24), but the WHO 2019 classification of digestive system tumors and 2022 classification of (neuro)endocrine tumors separate well-differentiated NET from poorly differentiated NEC on the basis of the histological phenotype (2, 25). In cases of an ambiguous entity, molecular analysis or staining of Rb1 and p53 can point towards the presence of a NEC (26).

 

NET are divided into grade 1, 2 and 3, whereas NEC by definition are grade 3. NET grading is discerned through the combination of mitotic and ki67 index, with the highest value counted (Table 2) (2, 25). Due to the differences in biological behavior, tumor grading is key to management of GI NET, especially in cases of metastatic and consequently incurable disease.

 

Table 2. Classification of gastrointestinal neuroendocrine neoplasms, according to 2022 WHO classification of endocrine and neuroendocrine tumors and 2019 WHO classification of tumors of the digestive system

Well-differentiated NEN

 

Ki67 proliferation index

Mitotes per 2 mm2

NET Grade 1

<3%

<2

NET Grade 2

3–20%

2–20

NET Grade 3

>20%

>20

Poorly differentiated NEN

Small cell NEC

Large cell NEC

>20%

>20

 

HORMONAL SYNDROMES IN NET

 

Due to their endocrine heritage, gastrointestinal NET can produce and secrete excessive amounts of hormonal substances, that can elicit clinical syndromes in patients (22). All patients presenting with a gastrointestinal NET should be examined by history taking and physical exam for the presence of a hormonal syndrome, as this has important therapeutic and prognostic consequences. In case of a suspected hormonal syndrome, appropriate biochemical analysis should be performed for the elevation of the causative hormonal peptides or amines (27).

 

Carcinoid Syndrome

 

The carcinoid syndrome is the most common hormonal syndrome encountered in gastrointestinal NET and even NEN in general. Estimations fluctuate that around 20% of patients with stage IV midgut NET suffer from carcinoid syndrome (28). It is mainly characterized by symptoms of secretory diarrhea and vasodilatory flushes. Occasionally, bronchospasms can also occur (29). In severe and long-standing cases carcinoid heart disease (CHD) can arise, characterized by plaque-like depositions in mainly right-sided heart valves and endocardium (30). Following acute stressors, some NET associated with carcinoid syndrome are able to secrete massive amounts of vasoactive compounds, leading to hemodynamic instability. This type of vasodilatory shock, also known as carcinoid crisis, can be defined as an acute onset of stressor-induced hemodynamic instability in patients with carcinoid syndrome and can be observed during the induction of anesthesia and after tumor lysis following embolization or peptide receptor radionuclide therapy (31).

 

The principal effector of carcinoid syndrome is thought to be the amine serotonin (5-hydroxytryptamine) (32), which is also secreted physiologically by several subtypes of neuroendocrine cells in the gut and lungs. A variety of preclinical and clinical studies support a central role of serotonin in the pathophysiology of carcinoid syndrome-related diarrhea and CHD, while its role in flushing in carcinoid syndrome patients is still controversial. Other hormonal substances postulated to contribute to the carcinoid syndrome include tachykinins, catecholamines, kallikrein and histamine (33).

 

Carcinoid syndrome predominantly arises in NET of midgut origin, comprised of jejunum, ileum, cecum, and ascending colon. This location specificity is presumably due to carcinogenesis within the enterochromaffin (EC) cell, which uses serotonin as its main secretagogue to communicate with the autonomous nervous system and influence bowel motility (4). This hormonal syndrome can also be encountered in bronchial NET (typical or atypical carcinoid) or NET of other origin (e.g., ovarian, pancreatic, unknown primary). Importantly, tumor seeding beyond the portal circulation is a prerequisite for carcinoid syndrome, as its causative hormones are inactivated by hepatocytes (34). For midgut NET, carcinoid syndrome thus hallmarks spread beyond locoregional disease, with liver metastases being present in more than 90% of cases. Alternatively, the tumor sites may secrete through the retroperitoneal or ovarian/testicular venous drainage, effectively bypassing the portal circulation and drain directly on the inferior caval vein.

 

The presence of carcinoid syndrome is a negative prognostic indicator, which is likely caused by its association with tumor bulk (28, 35). Within this spectrum, CHD is also associated with decreased survival in patients in univariate analyses (36). Because of these features carcinoid syndrome should be diligently investigated in all patients with NET and actively managed alongside antiproliferative therapy (see management section below).

 

Other Functioning Syndromes

 

Besides carcinoid syndrome, other NEN-associated hormonal syndromes are predominantly encountered in patients with a panNEN. Duodenal NET can in rare cases elicit hormonal syndromes that are also seen in pancreatic NET, such as gastrinoma (16), VIPoma (37), and somatostatinoma (38). Ectopic hormonal production has also been described in gastrointestinal NET in limited case reports. However, these functioning syndromes are more frequented encountered in pancreatic (ACTH, PTHrP, GHRH) or lung NET (SIADH, ACTH), see the Endotext chapter on Paraneoplastic syndromes related to Neuroendocrine Tumors (39).

 

PRIMARY NET LOCATIONS

 

Esophagus

 

Well-differentiated NET of the upper alimentary tract are extremely rare. The esophagus is a predilection place for the occurrence of NEC (40). Alternatively, mixed neuroendocrine-non neuroendocrine neoplasms (MiNEN) can be encountered in the esophagus, similar to other gastrointestinal sites. Formerly these tumors were designated as Mixed adeno-neuroendocrine carcinoma (MANEC). This aggressive tumor entity is comprised of both a NEN component (NET or NEC) as well as an adenocarcinoma component, with the latter being responsible for the prognostic outcome (2).

 

Stomach

 

The neuroendocrine cells in the stomach can give rise to several NEN subtypes, depending on the underlying pathophysiology. Central to understanding gastric NEN is the dependency of the histamine-producing enterochromaffin-like (ECL) cells on gastrin stimulation. Chronic hypergastrinemia due to several causes can lead to ECL cell hyperplasia and gastric NET formation, so called ECLoma. When an ECLoma occurs during compensatory gastrin elevations this is termed a type I gastric NET (41), accounting for 75-80% of gastric NEN. This is most commonly caused by atrophic gastritis due to antibodies against intrinsic factor or parietal cells, which is also causative for pernicious anemia. Alternatively, type I gastric NET have been described following Helicobacter pylori infection, chronic use of proton pump inhibitors, or mutations in the proton pump gene (ATP4A) and resulting hypergastrinemia (42-45). When ECLoma arise due to a gastrin-producing NET in the pancreas or duodenum (Zollinger-Ellison syndrome), these are termed type 2 gastric NET, which is responsible for 5% of all gastric NET cases. This pathology is generally restricted to patients with MEN-I and a duodenal gastrinoma (46). A well-differentiated gastric NET arising in the presence of normal fasting gastrin levels is termed a type 3 NET and accounts for approximately 15-20% of gastric NET. Some authors have proposed the rare gastric NEC as the type 4 gastric NEN (9), Table 3.

 

Table 3. Subtypes of Gastric Neuroendocrine Neoplasm

 

Hypergastrinemia, ECL cell hyperplasia

Growth

Features

Gastric NET type 1

Yes

Indolent

Secondary to atrophic gastritis, helicobacter pylori infection, proton pump inhibition or ATP4Amutation

Gastric NET type 2

Yes

Indolent

Secondary to gastrinoma (Zollinger Ellison syndrome)

Gastric NET type 3

No

Intermediate

Sporadic

Gastric NEC type 4

No

Aggressive

Sporadic

 

Biological behavior of the gastric NEN subtypes differs widely with generally indolent course for type 1 and 2 NET, which are predominantly grade 1 and can be characterized by multiplicity (47-49). Only a few metastatic cases have been reported in the literature, without clear evidence of impaired survival (50). Type 3 gastric NET and type 4 gastric NEC were previously considered as a single subtype, which was accompanied by a high rate of metastases and poor survival outcome. However, recent analyses show lower grade, metastatic potential, and better outcome of type 3 gastric NET than previously assumed (51, 52).

 

The vast majority of gastric NET is clinically non-functional, although ghrelin production has been described in NET presumably derived from gastric H cells, see Endotext chapter on Ghrelinoma (53).

 

Duodenum

 

A rare subtype of gastrointestinal NET, duodenal NET are often incidentally discovered during esophagogastroduodenoscopy (Figure 1A). They are characterized by intramural lesions which might sometimes only be visible on endoscopic ultrasound. Bleeding or ulceration is rare, but can be a presenting symptom (54). The majority of duodenal NET are localized and grade 1-2, particularly for tumors smaller than 1.0 cm. Metastatic potential increases with size and can be present at diagnosis or occur during follow-up (55, 56). Due to the nature of the neuroendocrine cells in the duodenum several hormonal syndromes can be encountered, such as gastrinoma or VIPoma. Somatostatin-expressing NET near the ampulla of Vater have been described as part of neurofibromatosis type 1 (57). Some of the larger duodenal NET cannot be effectively localized as originated from either duodenum or pancreas due to the overlapping anatomy.

 

Figure 1. Endoscopy in gastrointestinal NET. (A) Endoscopic image of a 5 mm submucosal lesion in the duodenal bulb. Fine needle aspiration confirmed a grade 1 duodenal NET, which was subsequently removed by endoscopic mucosal resection. (B) Endoscopic view of an 8 mm rectal NET, grade 1, which was successfully resected by endoscopic submucosal dissection.

 

Small Intestinal (Jejunum and Ileum)

 

The classic site for well-differentiated NET in the gastrointestinal tract is the small intestine, particularly the terminal ileum. NET are the most common malignancy in the small intestine, followed in incidence by adenocarcinoma and lymphoma (58). Almost all small intestinal NET are low to intermediate grade and can potentially show indolent growth (59). NEC of the small intestine are extremely rare. As EC cells are the predominant neuroendocrine cell in the small intestine, metastatic small intestinal NET are most often associated with the carcinoid syndrome (60).

 

At presentation, the majority of small intestinal NET are metastasized, with a predilection for lymph node and liver metastases (59). In some cases, the primary tumor cannot be visualized despite modern imaging techniques, such as PET/CT. Lymphogenic spread of small intestinal NET occurs locally within the mesentery. The finding of NET accompanied by a mesenteric mass hints towards a small bowel origin of the NET. Unique to small intestinal NET, mesenteric metastases can develop extensive fibrosis (Figure 2). This is seen on cross-sectional imaging as fibrotic strand radiating from a solid mesenteric mass, in a spoke-wheel pattern (61). This pathognomonic feature of small intestinal NET can lead to chronic bowel ischemia due to compression of venous drainage, leading to intermittent abdominal cramps or colicky pain, particularly after a large meal. Ultimately, ileus or bowel perforation can occur. In one study of 530 patients with small intestinal NET, mesenteric fibrosis was found to be progressive in 13.5% of cases with a median time to growth of 40 months, signifying slow progression (62). Although mesenteric fibrosis can lead to fatal complications and is associated with overall survival in univariate analysis, it was not associated with a worse overall survival in multivariate analysis (63).

 

Figure 2. Mesenteric fibrosis in midgut NET. (A) Transversal and (B) coronal plane contrast-enhanced CT images of a patient with a cecal NET and a mesenteric metastasis (arrow). A desmoplastic reaction consisting of fibrotic strands can be seen radiating from the mesenteric tumor mass, which can compromise venous blood flow from the bowel. The mass is partly calcified.

 

Hepatic metastases of small intestinal NET can be much larger than the primary tumor or lymph nodes. Even in the presence of extensive bilobar metastases, the function of the liver is often preserved, although isolated hyperammonemia due to shunting has been described in selected cases (64).

 

Appendix

 

In the majority of cases, appendix NET are incidentally encountered during appendectomy because of appendicitis. A contributory role of the potentially obstructive tumor has been attributed to the occurrence of appendicitis, but this has not been proven to date. Because of its association with appendicitis, appendix NET have a peak incidence in adolescents and young adults (65). Most appendix NET cases are confined to the appendix and have a favorable proliferation index (grade 1 or low 2). Development of lymph node metastases can be seen in up to 25% of appendix NET patients, whereas distant metastases are rare (66). Contrary to origin NET within the midgut, carcinoid syndrome is rarely encountered in appendix NET patients, potentially due to other cell of origin and limited metastatic spread and tumor bulk.

 

Colon

 

NET arising in the caecum and ascending colon generally show a biological behavior that is similar to that of small intestinal NET. Together these are termed midgut NET due to their common embryological origin and vascularization by the superior mesenteric artery and vein. Consequently, cecal and ascending colonic NET are often low-grade tumors, can be associated with carcinoid syndrome when metastasized beyond the portal circulation, and give rise to fibrotic complications (67).

 

Contrarily, NEN in the transverse and descending colon are more aggressive with a predilection for the occurrence of NEC. These NEC share common features with adenocarcinomas of the colon, like molecular background (11). Hormonal syndromes are seldomly encountered in these colon NEC.

 

Rectum

 

Unlike the distal colon, NEN in the rectum show a preference for well-differentiated NET (68). Most rectal NET are incidentally discovered during colonoscopy (Figure 1B). A rise in rectal NET incidence rates has been detected that coincided with the increased use of diagnostic colonoscopy (69). At the time of detection, tumor size is often small (< 1 cm) signifying indolent behavior and small risk of metastatic spread (70). However, a subset of rectal NET can present in locally advanced stages and be associated with metastatic spread. Although their venous drainage is not connected to the portal vein, rectal NET are rarely associated with hormonal syndromes, presumably due to their neuroendocrine cell type of origin.

 

DIAGNOSIS

 

Histopathology

 

Obtaining histology for evaluation and confirmation of diagnosis remains essential in the work-up of a gastrointestinal NEN, even in the setting of modern imaging techniques and circulating biomarkers. The diagnosis of a NEN can be suggested through histological findings on H&E staining, such as an organoid pattern, absence of necrosis, low nucleus to cytoplasm ratio, and salt and pepper chromatin. Ultimately, the histological diagnosis requires positive immunohistochemical staining of neuroendocrine markers (71). Most commonly used neuroendocrine markers include synaptophysin and chromogranin A, although N-CAM (CD56) has also been advocated as such in the past. Staining with either synaptophysin or chromogranin A should be positive, with the former having a higher positivity rate in gastrointestinal NEN (72). Expert pathological examination is advised in uncertain cases, for instance in neoplasms with overlap with other malignancies, such as carcinomas with neuroendocrine differentiation, amphicrine carcinoma and MiNEN (25, 73).

 

Besides for confirming the diagnosis, histopathological evaluation is required for tumor grading according to the WHO classification. First, the distinction between a poorly differentiated NEC and a well-differentiated NET is crucial as shown above. This distinction is made on the basis of cellular morphology (74). Second, each pathological evaluation of a NET specimen should include grading through evaluation of differentiation, ki67 (MIB1) proliferation index and mitotic index (Table 2). Importantly, tumor grade can be heterogenous within or between tumor lesions as well as change over time (75, 76). The disease course over many years in patients can be accompanied by an increase in proliferation indices and grade over time, providing rationale for repeat biopsies in selected patients with disease progression. Altogether, grading provides key information for clinical decision making across all stages and primary locations of gastrointestinal NET. The subclass of grade 3 well-differentiated gastrointestinal NET was only introduced as recent as 2019 (2), which limits the clinical studies and experience on the management of this rare subtype.

 

Immunohistochemical analysis can also helpful in cases of an unknown primary tumor. Although the prevalence of an unknown primary tumor has decreased due to contemporary PET imaging, up to 5% of NET can present with an unknown primary (77). Positive staining for the following immunohistochemical marker is specific for different primary origins of NET: TTF-1 for foregut tumor, ISL-1 or PAX8 for pancreatic tumor, CDX-2 for midgut tumor, and SATB2 for hindgut tumor (78-81).

 

Biochemistry – General

 

Historically, elevated levels of biochemical markers have been directly linked to the diagnosis of a NET. While this can be true for certain hormones eliciting clinical syndromes when taken under controlled conditions, the vast majority of NET cannot be diagnosed through the use of a circulating biomarker. At most, a biomarker can be used during follow-up when it is elevated in a particular patient as a marker of disease recurrence or activity (27, 82).

 

Chromogranin A (CgA) has been extensively studied since the 1990s as a diagnostic and prognostic biomarker for gastrointestinal and other NET. This acid glycoprotein is stored within the secretory vesicles of neuroendocrine cells and co-secreted with the hormones upon stimulation. In a meta-analysis of 13 studies including 1260 patients with a NET sensitivity of CgA was 73%. In healthy controls, CgA levels were elevated in less than 5%, securing an excellent specificity. However, when compared to subjects with other gastrointestinal, renal, or oncological disease the specificity can drop to ranges of 50-60% (83), making CgA a poor diagnostic marker in patients presenting with abdominal complaints or a tumor. Measurement of CgA for this indication has led to many unnecessary clinical investigations, e.g., endoscopy, cross-sectional and functional imaging, into the cause of an elevated CgA (84) and should be discouraged.

 

Circulating CgA levels are associated with tumor bulk and consequently are correlated to a worse prognostic outcome (85). Because of its link to tumor bulk, CgA can be used during follow-up to track disease activity, although it should never replace imaging due to insufficient sensitivity and specificity of detecting progressive disease.

 

Neuron-specific enolase (NSE) represents another circulating marker on neuroendocrine cells. Mostly studied in small cell lung cancer, NSE is also elevated in a subset of gastrointestinal NET patients. Its sensitivity and specificity for the diagnosis of NET is approximately 40% and 60%, respectively (85, 86), and thereby inferior to that of CgA. Importantly, NSE levels tend to be more increased in aggressive disease. Consequently, a sudden rise in NSE could herald the occurrence of dedifferentiation in a NET.

 

Other circulating neuroendocrine markers, like pancreatic polypeptide and neurokinin A, have been used as diagnostic biomarkers in the past, but due to their overall lack of sensitivity or specificity their use in clinical practice has disappeared (27).

 

Because of the inferior diagnostic characteristics of the peptides described above an mRNA transcript-based marker called the NETest was developed. Through multiplex PCR and a machine learning-based algorithm, the NETest provides a number on a 100-point scale, where an outcome above 20 has been used for optimal diagnostic cut-off (87). In a meta-analysis of 6 studies the sensitivity and specificity of the NETest was 89-94% and 95-98%, respectively (88). An independent study employing serial sampling in 132 patients with gastroenteropancreatic NET showed a high rate of fluctuation in the NETest despite stable disease during follow-up (89). This technique is of interest to the field, but as of yet there are restrictions regarding the availability in clinical practice, costs, and reimbursement. Hopefully, these developments will lead the way towards more superior multianalyte diagnostic biomarkers for gastrointestinal NET in the future.

 

Biochemistry – Specific

 

When patients present with features compatible with a NET-associated functioning syndrome dedicated analysis should be performed. The reader is referred to other Chapters in Endotext for hormonal analysis of Gastrinoma (16), Insulinoma (90), VIPoma (37), Glucagonoma (91), Somatostatinoma (38), Ghrelinoma (53), and Paraneoplastic Syndromes (39). The latter included the hormonal work-up of NET-associated hypercalcemia, hyponatremia, Cushing’s syndrome, acromegaly and hypoglycemia.

 

Although the majority of gastrointestinal NET are not accompanied by a hormonal syndrome, the carcinoid syndrome is the most common hormonal complication. Because patients can be asymptomatic but still at risk for complications such as carcinoid crisis or CHD, all patients with advanced gastrointestinal NET should undergo biochemical evaluation for the carcinoid syndrome at baseline and when clinical suspicion arises during follow-up (29).

 

Serotonin (5-hydroxytryptamine) is the main but not exclusive culprit in the carcinoid syndrome. Upon secretion it is mainly stored in platelets, but a proportion freely circulates in the blood. It is metabolized by hepatocytes to 5-hydroxyindolaceticacid (5-HIAA), which is more stable than serotonin and excreted in the urine. 24-hour urine 5-HIAA levels are the best-established biomarker for the carcinoid syndrome, with 50 µmol/24h used as the optimal diagnostic cut-off (29, 92). Urinary 5-HIAA levels correlate with tumor bulk and multiple studies have described an association in univariate analyses with survival in CS patients, which did not persist in multivariate analyses (93-95). 5-HIAA level associate with the risk of developing CHD, with levels above 300 µmol/24h conferring a 2.7-fold increased risk of the development of CHD (36). Alternatively, 5-HIAA can be measured in plasma or serum, resulting in a slightly lower sensitivity/specificity compared to 24h urine collection (96, 97). Venous sampling saves on the cumbersome collection of 24h urine, but its availability is currently limited. Similarly, platelet serotonin levels are associated with carcinoid syndrome, but few labs can perform the assay (98). Although several other peptides, including neurokinin A, bradykinin, and histamine, have been associated with the occurrence of carcinoid syndrome, these markers have no utility in the diagnostic workup in clinical practice.

 

NT-proBNP is u useful biomarker to screen for the presence of CHD in patients with established carcinoid syndrome (99). An NT-proBNP level below 260 ng/mL (31 pmol/L) has a negative predictive value of 97%, thereby effectively ruling out the presence of CHD (100). Patients with NT-proBNP levels above 260 mg/mL should be referred for echocardiography to confirm or exclude the presence of CHD.

 

Cross-Sectional Imaging

 

Despite the developments in biochemistry and functional imaging, cross-sectional imaging remains the cornerstone of follow-up of NET. Furthermore, as more NET are incidentally discovered on imaging, it is important to be aware of typical or even pathognomonic radiological features of NET. On contrast-enhanced computer tomography (CT) scan gastrointestinal NET typically present as hypervascular lesions in the bowel wall (101). The majority of NET have enhanced intravenous contrast uptake in arterial phase, making it relevant to include an early arterial scan phase next to a venous or portal phase in case of a suspicion of a NET (102). Primary NET lesions in the small intestine tend to be small and can easily be missed, whereas lymph node or distant metastases can be extensive. Fibrosis can occur in mesenteric NET metastases, leading to pathognomonic fibrotic strands radiating from the mesenteric mass (61)(Figure 2). Gastrointestinal NET predominantly metastasize to the liver, where single, multiple or extensive metastases can be found. Again, these are hypervascular and enhancing on arterial phase in the majority of cases (103) (Figure 3).

 

Figure 3. Cross-sectional imaging in gastrointestinal NET. Due to their hypervascular nature, NET primary lesions and metastases can be enhancing in early arterial phase. In case (A) diffuse hypervascular liver metastases of a small intestinal NET are visible. Not all NET (metastases) are hypervascular, as shown in case (B) with a single non-enhancing liver metastasis of small intestinal NET during arterial phase (arrow). The added value of including an early arterial phase after contrast injection (C) op top of venous phase imaging (D) is illustrated within a patient with a small intestinal NET, where visibility of a segment 3 NET metastasis is improved during arterial scan. MRI, particularly diffusion weighted imaging (DWI), can improve the detection rate of small liver NET metastases (E).

 

Magnetic resonance imaging (MRI) is superior to CT with regard to liver and bone metastases, particularly with contrast enhancement and diffusion-weighted imaging (DWI) (104, 105) (Figure 3). For small liver neuroendocrine metastases, MRI even has a higher lesion-based sensitivity than contemporary SSTR-based PET imaging (see below) (106). In rectal NET, MRI is also helpful to stage local growth and lymph node metastases (107). MRI has caveats in the detection of the primary tumor of the bowel, mesenteric, or peritoneal metastases.

 

Endoscopy

 

Endoscopy is often the modality used leading to the incidental detection of a gastrointestinal NET, particularly within primary locations in the stomach or rectum (Figure 1). Primary tumors of gastroduodenal or rectal origin can also be missed on cross-sectional imaging, providing rationale for performing endoscopy or endoscopic ultrasound (EUS) to stage locoregional disease (67, 108). The added value of endoscopy in advanced disease is generally of limited value, unless the aim is to obtain histology. Alternatively, obtaining histology from metastases could be more informative as these can have a higher grade than the primary tumor and ultimately determine the patient prognosis (76).

 

Nuclear Imaging

 

Over 90% of well-differentiated NET express somatostatin receptors, which can be used for functional imaging. Somatostatin is a hormone, whose physiological actions are to inhibit hormonal production and release from neuroendocrine cells, for instance in the pituitary, pancreas, and intestine (109). It binds to one or more of five somatostatin receptor subtypes expressed on the cell membrane. Radiolabeled somatostatin analogues (SSA) were developed in the 1980s to image gastrointestinal and pancreatic NET. First, Octreoscan® with gamma-emitter 111In-pentreotide was shown superior to cross-sectional imaging in NET using planar and SPECT imaging (110). In the recent ten years, 68Gallium-labeled SSA (68Ga-DOTATATE, 68Ga-DOTATOC, 68Ga-DOTANOC) suitable for PET imaging have replaced 111In-pentreotide as the preferred imaging modality. Importantly, 68Ga-DOTA-SSA PET changes clinical management in 40-50% of cases, according to two meta-analyses (111, 112), and as such constitutes a key diagnostic modality in the NET armamentarium (Figure 4). The PET can be combined with diagnostic, contrast-enhanced CT (PET/CT) or MRI (PET/MRI) for hybrid imaging. Pitfalls include PET-positive granulomatous disease, meningioma, renal cell cancer, and lymphoma. Expression of the somatostatin receptors decreases with increasing proliferative capacity in NET, making it very useful in low-to-intermediate grade NET but less sensitive in higher grade NET or NEC. Recently, 64Cu-DOTA-SSA PET/CT and 18F-AIF-NOTA-SSA have been introduced with similar or slighter superior diagnostic capability compared to 68Ga-DOTA-SSA PET (113, 114).

 

Alternatively, 18F-DOPA PET has been advocated by several centers as superior to 68Ga-DOTA-SSA PET, particularly for midgut NET (115). Although this may vary between patients and mostly pertain to tumor count rather than to change in management, 68Ga-DOTA SSA also has therapeutic consequences for theranostics using unlabeled (‘cold’) SSA and peptide receptor radionuclide therapy (PRRT) with radiolabeled (‘hot’) SSA (see below).

 

Figure 4. 68Ga-DOTA-SSA PET imaging. 68Ga-DOTA-SSA PET staging is superior to anatomical imaging and 111In-pentreotide SPECT (Octreoscan). In this case of a patient with stage IV small intestinal NET, PET imaging detected more lesions than Octreoscan, scanned within 3-month timeframe without anatomical progression. In the same patient, multiple liver metastases are detected on hybrid PET/CT imaging (arrow), which were not visible on contrast-enhanced CT (CECT).

 

Similar to other malignancies, a subset of NET metabolize increased amounts of glucose, which makes them amenable to imaging with 18F-fluorodeoxyglucose (FDG) PET. Uptake of 18F-FDG PET in NET increases with aggressiveness, making it the preferred imaging modality in NEC and higher-grade NET (116, 117). Positive FDG uptake of NET is associated with growth potential and consequently several studies have established that FGD uptake constitutes a prognostic marker for a worse survival outcome (118).

 

MANAGEMENT

 

Surgery

 

Radical resection remains the cornerstone in the management of locoregional stages of gastrointestinal NET. Metastatic spread is dependent on the location and size of the primary tumor and adequate staging should be performed accordingly, preferably through hybrid cross-sectional and 68Ga-DOTA-SSA PET imaging (102). If the disease is confined to the local tumor (stage I-II) or locoregional lymph nodes (stage III), the option of a surgical oncological resection should be evaluated. If the NET can be radically resected the outcome is very favorable with 10-years survival outcomes of >90% for all primary sites. A large registry series from Canada did find that recurrence rates can increase up to 60% for small intestinal NET and 40-50% for other NET in a 15-year postoperative period (119). Given the retrospective nature of this series and contemporary preoperative imaging it remains uncertain whether recurrence rates of current therapeutic interventions are still this high.

 

For stage I gastroduodenal NET, metastatic spread is limited and endoscopic resection of the NET can be considered (108). This pertains to gastric type I and type II NET up to 2 cm without muscle invasion and duodenal NET localized at safe distance from the Vater’s ampulla. Similarly, an endoscopic resection can be performed in stage I rectal NET, as the risk of lymph node metastases is limited to less than 3% (67). Resection from both tumor subtypes should be performed by endoscopic mucosal resection (EMR), endoscopic submucosal dissection (ESD), or endoscopic full thickness resection (eFTR) rather than snare polypectomy due to the submucosal growth pattern of NET. Successful removal of type I gastric NET or stage I rectal NET is are high (>85%) with slight superiority of ESD over EMR, while eFTR might approach 100% radical resection rates (120-122). In cases of an inadequate endoscopic resection further imaging should be performed and a step-up endoscopic approach or surgical resection should be considered.

 

Patients with oligometastatic disease might also benefit from an upfront surgical approach. As the liver is the predominant site for metastatic disease, concomitant surgical resection and/or interventional tumor ablation should be considered in patients with limited liver involvement (123). This can potentially cure the patient, but it should be noted that modern imaging techniques detect approximately one-third of liver metastases compared to histological evaluation (124, 125). The presence of micrometastases should be factored into the management process. Despite this, long-term outcomes can be excellent in cases of upfront surgery in oligometastatic disease. A potential advantage of tumor debulking in this setting could be the delay of the need to start systemic therapy. Several series have also described survival benefits of extensive liver metastases resection (126-129), but these concern mostly retrospective series, which might introduce selection bias, and data was often collected before the advent of currently available molecular therapies.

 

Resection of the primary tumor in the context of stage IV or metastatic disease is controversial. Whereas retrospective studies have supported a survival benefit in patients whose primary tumor was resected compared to those that were not operated (130-132), this was later refuted in other series or after propensity score-matched controls (63, 133). Importantly, the disease course locoregionally can be indolent, and in one series only 13% of mesenteric masses showing significant progression after a median follow-up time of 40 months (62). Patients with advanced midgut NET and recurrent complaints from the primary tumor or (fibrotic) mesenteric mass should undergo operation to explore the possibility of a palliative resection or alternatively, an intestinal bypass.

 

Palliative Management

 

Patients with unresectable or advanced gastrointestinal NET are in a palliative setting and the different treatment modalities should be weighed in terms of efficacy and toxicity. Given the wide range of gastrointestinal NET subtypes, the treatment chosen should align with the biological behavior of the tumor as well as the characteristics of the individual patient (Figure 5). Factors to consider in the management of gastrointestinal NET include: tumor grade, growth rate and location(s), symptoms, presence of a hormonal syndrome, performance score, comorbidities, previous therapies, availability of treatments and patient preference.

 

Figure 5. Stage IV gastrointestinal NET. There is a wide heterogeneity in clinical presentation of gastrointestinal NET in advanced or metastatic setting. On these maximal intensity projections of 68Ga-DOTATATE PET, there are 8 different clinical scenarios of stage IV gastrointestinal NET. Despite the similar disease stage, all these patients deserve personalized management of their disease according to several patient- and tumor-specific factors. For optimal management, choice of treatment should be discussed in an experienced multidisciplinary setting.

 

Active Surveillance

 

One potential option to consider is to perform active surveillance in asymptomatic patients with advanced, grade I or low-grade II NET with limited tumor bulk. Evidence for this strategy can be found in placebo-controlled trials. First, the median time to progression in placebo-treated patients was 6 months in the phase III randomized PROMID trial in midgut NET patients (134). Second, in the phase III randomized CLARINET trial in patients with nonfunctioning GEP NET, patients randomized to placebo had a median progression-free survival (PFS) of 18 months (135). Consequently, not all tumors show clear growth potential over time and selected patients can thus safely refrain from costly and potentially toxic medication. This strategy should not be adopted in patients with symptomatic, functioning, high-grade, quickly progressive, or high tumor volume disease. Follow-up cross-sectional imaging every 3-6 months is advised for gastrointestinal NET patients undergoing active surveillance.

 

Somatostatin Analogs

 

Before their role in imaging, SSA were developed for their potential antihormonal effects. The SSA octreotide was found to effectively reduce serotonin production in patients with carcinoid syndrome and other NEN-associated functioning syndromes (136). Following its long-term application in functioning NET, antitumoral efficacy was tested in the PROMID and CLARINET trials. The German multicenter PROMID study randomized 85 midgut NET patients to 4-weekly 30 mg octreotide long-acting release (LAR) injections or placebo injections (134). These patients were in the beginning of their disease course with a median time from diagnosis of 4 months and had on average limited liver tumor load and grade I. In an intention to treated (ITT) analysis median time to progression was 14.3 months in octreotide LAR-treated patients versus 6.0 months in the placebo group (P=0.000072). Overall survival (OS) was not different between the groups. The effect of SSA is predominantly stabilization of disease as only one patient in both treatment groups experienced a partial response. Overall, octreotide LAR treatment was well tolerated, although diarrhea, flatulence, and bile stones were more frequently observed in the SSA-treated group.

 

The international multicenter CLARINET trial randomized 204 patients with advanced nonfunctioning GEP NET to 4-weekly injections of 120 mg lanreotide autogel or placebo injections (135). Tumors were grade I and II with ki-67 index up to 10% and mostly from pancreas or midgut origin. Over 80% of patients had not received previous antitumoral treatment and tumor progression before randomization was only shown in 4-5% of patients. ITT analysis revealed that PFS was significantly longer in lanreotide-treated patients compared to placebo (median not reached versus 18.0 months, P<0.001). The benefit of lanreotide persisted in most predefined subgroups across primary origin, tumor grade, and liver involvement. Safety of lanreotide was good, with known side effects of gastrointestinal complaints, exocrine pancreas insufficiency, and hyperglycemia. Interestingly, the open label extension study of the CLARINET showed a median PFS of 33 months in those continuing lanreotide, while patients in the placebo group – with a median PFS of 14 months - who crossed over to lanreotide after progression had a median second PFS of 18 months (137). This again supports the possibility of considering active surveillance in a subset of patients with indolent disease. Overall survival (OS) in the core CLARINET study was not significantly different between treatment groups, but was also biased by crossover from placebo to lanreotide.

 

Together these landmark trials have positioned SSA as first-line antiproliferative treatment for well-differentiated gastrointestinal NET, particularly in patients without signs of high tumor volume or aggressive disease course. Injections with octreotide LAR or lanreotide are every 4 weeks in the gluteal area intramuscularly or deep subcutaneously, respectively. Overall tolerability is excellent, although patients should be counselled on the potential gastrointestinal adverse effects, e.g., diarrhea, flatulence, nausea, stool discoloration, after the first administration, which tend to dissipate after repeated injections. Long-term concerns include hyperglycemia and bile stones. Although preventive cholecystectomy has been advocated in the past, this practice has been abandoned in most expert centers (138).

 

Several retrospective series and clinical experience supported the use of SSA dose escalation in patients with mild progressive disease (139). These studies suggest that increasing the injected dose or injection frequency might be accompanied by improved antiproliferative control. First prospective evidence of this effect came from the NETTER-1 study designed to investigate the effect of peptide receptor radionuclide therapy (PRRT) with 177Lutetium-DOTA-octreotate (177Lu-DOTATATE) (140). Patients enrolled in this study had advanced, progressive midgut NET on regular dose of SSA and were randomized between PRRT and an escalated dose of 60 mg of octreotide LAR every four weeks. Patients in the high-dose SSA control group had a medium PFS of 8.4 months, supporting some antiproliferative effect of SSA dose escalation after disease progression on a regular dose of SSA. The CLARINET forte single-arm, phase II trial was designed to study the efficacy of lanreotide dose escalation in midgut and pancreatic NET patients with disease progression on standard lanreotide dose in the previous 2 years (141). In the midgut NET cohort, 51 patients were included with grade 1-2 disease and 57% of patients had – generally limited - hepatic metastases. After dose escalation to lanreotide 120 mg every 2 weeks median PFS in this cohort was 8.3 months, while disease control rate (partial response or stable disease as best outcome) was 73%. Importantly, no deterioration of quality of life and no additional treatment-related safety concerns were observed in patients treated with high-dose lanreotide.

 

SSA treatment should be given lifelong in patients with carcinoid syndrome and other SSA-responsive functioning syndromes for which these drugs are registered and approved (29, 142). This includes continuation of treatment after radiological or clinical progression and initiation of a second-line of treatment. Whether SSA should be continued in nonfunctioning gastrointestinal NET disease is a matter of controversy and no prospective data is available to guide this. Intriguingly, 50% of panelists in the NANETS guideline supported continuing SSA treatment, while 50% supported stopping treatment upon progression (143).

 

The pan-somatostatin receptor agonist pasireotide has been investigated in NET based on the hypothesis that targeting more somatostatin receptor subtypes might have an additive antiproliferative effect compared to octreotide and lanreotide, which predominantly target the somatostatin receptor subtype 2 (144). However, early phase clinical trials provided insufficient grounds to pursue further clinical development of this drug in NET (145, 146).

 

Peptide Receptor Radionuclide Therapy

 

Similar to the diagnostics and therapeutics of thyroid disease with radioactive iodine, the discovery of molecular somatostatin receptor imaging also heralded the advent of targeted somatostatin receptor-based radionuclide therapy. Following initial developments with 111In-pentreotide and 90Yttrium-DOTATATE, the short-range beta-emitter 177Lutetium coupled to DOTATATE (177Lu-DOTATATE) was introduced in 2000 (147). This technique of targeting the somatostatin receptor on tumor cells with internal radiation was termed PRRT.

 

Individual phase II trials at several centers showed promising antitumoral effects on somatostatin receptor-positive NET, including gastrointestinal subtypes (148). The multinational phase III randomized NETTER-1 trial established PRRT with 4 cycles of 177Lu-DOTATATE as an effective therapy for advanced, somatostatin receptor-positive midgut NET (140). In this trial, 229 patients were randomized between PRRT, including 30 mg octreotide LAR between cycles and 4-weekly after the fourth cycle, and 60 mg octreotide LAR every four weeks. Patients had a grade 1-2 midgut NET that was progressive on SSA before enrollment. The median PFS in the PRRT group was not reached compared to 8.4 months in the high-dose SSA group. Benefit in PFS prolongation was evident across all pre-specified subgroups. Risk of progression or death was 79% and decreased in the patients treated with PRRT. The study confirmed known side effects of 177Lu-DOTATATE, including nausea, fatigue, abdominal pain, and diarrhea. Two percent of patients experienced grade 3 or higher thrombocytopenia, while 2 patients (1.8%) developed myelodysplastic syndrome following PRRT. In a meta-analysis of 28 studies comprising 7334 patients treated with 90Y-DOTATOC or 177Lu-DOTATATE, the combined incidence of myelodysplastic syndrome and acute myeloid leukemia after PRRT was 2.6% (149). Final analysis of the NETTER-1 study revealed that the median OS in the PRRT group was 48.0 months compared to 36.3 months in the high-dose SSA group, which was not significantly different (150). Crossover of 37% of the patients randomized to high-dose SSA, long-term survival with multiple other treatment lines and insufficient statistical power could have contributed to the failure of reaching this secondary endpoint. Another key secondary endpoint was reached: time to deterioration of quality of life was significantly longer in patients treated with PRRT compared to those treated with high-dose SSA (151).

 

Although the NETTER-1 only included midgut NET patients, the phase II Erasmus MC Rotterdam data were used to obtain regulatory approval of 177Lu-DOTATATE for all gastrointestinal (and pancreatic) NET subtypes (152). Importantly, PRRT also induced tumor response in 18% of midgut NET patients in the NETTER-1 study and 39% of various NET patients in the Rotterdam study, which makes it a potential cytoreductive therapy. Standard protocol of PRRT included four infusions of 7.4 GBq 177Lu-DOTATATE spaced 8 (range 6-12) weeks apart. PRRT should preferably be administered in the absence of long-acting SSA (4-6 weeks) or short-acting SSA (24 hours) due to competition at the receptor level. An amino acid solution of 2.5% lysine and arginine is co-infused with 177Lu-DOTATATE in order to saturate the renal reuptake of radioactive peptide and prevent radiation-induced nephrotoxicity. This limits the incidence of severe renal insufficiency after PRRT to less than 1% (152). Special considerations should be applied to patients with pre-existing cytopenia or clonal hematopoiesis, impaired renal function or hydronephrosis, massive liver tumor bulk, mesenteric fibrosis, or nervous system involvement (153). Patients with a severe functioning syndrome are at risk of an exacerbation of symptoms or hormonal crisis following temporary SSA withdrawal or tumor lysis with PRRT. Although the risk is minor at 1% incidence in retrospective series and limited to patients with severe hormonal hypersecretion (154, 155), adequate management through supportive measures and swift re-introduction of SSA should be employed to prevent a hormonal crisis.

 

There is a possibility for salvage PRRT when progressive disease (re-)occurs after a period of disease control following 4 cycles of PRRT. Several retrospective series have described renewed disease control or even response after additional cycles with 177Lu-DOTATATE after progression. In the largest series to date of 181 patients with gastrointestinal, pancreatic, bronchopulmonary, or unknown origin NET, salvage PRRT with two cycles was administered if disease progression occurred after a period of at least 18 months after the first cycle of the initial PRRT (156). The median PFS after salvage PRRT was 14.6 months and thereby approximately 50% of the initial PRRT, while disease control was observed in 75% of patients. Salvage PRRT was not associated with increased rates of myelotoxicity or nephrotoxicity. In patients that respond favorably to salvage PRRT, future cycles can be considered when progressive disease once again arises, although clinical outcome data of additional treatments are scarce.

 

Targeted Therapy

 

The mammalian target of rapamycin (mTOR) protein is a central proliferative factor in many cancer cells. Inhibition of the mTOR pathway has been investigated for several malignancies, including NEN. The RADIANT-2 multicenter phase III trial investigated whether the oral mTOR inhibitor everolimus had efficacy in patients with advanced NET and carcinoid syndrome (157). In total, 429 patients with progressive and advanced grade 1-2 disease were randomized between everolimus 10 mg q.d. plus octreotide LAR 30 mg every 4 weeks or placebo plus octreotide 30 mg every 4 weeks. Primary sites included among others small intestine (52%), lung (10%), colon (6%), and pancreas (6%). Baseline characteristics between the groups were not well balanced with regard to WHO performance status, primary sites, and prior use of chemotherapy. The median PFS was 16.4 months in the everolimus combination group compared to 11.3 months in the placebo combination group (p=0.026). This analysis encompassing central review of radiological images did not reach the pre-specified cut-off for superiority. Median OS was 35.2 months in the placebo-octreotide LAR group compared to 29.2 months in the everolimus-octreotide LAR group, which was not a statistically significant difference, but more deaths related to respiratory or cardiac disease were observed in the everolimus arm.

 

In the RADIANT-4 phase III trial, patients with advanced, progressive, grade 1-2, nonfunctioning NET of gastrointestinal or lung origin were included (158). Here, 302 patients were randomized 2:1 to everolimus 10 mg q.d. or placebo. Approximately 60% of patients had a gastrointestinal NET, while 80% had liver metastases, generally with limited liver tumor bulk. Median PFS was longer in the everolimus-treated patients at 11.0 months versus 3.9 months in the placebo group. This difference was significant after central radiology review as well as after local review (P<0.00001). Despite a 36% reduction in the risk at death in the everolimus group, overall survival was not significantly improved. Partial response was obtained in 2% of patient treated with everolimus, while stable disease was observed in 81%. Given the outcomes of the RADIANT-2 and RADIANT-4 trials, everolimus appears to be better suited for nonfunctioning NET than functioning NET.

 

Everolimus use is associated with a high rate of side effects, such as stomatitis, rash, diarrhea, fatigue, diabetes, infections, and non-infectious pneumonitis. Dose reductions or interruptions are necessary in up to two-thirds of NET patients taking everolimus (158). No benefit in terms of quality of life has been proven for everolimus (159), with potentially a decrease in quality of life in patients with extrapancreatic NET (160).

 

Multitarget tyrosine kinase inhibitors (MTKI) are another form of targeted therapy that can exert potent anti-cancer effects. Sunitinib is an oral multireceptor MTKI which has been investigated in panNET patients. In a phase II study, suninitib showed encouraging antitumoral activity in 61 pancreatic NET with partial response observed in 17% (161). While the median time to progression of 10.2 months in 41 patients with gastrointestinal and lung NET treated with sunitinib exceeded the 7.7 months observed in panNET patients, further development of sunitinib in gastrointestinal NET was not pursued due to the low response rate of 2.4%. A subsequent phase III trial in panNET patients showed that sunitinib improved PFS and OS in panNET patients (162), which led to registration of this drug for NET of pancreatic origin only.

 

Another MTKI surufatinib was tested in two phase III studies in China in pancreatic and extrapancreatic NET, respectively (163, 164). In the multicenter, randomized SANET-ep trial 198 patients with advanced, grade 1-2, progressive NET of gastrointestinal (47%), thoracic (24%), or other origins were randomized 2:1 to oral surufatinib 300 mg or placebo once daily (164). The median PFS after central review in the surufatinib group was 7.4 months compared to 3.9 months in the placebo group (P=0.037), which appeared to be independent of the subgroups studied. There was a large difference with the local radiology review, which tended to overexaggerate the effect of surufatinib on PFS. OS was not different between the groups at the time of the interim analysis. Partial response and stable disease were observed in 10 (8%) and 88 (70%) out of 126 patients, respectively, in the surufatinib arm. Relevant treatment-related side effects included hypertension, proteinuria, anemia and elevated liver enzymes. Quality of life did not improve in the surufatinib arm, while surufatinib-treated patients experienced more diarrhea than those in the placebo arm (165). Based on the SANET-ep study and its partner SANET-p study in panNET patients, surufatinib is registered in China for the treatment of nonpancreatic and pancreatic NET. Surufatinib is thus far not registered for these indications by the FDA or EMA.

 

Several other MTKI have shown potential for antiproliferative activity in NET patients. These include pazopanib (166), lenvatinib (167), and axitinib (168). Further phase III data are necessary before these MTKI can be considered in gastrointestinal NET.

 

Immunotherapy: Interferon-Alpha and Immune Checkpoint Inhibitors

 

In the 1980s, the advent of interferon as a novel cancer drug was also investigated in NEN. Several uncontrolled series supported antiproliferative and antihormonal effects of interferon alpha in mostly small intestinal NET (169, 170). The proinflammatory effects of interferon alpha however led to side effects of flu-like symptoms, myalgia, asthenia, auto-immune diseases, and diarrhea, limiting its tolerability in patients. Compared to SSA, interferon alpha had comparable antiproliferative effects (171). Long-acting interferon alpha appears to be better tolerated and was shown to produce antitumor effect in a single retrospective series in 17 patients (172). 

 

Immunotherapy with immune checkpoint inhibitors has revolutionized treatment of several malignancies, including melanoma and non-small cell lung cancer. However, infiltration of immune cells, like T-cells, is a rare occurrence in NET samples (173-175). In line with these preclinical findings, immune checkpoint inhibition in clinical (basket) trials have failed to show positive effects in well-differentiated NET (176-178).

 

Chemotherapy

 

In contrast to panNET there are no phase III clinical data to support the use of chemotherapy in gastrointestinal NET. Presumably in part through their well-differentiated nature, response rates to chemotherapy have been disappointing and further clinical development halted (179). Consequently, ENETS 2016 and NANETS 2017 guidelines do not support the use of chemotherapy in gastrointestinal NET (143, 180). The EMSO 2021 guideline does advocate the use of either FOLFOX (5-fluorourical, oxaliplatin) or TEMCAP (temozolomide, capecitabine) in selected cases with high grade 2 gastrointestinal NET in third-line or higher setting, although this is not supported by prospective clinical data (181).

 

Supportive Therapy

 

Due to the primary tumor and metastasis locations as well as the sequalae of hormonal overproduction and therapeutic interventions, patients with gastrointestinal NET can be in a poor clinical condition. Inadequate nutrient intake and uptake in these patients leads to increased incidence rates of weight loss, muscle atrophy, and decreased performance status (182). Consequently, all gastrointestinal NET patients should be screened on dietary intake and referred to dieticians if they are at risk of weight loss. High-protein, high-calorie supplements should be prescribed if regular dietary advice is insufficient to prevent weight loss. In cases of suspected reduced calorie uptake due to exocrine pancreatic insufficiency, often encountered during SSA treatment, or bile acid diarrhea, due to bowel resection, a trial of pancreatic enzyme supplements or bile acid sequestrants can be considered.

 

In some cases, patients can be refractory to these interventions and escalation should be considered. This is particularly true for patients with extensive bowel resections leading to short bowel syndrome and those with severe desmoplastic reaction surrounding mesenteric metastases of small bowel NET. Food intake in the latter group might also be compromised by intermittent venous ischemic pain precipitated by meals. Tube feeding through nasogastric tube should be considered in selected cases. In case enteral feeding fails to improve the clinical situation, total parenteral nutrition can serve as a last resort for these refractory cases. Treatment with total parenteral nutrition up to 5 years has been successfully implemented in severe cases of NET (183).

 

Besides nutritional support, physical therapy should also be offered to patients in order to improve their clinical performance status. Finally, given the impact of an incurable disease and its complaints psychosocial support should be discussed with patients and made accessible, if needed (184).

 

MANAGEMENT OF CARCINOID SYNDROME

 

Patient with gastrointestinal NET and the carcinoid syndrome require dedicated management of their hormonal symptoms. Quality of life in these patients is severely decreased, even when compared to patients with other – generally more aggressive – cancers (185). Prompt recognition of symptoms of flushing and diarrhea is key to specific management, while the complications of mesenteric fibrosis and CHD should also be screened and treated adequately (29).

 

The cornerstone of the management of the carcinoid syndrome is SSA. Since the 1980s octreotide and later lanreotide have been shown to lead to biochemical and clinical responses in patients with the carcinoid syndrome. In a meta-analysis comprising 1945 interventions in 33 studies, SSA significantly decreased 5-HIAA excretion in 45-46% of patients, while flushing and diarrhea were decreased in 69-72% and 65%, respectively (186). Also given its favorable tolerability, all patients should be started on SSA soon after a confirmed diagnosis of carcinoid syndrome.

 

Although patients with carcinoid syndrome in the majority of cases have widespread disease, the option of cytoreductive therapy by surgical resection or ablation or intra-arterial liver embolization can be considered in selected cases. If the vast majority of tumor bulk can be resected or embolized, this can lead to biochemical responses and clinical benefit for the patient (186). These options should be weighed also considering the level of serotonin overproduction, tumor growth rate, and efficacy of SSA. Importantly, SSA should be initiated before interventional therapy is commenced in order to reduce the risk of a carcinoid crisis (187).  

 

Patients with persistent symptoms despite label doses of SSA are designated as having refractory carcinoid syndrome. Several systemic options are available for treatment and these should be weighed on an individual basis guided by tumor bulk, rate of progression, severity of symptoms, and availability. Dose escalation of SSA can be attempted and leads to symptomatic improvement in 72-84% of patients (186). Alternatively, a randomized controlled trial has proven efficacy of the oral drug telotristat ethyl in controlling diarrhea in patients with refractory carcinoid syndrome (188). This serotonin synthesis inhibitor, dosed at 250 mg t.i.d., decreased bowel movements in approximately half of the cases and with a mean reduction of 0.8 bowel movements per day, whilst having no significant effect on flushing. A drug trial of three months is generally advised with stopping of telotristat ethyl if no benefit has been obtained after this time. Clinical symptoms improved in patients treated with PRRT in the NETTER-1 trial (140), although no sub-analysis was performed for carcinoid syndrome patients. In a retrospective series of 24 patients with stable disease or severe, refractory carcinoid syndrome, PRRT with four cycles of 177Lu-DOTATATE effectively reduced flushes and diarrhea in 67% and 47% of patients, respectively (155). Therefore, PRRT constitutes a viable option for refractory carcinoid syndrome patients with aggressive or progressive disease. In the past, interferon-alpha injections have been shown to diminish diarrhea and flushing resulting from carcinoid syndrome. Its antihormonal effect on top of SSA was limited (189), however, and given its poor tolerability interferon-alpha is reserved to selected cases, refractory to the above-mentioned options. Anecdotal reports support the use of serotonin receptor antagonists, like granisetron or ondansetron, and antihistamines (H1 and H2 receptor blockers) in refractory carcinoid syndrome.

 

Importantly, the patient should be counselled on supportive therapy, which could include the use of antidiarrheals, like loperamide or morphine, adaptation of dietary intake, including avoidance of alcohol, tryptophan-containing or spicy foods, and the avoidance of stressors (29). Patients with severe carcinoid syndrome are at a high risk of a catabolic state and vitamin deficiencies. Patients should be referred to a dietician and adequately monitored and supplemented for vitamin deficiencies, particularly for vitamin B3 or niacin and fat-soluble vitamins.

 

Patients suffering from CHD should be evaluated by cardiologists experienced in right-sided cardiac pathology. Dedicated echocardiographic evaluations should be performed, preferably through standardized protocols (190). Fluid and salt restriction comprise first-line treatment of right-sided heart failure due to tricuspid valve regurgitation or pulmonary valve regurgitation or stenosis in the context of CHD. Alternatively, loop diuretics can be prescribed to treat fluid overload and edema. Severe symptomatic patients should be discussed in a multidisciplinary team for evaluation of surgical valve replacement (191).

 

PROGNOSIS AND FOLLOW-UP

 

Resection is the only potential cure for gastrointestinal NET. Recurrence is however frequently observed in NET patients operated on with curative intent (119). Exceptions that are associated with excellent curation rates after local resection include T1-T2 appendiceal, gastric, duodenal, or rectal NET. Long-term imaging follow-up is mandated for the other subtypes of gastrointestinal NET after resection of localized, locoregional, or oligometastatic disease.

 

In a US registry study of almost 100,000 NET patients, median overall survival was 112 months and 62% of patients died of disease-related causes (192). All-cause mortality was 4.3-fold higher in all NET patients, compared to the general population, while patients with stage IV disease had 35-fold elevated risk of mortality. Whereas patients with localized disease still have an elevated standardized mortality ratio, the risk of non-cancer death is higher than cancer-related death in patients with non-metastatic gastrointestinal NET (193). Primary site, stage or grade are tumor-specific prognostic markers, while age, sex, comorbidities and socio-economic status constitute patient-specific factors that are associated with overall survival (7, 8, 192-194). Over the last few decades, NET management has improved considerably with the advent of superior classification, imaging, and biochemical diagnostics and treatment modalities. These developments, combined with expert multidisciplinary team care in dedicated NET centers, have likely contributed to the observed improvement in overall survival in patients with gastrointestinal NET (7, 8). However, survival of gastrointestinal NET patients is still limited, particularly in those with advanced disease, prompting the need for future innovation in the fields of early detection of disease (recurrence), novel druggable targets, and personalized management for NET.

 

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Hypoglycemia in Neonates, Infants, and Children

ABSTRACT

 

Hypoglycemia in neonates, infants and children should be considered a medical emergency that can cause seizures, permanent neurological injury, and in rare cases, death, if inadequately treated. Under normal conditions, glucose is the primary fuel for brain metabolism. Due to the metabolic demands of the developing brain, infants and children have increased rates of glucose utilization as compared to adults. Normal regulation of glucose during fasting requires integration of glycogenolysis, gluconeogenesis, and fatty acid oxidation coordinated by various hormones. In the first days of life, the time course of the physiologic transitional changes to autonomous glucose regulation may overlap with presentation of inherited and acquired pathologic forms of hypoglycemia, introducing inherent challenges and controversy in addressing neonatal hypoglycemia. Therefore, a careful approach to the neonate with hypoglycemia is critical to determine the precise etiology so that rapid and appropriate interventions can be implemented to avoid permanent neurological injury. After infancy, hypoglycemia is uncommon, but, up to 10% of children older than one year of age presenting to emergency rooms with previously undiagnosed hypoglycemia have a serious underlying condition requiring long-term treatment. An important caveat in the pediatric population is that the classical definition of hypoglycemia, Whipple’s triad, is of limited use as young children are unable to reliably communicate symptoms. At all ages, determining the cause of the hypoglycemia is paramount for establishing specific and effective treatment to prevent further episodes of hypoglycemia and long-term neurological sequelae. The majority of hypoglycemic events in infants and children with hypoglycemic disorders occur during periods of fasting. Evaluation of key metabolic fuels and hormones (the critical sample) during a supervised fast, or at the time of spontaneous hypoglycemia, thus permits classification and relevant treatment of hypoglycemia disorders.

 

INTRODUCTION

 

Hypoglycemia is the biochemical finding of a plasma glucose lower than normal for age.  Hypoglycemia itself is not a diagnosis but rather reflects an underlying perturbation in metabolic adaptation, which may be as simple as prolonged fasting in a child with an intercurrent illness, or a complex genetic disorder. It is critical for the physician at all times to determine the etiology of hypoglycemia while at the same time treating critical low blood glucose and stabilizing the person with hypoglycemia.

 

In this chapter, we outline the basic physiology of glucose regulation, the change in glucose homeostasis in the immediate newborn period and describe the common diseases that cause hypoglycemia in childhood. We discuss the definitions of hypoglycemia, pitfalls in the measurement of blood glucose concentration, the critical importance of glucose as a fuel for energy in the brain, and the implications of hypoglycemia on brain damage. For information on hypoglycemia related to diabetes and its treatment see the chapter entitled “Hypoglycemia During Therapy of Diabetes” in the Diabetes Mellitus and Carbohydrate Metabolism---Diabetes Manager section of Endotext (1).

 

PHYSIOLOGY OF GLUCOSE REGULATION

 

An understanding of the physiology of glucose regulation is critical in order to understand the etiology of the different hypoglycemic disorders. By utilizing a fasting systems approach to diagnosis, one can rapidly pinpoint the general physiological system disrupted and with appropriate examination of blood and urine at the time of hypoglycemia (the critical sample) one can identify the diagnosis relatively quickly. This approach is particularly useful because apart from the newborn period (2), the vast majority of causes of hypoglycemia in children are caused by abnormalities of fasting adaptation. Rare exceptions to this rule include postprandial hypoglycemia typically related to gastrointestinal surgery such as Nissen fundoplication (3), or esophageal atresia repair (4), protein induced hypoglycemia of certain genetic forms of hyperinsulinism (5,6), and the hypoglycemia triggered by the ingestion of fructose in hereditary fructose intolerance (7).

 

The recognition and identification of the etiology of hypoglycemic disorders in the immediate newborn period may be more complicated due to the changes in glucose homeostasis that occur during the transition from intra uterine to extra uterine life, typically defined as the first 12-72 hours of life, and will be discussed separately (2).

 

The Physiology of Fasting

 

The key to diagnosing the etiology of hypoglycemia is a good understanding of the three key metabolic systems that regulate the physiological response to fasting and the hormonal control over these systems. The first, glycogenolysis, involves the breakdown of glycogen and conversion to glucose 6 phosphate (G-6-phos). G-6-phos may either undergo glycolysis and be converted to lactate (8), or converted to glucose by glucose-6-phosphatase (G-6-Pase), and then released from the liver and transported to the brain for fuel. The second, gluconeogenesis, is the pathway by which fuels such as lactate, alanine, fructose and glycerol are converted into glucose. The third, fatty acid oxidation and ketogenesis, are the processes by which ingested fat and fat stores are converted either to acetyl-CoA for entry into the citric acid cycle (Krebs cycle) and generation of energy, or to beta-hydroxybutyrate which is then transported to tissue such as the brain for energy production. An essential role of fatty acid oxidation is the production of an alternate fuel to glucose for energy production. This process conserves glucose for those tissues that can only metabolize glucose (such as red blood cells). Each of these mechanisms of fasting adaptation are finely regulated to maintain the plasma glucose between 70 and 110 mg/dL (3.9 to 6.1 mmol/L) by a combination of insulin to utilize or store glucose, and the counter regulatory hormones to mobilize and release glucose (Table 1). Insulin, the main hormone secreted in the fed state, suppresses glycogenolysis, gluconeogenesis, lipolysis, and ketogenesis. The counter regulatory hormones glucagon, cortisol, growth hormone, and epinephrine are the predominant hormones secreted in the fasting state and have overlapping effects on these processes. Because of the critical importance of these 3 processes (glycogenolysis, gluconeogenesis and fatty acid oxidation) in preventing hypoglycemia, there is overlap in hormonal control of the systems with both glucagon and epinephrine stimulating glycogenolysis, cortisol and glucagon stimulating gluconeogenesis, growth hormone and epinephrine stimulating lipolysis and finally glucagon and epinephrine stimulating ketogenesis. 

 

Table 1. Hormonal Control of Fasting Adaptation

Hormones

Glycogenolysis

Gluconeogenesis

Lipolysis

Ketogenesis

Cortisol

 

 stimulates

 

 

Growth Hormone

 

 

 stimulates

 

Glucagon

 stimulates

 stimulates

 

 stimulate

Epinephrine

 stimulates

 

 stimulates

 stimulates

 

Hormonal Control of Fasting

 

Following a meal, insulin is the predominant secreted hormone as glucose, and other fuels, are absorbed, facilitating glucose entry into cells and its utilization for energy. Under the influence of insulin, excess glucose is stored as glycogen in the liver for use later in fasting. As the plasma glucose starts to fall below 85 mg/dL insulin secretion is reduced and then suppressed (Figure 1). As the blood sugar continues to fall to around 70 mg/dL, the rapidly acting counter regulatory hormones glucagon and epinephrine are secreted. This initially drives glycogenolysis which supplies glucose from the liver for up to 4-8 hours in infants and 8-12 hours in children and young adults. Cortisol and growth hormone secretion stimulate gluconeogenesis and lipolysis providing amino acids, glycerol, and free fatty acids for metabolism to ketones.

Figure 1. Relationship of hormone secretion to plasma glucose levels.

 

Brain Fuel Metabolism/Energy Production

 

As the plasma glucose levels approach 50 mg/dL the ability of the blood brain barrier to transport glucose into the brain for maximal usage, begins to become limited (9). The brain responds by utilizing alternative fuels for energy (lactate, beta-hydroxybutyrate) or in the absence of alternate fuels (as occurs in hyperinsulinism) cuts down nonessential functions in order to conserve energy. When the glucose levels drop below 30 mg/dl cerebral blood flow increases in an attempt to increase glucose delivery (10). In conditions of prolonged fasting, as beta-hydroxybutyrate levels rise, monocarboxylate transporter 1 (MCT1) transports the beta-hydroxybutyrate across the blood brain barrier, which presents the brain with an alternative fuel for energy production. With very prolonged fasting, the brain is able to switch from utilizing almost 100% glucose for energy production to utilizing almost all ketones (11). In disease conditions such as glycogen storage disease (GSD) type 1, glycogenolysis results in elevated lactate levels because of the inability to de-phosphorylate G-6-phos and generate glucose that can be transported out of the liver. As a result, the plasma glucose falls rapidly, and the plasma lactate levels rise to 5-10 mmol/L (4-5 times normal levels). Carriers such as MCT1 transport this lactate across the blood brain barrier where the brain can efficiently metabolize it in the presence of oxygen through the citric acid cycle and produce the energy needed for brain function. Indeed, animal studies have demonstrated that the cerebral metabolic rate of oxygen consumption does not fall significantly during the initial phase of hypoglycemia when either ketones or lactate are available as an alternate substrate. In patients with diabetes, lactate infusions can prevent insulin induced neuroglycopenia (12). In addition, humans undergoing a ketogenic diet were able to transition from utilizing primarily glucose as brain fuel to ketones providing 17% of whole brain energy requirements with no overall change in the cerebral metabolic rate (13). It is for this reason that that hypoglycemia itself does not cause brain damage, it is a lack of fuel (glucose, beta-hydroxybutyrate or lactate combined) that causes brain damage. In addition to a lack of fuels for energy production a lack of oxygen supply to the brain prevents the utilization of lactate which can dramatically worsen energy failure in the brain.

 

In non-physiological conditions when the plasma glucose continues to drop down to 30 mg/dL or lower, cerebral spinal fluid glucose levels become almost zero and in the absence of either ketones or lactate essential functions of the brain stop and cell death begins to occur (14).  Breakdown of the phospholipids in the brain provides free fatty acids and breakdown of protein provides gluconeogenic substrates but also increases brain ammonia levels 10-15 fold (15). Whilst breakdown of tissues provides fuel for energy production, this process also damages vital cells and organelles causing permanent cellular destruction. Once the production of energy is insufficient to maintain adequate high energy phosphate compounds, the infant or child will become comatose and have an isoelectric electroencephalogram. It is not known exactly how long glucose and the alternate fuel levels need to be low to cause harm nor how low the total fuels need to be prior to the onset of permanent brain damage; however, it is likely to differ based on availability of alternative fuels, rates of brain metabolism (increased in seizures), and degree of plasma oxygenation. In conditions such as hyperinsulinism, where there are no alternate fuels available and when patients may have seizures which both increase brain energy needs and decreases the availability of oxygen in the blood stream, all these factors combine and may cause profound brain damage (16).

 

It is clear that not all hypoglycemia is equal, and the responsible physician must assess the etiology of the hypoglycemia, the likelihood of the presence of alternate fuels, and the presence of good blood flow and oxygenation in order to understand the danger of any given episode of hypoglycemia. The importance of correctly identifying the etiology of the hypoglycemia thus affects not just the long-term approach to management but also the immediate approach to the infant or child. This also explains why efforts to define a single blood glucose value that predicts brain damage is impossible and why efforts to define neurological outcome relative to glucose levels alone are not valid.

 

DEFINITION OF HYPOGLYCEMIA

 

For the reasons stated above, a single measurement of glucose does not reflect the total energy availability to the brain. Therefore, when one tries to define hypoglycemia, one should consider why a definition is required. We suggest that the definition of hypoglycemia needs to include three critical aspects. 

 

  • Diagnostic hypoglycemia is the level of glucose required to make a diagnosis of the etiology of the hypoglycemia.
  • Therapeutic hypoglycemia is the level of glucose one should aim to stay above during treatment of hypoglycemic disorders.
  • The concentration of glucose at which hypoglycemia causes brain damage is unknown and practically there is no such value.

 

Diagnostic Hypoglycemia 

 

Evaluation of a blood and urine sample when the plasma glucose is less than 50 mg/dL is essential in determining the etiology of hypoglycemia. This allows a determination of the metabolic profile at the time of hypoglycemia. This sample is often referred to as a “critical sample” and typically includes both blood (plasma) and urine samples, which are analyzed for the analytes in Table 2.

 

Table 2. The Critical Sample: Blood and urine samples to be drawn at a time of hypoglycemia (plasma glucose <50mg/dL) to guide the diagnosis of the etiology of hypoglycemia with additional testing for certain conditions.

Plasma

     Glucose

     Insulin

     Cortisol

     Growth hormone

     Beta-hydroxybutyrate

     Free fatty acids

     Acylcarnitine profile

     Ammonia

     Liver function tests

Urine

     Urine organic acids

In suspected insulin administration

     C-peptide

     Specific insulin assays to measure biological insulin only

     Sulfonylurea screen

In suspected insulinoma

     Proinsulin

     C-peptide

     Sulfonylurea screen

In suspected fatty acid oxidation defects

     Free and total carnitine

 

The critical sample can be drawn either at a time of spontaneous hypoglycemia or at the end of a fasting study in which plasma glucose less than 50 mg/dL is deliberately induced. Once the plasma glucose is <50 mg/dL, the counter regulatory hormones should be elevated, and insulin suppressed. The metabolic systems of glycogenolysis, gluconeogenesis, fatty acid oxidation, and ketone utilization should be underway and with glucagon administration, there should be no glycemic response as the liver should have utilized all the glycogen stores. Interpretation of the critical sample is the key to making the correct diagnosis (Table 3).  Figure 2 is a simple diagnostic algorithm to aid the provider.

 

Table 3. The Differential Diagnosis of Hypoglycemia in Neonates, Infants, and Children Based on the Results of the Critical Sample.

Disorder

Plasma Fuels when glucose <2.8 mmol/L

Plasma Hormones at End of Fast

Clinical Features

Lactate

mmol/L

FFA

mmol/L

BOHB

mmol/L

Insulin (µu/mL)

Cortisol (µg/dL)

GH (ng/mL)

ΔPG following glucagon (mg/dL)

Normal infants

0.7-1.5

>1.7

2-4

<2

>18

>10

<30

Normal

Hyperinsulinism

N

<1.7

<1.8

>1

N

N

>30

LGA

Cortisol deficiency

N

N

N

N

<14*

N

N

Hyperpigmentation if primary

GH deficiency

N

N

N

N

N

<8

N

Short stature

Panhypopituitarism

N

Low-N

Low-N

N

Low

Low

N

Short stature, midline facial malformation, optic hypoplasia, micro/small penis

Epinephrine deficiency (beta-blocker)

N

<1.5

<2

N

N

N

N

 

Debrancher deficiency (GSD III)

N

N

N

N

N

N

N

Hepatomegaly 4+

Phosphorylase deficiency (GSD VI)

N

N

N

N

N

N

N

Hepatomegaly 2+

Phosphorylase kinase deficiency (GSD IX)

N

N

N

N

N

N

N

Hepatomegaly 2+

Glycogen synthase deficiency (GSD 0)

N

N

N

N

N

N

N

 

Glucose 6-phosphatase deficiency (GSD la and lb)

4-8 +

N

<2

N

N

N

Normal glucose elevated lactate

Hepatomegaly 4+

Fructose 1, 6-diphosphatase deficiency

4-8 +

N

N

N

N

N

N

Hepatomegaly 1+

Pyruvate carboxylase deficiency

4-8 +

N

N

N

N

N

N

 

*Depending on sensitivity of the assay used (17). Note that findings of a single low growth hormone or cortisol level at the time of hypoglycemia has poor specificity for deficiency of either hormone (18,19). Stimulation testing may be needed to confirm the diagnosis. FFA, free fatty acids; GH, growth hormone; GSD, glycogen storage disease; LGA, large for gestational age; N, normal; PG, plasma glucose. Adapted from De Leon DD, Thornton P, Stanley CA, Sperling MA. Hypoglycemia in the Newborn and Infant. In: Sperling MA, Majzoub JA, Menon RK, Stratakis CA, eds. Sperling Pediatric Endocrinology. Fifth ed: Elsevier; 2021 (20).

 

Figure 2. Hypoglycemia diagnosis based on plasma metabolic fuel responses. Measurement of lactate as a gluconeogenic substrate, FFA from adipose tissue lipolysis, and BOHB at the time of hypoglycemia segregates major groups of hypoglycemia disorders. FFA, free fatty acids; GH, growth hormone; HCO3, bicarbonate; BOHB, beta-hydroxybutyrate. Adapted from Thornton PS, Stanley CA, De Leon DD, Harris D, Haymond MW, Hussain K, Levitsky LL, Murad MH, Rozance PJ, Simmons RA, Sperling MA, Weinstein DA, White NH, Wolfsdorf JI, Pediatric Endocrine S. Recommendations from the Pediatric Endocrine Society for Evaluation and Management of Persistent Hypoglycemia in Neonates, Infants, and Children. J Pediatr. 2015;167(2):238-245 (21).

 

Therapeutic Hypoglycemia

 

Generally, the target to treat infants and children with known hypoglycemic disorders is to keep the blood glucose above 70 mg/dL. There are certain conditions when the target maybe higher such as patients in acute decompensation with fatty acid oxidation defects where the goal is to stimulate insulin secretion which will prevent lipolysis and then fatty acid oxidation. In these circumstances it may require that the glucose levels are elevated to greater than 85 mg/dL.  Thus, in this case, getting the blood sugar up to 70 mg/dL will prevent the consequences of hypoglycemia but will not rapidly reverse the breakdown of lipids to free fatty acids and glycerol and thus will not stop the accumulation the abnormal metabolites of fatty acid oxidation. In children with GSD 1 the provision of adequate glucose to get the blood sugar greater than 70 mg/dL will provide the brain with adequate glucose for energy, however raising the blood sugar too high will drive glucose to lactate and thus worsen lactate levels. So, for individuals with GSD 1 the goal is to maintain the glucose at a level that will maximally suppress lactate levels (70-85 mg/dL) without triggering insulin release.

 

A second reason to maintain the plasma glucose greater than 70 mg/dL is to prevent hypoglycemic unawareness. Recurrent episodes of glucose levels less than 70 mg/dL over time will blunt the release of epinephrine by the autonomic nervous system. The secretion of epinephrine triggers awareness by the child and young adult of impending neuroglycopenia and allows them to react by food seeking behavior to prevent further hypoglycemia. After every episode of hypoglycemia, this counter regulatory response is blunted for up to 5 days and if the hypoglycemia recurs inside this period, the response is blunted even more. This failure to secrete epinephrine in response to hypoglycemia is hypoglycemia associated autonomic failure (HAAF) (22).

 

NEONATAL TRANSITIONAL GLUCOSE REGULATION

 

The transition from intrauterine to extra uterine life is a critical time for the neonate. In utero, the fetus is exposed to seemingly limitless supplies of glucose, amino acids, and other fuels necessary for growth and development, through the maternal placenta unit. Because of the insulin resistance of pregnancy, maternal plasma glucose levels are higher than in the non-pregnant state. Glucose is transported across the placenta by facilitated diffusion and fetal plasma glucose levels are approximately 8-15 mg/dL lower than maternal levels. Fetal plasma glucose levels are determined by maternal plasma glucose levels, however fetal insulin secretion is regulated by fetal plasma glucose levels. Recent data have shown that the threshold for insulin secretion in the fetus is lower than the adult and that this is controlled at the level of the KATP channel by decreased trafficking of the channel to the beta cell plasma membrane (23). The function of insulin in the fetus is to act as the main anabolic hormone and drive fetal growth. At the time of birth and clamping of the umbilical cord this constant supply of glucose is interrupted. The now newborn has to suddenly adjust initially to no glucose and soon thereafter to limited glucose input via, intermittent feeding and a nutrition source that is primarily protein (colostrum). The recent glucose in well babies study (GLOW) has shown that this transition can last up to 72-96 hours in normal breast-fed babies and consists of two phases (24): initially a hypoketotic hypoglycemic phase, and then a ketotic euglycemic/hypoglycemic stage until the mother’s milk comes in (Figure 3).

 

Figure 3. Glucose and beta-hydroxybutyrate levels in healthy term newborns over the first 96 hours of life demonstrating the period of transitional hyperinsulinism during adaptation to extrauterine life followed by the period of hyperketotic euglycemic/hypoglycemic phase of starvation until breast milk has come in and the neonate has adequate caloric intake. Stanley CA, et al. Figure 1. From Stanley CA, Thornton PS, De Leon DD. New approaches to screening and management of neonatal hypoglycemia based on improved understanding of the molecular mechanism of hypoglycemia. Front Pediatr. 2023;11:1071206 (25) CC BY 4.0. Adapted from Harris DL, Weston PJ, Harding JE. Alternative Cerebral Fuels in the First Five Days in Healthy Term Infants: The Glucose in Well Babies (GLOW) Study. J Pediatr. 2021;231:81-86 e82 (26).

 

In healthy newborns with normal birth weight, the glycogen stores from the liver built up during pregnancy, provide the initial glucose support. In the healthy newborn, liver glycogen concentration is the highest of all times in life and can supply the newborn with glucose for up to 12 hours. In preterm infants and infants born small for gestational age (SGA) or with intra-uterine growth retardation (IUGR), this supply is dramatically diminished thus increasing the risk of hypoglycemia in these babies. In addition, in the immediate newborn period, lactate levels are elevated (24), and gluconeogenesis from lactate rapidly increases over the first few hours of life, as the rate limiting enzyme of gluconeogenesis, phosphoenolpyruvate carboxy-kinase (PEPCK) increases to adult level by 24 hours of life. In the immediate post-natal hours, ketone levels are inappropriately low for the plasma glucose due to the lower threshold for insulin secretion but over the first 48 hours as the threshold for glucose stimulated insulin release rises, plasma ketone concentration begins to increase. In addition, medium chain fatty acids from colostrum are directly absorbed and transported to the liver through the portal circulation and undergo beta oxidation to generate ketones. In starved breastfed infants, ketones can reach 2 mmol/L by 48-72 hours of life (26).

 

The newborn rapidly adjusts from living in a steady anabolic state to an intermittent catabolic state until nutrition becomes adequate to supply sufficient energy to grow. In the relatively hypoxemic environment of in-utero life, insulin has a lower threshold for secretion to ensure the fetus remains in an anabolic state. After birth the newborn must adjust rapidly from the steady secretion of insulin associated with consistent fetal glucose availability to rapidly changing plasma glucose levels with feeding and to be able to deal with intermittent fasting. Over the first 12-24 hours of life the threshold for insulin secretion rises to the more typical 80-85 mg/dL seen in older infants, children and adults. All of this occurs while awaiting maturation of all the enzymes needed for gluconeogenesis and fatty acid oxidation. The consequences of these changes are that in the first 1-2 hours of life the blood glucose concentration falls to a mean of approximately 55 mg/dL (Figure 3). Gradually over the next 12-48 hours the plasma glucose concentration starts to rise to levels (60 mg/dL) approaching normal adult levels and by 72-84 hours of life, transition is complete and plasma glucose levels are in essence similar to adults (70 to 110 mg/dL) (2,24). During the first 24-48 hours of life upwards of 35-45% of normal healthy term babies may have occasional plasma glucose levels less than 50 mg/dL, however by 72-84 hours of life persistent plasma glucose levels less than 60 mg/dL reflect an underlying pathological problem (21).

 

Approach to Neonatal Glucose Screening and Treatment

 

The dilemma for physicians caring for newborns is how to differentiate babies having normal transitional glucose regulation with transient hypoglycemia from those with pathological hypoglycemia due to conditions such as perinatal stress-induced hyperinsulinism (PSHI).  The 2015 Pediatric Endocrine Society (PES) recommendations (21) guide the physician on how to differentiate physiological plasma glucose levels less than 50 mg/dL from pathological causes of hypoglycemia in the first days of life. They recommend that normal healthy term babies with no symptoms of hypoglycemia do not require glucose monitoring. Babies at risk for hypoglycemia such as those with IUGR, those born large for gestational age (LGA) or SGA, those born late pre-term, and those in whom maternal factors increase the risk of hypoglycemia such as maternal hypertension, preeclampsia, and eclampsia should be monitored.  In addition, babies who have symptoms consistent with hypoglycemia (Table 4) should also be screened for hypoglycemia. 

 

Table 4. Symptoms and Signs of Hypoglycemia

Neurogenic symptoms appear when glucose <70 mg/dL (<2.8mmol/L)

     Jitteriness (neonates), shakiness

     Tachycardia

     Pallor

     Hypothermia

     Hunger

     Sweating

     Weakness

Neuroglycopenic symptoms appear when glucose <45-50 mg/dL (2.5-2.8 mmol/L)

     Poor feeding (neonates)

     Apnea (neonates)

     Floppiness (neonates)

     Weak/high-pitched cry (neonates)

     Lip smacking and eye twitching (neonates)

     Headache

     Confusion

     Irritability, outbursts of temper

     Bizarre neurological signs

     Motor and sensory disturbances

     Lethargy

     Decreased muscle tone

     Unconsciousness

     Seizure

           

The PES guidelines recommend that the target to treat these infants be 50 mg/dL but if intravenous glucose is required indicating a more serious problem, the target should be 60-70 mg/dL. After 48 hours of life the target for treatment is 60 mg/dL. The recommendations also state that if a known hypoglycemic disorder is identified then the target for treatment is to maintain the blood glucose greater than 70 mg/dL. These goals should be achieved initially by appropriate resuscitation in the newborn period with the avoidance of cold stress to the baby, early skin to skin contact, early breast feeding or if chosen by mothers, bottle feeding (27).  Supplemental glucose can be given with dextrose gel (28). In neonates with symptomatic hypoglycemia or those in whom the above measures fail to maintain the plasma glucose above 50 mg/dL intravenous glucose therapy should be initiated at a glucose infusion rate (GIR) of 4-6 mg/kg/min with or without a 200 mg/kg bolus of IV dextrose. As shown. in Figure 4, within 10 minutes following an IV dextrose bolus of 200 mg/kg followed by a GIR of 8 mg/kg/min, plasma glucose levels reach close to 90% of the glucose concentration measured at 60 minutes. Thus, in patients with dangerously low glucose levels (<30 mg/dL) plasma glucose levels should be rechecked in 10-15 minutes to demonstrate correction of the hypoglycemia and if the glucose has not achieved the target level, then a repeat bolus and increase in the IV infusion rate of glucose should be implemented. In this manner, severe hypoglycemia can be rapidly corrected without significant overcorrection. At all times during treatment of hypoglycemia, the newborn infant should be encouraged to continue to feed orally, unless the patient is seizing or has significant respiratory distress in which case feeding should be withheld temporarily. 

 

Figure 4. The effect of a 200 mg/kg IV mini-bolus in addition to starting a glucose infusion rate of 8 mg/kg/minute compared to just starting 8 mg/kg/minute infusion rate alone. Reprinted from J. Pediatr, 97(2), Lilien LD, Pildes RS, Srinivasan G, Voora S, Yeh TF., Treatment of neonatal hypoglycemia with minibolus and intravenous glucose infusion, 295-298, 1980, with permission from Elsevier (29).

 

The single most important clinical differentiators of pathological hypoglycemia from transitional hypoglycemia in the newborn period are the presence of neuroglycopenic signs of hypoglycemia (apnea, lethargy, seizures) and the need for intravenous glucose treatment to correct low glucose levels. In both these circumstances the newborn should undergo a fasting study of 6-9 hours to demonstrate that normal glucose regulation has returned (ability to keep glucose >60-70 mg/dL for 6-9 hours) prior to discharge from the hospital. In babies who have hypoglycemia within 6-9 hours of commencing fasting an underlying pathological cause should be sought prior to discharge and appropriate therapy implemented. For babies with persistent glucose <60 mg/dL after 48 hours of life the use of point of care ketone screening may assist in detecting those babies with failed breast feeding from those with the more serious hypoketotic forms of hypoglycemia such as hyperinsulinism, hypopituitarism, or the fatty acid oxidation defects. In the case of persistent hypoglycemia with hypoketosis, further investigations need to be done to determine the etiology.

 

CLINICAL SYMPTOMS AND SIGNS OF HYPOGLYCEMIA

 

Classical symptoms and signs of hypoglycemia are outlined in Table 4. It is important to note that children <5 years of age will generally have hypoglycemic unawareness and not be able to recognize the neurogenic symptoms of hypoglycemia. Neonatal hypoglycemia, by virtue of neonates being unable to communicate in a complex way, may be difficult to detect as many of the signs of hypoglycemia occur in normal neonates (30). Subtle signs such as poor feeding, sleepiness, and jitteriness occur in many non-hypoglycemic babies and clinical judgement as to when to check glucose is required. However, if in doubt it is better to check blood glucose (21). For more serious symptoms, such as lethargy, seizures, apnea and coma, screening point of care glucose should be performed and hypoglycemia simultaneously confirmed by laboratory measured plasma glucose. Older children with acquired hypoglycemia such as that caused by insulinoma, often have hypoglycemic unawareness due to the frequency of hypoglycemia and only demonstrate neuroglycopenic signs. All neonates, infants, and children with neuroglycopenic symptoms or signs must have a plasma glucose concentration checked and if <60-70 mg/dL serious consideration of hypoglycemia as a cause should be entertained.

 

HORMONAL CAUSES OF HYPOGLYCEMIA

 

Hyperinsulinism

 

Hyperinsulinism refers to the group of hypoglycemic disorders caused by dysregulated, excessive insulin secretion or action via signaling. Insulin secretion from pancreatic beta-cells is tightly regulated and predominantly controlled by the plasma glucose concentration (Figure 5). In normal circumstances glucose enters the beta-cell via insulin-independent glucose transporters and is phosphorylated by glucokinase to G-6-phos. Glucokinase acts as the “glucose sensor” setting the threshold for insulin secretion; normally, insulin secretion is triggered when plasma glucose levels are above 85 mg/dL. Metabolism of G-6-phos leads to an increase in the intracellular adenosine triphosphate (ATP) to adenosine diphosphate (ADP) ratio which regulates subsequent closure of the ATP-sensitive plasma membrane KATP channels, membrane depolarization, activation of voltage-gated calcium channels, calcium influx, and release of insulin from stored granules. Amino acid metabolism also influences insulin secretion. Leucine allosterically activates glutamate dehydrogenase, increasing oxidation of glutamate to alpha-ketoglutarate, thereby increasing the ATP-to-ADP ratio, triggering the insulin secretion cascade. Glutamine mediates glucagon-like peptide 1 (GLP-1) receptor signaling, which acts as an “amplification pathway” for insulin secretion.

 

Figure 5. Diagram of the pathways stimulating beta-cell insulin secretion. Glucose enters the beta-cell via glucose transporters and is phosphorylated by GCK to G-6-phos. Oxidation of G-6-phos in mitochondria increases the ATP-to-ADP ratio, leading to closure of plasma membrane ATP-sensitive KATP channels (comprised of SUR1 and Kir6.2 subunits), inhibition of K+ efflux, membrane depolarization, opening of voltage-dependent Ca++ channels, Ca++ influx, and release of insulin from storage granules. Amino acids stimulate insulin secretion through glutamine-mediated amplification of GLP-1 receptor signaling. Leucine stimulates insulin secretion by increasing the oxidation of glutamate via activation of GDH, thereby increasing the ATP-to-ADP ratio and triggering the insulin secretion cascade. HK1 and MCT1 are not normally present in the beta-cell. Diazoxide suppresses insulin secretion by activating the KATP channel to remain open. Somatostatin suppresses insulin secretion downstream of Ca++ signaling. Known sites of defects associated with congenital hyperinsulinism are indicated by bold and underlined font and include GCK (glucokinase), HK1 (hexokinase 1), PGM1 (phosphoglucomutase 1), MCT1 (monocarboxylate transporter 1), UCP2 (uncoupling protein 2), SCHAD (short-chain 3-hydroxyacyl-coenzyme A dehydrogenase), GDH (glutamate dehydrogenase), HNF1A (hepatocyte nuclear factor 1A), HNFA (hepatocyte nuclear factor 4A), SUR1 (sulfonylurea receptor 1), Kir6.2 (inwardly rectifying potassium channel 6.2). Other abbreviations: OAA, oxaloacetate; PEP, phosphoenolpyruvate; α-KG, α-ketoglutarate; GAD, glutamic acid decarboxylase; GABA, γ-aminobutyrate, GHB, γ-hydroxybutyrate; SSA, succinic semialdehyde; Ins, insulin. Reprinted from Stanley CA, Perspective on the Genetics and Diagnosis of Congenital Hyperinsulinism Disorders, J Clin Endocrinol Metab, 2016, 101(3):815-826 by permission of Oxford University Press and Endocrine Society (31).

 

In neonates, hyperinsulinism may occur as a transient issue due to intrauterine factors, in association with recognized clinical syndromes, or may reflect genetic mutations in the pathway of insulin secretion (Figure 5). In older children, acquired forms of hyperinsulinism, including insulinoma, autoimmune causes, and medications are more common. However, late presentation of monogenic forms of hyperinsulinism remain possible (Table 5).

 

Table 5. Classification of Hyperinsulinism Disorders in Infants and Children.

Acquired neonatal HI

Risk Factors

Clinical features

 

Maternal diabetes, including gestational diabetes

Large for gestational age (LGA)

Cardiac Hypertrophy

 

Perinatal stress-induced HI

Small for gestational age (SGA)

Maternal hypertension, pre-eclampsia, eclampsia

 

Maternal drugs

Ritodrine, sulfonylurea, high GIR during labor etc.

Acquired non-neonatal HI

Categories

Clinical features

 

Neoplastic HI

Insulinoma (sporadic or MEN1)

 

Surgically induced HI

Post-gastric bypass, post-fundoplication for gastro-esophageal reflux (NIPHS: non-insulinoma pancreatogenous hypoglycemia syndrome)

 

Drug-induced HI

Antidiabetic medications (Insulin, sulfonylureas)

 

Autoimmune HI (anti-insulin or insulin receptor-activating antibodies)

Spontaneous or associated with drugs or viral infections

Hirata's disease (Insulin Autoimmune Syndrome: anti-insulin antibodies post sulfhydryl medications: methimazole, carbimazole, alpha-lipoic acid and post

measles virus, mumps virus, rubella virus, varicella zoster virus, coxsackie B virus and hepatitis C virus)

Genetic HI:  Isolated HI

Histology

Genes

 

Diffuse form

ABCC8, KCNJ11, GLUD1, GCK, HK1, HNF4A, HNF1A, HADH, SLC16A1, UCP2

 

Focal form

Paternally inherited AR variants of ABCC8 or KCNJ11

 

LINE- HI (Mosaic HI, Atypical HI)

Sporadic mosaic AD variants of ABCC8, GCK, and inappropriate expression of HK1

Genetic HI: Syndromic HI, select forms

Syndrome

Gene

 

Beckwith-Wiedemann syndrome

Genetic or epigenetic changes of imprinted region 11p15.5 (especially paternal UPD11p), mutations of imprinting control genes

Paternal UPD11p combined with paternal recessive ABCC8 or KCNJ11 mutation

 

Kabuki syndrome

KMT2D, KDM6A (usually mosaic)

 

Turner syndrome

Mosaic partial or complete X chromosome monosomy

HI mimickers: Hypoinsulinemic hypoketotic hypoglycemia

 

 

Autoimmune mimicker

Insulin resistance syndrome type B (anti-insulin receptor antibodies post viral infection (HIV, HTLV1, hepatitis C) or lymphoproliferative disease, or autoimmune disease)

 

Paraneoplastic secretion of pro-IGF2

Non-islets cells tumor hypoglycemia (NICTH, Doege-Potter syndrome)

 

Genetic disorders of insulin signaling

Mutations in AKT2, AKT3, PIK3CA, PIK3R2, CCND2, INSR

 

Fatty acid oxidation disorders

Abnormalities in the carnitine cycle, beta-oxidation, electron transfer and ketone synthesis. 

 

Adapted from De Leon DD, Arnoux JB, Banerjee I, Bergada I, Bhatti T, Conwell LS, Fu JF, Flanagan SE, Gillis D, Meissner T, Mohnike K, Pasquini TLS, Shah P, Stanley CA, Vella A, Yorifuji T, Thornton PS. International Guidelines for the Diagnosis and Management of Hyperinsulinism. Horm Res Paediatr. 2023 (32). 

 

Clinically, hyperinsulinism should be suspected when a higher than typical glucose infusion rate (GIR >8 mg/kg/minute) is required to maintain plasma glucose >70 mg/dL. Neonates with hyperinsulinism are often (but not always) born large for gestational age because insulin promotes fetal growth in utero.

 

Diagnosis is established by biochemical findings of inappropriate insulin action at the time of hypoglycemia (Table 6). These include inappropriately suppressed beta-hydroxybutyrate and free fatty acids, and a glycemic response to 1 mg intramuscular or intravenous glucagon administration (rise in plasma glucose >30 mg/dL within 40 minutes following glucagon administration) (33). Importantly, the diagnosis does not rest entirely on the presence or absence of detectable insulin and c-peptide levels at the time of hypoglycemia. Elevated insulin levels may not be observed in cases of HI if the laboratory specimen is hemolyzed (33), or when the plasma insulin concentration is below the detection threshold of the insulin assay utilized. Conversely, with improvements in assay sensitivity, plasma insulin may be reported as detectable in the absence of HI. Thus, accurate diagnosis of HI requires a comprehensive interpretation of biochemical markers of insulin action and does not rely solely upon an insulin level.

 

Table 6. Diagnostic Features of HI at the Time of Hypoglycemia (plasma glucose <50 mg/dL [2.8 mmol/L]).

Evidence of excessive insulin action at the time of hypoglycemia  

Suppressed plasma β-hydroxybutyrate (< 1.8 mmol/L) 

Suppressed plasma free fatty acids (< 1.7 mmol/L) 

Inappropriately large glycemic response to glucagon (≥ 30 mg/dL [≥1.7 mmol/L])

Increased glucose infusion rate required to maintain euglycemia (above normal for age):

>8 mg/kg/min for neonates

>3 mg/kg/min for adults

Evidence of excessive insulin secretion/inadequate suppression of insulin secretion at the time of hypoglycemia (these are less definitive than evidence of excessive insulin action)

Plasma Insulin >1.25 μU/mL (8.7 pmol/L)* 

C-peptide >0.5 ng/mL (> 0.17 nmol/L)*

*Note that these thresholds depend upon the assay utilized. Adapted from De Leon DD, Arnoux JB, Banerjee I, Bergada I, Bhatti T, Conwell LS, Fu JF, Flanagan SE, Gillis D, Meissner T, Mohnike K, Pasquini TLS, Shah P, Stanley CA, Vella A, Yorifuji T, Thornton PS. International Guidelines for the Diagnosis and Management of Hyperinsulinism. Horm Res Paediatr. 2023 (32).

 

Regardless of the etiology, prompt identification and treatment of hyperinsulinism is critical. Since insulin inhibits gluconeogenesis and ketogenesis, ketones and lactate are not sufficiently available as alternative fuels for the brain during hyperinsulinemic hypoglycemia. Consequently, the risk of brain injury is high. Initial management is thus to rapidly correct hypoglycemia via administration of IV dextrose bolus (200 mg/kg or 2 ml/kg D10%). Following this, continuous IV dextrose infusion should be started at a GIR of 4-8 mg/kg/min and quickly titrated (by 4 mg/kg/min if hypoglycemia persists on a GIR of 8 mg/kg/min) as needed to maintain plasma glucose >70 mg/dL. Some infants with hyperinsulinism may require GIRs as high as 20-30 mg/kg/min to maintain euglycemia. Higher concentrations of dextrose (D20%-D50%) may be utilized via a central line to minimize fluid overload in these settings. Glucagon can be administered intramuscularly if IV access is lost, or unable to be obtained, as a temporizing measure to raise plasma glucose. Glucagon can also be administered as a continuous IV infusion (doses of 2-3 mcg/kg/day up to 10 mcg/kg/day, or alternatively, infusion of 1 mg/day) to permit lowering of GIR (and thus fluid load) in cases where fluid overload is a concern.  In general, use of glucagon may be associated with up to 50% reduction in the GIR (34).

 

MONOGENIC FORMS OF HYPERINSULINISM

 

The incidence of congenital hyperinsulinism caused by genetic defects in the insulin secretion pathway is estimated at 1 in 40,000 live births (35). A higher incidence, of up to 1 in 2,500 births, has been described in Saudi Arabia, in a region of Finland, and in some of the Ashkenazi-Jewish population. Congenital hyperinsulinism can be classified by genetic etiology, histology, and response to treatment with diazoxide. At least 11 different monogenic causes have been identified. A high likelihood that yet undiscovered genetic etiologies exist is suggested by the low rate (approximately 50%) of mutation detection in patients with diazoxide-responsive forms of hyperinsulinism (36).

 

First-line treatment for congenital hyperinsulinism is diazoxide, a KATP channel opener that inhibits insulin secretion. Diazoxide therapeutic dose range is 5-15 mg/kg/day. Response to diazoxide should be assessed after 5 days of treatment with a carefully monitored fast (safety fast, Table 7). Responsiveness to diazoxide is both of clinical and diagnostic value (Figure 6). It is defined by maintenance of plasma glucose >70 mg/dL over the fasting period (Table 7) or a rise in beta-hydroxybutyrate >2 mmol/L prior to decline in plasma glucose below 50 mg/dL (37). Side effects of diazoxide include hypertrichosis (prevalence 30%), fluid overload — which may be complicated by pulmonary hypertension (prevalence 2-3%) — neutropenia and thrombocytopenia (prevalence 15%), and hyperuricemia (prevalence 5%) (38,39). To mitigate risks of fluid overload, empiric co-administration of a diuretic is recommended (40). Recommended surveillance on diazoxide includes echocardiogram, complete blood count with differential, electrolytes, and uric acid level at baseline and 5-7 days after diazoxide initiation. Following this, it is recommended to measure complete blood count with differential, electrolytes, and uric acid levels every 6 months (38-40).

 

Table 7. Safety/Cure Fasting Test Procedure

Have blood drawing IV line in place 

Check glucose (POC meter) and beta-hydroxybutyrate every 2-3 hours until glucose <70 mg/dL; then every 2 hours until <60 mg/dL; then hourly until < 50mg/dL

When glucose <60mg/dL by POC meter, send specimen for laboratory confirmation of plasma glucose

Terminate fast when: 

Plasma BOHB >2 mmol/L on two separate samples 1 hour apart, or

Plasma glucose <50 mg/dL, or  

Duration of fasting

     Safety fast: >9-12 hours in <1 month old, or >12 hours in 1 month-1 year old, or >18

hours in >1 year old

     Cure fast: >18 hours in <1 year old, or >36 hours in 1-10 years old, or 72 hours in >10

years old 

Adapted from De Leon DD, Arnoux JB, Banerjee I, Bergada I, Bhatti T, Conwell LS, Fu JF, Flanagan SE, Gillis D, Meissner T, Mohnike K, Pasquini TLS, Shah P, Stanley CA, Vella A, Yorifuji T, Thornton PS. International Guidelines for the Diagnosis and Management of Hyperinsulinism. Horm Res Paediatr. 2023 (32).

 

Notably, most children with hyperinsulinism due to mutations in genes encoding the KATP channel will not respond to diazoxide. Histologically, there are several forms of KATP channel hyperinsulinism including focal, diffuse and atypical. Many of these children will have a focal form of hyperinsulinism that can be cured by surgery (see below). In children with diazoxide-unresponsive hyperinsulinism, genetic testing that includes sequencing of KATP channel genes should be sent on DNA from the affected child and their parents simultaneously. This approach permits timely identification of children likely to have focal hyperinsulinism, and who can be cured by surgery. Sending the parental DNA with the child saves 1-2 weeks of time and many of the laboratories perform the testing free of charge if a mutation is found in the child in which diagnosing the parent of origin will change the management. In addition, rapid genetic testing with a turnaround time of 4-7 days is critical in the management of diazoxide-unresponsive hyperinsulinism because this quickly allows the physician to determine who should be referred to a multidisciplinary hyperinsulinism center for imaging with 18F-DOPA PET scan which can currently be used only under an investigational new drug license (IND) and is only available in several places in the country. Obtaining results of the patient and both parents within 7 days compared to 28-40 days if sent to a conventional genetic laboratory could save upwards of $100,000 to $200,000 and 21 days of hospital stay during which time the patient is at risk of severe hypoglycemia, development of feeding intolerance, line infections, and other iatrogenic complications of prolonged hospitalization.

 

Figure 6. HI Diagnostic and Treatment Algorithm. Once HI is diagnosed, effectiveness of diazoxide treatment needs to be assessed. Responsiveness to diazoxide is shown by demonstrating the ability to fast an age-appropriate interval (minimum 9 hours for neonate) with plasma glucose >70 mg/dL and/or generate beta-hydroxybutyrate >2 mmol/L prior to plasma glucose <50 mg/dL. For patients unresponsive to diazoxide, expedited genetic testing is obtained to differentiate diffuse and focal forms of HI. 18F-DOPA PET/CT is performed when genetic testing is suggestive of possible focal disease. For patients with diffuse, diazoxide-unresponsive disease, intensive medical therapy is initiated, with near-total pancreatectomy reserved for medically unresponsive cases. 18F-DOPA PET/CT 18-fluoro-L-3,4-dihydroxyphenylalanine positron emission tomography.

 

Second-line medical management options include somatostatin analogues – octreotide and the long-acting analog lanreotide - and enteral dextrose. Enteral dextrose is administered as a continuous infusion of 20% dextrose solution via nasogastric or gastrostomy tube (maximum enteral GIR 10 mg/kg/min). Octreotide is a short-acting somatostatin analogue administered multiple times per day subcutaneously (dose range: 2-20 mcg/kg/day, divided every 6-8 hours). Octreotide should not be used in children <2 months of age due to an association with fatal necrotizing enterocolitis. Lanreotide is used in children >1 year of age (administered as 60 mg injection monthly) (41). Several new therapies, including glucagon analogues, oral somatostatin analogues, insulin receptor modulators, and GLP-1 receptor antagonists, are under development (42).

 

In diffuse congenital hyperinsulinism cases that do not respond to medical treatment, near-total pancreatectomy is performed. Near-total pancreatectomy is palliative, not curative; significant hypoglycemia persists in up to 50% of children. Additionally, this procedure is complicated by development of exocrine pancreatic insufficiency and late-onset post-pancreatectomy diabetes.

 

KATP Hyperinsulinism (KATP HI)

 

The most common and severe form of congenital hyperinsulinism, KATP HI, is caused by inactivating mutations in ABCC8 or KCNJ11. Both located on chromosome 11p15.1, these genes each encode a subunit of the pancreatic beta-cell KATP channel. Inactivation of the KATP channel results in beta-cell depolarization (Figure 5), and inappropriate secretion of insulin. In addition to severe fasting hypoglycemia, KATP HI is characterized by protein-induced hypoglycemia mediated by GLP-1 receptor signaling (6).

 

KATP HI is histologically classified as diffuse, in which all beta-cells are affected, focal, in which a localized subset beta-cells are affected, or less commonly, atypical (also termed Localized Islet Nuclear Enlargement [LINE-HI]). Focal KATP HI results from a “two hit” mechanism involving paternal transmission of a recessive KATP HI mutation and a somatic loss of heterozygosity for the maternal 11p15 region yielding imbalanced expression of imprinted tumor suppressor genes (43). Dominant or recessive mutations in KATP HI genes cause diffuse KATP HI. Often, children with atypical histology (LINE-HI) do not have an identifiable mutation in standard sequencing of peripheral blood; however, low-level mosaic mutations are increasingly recognized as causative (44).

 

Infants with diffuse forms of KATP HI are often born large for gestational age and present with symptomatic hypoglycemia in the first few days of life. While infants with the focal form of KATP HI are more likely to have normal birth weight and present at an older age than those with diffuse disease, the two histologic forms are often indistinguishable in clinical practice (45). The recessive, focal, and atypical (LINE-HI) forms of KATP HI are usually not responsive to diazoxide. In contrast, dominant KATP HI may be diazoxide responsive due to retained partial function of KATP channels.

 

For infants with diazoxide-unresponsive hyperinsulinism, the goal is to identify those children with focal KATP HI since these children can be cured by surgery. Findings of a single recessive KATP mutation in the father, but not the mother, will have a 94% positive predictive value for focal hyperinsulinism (36) in the symptomatic infant. When suspected, 18-fluoro-L-3,4-dihydroxyphenylalanine positron emission tomography (18F-DOPA PET) is used to localize the focal lesion and guide surgical excision (46,47). Surgical cure rates for focal hyperinsulinism exceed 95%, when performed by experienced surgeons at a multidisciplinary hyperinsulinism center (48). 

 

For patients with diffuse KATP HI, intensive medical management is attempted, initially with continuous enteral dextrose (maximum enteral GIR 10 mg/kg/min). Octreotide can be added after 2 months of age (as above). Surgical management (near-total pancreatectomy with gastrostomy tube placement) is reserved for patients who fail to achieve adequate glycemic control with intensive medical therapy because this procedure is not curative and carries long-term risks of exocrine pancreatic insufficiency and insulin-dependent diabetes mellitus (45,49). Notably, regardless of initial treatment, the severity of hypoglycemia tends to improve with age in children with diffuse KATP HI. Determination of optimal management strategy thus depends on balancing short/intermediate-term risks of suboptimal hypoglycemia control and labor-intensive home management with potential further increased risk of long-term risk of adverse neurodevelopmental outcomes in the case of medical management versus inevitable post-pancreatectomy complications in the case of surgery. Management decisions are thus informed by the initial severity of hypoglycemia, responsiveness to intensive medical therapy, and the preferences and values of the child’s family. These children thus require specialized care and should be referred to a multidisciplinary hyperinsulinism center.

 

Glycemic status should be assessed in all children following pancreatectomy. Those children who do not require dextrose to maintain euglycemia postoperatively should undergo fasting study to demonstrate whether they are cured or need further medical management (Table 7) (32). Cure of HI can be demonstrated by the development of hyperketonemia (beta-hydroxybutyrate >1.8 mmol/L) prior to development of hypoglycemia (glucose <50 mg/dL). 

 

Later in life, dysregulated insulin secretion in diffuse KATP HI may additionally manifest as gestational, and in some cases insulin-dependent, diabetes mellitus even in the absence of prior pancreatectomy. This finding has been observed both in dominant and recessive forms of diffuse KATP HI (50,51). Mechanisms underlying the switch from hypoglycemia in early life to hyperglycemia later on remain incompletely understood. Impaired glucose-stimulated insulin secretion has been implicated based upon findings of reduced first-phase and maximal glucose-stimulated insulin secretion during oral glucose tolerance testing in adults with dominant KATP (51), and reduced acute insulin response to graded IV glucose infusion in children with recessive KATP HI (50). Impaired insulin secretory response to glucose (beta-cell “glucose blindness”) has also been proposed to underlie progression from hyperinsulinemic hypoglycemia to hyperglycemia in maturity-onset diabetes of the young (MODY) type 1 and type 3 (discussed below) (52-54). In mouse models of KATP HI, increased beta-cell apoptosis has been observed prior to the development of hyperglycemia, suggesting that a progressive decline in beta-cell mass may also play a role (55).

 

GCK Hyperinsulinism (GCK HI)

 

Dominant activating mutations in the GCK gene (chromosome 7p13), encoding glucokinase, cause hyperinsulinism by increasing the affinity of glucokinase for glucose, thereby lowering the threshold for pancreatic beta-cell insulin secretion (Figure 5). Clinical phenotype is highly variable, even within the same family. Presentation ranges from severe hypoglycemia at birth with large for gestational age birth weight, to milder hypoglycemia detected in adulthood. Response to diazoxide is also variable. In severe cases, near-total pancreatectomy may be required.

 

HK1 Hyperinsulinism (HK1 HI)

 

The HK1 gene (chromosome 10q22.1) encodes hexokinase, which has a much higher affinity for glucose than glucokinase. Normally, expression of HK1 is suppressed in pancreatic beta-cells postnatally. Dominantly inherited variations in non-coding regions of the HK1 gene result in aberrant beta-cell expression of hexokinase. As a consequence, appropriate suppression of insulin secretion at low plasma glucose levels is impaired, resulting in hypoglycemia (56). The clinical phenotype is variable. Most affected individuals present in the first weeks of life, but delayed presentation is not infrequently reported. Severity ranges from severe symptoms at birth to mild symptoms detected only following identification of an affected relative. Response to diazoxide is similarly heterogeneous and some affected individuals have required pancreatectomy  (56,57).

 

GDH Hyperinsulinism (GDH HI)

 

Dominant activating mutations in the GLUD1 gene (chromosome 10q23.2), encoding glutamate dehydrogenase (GDH), cause the hyperinsulinism hyperammonemia syndrome. Constitutively hyperactive GDH results in increased oxidation of glutamate to ammonia and alpha-ketoglutarate, the latter of which enters the citric acid cycle, thereby increasing the ATP-to-ADP ratio, triggering insulin secretion (58). Profound protein-induced hypoglycemia occurs because the amino acid leucine is potent allosteric activator of GDH (Figure 5).

 

Individuals with GDH HI typically have normal birth weight and later age of presentation (median age 4-5 months). In addition to fasting and protein-induced hypoglycemia, GDH HI is associated with an increased risk of epilepsy as well as higher rates of intellectual impairment, both of which appear to be independent of hypoglycemic neurological injury (59). Rates of learning and intellectual impairments have ranged from 37-77% in studies of children with GDH HI in which these outcomes were measured (59-61). The characteristic seizure type observed is generalized, atypical absence (62). These seizures occur in the setting of euglycemia and notably are distinct from the focal-onset seizures that may occur following hypoglycemic brain injury (62). Aberrant GDH activity in the central nervous system, and resultant altered glutamate balance, have been hypothesized to underlie these neurological differences. However, the mechanism by which these deficits occur has not yet been definitively established.

 

Persistent hyperammonemia (ammonia elevation 2-5 the normal range) due to GDH overactivity in the kidney is a cardinal feature but appears to be clinically asymptomatic (63). Importantly, affected individuals do not manifest symptoms of acute hyperammonemia encephalopathy (lethargy, headache, vomiting) as do children with urea cycle disorders. Plasma ammonia levels are not influenced by dietary protein load, nor are they lowered by typical therapies for hyperammonemia (sodium benzoate, N-carbamyl-glutamate) (64). The finding of hyperammonemia is thus useful in establishing a clinical diagnosis of GDH HI. However, once identified, plasma ammonia levels do not require serial monitoring or targeted intervention.

 

Hypoglycemia in GDH HI is usually well-managed with diazoxide and dietary modification. While dietary protein should not be restricted, it is imperative that affected individuals consume carbohydrate prior and concomitant to protein intake. Most individuals with GDH HI will respond to a 2:1 gram ratio of carbohydrates to protein to prevent protein induced hypoglycemia but some will need ratios of 3:1. Typically breast milk or formula milk will not trigger hypoglycemia, but once solid foods are introduced, especially meats, care must be taken to prevent protein induced hypoglycemia. The cardinal warning sign of this is patients in whom glucose control was adequate including fasting overnight but who suddenly develop post prandial hypoglycemia.

 

A formalized protein challenge test (Table 8) may be performed to evaluate adequacy of treatment in individuals with GDH HI. This test is also helpful to evaluate protein sensitivity in KATP HI, HADH HI (below), and congenital HI with negative genetic testing. A drop in the plasma glucose of more than 10 mg/dL or below 70 mg/dl is considered an abnormal result (evidence of protein sensitivity). Because this test must be done following a 3-4 hour fast to ensure the glucose levels are stable prior to starting the test it can only be done in patients whose fasting glucose is controlled. Patients who are very protein sensitive may drop the plasma glucose in the first 15-60 minutes.

 

Table 8.  Oral Protein Challenge Test Procedure

Make patient NPO for food and carbohydrate containing fluids for 3-4 hours pre procedure

Insert peripheral intravenous line and have dextrose 10% available for emergency use

Measure baseline glucose and insulin

Administer 1g/kg of food protein PO over 10-15 minutes. Alternatively, protein powder may be used (administered via nasogastric or gastrostomy tube).

Measure glucose and insulin every 30 minutes for 3 hours

If the plasma glucose drops to <60 mg/dL terminate test with carbohydrate drink of 15 g or intravenous push of 200 mg/kg (2ml/kg D10%)

 

HADH Hyperinsulinism (HADH HI)

 

Inactivating mutations in HADH (chromosome 4q25) cause a rare, autosomal recessive form of diazoxide-responsive hyperinsulinism. The HADH gene encodes short chain 3-hydroxyacyl-coenzyme A dehydrogenase (HADH, also referred to as SCHAD) which inhibits GDH and also plays a role in mitochondrial fatty acid beta-oxidation. Loss of normal GDH inhibition results in a similar phenotype as GDH HI with fasting and protein-induced hyperinsulinemic hypoglycemia, but without hyperammonemia. Elevated levels of 3-hydroxybutyryl-carnitine in plasma and 3-hydroxyglutaric acid in urine may serve as clues to the diagnosis in some but are not universally observed (65). Treatment is with diazoxide and dietary modification as in GDH HI. 

 

HNF1A and HNF4A Hyperinsulinism (HNF1A and HNF4A HI)

 

Dominant inactivating mutations in the genes encoding transcription factors hepatocyte nuclear factor 1 alpha and hepatocyte nuclear factor 4 alpha, cause both hyperinsulinism and maturity-onset diabetes of the young (MODY3 and MODY1, respectively). Affected infants are often born large for gestational age. Severity of hyperinsulinism varies from transient neonatal hypoglycemia to persistent hyperinsulinism requiring treatment into school age (66). The p.Arg63Trp HNF4A mutation is associated with an additional extra-pancreatic phenotype of renal Fanconi syndrome and hepatic dysfunction (66,67). Response to diazoxide is often robust. Establishing the diagnosis has important implications both for the affected child, who requires ongoing surveillance after hyperinsulinism resolution due to the risk of developing diabetes later in life, and for family members carrying the mutation who could benefit from early diagnosis of diabetes or targeted therapy (i.e., sulfonylureas).

 

MCT1 Hyperinsulinism (MCT1 HI)

 

Dominant mutations in the non-coding regions of SLC16A1 (chromosome 1p13.2), encoding monocarboxylate transporter 1 (MCT1), result in exercise-induced hyperinsulinism (68). MCT1

catalyzes transport of monocarboxylates, such as lactate, pyruvate and beta-hydroxybutyrate, across the plasma membrane. Normally, MCT1 expression is disallowed in pancreatic beta cells. Promoter-activating mutations induce inappropriate MCT1 expression in beta cells, permitting uptake of pyruvate during exercise when plasma pyruvate is elevated. Pyruvate metabolism leads to increased ATP production, and resultant pyruvate-stimulated (exercise-induced) insulin release despite hypoglycemia (69). Response to diazoxide is variable, and carbohydrate loading prior to exercise is recommended to control hypoglycemia. Nonfunctional variants in the coding regions of SLC16A1 cause ketotic hypoglycemia (see section on Pathologic Ketotic Hypoglycemia and Ketone Utilization and Transport Defects). This is a very uncommon clinical entity.

 

UCP2 Hyperinsulinism

 

Dominant inactivating mutations in the UCP2 gene (chromosome 11q13.4) encoding uncoupling protein 2 (UCP2) have been associated with a diazoxide-responsive form of hyperinsulinism (70). Following initial reports, the prevalence of UCP2 variants in the general population has been found to be high, raising the role of UCP2 variants as a monogenic cause of hyperinsulinism into question (71).

 

SYNDROMIC HYPERINSULINISM

 

Hyperinsulinism is a feature of several recognized syndromes. These include the overgrowth syndromes: Beckwith-Wiedemann, Sotos, Simpson-Golabi-Behmel, and Perlman syndromes, as well as Kabuki syndrome, Turner syndrome, Tyrosinemia type 1, Usher syndrome type 1C (in which there is contiguous gene deletion at 11p15.2 including ABCC8), Rubinstein-Taybi syndrome, and several congenital disorders of glycosylation, among others (72). Beckwith-Wiedemann, Kabuki, and Turner syndromes are most frequently observed (72), and are discussed in the sections below along with the congenital disorders of glycosylation associated with hyperinsulinism.

 

Beckwith-Wiedemann Syndrome

 

Beckwith-Wiedemann syndrome, caused by genetic or epigenetic changes on chromosome 11p15.5, is an overgrowth disorder with classical features of macrosomia, macroglossia, hemihypertrophy, abdominal wall defects, and embryonal tumors. Due to the varying molecular etiologies, and the postzygotic nature of the epigenetic changes in most cases, affected children can present with a variety of clinical features along a spectrum of “classic” to “atypical” to isolated lateralized overgrowth (73). Hyperinsulinism occurs in approximately 50% of all cases and is the presenting symptom of Beckwith-Wiedemann syndrome in 16% of cases (73). While the hyperinsulinism is typically mild in severity and resolves within the first days to years of life, in roughly 5% of cases (particularly cases due to paternal uniparental isodisomy for chromosome 11p), it can be severe and persistent, requiring pancreatectomy (74). Hyperinsulinism persisting beyond the first week of life is considered a cardinal feature of Beckwith-Wiedemann syndrome (75). Thus, all patients presenting with hyperinsulinism should be evaluated for subtle limb asymmetry and other suggestive features (Table 9) (75). Molecular testing for investigation of Beckwith-Wiedemann syndrome should be considered in these patients. Additional suggestive features in the context of a hyperinsulinism evaluation include marked pancreatic enlargement and diffuse 18-F-DOPA uptake, or alternatively, very large areas of focal 18-F-DOPA uptake, on PET/CT imaging (76). In the latter setting, areas of increased involvement on PET imaging may be used to tailor the extent of pancreatectomy. Histologically, resected pancreatic tissue in cases of Beckwith-Wiedemann syndrome are characterized by a dramatic increase in endocrine tissue relative to the amount of exocrine tissue, often with a loss of the normal lobular architecture, and prominent trabecular arrangement of endocrine cells (76,77). Since the genetic or epigenetic changes causing Beckwith-Wiedemann syndrome usually occur during embryonal development, yielding a mosaic pattern, failure to detect these changes in blood (leukocytes) is thus not conclusive, and additional testing (e.g., from skin or pancreas) may be required.

 

Table 9.  Clinical Features of Beckwith-Wiedemann Syndrome (BWS)

Cardinal features (2 points per feature)

Macroglossia

Exomphalos

Lateralized overgrowth

Multifocal and/or bilateral Wilms tumor or nephroblastomatosis

Hyperinsulinism (lasting >1 week and requiring escalated treatment)

Pathology findings: adrenal cortex cytomegaly, placental mesenchymal dysplasia or pancreatic adenomatosis

Suggestive features (1 point per feature)

Birthweight >2SDS above the mean

Facial nevus simplex

Polyhydramnios and/or placentomegaly

Ear creases and/or pits

Transient hypoglycemia (lasting <1 week)

Typical BWS tumors (neuroblastoma, rhabdomyosarcoma, unilateral Wilms tumor, hepatoblastoma, adrenocortical carcinoma or phaeochromocytoma)

Nephromegaly and/or hepatomegaly

Umbilical hernia and/or diastasis recti

Score interpretation

≥4: Clinical diagnosis of classical BWS. Genetic testing for investigation and diagnosis of BWS recommended. Note that clinical diagnosis does not require the molecular confirmation of an 11p15 anomaly.

≥2: Merit genetic testing for investigation and diagnosis of BWS

Patients with a score of ≥2 with negative genetic testing should be considered for an alternative diagnosis and/or referral to a BWS expert for further evaluation

Adapted from Brioude F. et al, Expert consensus document: Clinical and molecular diagnosis, screening and management of Beckwith-Wiedemann syndrome: an international consensus statement. Nat Rev Endocrinol. 2018;14(4):229-249 (75).

 

Kabuki Syndrome

 

Kabuki syndrome is caused by dominant mutations in KMT2D (~75% of cases) or X-linked mutations in KDM6A. While the true incidence of hyperinsulinism in Kabuki syndrome is unknown, it is increasingly recognized as a feature of this disorder, often as the presenting feature (78). Clinically, affected children have distinctive facial features – long palpebral fissures with eversion of the lateral lower eyelid, arched eyebrows, and prominent ears – skeletal anomalies, intellectual disability, and post-natal growth deficiency. Congenital heart defects, genitourinary and gastrointestinal anomalies, and immune dysfunction may also be observed. Haploinsufficiency of KDM6A has been proposed as the pathophysiologic mechanism of hyperinsulinism, and human islets treated with KDM6A inhibitor demonstrate abnormal insulin secretion (79). Most cases are diazoxide-responsive. Somatostatin analogues have been used with success in cases where diazoxide was contraindicated due to cardiac comorbidity.

 

Turner Syndrome

 

The incidence of hyperinsulinism in infants with Turner syndrome is roughly 50 times that expected in the general population (79). As in Kabuki syndrome, haploinsufficiency of KDM6A (located on X chromosome) has been proposed as the underlying mechanism. Many, but not all, children with Turner syndrome and associated hyperinsulinism are diazoxide-responsive.

 

FOXA2 Hyperinsulinism

 

Inactivating mutations in FOXA2, encoding the transcription factor forkhead box A2 (Foxa2), have been associated with a clinical phenotype of congenital hyperinsulinism, hypopituitarism, and endodermal-derived organ anomalies (80,81). Treatment with both pituitary hormone replacement and diazoxide has been reported to be effective.

 

Congenital Disorders of Glycosylation

 

Monogenic defects in the synthesis of oligosaccharides are responsible for congenital disorders of glycosylation (CDG), over 100 of which have been identified to date. Endocrine dysfunction (including growth failure, hypothyroidism, hypogonadotropic hypogonadism) is common to many congenital disorders of glycosylation because both endocrine peptides and their receptor targets are glycosylated. These disorders have a wide phenotypic spectrum, and three have been associated with hyperinsulinism: phosphomannomutase 2 deficiency (PMM2-CDG, formerly CDG-1a), mannose phosphate isomerase deficiency (MPI-CDG, formerly CDG-1b), and phosphoglucomutase 1 deficiency (PGM1-CDG, formerly CDG-1t, also formerly referred to as GSD XIV). PMM2-CDG is the most common congenital disorder of glycosylation. Hyperinsulinism in PMM2-CDG has been proposed to result from impaired function of beta-cell KATP channels and most cases have been diazoxide-responsive (82). MPI-CDG predominantly manifests with gastrointestinal and hepatic involvement (protein losing enteropathy, liver dysfunction and fibrosis), and hyperinsulinemic hypoglycemia. MPI-CDG is treated with mannose, however hyperinsulinism-specific therapies (e.g., diazoxide) may also be required to adequately manage hypoglycemia (83). PGM1 catalyzes the interconversion of G-1-phos and G-6-phos and is thus involved in glycogenesis, glycogenolysis, and gluconeogenesis. Both fasting ketotic hypoglycemia, due to the role of PGM1 in these metabolic pathways, and post-prandial hyperinsulinemic hypoglycemia, due to a lowered threshold for glucose-stimulated insulin secretion, are observed in PGM1-CDG. Thus, this condition mimics GSD 0 and should be considered in that differential diagnosis. Diagnosis can be established by biochemical or molecular testing. Biochemical methods include analysis of serum transferrin glycoforms (also termed carbohydrate-deficient transferrin analysis) by isoelectric focusing or by mass spectroscopy to determine the number and presence of incomplete sialylated N-linked oligosaccharide residues linked to serum transferrin (84). If biochemical testing is not suggestive of a particular CDG, molecular testing approaches include multigene panels or more comprehensive genomic (whole exome, whole genome) testing.

 

TRANSIENT AND PERINATAL STRESS-INDUCED HYPERINSULINISM

 

Transient hyperinsulinism occurs secondary to maternal factors, most commonly gestational diabetes mellitus. In uncontrolled gestational diabetes, hyperglycemia induces fetal hyperinsulinism resulting in macrosomia and hypoglycemia following delivery. Transient hyperinsulinism can also result from maternal use of medications affecting glucose homeostasis, including hypoglycemic agents (e.g., oral sulfonylureas), terbutaline, or propranolol. Hyperinsulinism due to these factors resolves within the first days of life. Resolution can be confirmed by performing a 6-9 hour fast and demonstrating the baby can maintain plasma glucose >60-70 mg/dL throughout. If hyperinsulinism persists beyond 5-7 days of life alternate causes should be sought, particularly perinatal stress-induced hyperinsulinism (see below). 

 

Perinatal factors are also associated with development of perinatal stress-induced hyperinsulinism (PSHI), which has a more prolonged course than transient hyperinsulinism.  Neonates with perinatal complications such as birth asphyxia, maternal preeclampsia, prematurity, intrauterine growth retardation, or other peripartum stress may develop PSHI. As previously noted, fetal hypoxia results in decreased trafficking of KATP channels to the beta-cell membrane, decreasing the threshold for insulin secretion (23,85). Hyperinsulinism spontaneously resolves within weeks to months as beta-cell insulin regulation normalizes. Median age of resolution is six months. By definition, PSHI resolves by one year of age. PSHI typically responds to treatment with diazoxide, typically at doses on the lower end of the therapeutic range (5-7.5 mg/kg/day). Rates of adverse effects of diazoxide may be higher in children with PSHI, and empiric initiation of diuretic and close monitoring are paramount (39). Given these factors, it is recommended to start with a diazoxide dose of 5 mg/kg/day, initially, and to increase the dose after 3-5 days of treatment if adequate response is not achieved. Timing of initiating diazoxide in cases of suspected PSHI should be tailored to the infant’s overall clinical course. For infants with ongoing intensive care nursery needs (e.g., intubation, warming bed, parenteral feeds), plasma glucose support with IV or enteral dextrose-containing fluids offers optimal initial management, especially as some infants will demonstrate resolution of hyperinsulinism before they are otherwise prepared for hospital discharge. In these cases, repeat fasting evaluation should be performed prior to discharge to assess for resolution versus need for initiation of targeted treatment. As above, in these at-risk infants in whom hypoglycemia is considered likely to resolve within a short time, resolution can be confirmed by performing a 6-9 hour fast and demonstrating the baby can maintain plasma glucose >60-70 mg/dL throughout. Diazoxide should be initiated for infants approaching discharge in whom hyperinsulinemic hypoglycemia has not yet resolved, and safety fast (Table 7) should be performed to confirm adequate diazoxide efficacy. While the diagnosis of PSHI may be suspected by the clinical history, it is established only when hyperinsulinism resolution is confirmed by a repeat fasting test after treatment has been discontinued, cure fast (Table 7).

 

ACTIVATING MUTATIONS IN THE INSULIN SIGNALING PATHWAY

 

Activating mutations in insulin signaling pathway genes, including AKT2, AKT3, and PIK3CA, cause hypoglycemia with biochemical findings of inappropriate insulin action, but with low or absent plasma insulin levels (86). Asymmetric somatic overgrowth may serve as a clinical clue to the diagnosis. Frequent feedings or continuous enteral dextrose are effective treatments. 

 

ACQUIRED FORMS OF HYPERINSULINISM

 

Insulinoma

 

Insulinomas are pancreatic neuroendocrine tumors. The incidence of pediatric insulinoma is unknown, however, these lesions are less common in children than in adults (1-3 cases per million per year) and are thus exceedingly rare. While most pediatric cases present in adolescence, presentation as young as 2 years of age has been described.

 

Insulinomas are typically benign, solitary lesions. They can occur sporadically, or in association with multiple endocrine neoplasia, type 1 (MEN1). The frequency of MEN1 mutations in children with insulinoma has been reported to range 26-42% (87,88), which is higher than that in adults (5-10% in adults) (89). Clinically, insulinomas typically manifest with recurrent episodes of fasting hypoglycemia associated with neuroglycopenic symptoms. Weight gain is commonly noted at presentation, and occurs due to increased carbohydrate intake to treat symptoms of hypoglycemia (88). Notably, however, hypoglycemia unawareness is common. This is because repeated and prolonged hypoglycemia episodes can both decrease the counter regulatory hormonal response to hypoglycemia and induce unawareness of the autonomic and neuroglycopenic symptoms of hypoglycemia (90). Consequently, delays in establishing the diagnosis and initial misdiagnosis with neurologic and psychiatric disorders are not uncommon (91).

 

Suppressed beta-hydroxybutyrate, free fatty acids, and IGF-BP1, with inappropriately elevated proinsulin, insulin, and c-peptide levels at the time of hypoglycemia are consistent with the diagnosis. However, these biochemical findings do not differentiate insulinoma from sulfonylurea ingestion or congenital hyperinsulinism. Consequently, surreptitious use of insulin secretagogues (discussed in the section Exogenous hypoglycemia below) must be excluded in all suspected cases of insulinoma. Once the diagnosis is made, localization of the insulinoma is critical to direct the definitive treatment, surgery. Various imaging modalities have been used, including endoscopic ultrasound, computerized tomography (CT), magnetic resonance imaging (MRI), single-photon emission CT (SPECT), positron emission tomography (PET) and intraoperative ultrasound, each with variable sensitivity. The addition of GLP-1 receptor agonists (exendin-4) has increased the sensitivity of nuclear imaging modalities for detecting insulinomas, and exendin-4 PET/CT appears to be more sensitive than exendin-4 SPECT/CT (92). Historically, arterial calcium stimulation with venous insulin sampling was used, however, these invasive procedures have become less common with improvements in the imaging modalities available. Insulinomas are typically small lesions measuring <1 cm, and multiple lesions may be present. Preoperative localization can be challenging, and use of multiple imaging modalities may be required.

 

Diazoxide may be effective treatment in patients awaiting surgery or for whom the lesion cannot be localized. Surgical excision is curative, and prognosis is generally excellent. Genetic testing for MEN1 should be conducted in all patients, and appropriate screening should be initiated if a mutation is found. Insulinomas may be recurrent, with higher risk of recurrence in those with MEN1. For more information on histopathology, risks of malignancy, and suggested follow up protocols see the chapter entitled “Insulinoma” in the Diffuse Hormonal Systems and Endocrine Tumor Syndromes section of Endotext (93).

 

Autoimmune Hypoglycemia

 

Autoimmune hypoglycemia may result from the development of antibodies to insulin, referred to as Hirata disease, or to the insulin receptor. Onset may be triggered by viral infection or medication in a susceptible individual, and association with specific HLA haplotypes has been reported. Biochemically, plasma beta-hydroxybutyrate and free fatty acids are inappropriately low at the time of hypoglycemia, and c-peptide is suppressed. When autoimmune hypoglycemia occurs due to antibodies to insulin, plasma insulin levels may be very high (>1000 pmol/L), due to interference of insulin antibodies with the assay. Detection of insulin antibodies can confirm the diagnosis in patients naïve to exogenous insulin, which must be excluded. Autoimmune hypoglycemia is a spontaneously remitting condition. Various immune modulating treatments, including glucocorticoids, plasmapheresis, intravenous immunoglobulin, and rituximab have been utilized. A comparison of the different therapeutic approaches has not been conducted, owing to the rarity of this condition and its self-resolving course.

 

Post-prandial Hypoglycemia (Late Dumping Syndrome)

 

Post-prandial hypoglycemia (late dumping syndrome) occurs due to disrupted gastric motility, most commonly as a consequence of gastrointestinal surgery. In children, fundoplication surgery is implicated most frequently, whereas in adults, bariatric surgery is the most common cause. Hypoglycemia usually develops 1-3 hours after a meal, and results from imbalance between glucose absorption and insulin secretion. Rapid gastric emptying and intestinal absorption of carbohydrate, result in early hyperglycemia and exaggerated GLP-1 secretion, both of which trigger an exaggerated insulin response (94). The diagnosis can be confirmed by serial monitoring of insulin and glucose following feeding or with formal mixed meal tolerance testing. Fasting studies may be required to fully distinguish fasting hypoglycemia from post-prandial hypoglycemia (which may be comorbid in some patients). When conducting fasting studies in children with risk factors for (gastrostomy tube placement, Nissen fundoplication, esophageal or ileal surgery), or suspected, post-prandial hypoglycemia, it is important to slowly taper off feeds to avoid confounding of the fasting tolerance assessment by “dumping.” Treatment is often dietary manipulation. Decreasing the volume or rate of feeding, tapering the rate of feeding prior to stopping, increasing dietary fat, and decreasing simple carbohydrates may all be helpful. In older children, acarbose, which acts to slow carbohydrate digestion, has been used successfully. The efficacy of these approaches should be confirmed by repeat serial monitoring of glucose following at least two feeds to ensure plasma glucose is maintained within target range. In some cases, continuous enteral feeds, or enteral dextrose may be required. Typical treatments for genetic forms of HI such as diazoxide or octreotide generally have been unsuccessful. However, some of the novel therapies for HI under development (42,95), are also being studied in post bariatric surgery hypoglycemia.

 

Exogenous

 

Exogenous, factitious, and drug-induced hypoglycemia all refer to hypoglycemia that results from the use (intentional or accidental) of insulin or insulin secretagogues. Clinical clues to the diagnosis may include unusual or inconsistent histories, such as severe, recurrent hypoglycemia without typical precipitating factors (e.g., fasting, illness), or access to antidiabetic agents. Biochemical findings of elevated plasma insulin with suppressed c-peptide (or an insulin to c-peptide molar ratio >1) confirm exogenous insulin administration. Various insulin assays differ in their sensitivity to detect insulin analogs, so it is important to understand the detection abilities – and limitations – of the assay used. Failure to do so may result in incorrectly excluding the diagnosis of exogenous insulin administration. Information on the cross-reactivity of commercially available insulin formulations with the ordered insulin assay is available on the test information page of most laboratories and can also be requested. For example, currently, cross-reactivity of most insulin assays with glulisine is very low (96). When clinical suspicion is high, sending specimens for testing using different immunoassays with different insulin formulation cross-reactivity profiles may be helpful. In contrast, insulin secretagogues (e.g., sulfonylureas, meglitinides, GLP-1 receptor agonists) stimulate both insulin and c-peptide secretion. Consequently, the biochemical evaluation of hypoglycemia due to insulin secretagogue use may be indistinguishable from that of insulinoma. Specialized toxicology panels, including measurement of plasma or urine sulfonylureas, may be required to confirm the diagnosis. A high index of suspicion, and knowledge of hypoglycemia agents available in the home can help guide the evaluation. As with exogenous insulin administration, the laboratory evaluation is subject to pitfalls in sensitivity and interpretation, and consultation with the laboratory is recommended (97).

 

Hypoglycemia Due to Growth Hormone and Cortisol Deficiencies

 

Deficiencies in the counter regulatory hormones, growth hormone and cortisol – either in isolation, or more commonly, in combination – cause hypoglycemia. Growth hormone acts to stimulate lipolysis and decrease peripheral glucose uptake. Cortisol stimulates gluconeogenesis and release of gluconeogenic substrates, including alanine, from muscle. Although secretion of both growth hormone and cortisol is triggered by falling plasma glucose, findings of a single low growth hormone or cortisol level at the time of hypoglycemia has poor specificity for deficiency of either hormone (18,19). Stimulation testing may be needed to confirm the diagnosis.

 

In the older child, hypoglycemia due to growth hormone and/or cortisol deficiency is ketotic. However, in neonates, the biochemical picture may mirror that of hyperinsulinism due to both inappropriate conservation of glycogen reserves during hypoglycemia and immature ketogenesis at this age.

 

HYPOPITUITARISM

 

Hypopituitarism may be congenital or acquired. Congenital hypopituitarism may result from malformation of the hypothalamus and pituitary (e.g., holoprosencephaly, septo-optic dysplasia) or from mutations in transcription factors vital for normal hypothalamic-pituitary development (see the chapter entitled “Genetic Etiology of Congenital Hypopituitarism” in the Pediatric Endocrinology section of Endotext (98)). As discussed above, mutations in FOXA2cause both hypopituitarism and hyperinsulinism. Acquired hypopituitarism may develop following trauma, infection, tumor, intracranial surgery, or radiation. In neonates, hypoglycemia is often a presenting feature of panhypopituitarism. Other clinical clues in neonates include unconjugated hyperbilirubinemia, nystagmus, midline developmental defects (e.g., cleft lip and palate), and in males, micropenis or smaller than average penis. An MRI of the hypothalamic-pituitary region is essential and often reveals an ectopic “bright spot” indicating disruption of the normal descent of the neurohypophysis with interruption of hypothalamic releasing factors that regulate hormone secretion. In such cases, prolactin concentration may be elevated, whereas GH, TSH and ACTH are suppressed. In older children, the diagnosis may be suspected based upon clinical history, growth failure, or neuroimaging findings. Hypoglycemia is found more commonly in neonates with multiple pituitary hormone deficiencies compared to isolated growth hormone deficiency and therefore careful consideration of multiple hormonal deficiencies must be given when growth hormone deficiency is found to be the cause of hypoglycemia in neonates (99).  Hypoglycemia is treated by replacement of the deficient hormones. From a practical aspect some neonates and infants will need a higher-than-expected dose of cortisol replacement and may even need growth hormone treatment divided twice daily. A safety fast (Table 7) should be performed prior to discharge to ensure the therapy is effective.

 

ISOLATED GROWTH HORMONE DEFICIENCY

 

Growth hormone deficiency has an estimated prevalence of between 1:4,000-1:10,000. Growth failure is the most common presenting feature, but this typically does not manifest until after the first year of life. Other clinical clues include midface hypoplasia and altered body composition with truncal adiposity. Most cases of isolated growth hormone deficiency are idiopathic. Genetic, anatomic, and acquired causes are detailed in the chapters entitled “Disorders of Growth Hormone in Childhood” and “Genetic Etiology of Congenital Hypopituitarism” in the Pediatric Endocrinology section of Endotext (98,100). Growth factors (IGF-1 and IGFBP-3) are low for age and bone age is delayed. The diagnosis is confirmed via stimulation testing. Treatment is with recombinant growth hormone. Importantly, depending on the underlying etiology, there is the potential for other pituitary hormone deficiencies to develop over time. Periodic screening of pituitary function is thus recommended.

 

ISOLATED CORTISOL DEFICIENCY

 

Cortisol deficiency may result either from defects in the ACTH signaling pathway or from congenital (e.g., congenital adrenal hyperplasia or hypoplasia) or acquired (e.g., bilateral adrenal hemorrhage) defects in adrenal steroidogenesis. Isolated ACTH deficiency is extremely rare. Several genetic etiologies have been described to date, including mutations in TBX19, POMC, PCSK1, and NFKB2 (see the chapter entitled “Genetic Etiology of Congenital Hypopituitarism” the Pediatric Endocrinology section of Endotext (98)). Of these, mutations in TBX19 are most frequently detected. Affected neonates universally present with severe hypoglycemia, often with hypoglycemic seizures. The mortality rate is up to 25%. In contrast to isolated ACTH deficiency, children with adrenal insufficiency due to ACTH resistance or primary adrenal disorders will have elevated plasma ACTH levels and associated skin hyperpigmentation. Primary disorders of the adrenal gland may also manifest with hyponatremia, hyperkalemia, and/or ambiguous genitalia. Congenital adrenal hyperplasia, and other disorders of the adrenal gland are detailed in the chapter entitled “Congenital Adrenal Hyperplasia” in the Adrenal Disease and Function section of Endotext (101). Treatment is with cortisol replacement. Initially, stress dose concentrations of hydrocortisone should be used.

 

GLYCOGEN STORAGE DISORDERS

 

The glycogen storage disorders (GSD) are a group of conditions in which there is either abnormal storage or release of glycogen resulting in hypoglycemia and acidosis. The acidosis may be lactic or ketoacidosis depending on the type of GSD. For the purpose of this discussion, we will include GSD 1 caused by glucose-6-phosphatase (G-6-Pase)deficiency as a glycogen storage disorder although the enzyme also represents the terminal step in gluconeogenesis. The GSDs may affect both liver and muscle glycogen storage and for this chapter we will focus on those with primarily liver expression, which are responsible for the hypoglycemic GSDs.

 

Under fed circumstances, excess glucose is converted into glycogen and stored in liver and muscle. Liver glycogen (but not muscle glycogen as muscle does not have G-6-Pase) later becomes available during fasting to provide glucose for metabolism in the brain and the glucose dependent tissues (red blood cells and proximal convoluted tubule of the kidney). Glucose is phosphorylated to G-6-Phos by glucokinase and then to Glucose-1-phosphate (G-1-Phos) by phosphoglucomutase. G-1-Phos is the starting point for glycogen synthesis by glycogen synthase (GSD 0, gene GYS2, inheritance autosomal recessive [AR]) to form chains with alpha 1-4 linkages. Branch points in these chains are formed by alpha 1-6 linkages approximately every 10 glucose units. During the early stages of fasting, glycogen is broken down by glycogen phosphorylase and then by glycogen debrancher enzymes. First the alpha 1-4 links are cleaved into G-1-Phos by glycogen phosphorylase (GSD VI, gene PGYL, inheritance AR) until 4 glucose units remain and then the debrancher transferase (GSD III, gene AGL, inheritance AR) moves the last 3 alpha 1-4 linked glucose over to another chain and then cleaves the alpha 1-6 branch point releasing a single glucose molecule. At this stage, the G-1-phos molecules are then converted to G-6-phos which then either undergoes glycolysis for energy or dephosphorylation by G-6-Pase (GSD 1, gene GCPC inheritance AR) and released into the blood stream as glucose.

 

Glycogen Storage Disease Type 0

 

GSD 0 is caused by deficiency of glycogen synthetase, which is encoded by the GYS2 gene on chromosome 12p12.2 and inherited in an autosomal recessive manner. The main biochemical manifestations are both fasting ketotic hypoglycemia and postprandial hyperglycemia and hyperlactatemia (102). This is due to the inability of the liver to store excess postprandial glucose resulting in hyperglycemia and glycosuria. The G-6-phos undergoes glycolysis to pyruvate and then lactate. Later as fasting progresses, there are no liver glycogen stores available, and when the glucose drops below 85 mg/dL, insulin secretion is switched off and early ketosis occurs resulting in ketotic hypoglycemia. This typically happens after 6-12 hours of fasting. Dependence on gluconeogenesis also results in over-utilization of protein, and protein deficiency is common.   

 

Clinical features of GSD 0 may range from asymptomatic to recurrent episodes of ketotic hypoglycemia.  Typically, as infants transition off nighttime feeding, episodes of fasting hypoglycemia with hyperketonemia occur. Patients may also present during mild gastrointestinal disorders with ketotic hypoglycemia. They have no hepatomegaly and a normal critical sample with elevated counter regulatory hormones, elevated free fatty acids and ketones. They may have short stature, a history of failure to thrive and hyperlipidemia. In the most severe end of the spectrum, they may present with seizures and developmental delay in addition to hypoglycemia after a very short duration fasting. The condition should be suspected in children with a history of recurrent ketotic hypoglycemia or post prandial hyperglycemia and fasting ketonemia.

 

Diagnosis is made by demonstrating shortened fasting tolerance with ketotic hypoglycemia (103) (typically <12 hours in children under 7 years of age and <18 hours in adolescents). In addition, an oral glucose tolerance test (OGTT) performed after an overnight fast using 1.75 g/kg up to 75 g (one of the few appropriate uses of the OGTT for diagnosis of etiology of hypoglycemia) will demonstrate postprandial hyperglycemia with elevated lactic acid. Finally, a fed (2 hours post meal) glucagon stimulation test will fail to show elevated glucose response to glucagon in the most severe cases but may cause an increase in milder cases. Once the clinical diagnosis is suspected, genetic testing for confirmation of diagnosis is strongly recommended rather than liver biopsy.  

 

Treatment is avoidance of fasting (>3-4 hours), utilizing low glycemic index carbohydrate, and a high protein diet (2-3g/kg/day) during the day with meals and snacks to provide adequate amino acids for gluconeogenesis and overnight dextrose via gastrostomy tube or uncooked cornstarch (UCS) after age 1 year (1.5g/kg every 6 hours overnight). Glycosadeâ a soluble extended-release form of amylopectin cornstarch is available in the US for children over the age of 5 years and may be used in place of uncooked cornstarch. Early diagnosis and treatment may prevent the long-term complications of short stature and osteopenia from the recurrent keto- and lactic acidosis. 

 

Glycogen Storage Disease Type I

 

This is the most severe of the GSDs and causes profound hypoglycemia because of impaired glycogenolysis and gluconeogenesis with lactic acidosis, hyperuricemia, and hyperlipidemia.  Glycogen and triglycerides are stored in the liver resulting in massive hepatomegaly. Long-term consequences of GSD I include hepatic adenoma, renal Fanconi syndrome, renal failure, short stature, and osteoporosis. It occurs in approximately 1:100,000 births (104), and is caused by mutations in the gene for G-6-Pase, G6PC (GSD Ia), or G-6-P translocase 1, G6PT1 (GSD Ib).  Under normal circumstances G-6-P translocase 1 transports G-6-Phos into the endoplasmic reticulum, G-6-Pase then converts G-6-P to glucose which is then transported out of the endoplasmic reticulum by GLUT-2 (hence the similarity of Fanconi Bickel syndrome caused by GLUT2 deficiency to GSD 1).

 

In the postprandial phase, glycogen stored in the liver is broken down to G-6-Phos and from here can enter 3 metabolic pathways: 1) G-6-Phos enters the pentose phosphate shunt resulting in formation of uric acid. 2) G-6-Phos undergoes glycolysis to form pyruvate and then to lactic acid (which is transported to brain and used as fuel for energy production). 3) G-6-Phos undergoes glycolysis and forms acetyl CoA which in turn is converted into malonyl CoA which inhibits carnitine palmitoyl-transferase I leading to decreased oxidation of fatty acids (impaired ketone body production) and increased formation of lipids causing hyperlipidemia. Thus, the cardinal biochemical features of GSD 1 occur (hypoglycemia, hyperuricemia, hyperlactatemia, and hypertriglyceridemia).

 

Clinical features in the newborn may include hypoglycemia with a good response to feeding, however because many newborns breast feed every 2 hours GSD 1 is rarely identified in the new-born period. Despite the occurrence of hypoglycemia, newborns are rarely diagnosed because many physicians erroneously believe that if the glucose responds to feeding then ongoing glucose testing is not needed. However, if the PES recommendations (21) are followed and persistent glucose levels <50 mg/dL are noted in the first 48 hours of life and <60 mg/dL beyond that, then investigations should be done to determine the etiology. A six-hour fasting study will identify these patients and indeed great care must be taken if suspected because glucose levels typically fall very quickly (2.5-3.5 hours after a feed) and fall deeply to the 20-30 mg/dl range. As infants get older and feeding intervals start to stretch out to >6 hours over night, significant hypoglycemia and lactic acidosis occurs and often the children present because of the tachypnea caused by the acid base disturbance, rather than the hypoglycemia.  Neuroglycopenic symptoms are unlikely to occur due to the protective effect of lactate metabolism in the brain, but in circumstances of eating high carbohydrates and a rapid decline in glucose due to insulin release, the lactate levels may be low and the neuroprotective effects of lactate may not occur. In these circumstances seizures, coma, and sudden death may occur.  Clinical features of undiagnosed GSD 1a include massive hepatomegaly, short stature, and failure to thrive. Biochemically, patients have high lactate levels (typically >5mmol/L) with hypoglycemia, low ketones, abnormal transaminases, high uric acid, and hypertriglyceridemia. 

 

GSD Ib is caused by defects in the G6PT1 (also known as SLC37A4) gene and has all the same clinical findings as above but in addition has significant neutrophil dysfunction resulting in recurrent skin infections and later in life severe inflammatory bowel disease similar to Crohn disease. This form of GSD 1 represents about 10% of cases of GSD 1 and is an AR inherited condition with the gene found on chromosome 11q23.  It is estimated to occur in 1:1,000,000 births.

 

It is important to note that untreated GSD 1a/b patients rarely present with neuroglycopenic symptoms of hypoglycemia because lactate may be used a fuel for the brain, and they also rarely present with neurogenic symptoms as they develop hypoglycemic unawareness. Thus, the hepatomegaly, short stature, intermittent tachypnea, and the finding of lipemic serum rather than symptoms of hypoglycemia raise the clinical suspicion.   

 

Diagnosis of GSD Ia or Ib is made by finding the clinical features above and performing genetic testing for mutations in G6PC or G6PT1 to confirm the diagnosis. 

 

Treatment is to prevent hypoglycemia by providing glucose every 2.5-3 hours in neonates using fructose/galactose free formula. In GSD 1, fructose and galactose cannot be converted to glucose due to deficiency of G-6-Pase and so if given will worsen lactic acidosis, hyperlipidemia, and hyperuricemia. The goal of treatment is to maintain the plasma glucose >75mg/dl which is the threshold for the secretion of counter-regulatory hormones that drive glycogenolysis and glycolysis to lactic acid. This can be achieved by frequent oral feeding in newborns, with continuous gastrostomy tube feeds overnight, and in older infants (>1 year), toddlers and children giving uncooked starch (UCS) 1- 1.5 g/kg every 3-6 hours including overnight. Glycosadeâ, an extended-release waxy maize cornstarch, can be used in older children to avoid overnight dosing with a duration of action of 6-8 hours, but is not recommended under 5 years of age. Placement of a gastrostomy tube to provide intra gastric glucose overnight often improves the family’s quality of life and the patient’s metabolic control. One caveat to feeding fast acting carbohydrates is that the insulin production suppresses glycogenolysis and production of lactic acid so treated patients have a higher risk of neuroglycopenic symptoms and brain damage from profound hypoglycemia without lactic acidosis if regular therapy is interrupted or delayed. Typical dietary treatments include 65% carbohydrates, 10-15% protein and low fat of approximately 20-25%. A simple rule of thumb when providing IV glucose or continuous enteral glucose is to start at around 8 mg/kg/min and titrate until lactate is <2 mmol/L and glucose >75mg/dl. Chronic provision of excess glucose is not beneficial so care must be taken to find the ideal amount of glucose (to paraphrase Goldilocks, not too much, not too little, just right!). Because hepatic production of glucose generally is equal to brain utilization of glucose, neonates have a higher glucose requirement than children and children than adults due to the relative sizes of the brain to body. Overall, 30-40% of the daily carbohydrate should be long-acting carbohydrates.

 

Glycogen Storage Disease Type III

 

GSD III is caused by glycogen debrancher enzyme deficiency. This is encoded by the AGL gene on chromosome 1p21 and is inherited in an autosomal recessive manner (105). It occurs in about 1:100,000 similar to GSD I. GSD IIIa occurs in both liver and muscle and represents the majority of cases in the US while GSD IIIb occurs in liver alone. 

 

Clinical features of GSD III include fasting ketotic hypoglycemia and massive and firm hepatomegaly. Unlike GSD I, GSD III is characterized by normal lactic and uric acid levels and more severe elevations in liver function enzymes. In those with GSD IIIa marked elevations of creatine kinase (CK) appear before the clinical signs of proximal muscle wasting. 

 

Clinical diagnosis is made by the finding of short fasting induced hypoglycemia without lactic acidosis, hepatomegaly, marked elevation of transaminases often with high CK. At the time of hypoglycemia, glucagon will not cause a rise in the plasma glucose but 2 hours after a meal in the fed state it will trigger a rise in glucose unlike GSD I.  Genetic testing will identify mutations in the AGL gene.

 

Treatment is the avoidance of prolonged fasting using UCS in doses of 1-1.5g every 4-6 hours but unlike GSD I, patients with GSD III can utilize amino acids and efficiently carry out gluconeogenesis. Thus a high protein diet in addition to UCS can be very effective in preventing hypoglycemia, minimizing hepatomegaly, improving transaminases, improving growth and even proximal muscle wasting (106). Avoidance of too much carbohydrate is also important to avoid filling the liver, heart, and muscles with glycogen, which can cause long term harm.  A hypertrophic cardiomyopathy is a complication of excessive glycogen storage, but the muscle disease appears to be secondary to lack of an energy substrate during activity. A ketotic diet may help improve muscle disease in adults, but it has been associated with worsening of the hepatic transaminases and suboptimal growth in the pediatric population. 

 

Glycogen Storage Disease VI and IX

 

GSD VI is caused by glycogen phosphorylase and GSD IX by glycogen phosphorylase kinase.   Both conditions are remarkably similar and the most common of all the hepatic GSDs. In fact there has been a suggestion that GSD VI and IX together may account for a significant number of children with recurrent ketotic hypoglycemia (107). GSD VI is caused by mutations in PYGL and is inherited in an autosomal recessive form. On the other hand, there are 4 subunits of the phosphorylase kinase enzyme, and each is encoded by different genes including the X-linked gene PHKA2. PHKB mutations lead to an autosomal recessive form of GSD IX as do mutations in PHKG. The most severe form tends to occur in patients with genetic mutations in PHKG.

 

Clinical manifestations of GSD VI and IX are short stature and recurrent episodes of ketotic hypoglycemia. Unlike the hepatomegaly of GSDI and III in which the examiner will need to start palpating the liver from the anterior superior iliac spine in order not to miss a giant liver, the hepatomegaly of VI and IX may be very subtle or absent. Sometimes in younger children morning ketosis is found with euglycemia because after glycogen stores are depleted, gluconeogenesis and ketogenesis are activated and glucose levels remain normal. Thus, if suspecting GSD VI or IX, check morning beta-hydroxybutyrate and if >0.6 mmol/L after a normal overnight fast this would be suggestive of this disease. Also because of the reliance on gluconeogenesis, prealbumin and total protein levels may be low, and patients may complain of intermittent muscle aches without overt weakness.

 

Diagnosis is suspected by finding shortened fasting tolerance with accelerated development of ketosis in a patient with mild short stature and hepatomegaly. Mild elevations of liver transaminases and hyperlipidemia may occur. Absence of hepatomegaly does not rule out GSD VI or IX. Genetic testing is the diagnostic test of choice for those with either recurrent episodes of ketotic hypoglycemia or persistent finding of elevated beta-hydroxybutyrate after a simple overnight fast.

 

Treatment is avoidance of prolonged fasting and administration of UCS 1-2 g/kg at bedtime to prevent early morning ketosis. A high protein diet with complex carbohydrates is effective as gluconeogenesis is unaffected. A program of daytime carbohydrates for intercurrent illness and a plan for IV dextrose with vomiting is encouraged. By the time the child reaches adulthood fasting tolerance is of 12-18 hours overnight without ketones become possible and treatment is rarely required as an adult.

 

FATTY ACID OXIDATION AND KETONE BODY DISORDERS

 

Fatty Acid Oxidation Disorders

 

Fatty acid oxidation (FAO) occurs in the mitochondria and is the major source of energy production in the fasted state i.e., when glucose metabolism is insufficient to provide for energy needs. Typically, FAO starts when glycogen reserves are depleted in conjunction with an increase in gluconeogenesis. As insulin levels fall, hormone-sensitive lipase acts in the adipocytes to release 3 free fatty acids and 1 glycerol from the triacyl-glycerol (triglyceride) stored in the adipose tissue (108). The metabolism of the free fatty acids occurs in 3 major steps: 1) transport into the mitochondria via the carnitine shuttle, 2) long chain fatty acids undergo beta oxidation at the inner mitochondrial membrane, and then 3) medium and short chain fatty acid oxidation (FAO) occurs in the mitochondrial matrix. The result of FAO is the production of acetyl-CoA, which in the heart and skeletal muscle enters into the citric acid cycle and by oxidative phosphorylation generates energy for these tissues. The liver however converts acetyl-CoA into ketone bodies known as beta-hydroxybutyrate (BOHB, the main ketone body in the blood) and acetoacetate via hydroxyl methyl glutaryl-coenzyme A (HMG-CoA) synthetase and HMG-CoA lyase. The ketone bodies are exported to the brain for energy use. The liver also metabolizes the amino acids leucine and isoleucine into acetyl-CoA. Because fatty acids cannot cross the blood brain barrier, fatty acid oxidation is limited in the brain due to a lack of substrate. MCT1, a member of the monocarboxylate transporter family, transports the ketone bodies across the blood brain barrier. BOHB is then converted back to acetoacetate and then to acetyl-CoA which enters the citric acid cycle and generates energy in the form of adenosine triphosphate (ATP).  Studies have shown that as the plasma glucose falls the cerebral metabolic rate of glucose falls and as the plasma acetoacetate levels rise the cerebral metabolic rate acetoacetate rises replacing the lost metabolism of glucose (13). Thus, BOHB can add to glucose as a primary source of energy production by the brain. This protects the brain from hypoglycemic brain damage in circumstances of low glucose and high ketones (with the exception of patients with ketone utilization defects). This also highlights why untreated disorders of fatty acid oxidation plus ketone synthesis and utilization are dangerous as they result in accelerated development of hypoglycemia because of the loss of the glucose sparing ketones, resulting in energy failure in the brain.

 

Abnormalities of FAO tend to present either in periods of prolonged fasting often precipitated by intercurrent illness when the need for energy at a cellular level, increases, or during severe strenuous exercise. Common clinical features of these defects include fasting hypoglycemia with liver failure, hepatic encephalopathy, and muscular hypotonia.  Rhabdomyolysis following exercise is also common. Rare clinical effects might include cardiac arrhythmias and retinitis pigmentosa. The biochemical hallmark of FAO defects is hypoglycemia associated with elevated free fatty acids and inappropriately low ketone bodies (Table 3 and Figure 2). Coagulation defects, elevated liver function tests, and hyperammonemia may occur with massive elevation of serum CK levels.

 

FAO disorders are inherited as autosomal recessive conditions. The overall incidence has been reported to be approximately 1:9000 (109). Since the development of newborn screening for FAO disorders, the clinical presentation has changed with almost no patients presenting with hypoglycemia. Indeed, the incidence of hypoglycemia caused by previously unknown FAO disorder presenting in emergency room situations is dramatically reduced. In a study of approximately 220,000 children presenting at an emergency room between the ages of 0 and 18 years, 160 patients had previously undiagnosed hypoglycemia and none of them had a FAO defect (110). This compares to a study by Weinstein et al prior to universal newborn screen of FAO disorders in which FAO disorders represented 19% of previously undiagnosed hypoglycemia (111). Although most FAO defects are detected on newborn screening, rarely errors in the process may account for a missed case and it is always important to demonstrate in cases of hypoketotic hypoglycemia the absence of a FAO disorder.

 

This chapter will focus primarily on those disorders that primarily cause hypoglycemia and the acute treatment of the hypoglycemia.

 

DISORDERS OF FATTY ACID UPTAKE INTO MITOCHONDRIA AND THE CARNITINE CYCLE

 

Free fatty acids (FFA) are released from adipose tissue and travel to target cells where they are transported across the cell membrane by fatty acid transporter proteins. Once inside the cell they are esterified by acyl-CoA synthases and enter the carnitine cycle to enter the mitochondria. Carnitine palmitoyl transferase I (CPT I) catalyzes transfer of the acyl group from acyl-CoA to form acyl-carnitine and is the rate limiting step in FAO. The acyl-carnitine is transported across the mitochondrial membrane by carnitine acylcarnitine transferase (CACT) and once on the inside the acylcarnitine is converted back to acyl-CoA by CPT II. The acyl-CoA is now ready to undergo beta oxidation. The carnitine for these reactions is transported into the cell by the carnitine transporter. 

 

Disorders of the carnitine transporter, CPT I and CACT all cause hypoketotic hypoglycemia.  Both CPT 1 and CACT cause fasting-induced Reye syndrome with acute liver failure and can be suspected when hyperammonemia is found with hypoketotic hypoglycemia, elevated free fatty acids, and abnormal acylcarnitine profile. Carnitine transporter deficiency cause severe carnitine deficiency and dilated cardiomyopathy that is progressive and generally presents before hypoglycemic episodes. Diagnosis of carnitine transporter deficiency is suspected when total carnitine levels are very low (<10% normal) in conjunction with hypoketotic hypoglycemia and elevated CK levels in a patient with cardiomyopathy. Reye syndrome and acute liver failure also occur in CPT I and CACT and acute myoglobinuria with rhabdomyolysis occur in CPT II.

 

DISORDERS OF BETA OXIDATION

 

Beta-oxidation is the process whereby sequential molecules of acetyl-CoAs are cleaved off the long acyl-CoA inside the mitochondria, until the entire acyl-CoA has been broken down to acetyl-CoA (thus an 18-carbon acyl-CoA will generate 9 acetyl-CoAs). The first step in this reaction is carried out by four individual acyl-CoA dehydrogenase enzymes each acting on a different chain length acyl-CoA. These are the short, medium, long and very long chain acyl CoA dehydrogenase (SCAD, MCAD, LCAD and VLCAD) enzymes. The next three steps of FAO are carried out in conjunction with the tri-functional protein and involve the hydratase enzymes and both long chain and short chain 3-hydroxyacyl-CoA dehydrogenases (LCHAD and SCHAD). Finally electron transport flavoproteins transfer electrons from reducing equivalents produced by multiple pathways to the electron transport chain. Defects in the electron transport chain cause multiple acyl-CoA dehydrogenase deficiency (MADD) also known as Glutaric Aciduria II.

 

Clinical features of defects in beta-oxidation include hypoketotic hypoglycemia, associated with lethargy, vomiting, hypotonia seizures. Acute liver failure or Reye syndrome can occur, and cardiomyopathy is particularly severe in the longer chain disorders. It should be noted that ketones can be produced in variable amounts, but they are not sufficient to prevent hypoglycemia and the ratio of FFA to ketones is increased over normal. Individual FAO disorders have diagnostic acylcarnitine profiles and urine organic acid profiles and diagnosis may be made during an acute decompensation using these tools. However, one should never subject a patient suspected of having a FAO disorder to a fasting study for the purpose of diagnosis as it can precipitate an acute decompensation and death. If a FAO disorder is suspected, perform an acylcarnitine profile, total and free carnitine and test for urine organic acids in the well state, which may diagnose the condition without triggering a decompensation.

 

EMERGENCY TREATMENT OF FATTY ACID OXIDATION DISORDERS

 

Emergency treatment of hypoketotic hypoglycemia caused by FAO disorders involves correcting the hypoglycemia with a 200 mg/kg bolus of dextrose (best provided as 2 ml/kg Dextrose 10%) followed by administration of 5-10 mg/kg/min dextrose infusion with the goal of getting the plasma glucose above 85 mg/dl to turn on insulin secretion and suppress lipolysis. Treatment of elevated ammonia may be required if levels do not promptly fall with glucose administration.  Cardiopulmonary shock if present needs to be aggressively managed and liver failure and rhabdomyolysis need to be suspected and diagnosed early to implement treatment. Cerebral edema may occur particularly associated with elevated ammonia in undiagnosed cases of MCAD deficiency. Diuresis with possible alkalization of the urine can prevent acute renal failure in cases of extreme elevation of CK. Consultation with a metabolic expert is strongly recommended for endocrinologists not familiar with the ongoing management of children with FAO disorders. 

 

Ketogenesis and Ketone Utilization Defects

 

Ketone synthesis involves two primary enzymes involved in converting acetyl-CoA to acetoacetate, hydroxyl methyl glutaryl-coenzyme A (HMG-CoA) synthase and HMG-CoA lyase.  The ketone utilization defects are rare conditions in which ketogenesis is effective but there is an inability to either convert acetoacetate to aceto-acetyl-CoA by succinyl-CoA:acetoacetate transferase (SCOT) or acetoacetyl-CoA to acetyl-CoA by mitochondrial acetoacetic thiolase (MAT). These genetic defects are all autosomal recessive conditions. Finally, ketone transport into the brain can be diminished in patients with loss of function variations in SLC16A1 the gene encoding the monocarboxylate transporter 1 protein (MCT1) (112,113).

 

KETOGENESIS

 

There are significant similarities between the FAO defects and the ketogenesis disorders with hypoketotic hypoglycemia with or without hyperammonemia and hepatic encephalopathy.  Patients present in the newborn period or during intercurrent illness with relatively short episodes of fasting (12-18 hours). The biochemical hallmarks of HMG-CoA synthase deficiency are hypoglycemia with decreased ketones, elevated FFA, normal lactate and ammonia and normal urine organic acids and plasma amino acids whereas HMG-CoA lyase deficiency presents with hypoketotic hypoglycemia with elevated lactate and ammonia and very abnormal urine organic acid profile and elevated 3-methylglutaryl carnitine in the acylcarnitine profile. 

 

Treatment is similar to the FAO defects and includes rapid correction of hypoglycemia with 200 mg/kg intravenous bolus of dextrose (2 ml/kg Dextrose 10%) followed by an infusion of 5-8 mg/kg/min of glucose (3-5 ml/kg/h of Dextrose 10%). Treatment of the lactic acidosis with bicarbonate is not indicated unless life threatening acidosis is occurring as provision of glucose generally corrects the acidosis. Supportive care for hyperammonemia and hepatic encephalopathy should be provided.

 

KETONE UTILIZATION AND TRANSPORT DEFECTS

 

Ketone utilization defects generally present in the newborn period however some patients will survive the neonatal period and present later with intermittent severe metabolic acidosis due to ketoacidosis associated with fasting or intercurrent illness. Outside of an acute episode they may have elevated plasma BOHB >0.4 -0.6 mmol/L even when well fed indicating an inability to suppress ketones. Hypoglycemia is not the most common finding but can occur after prolonged fasting with or without hyperammonemia, hepatomegaly and encephalopathy. During fasting studies plasma BOHB continues to rise until progressive ketoacidosis occurs which is different to the rising and then stable ketosis of physiological fasting that stabilizes out as ketone utilization and ketogenesis balance out. 

 

Treatment is to provide glucose to increase insulin levels and suppress fatty acid oxidation.  This is typically achieved by providing a GIR of 8 mg/kg/min. Treatment of acidosis with bicarbonate therapy is controversial and should be used with caution in the severest cases.

 

 

CLINICAL APPROACH TO THE DIAGNOSIS OF THE ETIOLOGY OF HYPOGLYCEMIA

 

In order to diagnose the etiology of hypoglycemia one must first confirm the presence of hypoglycemia. Normal glucose levels are typically between 70 and 120 mg/dL and glucose levels less than 70 mg/dL in the face neurogenic or neuroglycopenic symptoms are suggestive of hypoglycemic disorders. In children (>5 to 7 years old) and young adults who are reliably able to report the symptoms of hypoglycemia, the finding of Whipple's triad (symptoms consistent with hypoglycemia, a measured plasma glucose confirming hypoglycemia, and improvement of symptoms with administration of glucose and correction of the hypoglycemia) is sufficient to warrant further investigation. For infants and younger children who are unable to reliably communicate symptoms, the Pediatric Endocrine Society (PES) guidelines suggests evaluation and management only of those whose plasma glucose concentrations are documented by laboratory quality assays to be below the normal threshold for neurogenic responses (60 mg/dL) (21).  For any patient with a low glucose value measured either by point of care meter using a finger stick blood sample or using a continuous glucose monitoring system, a plasma glucose needs to be obtained to confirm hypoglycemia prior to commencing a complete evaluation. This recommendation has been made because of the known inaccuracy of point of care glucose testing and of continuous glucose monitor testing for detecting blood glucose less than 70 mg/dL. Rather than providing children and their families with a glucometer for screening for low blood sugars at home, whenever safely possible, a standing order for a plasma glucose to be analyzed immediately, should be offered to the family. When they experience symptoms consistent with hypoglycemia, they can have a plasma glucose drawn in the lab to either confirm the presence of hypoglycemia or to demonstrate that these symptoms are not related to hypoglycemia. Thus, the presence or absence of Whipple's triad may be confirmed and only those with a high likelihood of hypoglycemia undergo further investigations. Studies have shown that the frequency of pathological hypoglycemia in patients in high-risk situations (for example the emergency room or attending a hypoglycemia clinic) who have had a documented low blood sugar associated with intercurrent illness will have a risk of a serious form of hypoglycemia of approximately 10% (110,114). 

 

History

 

The first step in the evaluation is to undertake a careful history specifically questioning for symptoms of hypoglycemia (Table 4), and timing of the symptoms, or measured hypoglycemia, relative to the last meal consumed. In pediatric patients, the vast majority of causes of hypoglycemia are precipitated by fasting. Documenting post prandial hypoglycemia in the absence of fasting hypoglycemic may suggest some very specific conditions, such as late dumping syndrome (Nissen fundoplication induced hypoglycemia, post bariatric surgery induced hypoglycemia), protein induced hypoglycemia found in GDH HI, HADH HI, and KATP HI, hereditary fructose intolerance, or a very rare presentation of insulinoma. Careful review of the history for the presence of neurogenic or neuroglycopenic symptoms should be performed. Neuroglycopenic symptoms are strongly suggestive of a serious underlying form of hypoglycemia and need rapid evaluation. A history of poor growth might suggest growth hormone deficiency, adrenal insufficiency (either primary or secondary), or GSD. Recurrent abdominal pain with nausea and vomiting is a classical symptom of severe adrenal insufficiency. A history of salt craving or darkening skin also are clues to primary adrenal insufficiency.

 

The most common time of presentation of hypoglycemia in childhood is in the neonatal period when the stress of transition from intrauterine to extra uterine life is greatest and genetic or metabolic forms of hypoglycemia most commonly present. It is important to always inquire about the neonatal period because of the possibility of missed diagnosis. Presentation to emergency rooms in association with intercurrent illness is the next most common time of presentation of hypoglycemia in childhood; it is recommended that emergency rooms should have protocols to draw the critical samples (Table 2) in patients who present with hypoglycemia, but with no previous etiology determined. If an emergency room does not have such protocols in place, we recommend their implementation, as up to 10% of all patients presenting to emergency rooms with previously undiagnosed hypoglycemia have a serious underlying condition requiring long-term treatment (110,114).

 

Physical Exam

 

The second step in the evaluation of the etiology of hypoglycemia is the physical exam. There are very few clues that can be obtained; however, it is critical not to miss those that are available. Short stature, with impaired growth velocity, or inappropriate height for the family, should suggest evaluation for growth hormone deficiency. Hyperpigmentation of the skin and or gums could indicate primary adrenal insufficiency with ACTH excess. Failure to thrive and weight loss could indicate chronic adrenal insufficiency. Central malformations such as cleft lip or palate could indicate an underlying pituitary problem. Scars on the abdominal wall or a gastrostomy tube could suggest a postsurgical form of hypoglycemia. Enlargement of the liver at a time when the patient is well would point to glycogen storage disorders, or if the patient is acutely unwell at the time of presentation a fatty acid oxidation defect might be more likely. Abnormal development of the genitalia might indicate adrenal hormonal production problems; a micropenis/small normal penis might indicate a growth hormone problem with or without hypogonadotropic hypogonadism.  Asymmetry of the body, either hemiatrophy or hemihypertrophy, could suggest an underlying syndrome such is Russell Silver Syndrome or Beckwith-Wiedemann Syndrome. Certain syndromes such as Down syndrome are associated with an increased incidence of ketotic hypoglycemia. Overgrowth syndromes, Turner syndrome, and Kabuki syndrome may be associated with hyperinsulinism (72,78,79).

 

Critical Sample at Time of Hypoglycemia

 

As noted above, a critical sample including blood and urine (Table 2) should be collected at the time of glucose less than 50 mg/dL. In this sample, the levels of intermediary metabolites and hormones in blood, ketones and organic acids in urine, and in certain circumstances the presence or absence of drugs such as insulin or sulfonylureas, will aid the physician to diagnose the etiology of the hypoglycemia. Interpretation of the critical sample commences with the determination of the presence or absence of ketosis and lactic acidosis as in Figure 2 and Table 3.

 

When a critical sample has not be obtained during a spontaneous episode of hypoglycemia, a fasting study should be performed to induce hypoglycemia (Table 10). Caution prior to admitting the patient for a fasting study, includes the need to rule out fatty acid oxidation defects by performing an acylcarnitine profile in the well state. Fasting studies should be performed in the inpatient setting in a unit of highly specialized nurses trained in the performance of fasting studies. Safety precautions such as having intravenous lines inserted for both blood drawing and infusing glucose in an emergency situation are very important. It is critical to have the ability to do accurate point of care glucose and ketone testing on venous samples or warmed capillary samples and to have a rapid turnaround on plasma glucose and plasma beta-hydroxybutyrate.  Intravenous glucose should be available for rescue and glucagon should also be available both for stimulation testing and for rescue when hyperinsulinism is suspected.

 

Table 10.  Diagnostic Fasting Test

Perform test only on a unit with trained medical and nursing staff who are experienced in the performance of fasting studies. 

1.     Have IV access and D10% (2-5 ml/kg) for emergency resuscitation.

2.     Measure glucose by POC meter every 2-3 hours until glucose <70 mg/dL (<3.9 mmol/L); then every 2 hours until <60 mg/dL (<3.3 mmol/L); then hourly until <50mg/dL (<2.8 mmol/L) 

a.     When glucose <60 mg/dL (<3.3 mmol/L) send specimen for laboratory confirmation of plasma glucose 

3.     Measure beta-hydroxybutyrate every 2-3 hours and when glucose <50mg/dL (<2.8 mmol/L)

a.     When plasma glucose ≤50 mg/dL (<2.8mmol/L) draw blood for the CRITICAL sample: 

glucose, insulin, beta-hydroxybutyrate, free fatty acids, ammonia, cortisol, growth hormone, lactate, acylcarnitine profile, urine organic acids

i.     Special circumstances: C-peptide, proinsulin, sulfonylurea screen, toxicology screen, serum amino-acids,

4.     Perform Glucagon Stimulation Test once CRITICAL samples are obtained 

1.              Measure glucose using POC meter and then give glucagon 30 mcg/kg or 0.5-1 mg by IM or IV push as long as glucose is <50 mg/dL (<2.8 mmol/L)

2.              Monitor glucose using POC meter every 10 minute for 40 minutes 

3.              Terminate test if glucose is still below 50 mg/dL (<2.8 mmol/L) after 30 minutes 

4.              After 40 minutes, may feed and resume treatment to maintain plasma glucose >70 mg/dL (3.9 mmol/L) 

Adapted from De Leon DD, Arnoux JB, Banerjee I, Bergada I, Bhatti T, Conwell LS, Fu JF, Flanagan SE, Gillis D, Meissner T, Mohnike K, Pasquini TLS, Shah P, Stanley CA, Vella A, Yorifuji T, Thornton PS. International Guidelines for the Diagnosis and Management of Hyperinsulinism. Horm Res Paediatr. 2023 (32).

 

When the results of the critical sample point to the likely area of metabolic perturbation (Figure 2), further testing may be indicated at times not necessarily at the time of hypoglycemia. For conditions such as hyperinsulinism, specific testing can further subclassify the etiology (such as protein sensitivity in GDH HI or HADH HI, or ammonia levels indicating GDH HI). In the case of low counter regulatory hormones found at the time of the critical sample, stimulation testing for growth hormone, cortisol, or ACTH deficiency can confirm if deficiencies in these hormones are the cause of hypoglycemia. One should never diagnose a hormonal deficiency as the cause of hypoglycemia on a single critical sample but rather only when dynamic testing has demonstrated deficiency (18,19). In cases suspected to be due to glycogen storage disease, liver biopsy is no longer indicated due to the morbidity of the procedure and genetic testing is now the preferred diagnostic method. This is also true for the disorders of fatty acid oxidation in which an acylcarnitine profile is not sufficient to make a diagnosis and genetic panels are preferable to skin biopsies the majority of the time. With current genetic testing technology, panels including many hypoglycemia disorder associated genes may be conducted for little more cost than a single gene test.

 

Approach to the Patient with Ketotic Hypoglycemia

 

There is a common misconception that children presenting with ketotic hypoglycemic, who do not possess an already identified underlying cause, have benign physiological idiopathic ketotic hypoglycemia. In recent years it has become clear that this is not correct (110,114). We outline an approach to patients with ketotic hypoglycemia that should allow differentiation between benign physiological ketotic hypoglycemia, pathological ketotic hypoglycemia associated with known underlying conditions and idiopathic pathological ketotic hypoglycemia (IPKH) in which there is clearly an abnormality of glucose regulation, but no genetic cause can be found (Figure 7).

 

Figure 7. Physiological vs. Pathological Ketotic Hypoglycemia.

 

BENIGN PHYSIOLOGICAL KETOTIC HYPOGLYCEMIA

 

Based on the normal physiology of fasting, if a person is fasted for long enough, they will develop a glucose <50 mg/dL and plasma beta-hydroxybutyrate >2 mmol/L. Studies have looked at the normal duration of fasting and found that time to glucose <50 mg/dL increases with age. Children 0-2 years can generally fast about 15-18 hours, children >2 years to 5 years can fast >24 hours, children >5 years to 10 years can fast about 36 hours, and teenagers to adults can fast 48-72 hours (115). Recently Pamar et al.  investigated children admitted for day surgery and found that only a small percentage developed beta-hydroxybutyrate levels >1 mmol/L by 12 hours of fasting (116). Thus, the finding of ketones in blood of >1 mmol/L after 12 hours of fasting in previously healthy and well-nourished children is unusual. However, the finding of ketosis after 24 -30 hours of no, or very poor, oral intake would be considered normal for most children over the age of 2 years. Thus, history is very important in differentiating benign physiological ketotic hypoglycemia due to prolonged starvation or intercurrent illness. It is our recommendation that previously healthy children who present with their first episode of ketotic hypoglycemia, who have a history consistent with prolonged starvation with or without intercurrent illness, who have elevated ketones >2 mmol/L and a normal physical exam, should not require further investigations. Children with recurrent episodes of ketosis despite precautions to avoid prolonged fasting need further investigation which may include admission for a fasting study. In addition to evaluating for an underlying etiology, this permits determination of the time to development of ketosis (by monitoring serial ketone levels, not just at the time of the critical sample) and hypoglycemia, which informs intervention. This is best achieved by a formal fasting study (Table 10) following three days of good feeding.

 

PATHOLOGICAL KETOTIC HYPOGLYCEMIA

 

The term pathological ketotic hypoglycemia is used to indicate that some underlying abnormality is causing disordered fasting tolerance. The key manifestation of this is ketotic hypoglycemia that occurs after an abnormally short fasting period, morning ketosis without hypoglycemia, or symptomatic ketosis causing vomiting and a vicious cycle of worsening ketosis, vomiting and dehydration. This can be secondary to hormonal deficiencies such as isolated growth hormone deficiency or cortisol deficiency (primary, secondary or tertiary). It can be caused by enzyme deficiencies in the glycogen storage pathway, disorders of gluconeogenesis, or disorders of ketone utilization or transport. In a small number of children, no cause can be found despite extensive clinical and genetic investigations. These children have idiopathic pathological ketotic hypoglycemia (IPKH). The approach to management of these children requires knowledge of the duration of fasting required to keep the beta-hydroxybutyrate <0.6 mmol/L and knowledge of how low the glucose will fall despite rising ketone levels. Thus, the therapeutic plan needs to be individually tailored to each child. Typical components will include high protein diet of 3 g/kg/day protein to promote gluconeogenesis and prevent catabolism of muscle and slow-release carbohydrates such as uncooked corn starch (UCS) or Glycosade®.  Many infants and children can be successfully treated with nighttime UCS and frequent high protein snacks during the day, but some will require intensive diets with monitoring of glucose and ketones, similar to individuals with GSD III, VI or IX. Because so little is known of the natural history of the severe forms of IPKH, careful review of metabolic control should be undertaken every few years to prevent under treatment as the patient grows but also to prevent over treatment since the natural ability to fast increases with advancing age.

 

CONCLUSIONS

 

Hypoglycemia in pediatric patients occurs predominately in the newborn period and during times of intercurrent illness, because it is most commonly caused by inherited hormonal or metabolic diseases. Rarer acquired forms of hypoglycemia must be suspected when initial presentation occurs in older children and adolescents. Because of the overlap of the normal transitional changes of glucose regulation in the newborn period with the most common time for the presentation of inherited hypoglycemic conditions, it is critical to screen for hypoglycemia and to determine the precise etiology so that rapid and appropriate interventions can be implemented. Newborn infants cannot be simply labeled as having hypoglycemia and discharged casually on frequent feeds. At the minimum a safety fast should be performed to ensure that the transient forms of hypoglycemia have truly resolved before discharge. Up to 10% of patients presenting with unexplained hypoglycemia in a pediatric emergency room setting will have a serious underlying metabolic or hormonal condition requiring long term care. It is critical that emergency rooms caring for children have protocols in place to identify these 10% of children, because these children are at risk of hypoglycemic brain damage. At all ages rapid intervention can prevent permanent neurological injury caused by the majority of conditions we discuss. 

 

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Chronic Fatigue Syndrome

ABSTRACT

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is an enigmatic medical condition that has growing prevalence across the globe, often diagnosed after exclusion of other medical or mental illnesses. As there is no clinical test to confirm the presence of this condition, the diagnosis is syndromic based on different clinical definitions. There was mixed evidence to support the use of a specific therapy that provides palliative effect. Pathophysiological hypotheses can be categorized into infection, immune, mitochondrial, neurobehavioral, or stress system (HPA axis and sympathetic nervous system) disorders. The prognosis of ME/CFS is mixed but recovery does occur in many cases, over time.  All-cause mortality rate is not increased.

CLINICAL DEFINITION

Fatigue is a term used to describe unexplained subjective, chronic, pervasive tiredness or weakness physically, mentally, or a combination of both. The term “myalgic encephalomyelitis” was first described in the United Kingdom after an outbreak of serious infection at the Royal Free Hospital in 1955 (1). The US originated term Chronic Fatigue Syndrome (CFS) was introduced by Holmes et al in 1988 (2). Several definitions of CFS have been developed, primarily to standardize research (3,4). The key symptoms expected in this condition was later refined in 1994 and named after Dr Fukada (3). However, it was particularly challenging to reach a consensus on a name for this condition as its etiology and pathology are unexplained. An important milestone was achieved on October 1, 2022 with the update to International Coding Disease (ICD-10-CM) that include a specific diagnostic code for myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), chronic fatigue syndrome (CFS) and myalgic encephalomyelitis (ME) (5). Prior to this, chronic fatigue syndrome was categorized in the “chronic fatigue, unspecified”, which could limit epidemiologic studies.

 

The 1994 US Centers for Disease Control and Prevention (CDC) Fukuda criteria for chronic fatigue syndrome comprise the following (3):

 

  1. Primary symptoms that are clinically evaluated, unexplained, persistent or relapsing fatigue, lasting at least 6 months. The fatigue is not the result of ongoing physical exertion, and resting, sleeping, or downgrading activity is non-restorative. The fatigue causes significant impairment in personal, social, and/or occupational domains and represents a substantial reduction in premorbid levels of activity and functional capacity.
  2. The concurrent presence of at least 4 of the 8 following symptoms over a 6-month period:
  • Impaired short-term memory or concentration.
  • sore throat.
  • tender lymph nodes/glands.
  •  
  • multiple-joint pain without swelling or redness.
  • headache of new type, pattern, or severity.
  • unrefreshing sleep.
  • post-exertional fatigue/malaise lasting longer than 24 hours.

 

The 2003 Canadian ME/CFS Case Criteria (CCC) specifies (4):

  • Post-exertional malaise must occur with rapid muscle or cognitive fatigability, taking 24 hours or longer to recover.
  • Unrefreshing sleep, myalgia, and arthralgia must be reported.
  • Two or more neurological/cognitive manifestations must be present.
  • At least one of autonomic, neuroendocrine, immune manifestations must be present.

 

This is a stricter criterion, compared to the Fukada Criteria and it is mainly used as case definition in research. Adults are diagnosed after 6 months of symptoms while pediatric cases were diagnosed after 3 months.

 

Nearly two decades after Fukada Criteria was introduced, the US Institute of Medicine (IOM), now known as National Academy of Medicine (NAM) proposed new diagnostic criteria in 2015 for chronic fatigue syndrome (CFS)/myalgic encephalomyelitis (ME) (5). These clinical diagnostic criteria followed a comprehensive analysis of the literature and expert consultation as below.

  1. Substantial reduction/impairment in the ability to engage in pre-illness levels of occupational, educational, social, or personal activities that persists for more than 6 months, is accompanied by fatigue that is often profound, is of new or definite onset, is not the result of ongoing excessive exertion, and is not substantially alleviated by rest.
  2. Post-exertional malaise (PEM).
  3. Unrefreshing sleep.
  4. In addition, patients are required to have at least one of the following two symptoms:
  • Cognitive impairment.
  • Orthostatic intolerance.

 

Symptoms must be present at least half of the time and have moderate, substantial, or severe intensity.

 

As a large group of patients remain stigmatized with the term ‘chronic fatigue syndrome’ (CFS), renaming the condition to 'systemic exertion intolerance disease' (SEID) was recommended to overcome the old stereotypes as CFS is more associated to a mental disorder rather than an organic illness (5). SEID highlights the somewhat unique feature of exertion intolerance, and consequent impaired functional capacity. SEID criteria may help with the treatment by increased diagnosis and awareness, calling attention to the major disabling symptoms, and by validating the major symptoms as real and debilitating. However, the new IOM criteria could increase the prevalence rate of this condition compared to the use of previous Fukada criteria due to the lack of specifying exclusionary illnesses (5).

DIAGNOSTIC APPROACH

The clinical diagnosis of CFS/ME is based on a constellation of symptoms where post-exertional malaise and fatigue are prominent; these are described in some definitions (Table 1) with an algorithm provided in Figure 1 (6). A thorough clinical assessment is necessary to exclude alternative medical and psychiatric diagnoses requiring specific treatment. For example, it is important to differentiate fatigue from weakness, which suggests a neuromuscular disease, and anhedonia from major depression. Hypersomnolence and sleep disorder suggests a need to exclude obstructive sleep apnea, particularly in groups at risk such as the obese.

 

Limited laboratory screening investigations are directed towards the discovery of subtle medical disorders. Unfortunately, there was no test with adequate sensitivity and specificity to verify the diagnosis of CFS/ME. The protean manifestations of CFS/ME suggest diverse causes, hence it is unlikely a single diagnostic test for CFS/ME will be developed. Routine laboratory investigations include a complete blood examination, erythrocyte sedimentation rate (ESR), calcium, phosphate, magnesium, blood glucose, serum electrolytes, thyroid stimulating hormone and free thyroxine levels, protein electrophoresis screen, C-reactive protein (CRP), ferritin, creatinine, rheumatoid factor, antinuclear antibody, creatine kinase and liver function, and routine urinalysis. Any other investigations should be carefully chosen on an individual basis depending on the clinical assessment and risk factors for other conditions. For example, sleep study may be considered in patients who have features of obstructive sleep apnea, while a morning cortisol concentration or a more definitive ACTH stimulation test may be considered for patients who have clinical features suggestive of adrenal insufficiency.

 

Although patients with CFS/ME tend to have more abnormalities on magnetic resonance imaging (MRI) and single-photon emission computed tomography (SPECT), the significance of these findings are unclear, hence routine neuroimaging is not recommended in the diagnostic process (7,8).

 

Some recent studies have suggested reduced circulatory and myocardial function in CFS, although the utility of routine cardiac assessment is not established (9,10).

 

Table 1. Clinical Working Case Definition of ME/CFS, published in 2000 (3,4)

A patient with ME/CFS will meet the criteria for fatigue, post-exertional malaise and/or fatigue, sleep dysfunction, and pain; have two or more neurological/cognitive manifestations and one or more symptoms from two of the categories of autonomic, neuroendocrine and immune manifestations; and adhere to item.

1. Fatigue: The patient must have a significant degree of new onset, unexplained, persistent, or recurrent physical and mental fatigue that substantially reduces activity level.

2. Post-Exertional Malaise and/or Fatigue: There is an inappropriate loss of physical and mental stamina, rapid muscular and cognitive fatigability, post exertional malaise and/or fatigue and/or pain and a tendency for other associated symptoms within the patient’s cluster of symptoms to worsen. There is a pathologically slow recovery period – usually 24 hours or longer.

3. Sleep Dysfunction:* There is unrefreshed sleep or sleep quantity or rhythm disturbances such as reversed or chaotic diurnal sleep rhythms.

4. Pain:* There is a significant degree of myalgia. Pain can be experienced in the muscles and/or joints, and is often widespread and migratory in nature. Often there are significant headaches of new type, pattern or severity.

5. Neurological/Cognitive Manifestations: Two or more of the following difficulties should be present: confusion, impairment of concentration and short-term memory consolidation, disorientation, difficulty with information processing, categorizing and word retrieval, and perceptual and sensory disturbances – e.g., spatial instability and disorientation and inability to focus vision. Ataxia, muscle weakness and fasciculations are common. There may be overload phenomena: cognitive, sensory – e.g., photophobia and hypersensitivity to noise – and/or emotional overload, which may lead to “crash” periods and/or anxiety.

6. At least one symptom from two of the following categories: (i) Autonomic Manifestations: orthostatic intolerance – neurally mediated hypotension (NMH), postural orthostatic tachycardia syndrome (POTS), delayed postural hypotension; lightheadedness; extreme pallor; nausea and irritable bowel syndrome; urinary frequency and bladder dysfunction; palpitations with or without cardiac arrhythmias; exertional dyspnea. (ii) Neuroendocrine Manifestations: loss of thermostatic stability – subnormal body temperature and marked diurnal fluctuation, sweating episodes, recurrent feelings of feverishness and cold extremities; intolerance of extremes of heat and cold; marked weight change – anorexia or abnormal appetite; loss of adaptability and worsening of symptoms with stress. (iii) Immune Manifestations: tender lymph nodes, recurrent sore throat, recurrent flu-like symptoms, general malaise, new sensitivities to food, medications and/or chemicals.

7. The illness persists for at least six months. It usually has a distinct onset, ** although it may be gradual. Preliminary diagnosis may be possible earlier. Three months is appropriate for children.

To be included, the symptoms must have begun or have been significantly altered after the onset of this illness. It is unlikely that a patient will suffer from all symptoms in criteria 5 and 6. The disturbances tend to form symptom clusters that may fluctuate and change over time. Children often have numerous prominent symptoms but their order of severity tends to vary from day to day. *There is a small number of patients who have no pain or sleep dysfunction, but no other diagnosis fits except ME/CFS. A diagnosis of ME/CFS can be entertained when this group has an infectious illness type onset. **Some patients have been unhealthy for other reasons prior to the onset of ME/CFS and lack detectable triggers at onset and/or have more gradual or insidious onset.

Exclusions: Exclude active disease processes that explain most of the major symptoms of fatigue, sleep disturbance, pain, and cognitive dysfunction. It is essential to exclude certain diseases, which would be tragic to miss: Addison’s disease, Cushing’s syndrome, hypothyroidism, hyperthyroidism, iron deficiency, other treatable forms of anemia, iron overload syndrome, diabetes mellitus, and cancer. It is also essential to exclude treatable sleep disorders such as upper airway resistance syndrome and obstructive or central sleep apnea; rheumatological disorders such as rheumatoid arthritis, lupus, polymyositis and polymyalgia rheumatica; immune disorders such as AIDS; neurological disorders such as multiple sclerosis (MS), Parkinsonism, myasthenia gravis and B12 deficiency; infectious diseases such as tuberculosis, chronic hepatitis, Lyme disease, etc.; primary psychiatric disorders and substance abuse. Exclusion of other diagnoses, which cannot be reasonably excluded by the patient’s history and physical examination, is achieved by laboratory testing and imaging. if a potentially confounding medical condition is under control, then the diagnosis of cfs can be entertained if patients meet the criteria otherwise.

Co-Morbid Entities: Fibromyalgia Syndrome (FMS), Myofascial Pain Syndrome (MPS), Temporo- mandibular Joint Syndrome (TMJ), Irritable Bowel Syndrome (IBS), Interstitial Cystitis, Irritable Bladder Syndrome, Raynaud’s Phenomenon, Prolapsed Mitral Valve, Depression, Migraine, Allergies, Multiple Chemical Sensitivities (MCS), Hashimoto’s thyroiditis, Sicca Syndrome, etc. Such comorbid entities may occur in the setting of CFS. Others such as IBS may precede the development of CFS by many years, but then become associated with it. The same holds true for migraines and depression. Their association is thus looser than between the symptoms within the syndrome. CFS and FMS often closely connect and should be considered to be “overlap syndromes.”

Overload phenomena affect sensory modalities where the patient may be hypersensitive to light, sound, vibration, speed, odors, and/or mixed sensory modalities.

Figure 1. Diagnostic algorithm adapted from IOM (6).

EPIDEMIOLOGY

The frequency of CFS has been assessed in two large-scale US community-based studies and a prevalence of 0.23-0.42% has been suggested (11,12). Another study suggested the global prevalence of CFS ranges from 0.4% and 2.5% (13).

 

CFS is at least twice as common in women as in men, occurs more frequently in minority groups, and in those with lower levels of education and occupational status (11, 14). Geographic location has not been shown to influence the prevalence of CFS but more recent study showed the condition is more common in certain countries such as the UK, Australia, and the USA (12, 14). Twin studies suggest that genetic factors play an important role (16). Population studies also associate elevated premorbid stress and childhood trauma, especially if complicated by psychopathology, with an increased risk of CFS (17,18).

 

An Australian sociodemographic cross-sectional study of patients diagnosed with CFS by their primary care physician was conducted over 2 years (2013-2015) (19). Participants were classified according to Fukuda criteria and international consensus ME/ICC criteria. CFS was most prevalent between 45-55 years, with a peak onset between 25-35 years with a high proportion of females affected (78.6%). Patients were predominantly Caucasian and highly educated. Of a total of 535 patients, only 30% met the Fukuda criteria and 32% met both Fukuda and International consensus ME/ICC criteria. 15% did not meet the criteria and 23% had exclusionary conditions. There was higher proportion of participants who were obese or overweight, (41.3% and 43.3% respectively) and were unemployed or on a disability pension. The results of this study may not be representative of all CFS/ME patients in the general population due to sample recruitment bias.

PATHOPHYSIOLOGY OF CHRONIC FATIGUE SYNDROME

Viral/Immune Hypotheses

For many years CFS was suspected to arise from a persistent response to an infection. Abrupt onset of symptoms and the presence of post-infectious fatigue after infections suggest this theory. There were also reports of a high frequency of antibody titers to specific, but varying, infectious agents (20). Epstein-Barr virus, human herpes virus 6, group B Coxsackie virus, human T-cell lymphotrophic virus II, hepatitis C, enteroviruses, and retroviruses, have all been proposed as etiological agents of CFS (21). However, to date, there has been no consistent evidence that CFS results from a specific infection (22). Moreover, there is data to indicate that global increases in humoral immune responses are seen in chronic stress states and that neurohormonal changes may account for these and other immune aberrations (20,23).

 

Recent study has examined the characteristics of cell function and receptors in CFS patients (24). Participants between 20 and 65 years old were recruited, by using the Fukuda criteria. Patient were classified as moderate (mobile) or severely affected (housebound). Blood was collected from all participants between 8am and 11am, and sent for lytic protein analysis, cell activity analysis, respiratory burst analysis and natural killer cell receptors analysis. The study demonstrated that there was significant decrease in natural killer cell cytotoxic activity in CFS patients and there is correlation between low natural killer cells cytotoxic activity and severity of CFS illness. CFS patients have alterations in Natural Killer receptors, adhesion markers and receptors on CD4, and CD8.

 

A prospective population-based cohort of 42,558 atopic patients and 170,232 controls without atopy were recruited between 2005-2007, with follow up until 2011. These 2 groups were similar in sex and age distributions, with a mean age of 47 years. The overall incidence rate for CFS in the atopy cohort (1.37 per 1000 person-year) was higher than in the non-atopy cohort (0.87 per 1000 person-year (25).  This suggests that that atopy might increase the risk of CFS/SEID.

Mitochondrial Hypotheses

Since mitochondria provide cellular energy, hypotheses of impaired mitochondrial function have been suggested to underlie CFS. Early studies have shown some associations between mitochondrial proteins and CFS, but these require confirmation (26).

Neuropsychiatric Hypotheses

Chronic fatigue syndrome has been suspected to be a neuropsychiatric disorder, or a type of depression (28). Although depression is frequent in CFS, most patients do not exhibit the characteristic self-reproach or biological features of endogenous depression. The depression often seen in CFS appears to be reactive and associated with marked frustration. However, the symptoms of depression can overlap with those of CFS. Profound fatigue is more commonly reported amongst CFS patients, than those with depression (28). Cognitive-behavioral models of CFS emphasize the importance of the interactions between cognitive, behavioral and biological variables in attempting to explain the genesis and maintenance of CFS. It may be that while organic factors may precipitate CFS, cognitive-behavioral factors may perpetuate the illness (28). Specifically, when individuals resume normal activity levels following an acute illness, it is common to experience symptoms of physical deconditioning. If individuals attribute these symptoms to signs of ongoing disease rather than deconditioning, they may resort to rest and inactivity in an attempt to "cure" the symptoms. A cycle of avoidance and symptom experience develops, which can lead to loss of control, demoralization and possible depression and anxiety. These psychological states can further perpetuate the illness through generating more symptoms.

 

The cognitive-behavioral model has been expanded to include personality as predisposing factors (29). This model proposes that predisposed people are highly achievement orientated perfectionists and base their self-esteem and the respect from others on their ability to live up to certain high standards (29). When such people are faced with factors that affect their ability to perform, such as a combination of excessive stress and an acute illness, their initial reaction is to persist and to attempt to maintain usual coping strategies. This behavior leads to exhaustion. In making sense of the situation a physical attribution for the exhaustion is made, which protects an individual's self-esteem by avoiding the suggestion that their inability to cope is a sign of personal weakness. The bias may lead to a focus on somatic rather than emotional aspects of the illness, and favors physical rather than psychological explanation. However, this model remains to be fully evaluated and it is poorly integrated with physiological aspects of CFS. There have been few systematic studies undertaken on the relationship between personality and CFS (28). However, a personality trait characterized by "perfectionism, high standards for work performance, responsibility and personal conduct and marked achievement orientation" was reported in interviews with individuals with CFS (30). Interviewees referred to a desire for accomplishment and success, aiming to achieve perfection. These desires were associated with the belief that “failure to meet these standards would indicate failure as a person, or unacceptability to others” (30).

Neurological Hypothesis

CFS as a primary brain disorder has been studied with neuroimaging including Magnetic resonance imaging MRI, Single-photon emission computed tomography (SPECT) Electroencephalogram (EEG), quantitative electroencephalogram (qEEG), and positron emission tomography (PET) (32-36, 40-41). A variety of abnormalities associated with CFS have been reported but the diagnostic or potential pathogenic implications of these findings are unknown.

Neuroendocrine Hypotheses

In recent years, there have been reports indicating neuroendocrine hypofunction, probably of hypothalamic origin, in chronic fatigue states. A tendency to hypocortisolism, has been identified, albeit inconsistently, in CFS patients. Relative hypocortisolism may reflect the primary abnormality in many CFS patients, such as a disorder of the brain regulation, or peripheral elements, of the stress system. Moreover, hypocortisolism may contribute to CFS symptomatology.

 

However, neuroendocrine studies in CFS have often led to contradictory results. Smaller studies may be confounded by differences between subgroups of CFS patients, such as duration of fatigue, concomitant hypotension and/or orthostasis, depression, familial occurrence, and other factors. Although melancholic major depression is associated with mild hypercortisolism, the hypocortisolism of CFS seems to persist in at least some patients with co-morbid depression (28). Moreover, hypocortisolism is a trait shared with other chronic idiopathic disorders, including post-traumatic stress disorder, fibromyalgia, and inflammatory disorders such as rheumatoid arthritis and asthma (18). Wyller et al. studied 120 CFS patients and 68 healthy controls, aged 12-18 years. CFS patients had higher levels of plasma norepinephrine, plasma epinephrine and FT4, with lower urine cortisol/creatinine ratios, (42). This accords with previous studies of attenuation of cortisol secretion and enhancement of the sympathetic nervous system activity in CFS.

THE STRESS SYSTEM AND CFS/SEID

Stress is defined as threat to homeostasis. It is generally accepted that acute stress system responses are adaptive, designed to re-establish homeostasis. However excessive and/or prolonged activation of the stress system can disturb normal physiology. The stress system comprises the hypothalamic-pituitary-adrenal (HPA) axis of which cortisol is the major mediator, and the sympathoadrenal system which produces the catecholamines epinephrine and the sympathoneural system producing norepinephrine. Both glucocorticoids and catecholamines act widely to mediate the stress response.

 

Stress results in stimulation of parvicellular neurons of the paraventricular nucleus (PVN) of the hypothalamus and the release of the neuropeptides corticotropin releasing hormone (CRH) and arginine vasopressin (AVP) into the hypophyseal portal blood system (Figure 2). The combined action of CRH and AVP on the anterior pituitary corticotropes stimulates secretion of adrenocorticotropin hormone (ACTH). Circulating ACTH acts on the zona fasciculata of the adrenal cortex to stimulate cortisol synthesis. Basal (unstressed) cortisol acts to prevent arterial hypotension by augmenting the effects of catecholamines, and maintain normoglycemia through insulin counter-regulation.

 

ACTH secretion is influenced by stress, a light-entrained circadian rhythm, and negative feedback at the hypothalamus. During acute stress, the amplitude and synchronization of the CRH and AVP pulsations in the hypophyseal portal system markedly increases, resulting in increases of ACTH and cortisol secretory episodes (43). Stress-induced cortisol secretion activates the central nervous system, increases blood pressure, elevates blood glucose, and suppresses the inflammatory/immune response to prevent tissue damage (44).

 

Cortisol action is mediated by ubiquitous cytosolic corticosteroid receptors and (45). Free cortisol, unbound to corticosteroid binding globulin (3-10%), diffuses through cell membranes and binds to the carboxy-terminal end of the cytosolic glucocorticoid receptor. On cortisol binding, the ligand-receptor complex translocates into the nucleus, where it interacts with specific glucocorticoid responsive elements (GREs) within DNA to activate gene transcription (45). The activated receptors also inhibit other transcription factors, such as c-Jun/c-Fos and NF-kB, which are positive regulators of the transcription of genes involved in the activation and growth of immune and other cells (46).

Figure 2. The neurohormonal connections of the stress system.

 

Several complementary sets of studies have examined basal and stimulated pituitary-adrenal gland function in CFS.

 

Two different types of heritable disorders of this axis have been described, where fatigue is the principal symptom. These include glucocorticoid resistance due to glucocorticoid receptor abnormalities, and mutations of the corticosteroid-binding globulin gene, the chief cortisol transport protein. These disorders are rare, but reinforce the notion that primary pituitary-adrenal abnormalities may produce chronic fatigue. Studies in the broader CFS patient group have generally detected relative hypocortisolism and altered dynamic responses, providing indirect evidence of a central nervous system under-stimulation of pituitary-adrenal function.

 

Familial glucocorticoid resistance is a rare syndrome characterized by diminished tissue effect of cortisol as a result of a glucocorticoid receptor defect. Glucocorticoid resistance is generally due to a loss of function mutation of the glucocorticoid receptor gene, although the genetic defect has not been identified in all cases. Decreased sensitivity to cortisol results in activation of the HPA axis, with increased ACTH and cortisol levels. In most cases, elevated cortisol levels sufficiently compensate to overcome the hormone resistance, thus these patients do not clinically manifest either cortisol excess or deficiency. Increased ACTH secretion also results in elevated mineralocorticoid and androgen levels resulting in hypertension and hirsutism (47). However, fatigue as an isolated symptom has been described in a 55-year-old woman with glucocorticoid resistance (48). Fatigue in this patient was intermittent, but blood pressure was constantly in the low-normal range, with no postural hypotension. Fatigue was sufficient to prohibit full-time work. Urinary cortisol was elevated (400-800nmol/24h; Range <300nmol/24h), as were plasma cortisol levels. A thermolabile glucocorticoid receptor was noted, specifically a temperature-induced reduction in dexamethasone binding, although a specific glucocorticoid receptor mutation was not reported. It has been proposed that fatigue in such cases is a result of insufficient overproduction of cortisol (49).

 

Further to this, recent studies of glucocorticoid receptor polymorphisms have found an association between certain haplotypes and CFS (50). Although speculative, polymorphisms may result in altered receptor sensitivity to cortisol, and thus, impaired tissue-effect of cortisol, resulting in relative hypocortisolism.

CORTICOSTERIOD BINDING GLOBULIN ABNORMALITIES AND CHRONIC FATIGUE

Corticosteroid-binding globulin (CBG), also known as transcortin, is the high-affinity plasma transport glycoprotein for cortisol (51). It is secreted by hepatocytes as a 383-amino acid polypeptide, after cleavage of a 22-amino acid signal peptide. Each CBG molecule contains a single high-affinity steroid binding site (51). Under circadian conditions, 80% of circulating cortisol is bound to CBG, 10-15% is bound to low-affinity albumin and 5-8% of circulating cortisol is unbound or free (51). Currently, only the free fraction is thought to be biologically active. CBG levels are generally stable. CBG is traditionally thought to function primarily as a carrier molecule for cortisol, but it may also serve as a buffer and as a reservoir, during secretory surges, or during times of reduced cortisol secretion, respectively. CBG may also have a specific-tissue cortisol delivery role, in particular enabling cortisol to act in an immunomodulatory capacity (52). High-affinity cortisol binding is saturated beyond cortisol levels of 500nmol/L, hence free cortisol levels rise exponentially at high cortisol concentrations (53). Under conditions of stress, elevated cortisol levels saturate available CBG and increase the free cortisol to above 20% (53).

 

CBG is involved in the stress response. Immune activation releases interleukin-6 (IL-6) which increases circulating free cortisol levels by two mechanisms. IL-6 stimulates cortisol secretion through activation of hypothalamic CRH neurons and it also inhibits CBG gene transcription thereby increasing the free cortisol fraction and thus, circulating glucocorticoid activity (54,55). In vivo, exogenous IL-6 results in a 50% reduction in CBG levels in humans. Severe illness, such as sepsis and burns, are associated with similar reductions in CBG levels, in conjunction with a similar rise in endogenous IL-6 (56,57). Similar falls in circulating CBG concentrations are seen in septic shock and low CBG concentrations have been shown to be an independent predictor of mortality in ICU patients (58). Stress-induced falls in circulating CBG concentrations may also relate to cortisol elevations, as low CBG levels are seen in Cushing’s syndrome or after anti-inflammatory glucocorticoid doses (57). This effect is probably mediated through the glucocorticoid receptor as glucocorticoid receptor knockout mice exhibit increased hepatic CBG expression and 50% increased plasma CBG levels (59).

 

CBG Lyon refers to a CBG gene mutation that was first described in a 43-year-old Moroccan woman presenting with chronic fatigue, depressed mood and low blood pressure, suggesting adrenal insufficiency (60). She had very low plasma cortisol levels, but normal ACTH levels. She was found to be homozygous for a point mutation in exon 5, leading to an Asp-Asn substitution, and a 4-fold reduction in CBG-cortisol binding affinity. Immunoreactive-CBG levels were 50% of the lower limit of normal, suggesting that the mutation affects CBG secretion or degradation. The proband’s four children were heterozygous for the mutation. A 10-member Brazilian kindred with the same genetic mutation and reduced CBG-binding affinity has also been described, having been discovered after low cortisol levels were detected in the proband, a homozygote, who presented with fatigue (61). One other kindred member was a homozygote, the rest were heterozygotes, all were normotensive and none experienced fatigue.

 

In 2001, a 39-member Italian-Australian family was reported, including 21 heterozygotes and 3 homozygotes with a novel complete loss-of-function (null) CBG gene mutation involving exon 2 (62). The null mutation is a point mutation leading to a premature stop codon corresponding to residue -12 (tryptophan) of the pro-CBG molecule. It resulted in a 50% reduction of or undetectable CBG levels in heterozygotes or homozygotes, respectively. The proband was investigated because of unexplained fatigue and low blood pressure, suggesting glucocorticoid deficiency, and the finding of low plasma but normal urine cortisol levels, suggesting CBG deficiency. Amongst kindred members who were homozygous or heterozygous for the mutation, there was a high prevalence of chronic fatigue and low blood pressure. Surprisingly, five members had the previously reported CBG Lyon mutation.

 

Hence, CBG gene mutations are associated, albeit, inconsistently, with fatigue. Amongst CFS patients, the Lyon and Null mutations have not been detected (63- 65). To date several CBG mutations were identified following investigations of patients presenting with low plasma cortisol in variety of medical conditions such as chronic fatigue (66).

PITUITARY-ADRENAL HORMONE ABNORMALITIES IN CHRONIC FATIGUE SYNDROME

Recent interest in the role of the HPA axis in CFS has arisen from the observation that conditions in which there is low circulating cortisol are characterized by debilitating fatigue. Addison’s disease, glucocorticoid withdrawal, and bilateral adrenalectomy are all associated with fatigue and with other symptoms also seen in CFS, including arthralgia, myalgia, disturbed sleep, and mood (67). Many studies provide inconsistent data on HPA axis function in patients with CFS, in part because of methodological differences, but also reflecting, perhaps, individual variation in HPA axis activity.

 

Urinary free cortisol levels in CFS patients have been found to be significantly lower, or no different to, controls (68-71). Plasma morning and late evening cortisol has been shown to be reduced in CFS/ME, but this finding has not been consistently reproduced, particularly when frequent plasma cortisol sampling has been performed (69,71). Salivary cortisol has emerged as a useful test to detect hypercortisolism because of its non-invasiveness and correlation with free blood cortisol levels. In CFS, salivary cortisol day-curves are blunted compared with controls, evening salivary cortisol levels are lower, and there is a blunted salivary cortisol rise in response to waking (72-75). DHEA and its long half-life sulphated metabolite DHEA-S represent major adrenal gland products in terms of mass. They represent important contributors to circulating androgen activity, particularly in women. DHEA and DHEA-S levels were shown to be lower in 15 CFS patients relative to 11 controls; furthermore, CFS patients did not display the usual decrease in DHEA:cortisol ratio with ACTH stimulation (76). A preliminary study in eight selected CFS patients with a subnormal 1μg ACTH stimulation test showed a 50% reduction in adrenal gland volume on CT scan (77). This finding might indicate that the hypocortisolism of CFS is due to a lack of ACTH stimulation or a primary adrenal abnormality. In a recent study, however, DHEA levels were higher in CFS patients and were correlated with higher disability scores (78).

 

To further examine the endocrine axes, stimulation testing is a classic endocrine paradigm, where subtle hypofunction may become more evident through the administration of stimulatory hormones or neuroactive agents. Nevertheless, as central control of endocrine axes cannot be directly assessed due to the lack of accessibility of the hypothalamic-pituitary circulation, the interpretation of the findings tends to be indirect. Often it is necessary to implicate underlying receptor up or down-regulation or secondary adrenal atrophy. Moreover, neuroactive agents often have incomplete specificity and the central neurotransmitter systems under study may in fact not be exclusively tested.

 

Dynamic endocrine testing with human CRH (pituitary stimulus) in CFS patients revealed a trend towards lower cortisol responses – which became statistically significant if ACTH responses were analyzed as a covariate (79). ACTH responses to CRH may also be blunted in CFS (80). Other studies have found a normal ACTH and cortisol rise to CRH in CFS patients, which contradict the hypothesis, and previous data, suggesting that CFS is associated with a blunting of the HPA axis (81).

 

Insulin hypoglycemia is a profound stimulus of ACTH and cortisol release, as it is likely to induce release of many hypothalamic ACTH secretagogues. Studies in CFS have revealed increased ACTH but normal cortisol responses after insulin hypoglycemia (82). This could be interpreted as indicating low CRH tone, with chronic CRH hyposecretion despite an intact CRH neuron, and secondary adrenal atrophy.

 

Naloxone is thought to stimulate ACTH and cortisol secretion by blocking tonic opioidergic inhibition of the CRH neuron. Naloxone mediated activation may be blunted in CFS suggesting it is the CRH neuron or pathways inhibitory to this neuron that lead to HPA axis hypofunction in CFS, rather than increased opioidergic tone (83). Other studies of CFS patients have a normal ACTH and cortisol response to naloxone (81).

 

The waking cortisol response, where cortisol levels rise 30-50% by 30 mins after waking compared to levels immediately on waking, is attenuated in chronic fatigue syndrome as a result of both higher waking and lower 30 min salivary cortisol levels, as documented in 75 CFS patients versus controls (82).

 

Another explanation for the hypocortisolism of CFS is increased glucocorticoid sensitivity, particularly in relation to the cerebral structures involved in glucocorticoid feedback such as the hypothalamic-paraventricular nucleus, the site of CRH neurons, and the anterior pituitary and hippocampus. Increased glucocorticoid sensitivity has been described in other stress-related hypocortisolemic disorders, such as post-traumatic stress disorder, and has recently been reported in a small study of CFS patients (85).

 

Finally, it is not known if the hypocortisolism of CFS is a response to chronic deconditioning since exercise is a potent stimulator of HPA axis function. Experimental acute exercise deprivation led to some symptoms relating to pain, fatigue and mood as well as lower cortisol in a subset of healthy individuals (86).

 

CFS is associated with prominent features of autonomic dysregulation such as postural hypotension, disturbances in temperature regulation, and altered skin microcirculation. The other arm of the stress system, the sympathetic nervous system with its outflow components, the sympathoneural and sympathoadrenal limbs have been less studied than cortisol in CFS. However, studies of both norepinephrine levels and a variety of tests of autonomic function suggest hyperactivity of the SNS, perhaps as a response to inadequate HPA axis responsivity (87,88).

 

The data suggesting relative hypocortisolism in CFS, along with the co-existence of fatigue, low blood pressure, and mood alterations in both Addison’s disease and CFS, have led to trials of hydrocortisone therapy in CFS. A randomized crossover trial in 32 CFS patients, of low-dose hydrocortisone (5mg or 10mg) treatment compared with placebo showed a reduction in self-reported fatigue scores after 1 month of treatment (89). In 28% of patients taking hydrocortisone, fatigue scores reached a predefined cut-off value similar to the normal population score. Only 9% of patients taking placebo achieved this reduction in fatigue score. However, another trial of hydrocortisone treatment in CFS, have subsequently shown no real benefit of treatment. The trial which included 70 patients, treated with hydrocortisone (16mg/m2 daily in 2 divided doses) for 3 months reported some improvement in symptom scales (90). It is of interest that those with the lowest cortisol levels and adrenal reserve were not the most symptomatic, nor were they more likely to respond to hydrocortisone treatment. Adverse effects including weight gain, increased appetite, and disturbed sleep, occurred in those taking hydrocortisone. Hydrocortisone treatment was also associated with significant adrenal suppression, on the basis of basal and ACTH-stimulated cortisol levels in 12 patients. The authors concluded that the risks of adrenal crisis outweighed any perceived benefit of treatment and therefore that systemic corticosteroids should not be used in the treatment of CFS (90).

 

Blockmans et al., reported six month randomized, placebo-controlled, double-blind, crossover study of hydrocortisone (5mg/day) and fludrocortisone in 100 patients fulfilling the CDC criteria for CFS (91). There was no benefit of treatment on self-reported fatigue or well-being.

 

Fludrocortisone (0.1-0.2mg) was tested in a placebo-controlled, double-blind crossover trial. No improvement in symptoms, treadmill exercise performance, or reaction time was observed in the 20 CFS patients who completed the trial (92).

 

The available scientific data indicates that the symptomatic benefit achieved with hydrocortisone or fludrocortisone replacement is, at best, marginal, and importantly, may be associated with clinically significant adverse effects, including adrenal suppression or features of glucocorticoid excess. These adverse effects outweigh any perceived benefit of treatment. Overall, hydrocortisone and fludrocortisone treatment in CFS patients is not justified. In addition, ACTH stimulation testing has no practical relevance in the routine assessment of CFS patients, and should not be used to formulate management decisions, but may be used to rule out adrenal insufficiency.

 

Although low cortisol may not be the chief source of disability in CFS, it may be a marker of therapeutic significance. For example, the response to cognitive behavioral therapy is reduced in those with lower urine free cortisol or an attenuated diurnal rhythm (93).

 

The COVID-19 pandemic has led to a variety of symptoms after acute illness recovery. The recovery process from COVID-19 varies between individuals, depending on factors such as the illness severity, age, and underlying comorbidities. Despite not having a widely accepted definition, Centers for Disease and Prevention and the World Health Organization (WHO) has agreed the acute symptoms of COVID can last up to four weeks following the onset of the illness (94,95). Various terminologies such as “long COVID’, “post-acute sequalae of SARS-CoV-2 infection”, “post-acute COVID-19” have been used to describe the prolonged symptoms following COVID-19. In this article, we will use Long COVID to describe the condition.

 

While Long COVID and chronic fatigue syndrome/myalgia encephalitis (CFS/ME) are distinct conditions, they do share some similarities in terms of symptoms and impact on individual’s lives. Both conditions are characterized by persistent and debilitating fatigue. It is worth noting that CFS/ME is diagnosed after fatigue present for at least six months, which is not relieved by rest while fatigue experienced in Long COVID can last for weeks, months or longer. The accompanying symptoms of Long COVID syndrome are broad and can affect multiple organ systems including respiratory and cardiac symptoms, which does not typically present in CFS/ME (94- 97). While the triggering event of long COVID is attributed to COVID itself, the triggering event of CFS/ME is not fully understood. Patients with long COVID syndrome may have symptoms consistent with and meet diagnostic criteria of CFS/ME where similar assessment and management strategy can be employed.

MANAGEMENT

Generally, all treatment for CFS/ME must be individualized aiming to address the most debilitating symptom first. No specific treatment is known to be successful for CFS as the current evidence for pharmacological or non-pharmacological interventions was heterogenous and inconclusive (98). However, diagnosis may help patients by providing a basis for prognostic advice and validating their need for assistance in their personal lives and workplace.

Symptomatic treatments, such as non-steroidal anti-inflammatory drugs or non-opiate analgesics for pain and counselling or antidepressants for major depression, are commonly used in ME/CFS although their efficacy has not been the subject of a long-term trial. Developing good sleep hygiene to provide sufficient rest is often part of the management strategy. The latest NICE guideline also suggested dietary strategies including adequate hydration, referral to dietician for patients at risk of weight gain or malnutrition, as well as vitamin D repletion for vitamin D deficiency. It is important to explain to patients with ME/CFS that there is insufficient evidence to support routine vitamin supplementations as treatment for the condition (NICE) (98). Patients with significant cognitive decline should be referred for further neurocognitive evaluation.

 

Cognitive behavioral therapy involves the provision of information and counselling to reduce the psychological impediments to recovery, as well as encouraging the patient to participate at an appropriate level of social and occupational activity. It is important for clinicians to establish a rapport as patients may be mistrustful due to prior negative health care experiences (99). In randomized-controlled trials comparing CBT to control conditions, the intervention has been shown to have a positive overall effect (21). Graded-exercise therapy may also be of benefit (22).

 

No pharmacological agent has been reproducibly shown to be effective in the treatment of chronic fatigue syndrome.

 

Rintatolimod is an antiviral, restricted Toll-like Receptor 3 (TLR3) agonist lacking activation of other primary cellular inducers of innate immunity. It also activates interferon-induced protein. A systemic review suggested some evidence that Rinatotolimod may improve symptoms of ME/CFS (100). Another double blind, randomized, placebo-controlled clinical trial showed statistically significant improvements in primary endpoints in phase II and phase III trials.  About 30-40% of ME/CFS patients can be expected to respond beneficially to Rintatolimod (101). Previous double-blind, randomized clinical trial of Rintatolimod showed an improvement in exercise tolerance and improvement of medication usage for CFS/ME-related symptoms (102). However, the application to the US Food and Drug Administration (FDA) was rejected in 2009 as the previous RCTs that failed to provide credible evidence of efficacy (103).  At present, Rintatolimod is only approved for use in Argentina. Therefore, some authorities suggest Rintatolimod should be considered an experimental drug until confirmatory studies are available (32).

 

Rituximab is an anti-CD20 monoclonal antibody. There may be some benefits shown in a small double-blind, placebo-controlled trials involving 30 patients, particularly in patients with self-reported fatigue, but a subsequent, larger study showed no difference in the treated group and the control group after 24 months of treatment (104,105).

 

A small trial revealed significant improvement in ME/CFS patients who received CoQ10 plus NADH supplementation, but a larger study is warranted to verify its beneficial effect in ME/CFS patients (106).

 

There is a list of therapies that have been trailed in the past, with no proven benefit over placebo. These therapies include acyclovir, antibiotics, cytokine inhibitors, galantamine, glucocorticoids, mofadanil, and methylphenidate (107-113).

PROGNOSIS

Overall, full recovery from untreated ME/CFS is rare but improvement of symptoms in long term is slightly more optimistic (114-116). However, the prognosis of ME/CFS also varies widely among individuals. The reported improvement rates range from 0 to 8% (117-122). Broad range improvement rate is reported at 17-64% (117,120,122,123). A study suggested although most patients with this condition improve, a significant proportion remain functionally impaired over time (118). Another study that was conducted using a questionnaire, reported 73% of patients remain functionally impaired at six weeks to six months but this improved to 33% at two to four years (115).

 

A systematic review showed the median full recovery only happened in 5% of patients (122). Another retrospective study that includes patients with unexplained debilitating fatigue lasting for more than six months but does not fulfil the criteria of ME/CFS showed complete resolution of symptoms only occurred in 2% of these patients (119).

 

As there was lack of operationalized criteria for recovery and improvement, the studies yielded contradictory results in terms of factors that predict the likelihood of recovery. Some studies suggested that old age is associated with poorer outcome while others did not support this hypothesis (118,119,124,125). There has been mixed evidence that shorter duration of illness to be a predictor of better improvement (118,121). Mixed evidence was demonstrated across studies with regards to a worse prognosis in patients with comorbid fibromyalgia (125-127).  There may be an increased risk of suicide (128).

 

ME/CFS has not been associated with increased mortality rate. Treatment is supportive and a defined pathogenesis has not been identified, despite a syndromic definition that is quite frequent and stable across individuals and populations. 

CONCLUSION

Many diagnostic criteria exist for MF/ CFS but the emphasis on exercise intolerance is thought to have significant specificity, although secondary features are also typical. The stress system has been shown to exhibit a reasonably consistent phenotypic pattern comprising relatively low cortisol and elevated sympathetic, particularly sympathoneural function. The etiology of ME/CFS is unknown and the mechanism of altered stress system function is uncertain. Several other pathogenetic mechanisms are proposed. Currently, some treatment trials have been promising and confirmation of their effect is awaited.

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Growth hormone Stimulation Tests in Assessing Adult Growth Hormone Deficiency

ABSTRACT

 

Adult growth hormone deficiency (GHD) is a clinical syndrome that can manifest either as isolated or associated with additional pituitary hormone deficiencies. Its clinical features are subtle and nonspecific, requiring GH stimulation testing to arrive at a correct diagnosis. However, diagnosing adult GHD can be challenging due to the episodic and pulsatile endogenous GH secretion, concurrently modified by age, gender, and body mass index. Hence, a GH stimulation test is often required to establish the diagnosis, and should only be considered if there is a clinical suspicion of GHD and the intention to treat if the diagnosis is confirmed. Currently, there is no ideal stimulation test and the decision to perform a GH stimulation test must factor in the validity of the chosen test, the appropriate GH cut-points, and the availability of local resources and expertise. For now, the insulin tolerance test remains the gold standard test, while the glucagon stimulation test and macimorelin test are reasonable alternatives to the insulin tolerance test, whereas the arginine test is no longer recommended because arginine is a poor GH secretagogue that requires a very low peak GH cut-point of 0.4 μg/L. In this chapter, we discuss published evidence of the GH stimulation tests used in the United States and the inherent caveats and limitations of each individual test. We propose utilizing the lower GH cut-point to 1mg/L for the glucagon stimulation test to improve its diagnostic accuracy in some overweight and all obese patients based on the clinical suspicion of having adult GHD, and summarize current knowledge and change of status of availability of the oral macimorelin test in the United States.

 

INTRODUCTION

 

Physiological growth hormone (GH) secretion from the anterior pituitary gland is episodic, pulsatile, and accounts for > 85% of total daily GH secretion (1). Due to its pulsatility, serum GH levels vary between peaks and troughs, with very low levels between pulses. Hypothalamic growth hormone–releasing hormone (GHRH) and somatostatin traverse the hypothalamic–pituitary portal system to stimulate and suppress GH production, respectively, by signaling through specific somatotroph cell-surface G protein-coupled receptors (2), while gastric-derived ghrelin also stimulates GH secretion and synergizes the action of GHRH (3). Additionally, other factors such as gender, nutritional status, sleep patterns, physical activity, and metabolic and hormonal signals from other endocrine glands, including glucocorticoids, thyroid hormones, and sex steroids, also play an important role in modulating day-to-day GH secretion (1). Growth hormone regulates its own secretion by a feedback mechanism that involves other peripheral mediators, such as insulin-like growth factor-I (IGF-I), free fatty acids, glucose, and insulin (4). Peripheral GH actions are primarily mediated through IGF-I synthesized mainly by the liver. Because IGF-I has a longer half-life in the circulation than GH, it is considered to provide an integrated measure of GH secretion. Like GH, serum IGF-I levels decline with aging (5), and tend to be low in obesity (6) and in patients with non-alcoholic fatty liver disease (7) that may overlap with the levels observed in younger GH–deficient patients. Hence, for these reasons, the diagnosis of adult GH deficiency (GHD) cannot be established in most patients by a random single measurement of serum GH or IGF-I level.

 

DIAGNOSIS OF ADULT GH DEFICIENCY: CURRENT PERSPECTIVE

 

Adult GHD is a rare heterogeneous disorder that commonly results from a variety of organic causes, including hypothalamic-pituitary tumors and/or their treatment, head trauma, and infiltrative diseases (8). This condition is characterized by decreased lean body mass and increased fat mass, dyslipidemia, cardiac dysfunction, decreased fibrinolysis and premature atherosclerosis, decreased muscle strength and exercise capacity, decreased bone mineral density, increased insulin resistance, and impaired quality of life (9). Treatment with GH replacement improves many, but not all, of these abnormalities (10, 11). However, due to the high cost of GH replacement (GH costs approximately $18,000 to $30,000 per year depending on the dose and brand used) (12) and concerns of potential long-term safety risks, particularly the development of diabetes mellitus, cancer and tumor recurrence, it is imperative that an accurate biochemical diagnosis is made so that appropriate GH replacement is offered to adults who are GH-deficient, and not for non-approved conditions (e.g., aging and sporting enhancement) (13, 14).

 

For the clinician, establishing the diagnosis of adult GHD is challenging because of the lack of a single biological end-point (e.g., growth failure in children with GHD). Other biochemical measurements like IGF-I, IGF-binding protein-3, or GH secretion over a 24-hour period have shown poor diagnostic value as there is an overlap between healthy and adults with GHD, particularly in adults > 40 years of age (5, 15). Hence, a GH stimulation test is often required to establish the diagnosis, and should only be considered if there is a clinical suspicion of GHD and the intention to treat if the diagnosis is confirmed. Currently, there is no ideal stimulation test as each test has its pros and cons, and the decision to consider performing a GH stimulation test to diagnose adult GHD must factor in the validity of the chosen test and its GH cut-points, and the availability of local resources and expertise.

 

Clinical practice guidelines recommend the evaluation of adult GHD to be based on medical history, clinical findings, and utilizing the appropriate GH stimulation test for biochemical confirmation (8, 16-18). The exception of when GH stimulation testing can be exempted include those with organic hypothalamic-pituitary disease with ≥ 3 pituitary hormone deficiencies and low serum IGF-I levels [< -2.0 standard deviation scores (SDS)] (19), patients with genetic defects affecting the hypothalamic-pituitary axes, and those with hypothalamic-pituitary structural brain defects (8, 16, 18). Evaluation for adult GHD should not be performed in patients with no evidence of a suggestive history, e.g., sellar/parasellar mass lesion or a history of a hypothalamic–pituitary insult, such as surgery, radiation therapy, head trauma, or brain tumor. Conversely, GH stimulation testing should not be performed in patients with commonly encountered, generalized, nonspecific symptoms of weakness, frailty, fatigue, or weight gain, without a history of organic hypothalamic/pituitary disease, as such patients are unlikely to benefit from GH therapy (8, 16, 18). These considerations are important for the clinician when deciding which patients to consider testing for possible adult GHD. 

 

All GH stimulation tests are based on the concept that a GH secretagogue agent acutely stimulates pituitary GH secretion, and peak serum GH levels are detected by sequential blood sampling of serum GH levels after administration of the agent. The desired criteria of an ideal GH stimulation test should include the following: the ability to accurately and reliably differentiate adults with GHD from GH-sufficient individuals, high reproducibility, safety with minimal side-effects, affordability, and short test duration. It should also not be unpleasant to the patient and it should be simple to perform.

 

The insulin tolerance test (ITT) has historically been accepted as the gold-standard test for the assessment of adult GHD provided adequate hypoglycemia (blood glucose <40 mg/dL) is achieved (8, 16, 17). However, multiple drawbacks associated with the ITT hamper its wider use (20), and they include the requirement of close medical supervision by a physician throughout the test, the possibility of inducing severe life-threatening hypoglycemia, and the potential of causing seizures and altered consciousness resulting from neuroglycopenia in certain susceptible sub-populations. This test is also contraindicated in the elderly (> 65 years of age) and in patients who are at risk of and/or with a history of cardio-/cerebrovascular disease and seizures.

 

Finding a reliable alternative to the ITT for the diagnosis of adult GHD has been challenging. When the GHRH-arginine test was available in the United States before EMD Serono discontinued manufacturing the GHRH analog (Geref@) in November 2008 (8, 16, 17),  GHRH-arginine test became the most acceptable alternative to the ITT. Since then, the glucagon stimulation test (GST) has grown in popularity replacing the GHRH-arginine test as the test of choice if the ITT cannot be performed or is contraindicated (21). Previous studies have examined the diagnostic utility of the GST for adult GHD, but these studies have either not taken body mass index (BMI) into consideration (22, 23) or included only controls with normal BMIs (24, 25). Several recent retrospective studies have questioned the diagnostic accuracy of the GST when the GH cut-point of 3mg/L is applied to overweight/obese adults (26-29) and in those with glucose intolerance (28, 29), while Hamrahian et al. (30) demonstrated in a prospective study of 28 patients by comparing the GST to the ITT that a lower GH cut-point of 1 mg/L improved its diagnostic accuracy with a 92% sensitivity and 100% specificity.

 

In this document, we will discuss published evidence of the GH stimulation tests used in the United States and the inherent caveats and limitations of each individual test. The lower GH cut-point of 1 mg/L for the GST should be utilized to improve its diagnostic accuracy in some overweight and all obese patients. We will also summarize current knowledge of the oral macimorelin test as the only approved diagnostic test for adult GHD by the United States Food and Drug Administration (FDA) and the European Medicines Agency, and its change in status of availability in the United States.

 

GENERAL LIMITATIONS AND IMPORTANT CAVEATS WHEN INTERPRETING GH STIMULATION TESTS

 

The responses to all GH stimulation tests show intra-individual variability, and the GH cut-points vary depending on the test used. For the ITT and GST, the cut-points advocated by previous consensus guidelines were 3-5 μg/L and 2.5-3 μg/L, respectively (8, 16). Other GH stimulatory agents such as clonidine, L-DOPA, and arginine are weaker GH secretagogues, and would require very low GH cut-points with utilization of sensitive GH assays to achieve adequate specificity (e.g., arginine of 0.4 μg/L) (31). Hence, these tests are not recommended in the United States (8, 16). Other limitations include the relative lack of validated normative data based on age, gender, BMI, glycemic status, and the paucity of data for specific etiologies of adult GHD that have recently been described, such as traumatic brain injury, subarachnoid hemorrhage, ischemic stroke, and central nervous system infections (32, 33).

 

One of the caveats in interpreting the results of GH stimulation tests is that adult GHD itself is complicated by an increased susceptibility to central obesity (34). Obesity per se is a state of relative GHD (35-40), and earlier physiologic studies in obese individuals have shown that spontaneous GH secretion is reduced, GH clearance is enhanced, and stimulated GH secretion is reduced (40-42). Conversely, serum IGF-I levels are unaffected, or even increased, and this discordance is related to the increased hepatic GH responsiveness (43). The decreased serum GH levels in obesity up-regulate GH receptor and sensitivity. Furthermore, non-alcoholic fatty liver disease and non-alcoholic steatohepatitis are now recognized as being highly prevalent in overweight and obese adults with GHD (44), with consequent lower serum IGF-I levels being associated with increased severity of the disease (7). Thus, these data suggest that BMI-specific cut-points should be considered when testing patients for adult GHD. Table 1summarizes the accepted GH cut-points for the GH stimulation tests used in the United States, as recommended by different consensus guidelines.

 

Table 1. Accepted GH Cut-Points (µg/L) for GH Stimulation Tests Used in the United States by Different Consensus Guidelines for Diagnosis of Adult GHD

 

GRS 2007

(17)

 

AACE 2009

(16)

ES 2011

(8)

AACE 2019

(18)

ITT

 

< 3.0

≤ 5.0

< 3.0 to 5.0

≤ 5.0

GHRH-arginine

- BMI < 25 kg/m2

- BMI 25-30 kg/m2

- BMI ≥ 30 kg/m2

 

 

< 11.0

< 8.0

< 4.0

 

≤ 11.0

≤ 8.0

≤ 4.0

 

< 11.0

< 8.0

< 4.0

No recommendation as not commercially available in the United States

Glucagon

- BMI < 25 kg/m2

- BMI 25-30 kg/m2

- BMI ≥ 30 kg/m2

 

 

< 3.0

< 3.0

< 3.0

 

≤ 3.0

≤ 3.0

≤ 3.0

 

< 3.0

< 3.0

< 3.0

 

≤ 3.0

≤ 3.01 or ≤ 1.02

≤ 1.0

Macimorelin

 

Not commercially available in 2007

 

Not commercially available in 2009

 

Not commercially available in 2011

≤ 2.8

Arginine

 

Not recommended to be used

≤ 0.4

 

Not recommended to be used

No longer recommended to be used

 

1GH cut-point of ≤ 3.0 µg/L for patients with a high pre-test probability; 2GH cut-point of ≤ 1.0 µg/L for patients with a low pre-test probability.

AACE, American Association of Clinical Endocrinologists; BMI, body mass index; ES, Endocrine Society; GHRH, growth hormone releasing hormone; GRS, Growth Hormone Research Society; ITT, insulin tolerance test.

 

GROWTH HORMONE STIMULATION TESTS USED IN DIAGNOSING ADULT GH DEFICIENCY

 

Insulin Tolerance Test

 

The ITT remains accepted as the gold standard test for the assessment of adult GHD, with a GH cut-point of 3-5 mg/L when adequate hypoglycemia (blood glucose < 40 mg/dL) is achieved (8, 16, 17). This GH cut-point was originally proposed by Hoffman et al. (45) in 1994 based on GH responses to insulin-induced hypoglycemia, mean 24-hour GH levels derived from 20-min sampling, and serum IGF-I and IGFBP-3 levels in 23 patients considered GH-deficient due to organic pituitary disease, and in 35 sex-matched normal subjects of similar age and BMI. The ranges of stimulated peak GH responses separated GH-deficient (0.2-3.1 mg/L) from GH-sufficient (5.3-42.5 mg/L) patients. However, an overlap in mean 24-hour GH, IGF-I, and IGFBP-3 levels was observed, demonstrating the challenge in utilizing random single serum GH, IGF-I and IGFBP-3 levels to accurately differentiate GH-sufficiency from GHD.

 

Disadvantages of the ITT include the requirement of close medical supervision, may be unpleasant, and cautioned in some patients because of potential adverse effects (e.g., seizures or loss of consciousness resulting from neuroglycopenia), and contraindicated in elderly patients and in patients at risk of and/or with a history of cardio-/cerebrovascular disease and seizures. Furthermore, normoglycemic and/or hyperglycemic obese patients with insulin resistance may fail to achieve adequate hypoglycemia (46), necessitating the use of higher insulin doses (0.15-0.2 IU/kg), thus increasing the risk of delayed hypoglycemia. Although the ITT demonstrates good sensitivity, its reproducibility is another major limitation. Differences in peak GH responses have been demonstrated in healthy subjects undergoing ITT at varying times (47) and in women at different times of their menstrual cycle (48).

 

Table 2. Recommended Protocol for Performing the ITT

CONTRAINDICATIONS:

History of epileptic seizures, coronary artery disease, pregnancy, or age > 55 years.

PRECAUTIONS:

Patients commonly develop neuroglycopenic symptoms during the test and should be encouraged to report these symptoms (administration of IV anti-emetics can be considered).

Late hypoglycemia may occur (patients should be advised to eat small and frequent meals after completion of the test).

PROCEDURE:

Fast from midnight for 8-10 hours.

All morning medications can be taken with water (if the HPA axis is simultaneously assessed, then glucocorticoids should be withheld ≥ 12 hours before testing).

Weigh patient.

1Place IV cannula for IV access in both forearms.

2Administer IV human Regular insulin (standard dose: 0.05-0.1 units/kg for non-diabetic subjects with a BMI < 30 kg/m2 and high dose: 0.15-0.3 units/kg for subjects with a BMI ≥ 30 kg/m2).

SAMPLING AND MEASUREMENTS:

Baseline

Blood is drawn for glucose measurement with a glucometer.

Blood draw for baseline glucose, GH and IGF-I (cortisol and ACTH, if HPA axis is assessed simultaneously) levels will be sent to the laboratory for further analysis.

During the test

Blood samples are drawn from the IV line every 5-10 mins for measurement of glucose levels using a glucometer.

Signs and symptoms of neuroglycopenia are recorded.

When blood glucose levels from the glucometer approaches 45 mg/dL (2.5 mmol/L), blood samples are sent to the laboratory for measurements of blood glucose levels.

When symptomatic hypoglycemia is achieved (laboratory blood glucose < 40 mg/dL or 2.2 mmol/L), additional blood samples are collected to measure glucose and GH (+/- cortisol if the HPA axis is assessed simultaneously) levels at 20, 25, 30, 35, 40, 60 and 90 min.

The patient can begin drinking orange juice and eat to raise his/her blood glucose levels (IV 100 ml of 5% Dextrose can be administered if the patient cannot tolerate oral intake due to nausea or vomiting).

At the end of the test

Blood glucose levels measured from the glucometer should increase to levels > 70 mg/dL (3.9 mmol/L) before the patient is discharged from the testing unit.

INTERPRETATION:

If adequate (symptomatic) hypoglycemia is not achieved (< 40 mg/dL or 2.2 mmol/L), then adult GHD cannot be diagnosed.

Peak serum GH levels ≤ 5 µg/L at any time point during the hypoglycemic phase of the test is diagnostic of adult GHD.

CAUTION:

If adequate (symptomatic) hypoglycemia is not achieved (< 40 mg/dL or 2.2 mmol/L), then adult GHD cannot be diagnosed.

ACTH: adrenocorticotropic hormone, HPA: hypothalamic-pituitary-adrenal, IV: intravenous.

1Two IV lines are placed, one IV line is used for the administration of insulin bolus and possibly for administration of IV 5% Dextrose administration if the patient requires resuscitation from hypoglycemia, while the other IV line is used for repeated blood draws.

2In certain patients with BMIs > 30 kg/m2 who appear muscular with increased insulin sensitivity, clinical discretion is required in deciding the insulin dose for these patients. A dose of 0.05-0.1 units/kg may be more appropriate to prevent severe or delayed hypoglycemia.   

 

Glucagon Stimulation Test

 

Glucagon is reportedly to be more potent than arginine or clonidine in stimulating GH secretion (24, 25). Glucagon is also a more potent GH secretagogue when administered intramuscularly or subcutaneously compared to the intravenous route (49). However, the mechanism/s of glucagon-induced GH stimulation remains unclear, and one hypothesis is that glucagon decreases ghrelin-independent effects of glucose or insulin variations (50).

 

There have been three earlier studies that have assessed the GST in identifying adult GHD in patients with pituitary disorders (22, 23, 51). Gomez et al. (51) and Conceicao et al. (23) compared the diagnostic characteristics of GST to ITT and included a control group matched for age and sex in both studies, and for BMI in one study (51). Using receiver operating characteristic (ROC) analysis, both studies proposed that a GH cut-point of 3 mg/L provided optimal sensitivity and specificity (51, 52). Gomez et al. (51) also demonstrated an inverse correlation between age (R = - 0.389, P = 0.0075) and BMI (R = - 0.329, P = 0.025) with peak GH levels in healthy controls. These data suggest that there is a potential association between relative, but not organic, GHD in aging and obesity. However, this study was conducted in a European cohort, where the frequency and severity of obesity is generally to a lesser degree than in the United States (53). Conversely, Conceicao et al. (23) demonstrated that peak GH levels were unaffected by age in either the control or patient group, and neither were there any gender differences. Additionally, Gomez et al. (51)used intramuscular glucagon doses of 1 mg and 1.5 mg for body weights ≤ 90 kg and > 90 kg respectively, whereas Conceicao et al. (23) used intramuscular glucagon of 1 mg for all subjects. In another study, Berg et al. (22)demonstrated an optimal peak GH cut-point of 2.5 mg/L with 95% sensitivity and 79% specificity using ROC analysis. This study also reported lower peak GH levels with GST compared to ITT (5.1 vs 6.7 mg/L, P < 0.01) and a positive correlation between peak GH levels during ITT and GST (R = 0.88, P < 0.0001), but no correlation between BMI or age to peak GH responses (54, 55). However, these (22, 23, 51) and other earlier studies (24, 25, 49, 56) did not specifically evaluate patients with glucose intolerance; hence, the diagnostic accuracy of the GST in testing for GHD in this population remains unclear.

 

Advantages of the GST is its reproducibility, safety, and lack of influence by gender and hypothalamic GHD (21), whereas disadvantages include the lengthy test duration (3-4 hours), and the need for an intramuscular injection that might not appeal to some patients. Side-effects frequently reported include nausea, vomiting, and headaches ranging from < 10% (22) to 34% (54), mainly occur between 60-210 min and tend to resolve by 240 min into the test, and seem to be more pronounced in elderly subjects, where severe symptomatic hypotension, hypoglycemia, and seizures have been observed (57).    

 

However, since the publication of the 2009 American Association of Clinical Endocrinologists (AACE) (16) and 2011 Endocrine Society (8) Clinical Practice Guidelines, there have been several studies that have suggested that the fixed-dose GST using a GH cut-point of 3 mg/L may potentially over-diagnose adult GHD in a substantial number of overweight/obese subjects and in those with glucose intolerance. In two large retrospective studies, Toogood et al.(58) and Yuen et al. (29) found an inverse correlation between BMI and peak GH during the GST, and that this relationship appeared to be strongest with BMIs between 30 and 40 kg/m2 and seemed to plateau for those with BMIs > 40 kg/m2 (58). Alternatively, a negative correlation between BMI and peak GH following glucagon stimulation has been reported by Gomez et al. (51) in healthy subjects but not in patients with underlying pituitary disease. Dichtel et al. (26) evaluated 3 groups of overweight/obese men, i.e., controls who were younger than the patients, patients with 3-4 pituitary hormone deficits, and patients with 1-2 pituitary hormone deficits. Using ROC analysis, the GH cut-point of 0.94 mg/L provided the optimal sensitivity (90%) and specificity (94%), whereas BMI and amount of visceral adipose tissue inversely correlated with peak GH levels in controls. Almost half of the healthy overweight/obese individuals (45%) failed the GST using the 3 mg/L GH cut-point. Diri et al. (27) evaluated 216 patients with pituitary disease and 26 healthy controls and compared the GST to the ITT. These investigators used a GH cut-point of 3.0 mg/L for the ITT and two GH cut-points of 3.0 mg/L and 1.07 mg/L for the GST, yielding the diagnosis of adult GHD in 86.1%, 74.5%, and 54.2 % patients, respectively. Additionally, patient age, BMI, and number of pituitary hormone deficits correlated with IGF-I and peak GH levels. Twelve out of 26 (46.2 %) healthy subjects failed the GST using a GH cut-point of 3.0 mg/L, but none when the cut-point was lowered to 1.07 mg/L. Wilson et al. (28) studied 42 patients with a high pre-test probability of adult GHD. After excluding 10 patients with severe GHD based on peak GH levels ≤ 0.1 mg/L, these investigators found that body weight negatively correlated with GH area under the curve (AUC) (R = -0.45; P = 0.01) and peak GH response (R = -0.42; P = 0.02) and positively correlated with nadir blood glucose levels (R = 0.48; P < 0.01). Conversely, nadir blood glucose levels during GSTs inversely correlated with GH AUC (r= -0.38; p=0.03) and peak GH (r= -0.37; p=0.04), implying that patients with higher nadir blood glucose levels tended to have a lesser glucagon-induced GH response. Recently, Hamrahian et al. (30) compared the fixed-dose GST (1 mg or 1.5 mg in patients > 90 kg body weight) and weight-based GST (WB-GST: 0.03 mg/kg) with the ITT using a GH cut-point of 3.0 mg/L. Patients with hypothalamic-pituitary disease and 1-2 (n = 14) or ≥ 3 (n = 14) pituitary hormone deficiencies, and control subjects (n = 14) matched for age, sex, estrogen status and BMI undertook the ITT, GST and WB-GST in random order. Using ROC analyses, the optimal GH cut-point was 1.0 (92% sensitivity, 100% specificity) for fixed-dose GST and 2.0 mg/L (96% sensitivity and 100% specificity) for WB-GST. Therefore, lowering the GH cut-point from 3 mg/L to 1 mg/L is important to reduce misclassifying adult GHD in overweight (BMI 25-30 kg/m2) patients with a low pre-test probability and in obese (BMI > 30 kg/m2) patients.

 

It remains unclear whether hyperglycemia influences peak GH responses to glucagon stimulation, independent of central adiposity. No peak GH responses have been studied using the GST in normal controls > 70 years of age, and none of the previous studies included patients with poorly controlled diabetes mellitus. Studies by Yuen et al. (29) and Wilson et al. (28) demonstrated that higher fasting (range 90-316 mg/dL), peak (range 156-336 mg/dL), and nadir (range 52-200 mg/dL) blood glucose levels during the GST were associated with lower peak GH responses. Therefore, stratification of GH responsiveness by the degree of glycemia will be helpful to clinicians in interpreting the GST results in patients with impaired glucose tolerance and diabetes mellitus. Because these data are currently unavailable, caution should be exercised when interpreting abnormal GST results in these patients. Further larger prospective studies are needed to address the effects of varying degrees of hyperglycemia on the ability of glucagon to stimulate GH secretion.

 

Table 3.  Recommended Protocol for Performing the Glucagon Stimulation Test

CONTRAINDICATIONS:

Malnourished patients or patients who have not eaten for > 48 hours.

Severe fasting hyperglycemia > 180 mg/dL.

PRECAUTIONS:

Patients may feel nauseous during the test (administration of IV anti-emetics may be considered).

Late hypoglycemia may occur (patients should be advised to eat small and frequent meals after completion of the test).

PROCEDURE:

Fast from midnight for 8-10 hours.

All morning medications can be taken with water.

Weigh patient.

Place IV cannula for IV access in one forearm.

Administer IM glucagon (1.0 mg if patient body weight ≤ 90 kg and 1.5 mg if patient body weight > 90 kg).

SAMPLING AND MEASUREMENTS:

Blood is drawn for measurements of serum GH1 and blood glucose2 levels at 0, 30, 60, 90, 120, 150, 180, 210 and 240 mins.

INTERPRETATION:

Peak GH levels ≤ 3.0 µg/L in normal-weight (BMI < 25 kg/m2) patients and in

overweight (BMI 25-30 kg/m2) patients with a high pre-test probability, and ≤ 1.0 ug/L in

overweight (BMI 25-30 kg/m2) patients with a low pre-test probability and in obese (BMI >

30 kg/m2) patients at any time point during testing are diagnostic of adult GHD.

CAUTION:

Clinical suspicion of pre-test probability should be taken into consideration when interpreting GST results in patients > 70 years of age and in patients with impaired glucose tolerance and poorly controlled diabetes mellitus, as no peak GH responses have been studied in these patients.

IM: intramuscular, IV: intravenous.

1Serum GH: peak GH levels tend to occur between 120-180 mins; 2blood glucose: usually peaks around 90 mins and then gradually declines (not a requirement to interpret the test).

 

Macimorelin Test

 

Growth hormone secretagogues (GHSs) are peptidyl (GH-releasing peptide [GHRP]) and nonpeptidyl molecules that exert strong dose-dependent and specific stimulatory effects on the animal and human somatotrope secretion (59). These agents act as functional somatostatin antagonists by binding to their specific GH secretagogue receptor-1a in the hypothalamus and pituitary. The natural ligand for this receptor is the gut peptide ghrelin (60). Growth hormone secretagogues are now considered as ghrelin mimetic agents and can be administered parenterally (e.g., GHRP-2, GHRP-6, hexarelin) or orally (e.g., MK-677 and macimorelin).

 

Macimorelin (formerly known as AEZS-130, ARD-07, and EP-01572) is a novel GH secretagogue that binds the GHS-R1a receptor and to pituitary and hypothalamic extracts with a similar affinity to ghrelin (61). In healthy volunteers, it is readily absorbed with good stability and oral bioavailability, and effectively stimulates endogenous GH secretion (61). An open-label, crossover, multicenter trial examined the diagnostic accuracy of a single oral dose of macimorelin (0.5 mg/kg) compared to GHRH plus arginine in adults with GHD and healthy matched controls (62). Peak GH levels were 2.36 ± 5.69 and 17.71 ± 19.11 mg/L in adults with GHD and healthy controls, respectively, with optimal GH cut-points ranging between 2.7 and 5.2 mg/L (62). Macimorelin showed good discrimination comparable to GHRH plus arginine, with peak GH levels that were inversely associated with BMI in controls. In a recent multicenter, open-label, randomized, two-way crossover study, oral macimorelin was compared to the ITT to validate its use for the diagnosis of adult GHD (63). The GH cut-point levels of 2.8 mg/L for macimorelin and 5.1 mg/L for ITT provided 95.4% (95% CI, 87% to 99%) negative agreement, 74.3% (95% CI, 63% to 84%) positive agreement, 87% sensitivity, and 96% specificity. In both studies (62, 63), macimorelin was well-tolerated, reproducible, and safe. In December 2017, the United States FDA approved macimorelin for use as a diagnostic test for adult GHD and mandated the GH cut-point of2.8 mg/L to be used to differentiate patients with normal GH secretion from those with GHD. However, in the study by Garcia et al. (63), when the GH cut-point was increased to 5.1 mg/L for both macimorelin and ITT, negative agreement and specificity was unchanged at 94% (95% CI, 85% to 98%) and 96%, respectively, but interestingly, positive agreement and sensitivity was higher at 82% (95% CI, 72% to 90%) and 92%. Because measured serum GH levels are dependent on the GH assays used, using the GH cut-point of 5.1 mg/L for macrimorelin that is identical to the cut-point accepted for the ITT could be considered in patients with peak serum GH levels between 2.8 mg/L to 5.1 mg/L, especially if the patient has a high pre-test probability, e.g., history of surgery on a sellar/parasellar mass with 1-2 other pituitary hormone deficiencies. It is important to note that this test is not affected by age, BMI, or sex indicating its robustness for diagnosing adult GHD (64).

 

Main advantages of macimorelin are that the drug is orally administered, unlike the ITT, GHRH plus arginine or GST, that requires intravenous or intramuscular administration, and no risk of causing hypoglycemia. In addition, the test only lasts 90 minutes with 3-4 blood sample collections required, in contrast to more blood sample collections over 2 hours for the ITT and 3-4 hours for the GST. The most commonly reported side effect was mild dysgeusia, which did not require any intervention and resolved spontaneously (63). One drug-related serious adverse event was reported; that was in a subject with an asymptomatic QT interval prolongation on the electrocardiogram that resolved spontaneously within 24 h (62). Thus, careful assessment of the patient’s concurrent medications is recommended as well as discontinuation of strong CYP3A4 inducers, provided this is considered safe by the prescribing physician and with sufficient washout time prior to testing.

 

However, in August 2022, a press announcement stated that Novo Nordisk Healthcare AG provided a 270-day notice period to terminate the amended development and commercialization license agreement for macimorelin (MacrilenÒ) in the United States (65). This means that as of May 23, 2023, Aerterna Zentaris regained its full rights in the United States and Canada to macimorelin but because it has yet to find a partner in the United States to market macimorelin, it was further announced that sales of macimorelin will be temporarily discontinued and use of the agent beyond May 2023 will continue until its supplies in the United States runs out (66).

 

Table 4.  Recommended Protocol for Performing the Macimorelin Test

CONTRAINDICATIONS:

Drugs that may increase its plasma levels and prolong QT.

PRECAUTIONS:

Dysgeusia.

PROCEDURE:

Fast from midnight for 8-10 hours.

All morning medications can be taken with water.

Weigh patient.

Place IV cannula for IV access in one forearm.

Dissolve in water 1 (120 ml) or 2 pouches (240 ml) of macimorelin (≤ 120 kg = 1 pouch; > 120 kg = 2 pouches)

Calculate macimorelin dose (0.5 mg/kg as a single oral dose) and volume of water required to reconstitute macimorelin solution (patient body weight X kg = X ml macimorelin solution, e.g., patient with a body weight of 70 kg would require 70 mL of reconstituted macimorelin solution)

After volume of macimorelin is calculated, stir the solution gently and thoroughly for 2-3 min, and use within 30 min of preparation.

Draw the exact macimorelin volume of solution into a needleless syringe, transfer the exact volume of into a drinking glass, and instruct the patient to drink the entire volume of solution within 30 seconds.

SAMPLING AND MEASUREMENTS:

Blood is drawn for measurements of serum GH levels at 30, 45, 60 and 90 min.

INTERPRETATION:

Peak serum GH levels tend to occur between 45-60 mins.

When used according to prescribing package label, peak GH levels ≤ 2.8 µg/L at any time point is diagnostic of adult GHD.

CAUTION:

Peak GH levels ≤ 5.1 µg/L at any time point may be considered in patients with a high-pre-test probability to diagnose adult GHD, as this higher GH cut-point limits the risk of a false-positive diagnosis and maintains a high detection rate for GH-deficient patients because of the more potent GH stimulatory effect of macimorelin compared with the ITT.

Safety and diagnostic performance in patients < 18 and > 65 years of age, and in patients with impaired glucose tolerance and poorly controlled diabetes mellitus, and BMI-adjusted peak GH cut-points for overweight and obese patients is not established.

 

Summary of Tests

 

Table 5 displays a summary of the desirable test characteristics of GH stimulation tests currently available in the United States.

 

Table 5. Summary of Desirable Test Characteristics of each GH Stimulation Test Currently Available in the United States

Test

Accurate?

Safe?

Tolerability?

Simple?

Quick?

Available?

Cost

ITT

Gold standard

No2

No4

No

No

Yes

$

GST

Yes1

Yes3

No3

Yes

No

Yes

$

Macimorelin

Yes

Yes

Yes

Yes

Yes

Yes/No

$$$

1if appropriate BMI-specific GH cut-points are used; 2contraindicated in patients with a history hypoglycemia, history of previous seizures, in the elderly (> 65 years of age), and in patients at risk of and/or with a history of cardio-/cerebrovascular disease; 3caution in patients with propensity for nausea and vomiting, and elderly patients who may be at risk of developing symptomatic hypotension and dizziness (57); 4patients may not tolerate severe symptomatic hypoglycemia. GST, glucagon stimulation test; ITT, insulin tolerance test.

 

STANDARDIZATION OF GH ASSAYS

 

Accurate measurement of GH levels is critical for establishing the diagnosis of adult GHD because the analytical method influences the results of GH stimulation tests, which is dependent on specific GH cut-point levels. However, circulating GH is present in several different isoforms and isomers, including the most common variant of 22 kDa, and other smaller molecules, such as the 20 kDa GH variant. Monoclonal antibodies binding to a specific molecular form of GH are used to limit detection to the 22 kDa GH, but will not detect other GH isoforms. Other molecules similar to GH (e.g., placental GH and prolactin) could potentially cross-react and affect the measurement of GH levels. Growth hormone binding protein, to which approximately 50% of circulating GH is bound, can also cause interference in a GH assay. Furthermore, substantial heterogeneity exists among currently utilized assays due to the use of different standard preparations for calibration of GH immunoassays, and lack of harmonization between various GH assays makes it difficult to directly compare diagnostic cut-points across different published studies. Another source of confusion when interpreting data of GH stimulation tests was that some laboratories reported GH levels in activity (mU/L), whereas others used mass units (mg/L) (67).

 

Due to the heterogeneity of GH assays, it is important that GH assays utilize a universal GH calibration standard 98/574 (National Institute for Biological Standards and Control), a recombinant pituitary GH preparation of high purity (68). All assay manufacturers should also specify the validation of their assay, which should include specification of the GH isoforms detected (20 kDa GH, 22 kDa GH, and other isoforms), the analyte being measured, the specificities of the antibodies used, and the presence or absence of growth hormone binding protein interference.

 

CONCLUSIONS

 

The decision to perform GH stimulation tests should be based on the clinical suspicion of the treating endocrinologist. If the clinical suspicion is high, such as in a patient with history of surgery on a sellar mass, concurrent 1-2 other pituitary hormone deficiencies, and a low (< -2 SDS) or low-normal (< 0 SDS) serum IGF-I level, then performing GH stimulation testing is recommended. If the clinical suspicion is low, such as in cases where there is no suggestive history, such as hypothalamic-pituitary disease, surgery or radiation therapy, head trauma, or childhood-onset GHD, then the diagnosis of adult GHD should not be pursued and GH stimulation testing should not be performed. For now, the ITT remains the gold standard GH stimulation test, and the GST and macimorelin test (where available) are reasonable alternatives to the ITT. As the reliability of the GST GH cut-point of 3 mg/L in overweight/obese subjects and in those with glucose intolerance can misclassify some patients, the utilization of GH cut-points of the GST is now based on the clinician’s level of suspicion of the patient’s pre-test probability and underlying BMI. Macimorelin, a drug administered orally that was approved by the United States FDA in December 2017 is an attractive test because it is easy to conduct with high reproducibility, safe, and has comparable diagnostic accuracy to the ITT and GHRH plus arginine test. The factors that limit its wider is its high cost (one 60 mg macimorelin packet costs approximately $4,500) (69) and the potential of drug-to-drug interactions that may cause QT prolongation. Following the announcement in August 2022 that macimorelin will be temporarily discontinued in the commercial market effective May 2023, after supplies of macimorelin runs out in the United States, the ITT and GST will only be the two GH stimulation tests available to clinicians, limiting the choices of tests that can be used.

 

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Radiotherapy for Pituitary Tumors

ABSTRACT

 

Pituitary adenomas have been historically managed on a multidisciplinary level with surgery, medical therapy, and radiotherapy to control symptoms secondary to mass-effects and hypersecretion of hormones. While transsphenoidal surgery represents the standard initial approach in the majority of cases, radiotherapy is a valuable and effective treatment option for recurrent adenomas, or lesions not amenable to surgery or medical therapy. Following radiotherapy, tumor growth control (over 90% in most series), plus the normalization of hormones, occurs in a large proportion of treated patients, independent of tumor subtype. Over the last decades, radiotherapy technological advances have allowed the reduction of dose to uninvolved brain while maintaining an effective therapeutic dose to the tumor. This has generated debate on the superiority of some radiotherapy techniques over others. The clinical efficacy of conventionally-fractionated treatment (25 to 30 fractions delivered over 5 to 6 weeks), in the form of 3D-conformal radiotherapy (CRT) or intensity-modulated radiotherapy (IMRT) and the more refined “stereotactic” – highly conformal - fractionated radiotherapy (SFRT), can be compared to that provided by “radio-surgical” (SRS) techniques of irradiation (where the tumor is treated with single high dose of radiation). Due to the lack of randomized control trials addressing this issue, the evidence provided in retrospective studies of different radiotherapy technologies is critically reviewed in this chapter. 

 

INTRODUCTION

 

Pituitary adenomas are mostly benign tumors and comprise about 10% of all intracranial tumors [1, 2]. Radiotherapy has an important and long-established role as part of the multi-disciplinary management of both non-functioning and functioning adenomas. There has been a steady evolution in radiotherapy technologies since radiotherapy was first used to treat pituitary adenomas more than 100 years ago [3]. Despite decades of clinical experience, there remains a paucity of randomized clinical trials to enable a robust evidence-based approach to the optimal use of radiotherapy. This is to some extent compensated for by the large number of non-randomized largely retrospective case series which provide evidence on relevant clinical outcomes and toxicities associated with pituitary radiotherapy. Nevertheless, given the nature of the available data, there continue to be areas of controversy regarding the use of particular radiotherapy modalities. We review the available published data on modern radiotherapy techniques for the treatment of pituitary adenomas to provide a rational basis for the selection of radiotherapy technologies.

 

RATIONALE FOR PITUITARY RADIOTHERAPY

 

Traditional practice had been to use post-operative radiotherapy for all patients with a residual non-functioning pituitary adenoma after surgical resection, as it was considered that otherwise most would subsequently progress [4, 5]. With improvements in surgical techniques, and the development of magnetic resonance imaging (MRI), post-operative radiotherapy is no longer routinely used, even in the presence of residual tumor. The use of post-operative pituitary radiotherapy is now based on a risk assessment. In patients with non-functioning adenomas, radiotherapy is generally withheld until the time of progression, unless there are concerns of significant threat to function (vision) with tumor progression, or the histology raises concerns of earlier recurrence risk (e.g., atypical features, silent corticotroph adenoma). When radiotherapy is used for patients with progressive non-functioning adenomas, tumor control is achieved in over 90% of patients at 10 years, and in 85-92% at 20 years [5-13].

 

In patients with functioning adenomas, radiotherapy is used when surgery fails to achieve hormone normalization and/or when medical treatment is insufficient to control hormone secretion or is not considered appropriate, often due to toxicities. Hormone levels decline slowly following radiotherapy, consequently normalization may take from months to years to achieve. The time required to achieve hormone normalization is primarily related to the pre-treatment hormone levels. Nevertheless, despite this temporal delay, the majority of patients will eventually achieve normalization of excess pituitary hormone secretion following radiotherapy [14].

 

CURRENT TECHNIQUES OF PITUITARY RADIOTHERAPY

 

The principal aim of pituitary radiotherapy techniques has always been to deliver an effective treatment dose to the target tumor volume while at the same time minimizing the radiation dose delivered to surrounding normal tissues, thereby minimizing the risk of normal tissue damage. Improved radiotherapy treatment precision, with the use of the modern radiotherapy techniques described in this chapter, relies on the increased accuracy in tumor volume delineation achieved by using modern MRI imaging technology. Over the last twenty years there have been a number of developments in techniques for pituitary radiotherapy which have largely amounted to refinements of existing technologies. However, the overall success of modern high precision pituitary radiotherapy techniques is largely a function of the quality of a treatment center’s infrastructure and its expertise and accuracy in identifying the target tumor volume, rather than of the particular radiotherapy technique that is used to deliver treatment.

 

3D-Conformal RT

 

Until the last decade, the standard of care for pituitary radiotherapy was three-dimensional (3D) conformal radiotherapy (CRT). CRT uses pre-treatment computed tomography (CT) and MRI imaging for computerized 3D radiotherapy treatment planning. CRT treatment is planned and delivered using a non-invasive method of patient immobilization. The tumor is visualized on unenhanced magnetic resonance imaging co-registered with planning computed tomography (CT). The treatment target is delineated on the MRI scan (in the three orthogonal planes), while radiotherapy dosimetry is calculated using the CT scan data.

 

The treatment target comprises the visible residual tumor and also accounts for any pre-operative extension of disease whilst sparing the optic chiasm where possible after decompression. An isotropic margin of 5-10 mm is added to account for areas of uncertainty in volume delineation, the transsphenoidal surgical route and any set-up variation. The whole pre-operative extent of the tumor is not included within the treatment volume as debulking of large, and particularly cranially extending tumors, often leads to the return of normal anatomical structures to their pre-morbid positions with no residual tumor present. On the other hand, tumors are frequently not removed from the walls of the cavernous sinus, particularly if the sinus is involved, and so the lateral extent of the radiotherapy target does not tend to alter with surgery. The resulting volume outlined on the treatment planning system therefore encompasses both the visible tumor and also any regions of presumed residual tumor. Normal tissue structures adjacent to the pituitary, such as the optic chiasm and optic nerves, the brain stem and the hypothalamus, may also be outlined to aid in treatment planning, and also to enable the calculation and recording of normal tissue

dosimetry, although with conventional fractionated radiotherapy all the structures are treated to below the limits of radiation tolerance in terms of structural damage.

Figure 1. CT-MRI co-registration for planning purposes.

 

Reproducible patient immobilization is vital for the delivery of safe and accurate CRT. The immobilization system used should be well tolerated and must reliably minimize patient movement during both pre-treatment imaging and treatment delivery itself. The most commonly used system for immobilization for CRT is a custom-made closely fitting lightweight thermoplastic mask which is applied and molded directly to the patient’s face in the treatment planning process. The repositioning accuracy of this system is very good at around 3-5mm [15], and can be improved to 2-3mm, by using a tighter fitting but less comfortable mask [16].

 

CT imaging for CRT planning is performed with the patient lying in the radiotherapy treatment position within the immobilization system and co-registered with the MRI (Figure 1) 3D computerized radiotherapy planning is followed by robust quality assurance (QA) procedures to ensure the accuracy of the whole process both before and during treatment. The planning system defines the number, shape, and orientation of radiation beams to achieve uniform dose coverage of the target volume with the lowest possible dose to the surrounding normal tissues. As the dose to the tumor is below the radiation tolerance dose of the surrounding normal tissue structures, no specific measures are generally needed, or taken, during treatment planning to avoid the optic apparatus, hypothalamus, and brain stem. In any case, for many patients requiring pituitary irradiation, some of these entire normal structures lie within, or in close proximity to, the target volume and cannot be avoided without compromising the efficacy of treatment.

 

Localized irradiation is achieved using treatment in multiple beams each shaped to conform to the shape of the tumor using a multileaf collimator (MLC). Traditionally, beam arrangements used for CRT consisted of three fixed beams (an antero-superior beam and two lateral beams) (Figure 2).

 

Figure 2. Example of beam arrangement and dose distribution in a traditional CRT plan (one antero-superior beam and two lateral beams).

 

Intensity-Modulated RT

 

Techniques for varying the radiation dose intensity across a beam, by moving MLC leaves into the beam path, are now standard and are collectively referred to as intensity modulated radiotherapy (IMRT). IMRT is a form of 3D CRT which can spare critical structures, especially within a concave PTV. Although IMRT offers no significant advantage in comparison with CRT for target volume dose coverage [

], its improved conformality can allow for reduced radiation dose delivery to adjacent normal tissues. This can be of particular use in tumor with suprasellar extension, where the dose delivered to the medial temporal lobes can reduced. The technique of arcing IMRT (described as VMAT or RapidArc) offers a fast way of delivering complex IMRT and is increasingly used as an alternative to fixed-field techniques (Figure 3).

 

Figure 3. Example of beam arrangement and dose distribution in a static field IMRT plan (left) and in a VMAT plan (right) for the same patient. Note the better conformality of the high radiation dose region to the target volume in comparison with the CRT plan in Figure 2.

 

Patient immobilization and the imaging required for target volume definition are no different for IMRT treatment than for CRT as described above. Similarly, there are robust QA procedures to ensure the accuracy of IMRT treatment planning and delivery.

 

Stereotactic Radiotherapy Techniques

 

The term “stereotactic” is derived from long-established neurosurgical techniques, and denotes a method of determining the position of a lesion within the brain using an external 3D co-ordinate system based on a method of immobilization, usually an invasive neurosurgical stereotactic head frame [18-20]. Stereotactic radiotherapy originally referred to radiotherapy treatment delivered to an intracranial target lesion that was located by stereotactic means in a patient immobilized in a neurosurgical stereotactic head frame.

 

Stereotactic radiotherapy was first delivered with a multiheaded cobalt unit described as the gamma-knife (GK) which uses multiple cobalt-60 sources arranged in a hemispherical distribution with collimators to achieve a circumscribed spherical dose distribution of 4-18mm diameter [20]. Subsequent development of the GK has allowed larger non-spherical tumors to be treated by combining several radiation spheres using a multiple isocenter technique.

 

Due to the invasive nature of the GK stereotactic head frame (surgically fixed to the skull), GK radiation treatment is delivered as a single large dose during one combined treatment planning and delivery session. This single fraction stereotactic radiation technique was termed ‘radiosurgery’ [18]. The GK radiosurgical procedure aimed to create a non-invasive radiation-based analogue of an open neurosurgical ablation of an intra-cranial target lesion. It should be emphasized, however, that aside from the use of a surgically-fitted stereotactic frame, GK radiosurgery and open neurosurgery are quite distinct procedures, and GK radiosurgery is a radiotherapeutic rather than a surgicalintervention, particularly as the commonly used doses are not “ablative”.

 

Subsequently, linear accelerators (linacs) were adapted to deliver radiosurgery (single fraction radiation) using multiple arcs of rotation, achieving the same dose distribution as that delivered by the GK. With the introduction of non-invasive relocatable stereotactic head frames, which enabled stereotactic radiation to be given in a number of treatment sessions, stereotactic radiotherapy was delivered as fractionated treatment to conventional doses [21, 22]. Initially, specifically adapted linacs were required, but the precision of modern linacs is now such that they do not generally require modification for stereotactic radiotherapy. The improved patient immobilization, more accurate tumor target localization using cross-sectional image for treatment planning, and high precision radiation treatment delivery to the tumor target, enabled a reduction in the margins around the radiotherapy target volume (the gross tumor volume (GTV) to planning target volume (PTV) margin), therefore achieving greater sparing of surrounding normal tissues than can be obtained with standard CRT techniques.

 

The miniaturization of a 6MV linear accelerator has allowed for its mounting on a high precision industrial robotic arm, and this has been combined with real time kV imaging for target tracking during treatment to create a robotic frameless stereotactic radiotherapy machine that is commercially known as the Cyberknife (CK) [23]. The CK uses multiple narrow, low dose rate photon beams, which have to be summated, to create a dose distribution equivalent to that achieved with other techniques. The need to summate contributions from multiple narrow beams results in longer treatment times per fraction than with other techniques and requires that CK treatment be given as a single large fraction (SRS), or as a few large fractions delivered over the course of a week or so (hypofractionated stereotactic radiotherapy).

 

While the term stereotactic radiotherapy continues to be used, “stereotaxy” as initially used for neurosurgery and subsequently for target localization in radiotherapy is no longer necessary and not in routine use, as modern MR and CT imaging with on treatment image guidance allow for equivalent high-precision treatment delivery. The appropriate modern terminology for the best and most accurate techniques of treatment delivery should be high precision conformal radiotherapy. Nevertheless, the term stereotactic used in conjunction with fractionated treatment (see below), while largely outmoded, remains in use with no clear meaning other than presumably denoting accuracy. Stereotactic localization, however, largely remains the standard of practice with single fraction treatment (GK radiosurgery).

 

Radiotherapy Fractionation

 

TERMINOLOGY

 

The term ‘radiosurgery’ is used for radiation treatment that is given as a single large dose (a single fraction), and the term radiotherapy is used for treatment that is given as multiple, usually daily, small doses over a period of weeks (fractionated treatment). The fractionation of radiation treatment is a mechanism for protecting normal tissues, through recovery between fractions, and permits the delivery of higher total doses of radiation than can be given as single fractions [24].

 

Similarly, stereotactic radiotherapy to the pituitary can be given in multiple doses as fractionated stereotactic conformal radiotherapy (SCRT or fSRT), or as a single large dose when it is described as stereotactic radiosurgery (SRS). SCRT/fSRT is generally delivered using a linac. SRS has most frequently been delivered using a GK, but can also be delivered using a linac or a robotic arm mounted linac (CK). Treatment given in fewer large fractions is described as hypofractionated RT.

 

BIOLOGICAL RATIONALE

 

The use of single fraction SRS is based on a belief, prevalent in the literature, that there is greater clinical benefit from single fraction rather than fractionated irradiation for pituitary adenomas. This belief was based on radiobiological modelling which defines equivalent radiation doses and fractionation schemes through biologically derived parameters [24, 25], mainly from the radiobiology of malignant tumors and some normal tissues. Such models are not validated for single fraction treatments [26], and the corresponding biological parameters necessary to calculate equivalent radiation doses do not exist for benign tumors. Publications claiming theoretical benefit of single fraction radiosurgery over fractionated irradiation [25] are based on constants that are not derived from experimental data and may therefore be misleading.

 

The therapeutic effect of radiation on malignant tumors is thought to be due to tumor cell attrition, either as apoptosis, or reproductive cell death, secondary to radiation-induced DNA damage. As a consequence, the time taken for an irradiated tissue to manifest radiotherapy related effects is proportional to the rate of cell proliferation in the tissue. In tissues with rapidly proliferating cells (malignant tumors), radiation effects are expressed either during or immediately after a course of radiotherapy, while in a tissue with a slowly proliferating cell population, such as benign tumors, radiotherapy effects may take many months or years to manifest. It is assumed that the beneficial effects of radiation in pituitary adenomas conform to these same mechanistic principles with the radiation-induced depletion of pituitary adenoma tumor cells, and with the adenoma being considered a slowly proliferating tissue. As benign tumors are rarely grown in culture, the precise mechanism of the observed clinical benefit of irradiation is not elucidated and remains largely theoretical. The surrounding normal brain tissue is also considered to consist largely of slowly proliferating cell populations, although critical cell populations with faster turnover, such as blood vessels, are also present and are affected by radiation.

 

DOSE FRACTIONATION SCHEMES FOR PITUITARY ADENOMAS

 

Conventional CRT and fractionated SCRT are given to total dose of 45 to 50 Gy at 1.8 Gy per fractionation, once a day, five days per week. These treatment doses are below the tolerance of central nervous system neural tissue, and the risk of structural damage due to such treatment is <1% [27, 28]. While, theoretically, single large doses of radiation as used in SRS may result in a higher tumor cell kill than the equivalent total dose given over a small number of fractions, this is also true for the normal tissue cell population and leads to normal tissue toxicity which may not be acceptable if it affects critical regions such as optic chiasm [28].

 

As most pituitary adenomas requiring radiation treatment lie in close proximity to the optic apparatus, and to the cranial nerves in the cavernous sinus, SRS is suitable only for small lesions located away from critical structures, and the optic apparatus should not exceed single doses above 8Gy [28]. Fractionated SRT, using up to 5-fractions over a week course, is another feasible alternative fractionation scheme delivered by LINACs, Cyberknife or frameless radiosurgery.

 

For larger NFPA with chiasmatic involvement, hypofractionation can allow for safe delivery of enhanced biologically effective doses compared to conventional fractionation. The safety of this scheme has been recently reported in a cohort of NFPA, the majority with abutment or compression of optic chiasm, who had satisfactory local control compared to SRS with acceptable toxicity for visual preservation [29].

 

Linac Based SCRT/FSRT    

 

For fractionated stereotactic radiotherapy, patients are immobilized in a non-invasive relocatable frame with a relocation accuracy of 1-2mm [21, 22], or a precisely fitting thermoplastic mask system with an accuracy of 2-3mm [16]. Sub-millimeter repositioning accuracy can now be achieved with thermoplastic mask immobilization by means of image guidance techniques which can determine and apply daily online setup corrections [30]. As for conventional CRT, the GTV is outlined on an MRI scan co-registered with a CT scan. The PTV margin used for SCRT is smaller than for conventional CRT, typically in the region of 3-5mm based on the overall accuracy of the treatment system, the principal determinant of which is the repositioning accuracy of the patient in the immobilization device [31] and the ability to correct it with on treatment imaging (image guidance). For such precision treatment, accurate localization of the tumor volume is of paramount importance in order to avoid treatment failure due to exclusion of a part of the tumor from the treatment volume.

 

SCRT employs a larger number of radiotherapy beams than conventional CRT (usually 4-6). Each beam is conformed to the shape of the PTV using a narrow leaf MLC (5mm width known as mini MLC, or 3mm width known as micro MLC). MLC leaves can be used to modulate the intensity of the radiation beam during its delivery as in intensity-modulated radiotherapy (IMRT). More recently, arc-based or rotational techniques (volumetric modulated arc therapy or VMAT) have been introduced in the clinical practice to overcome some of the limitation of IMRT (complex planning and QA process). The continuous rotation of the radiation source allows the patient to be treated from a full 360° beam angle in a shorter time interval. Fractionated SCRT (fSRT) combines the precision of stereotactic patient positioning and treatment delivery with standard radiotherapy fractionation, which preferentially spares normal tissue. Complete avoidance of surrounding normal tissue structures, such as the optic apparatus, is not generally practiced, as the dose fractionation schemes used are below the radiation tolerance doses of the CNS. Nonetheless arc techniques are used to minimize the dose bilaterally to the temporal lobes with the aim of reducing the impact of treatment on patients’ cognitive function. The fractionated SCRT technique is suitable for pituitary adenomas of all sizes, regardless of their relationship to adjacent critical normal tissue structures.

 

Linac Based SRS

 

Linac based SRS can be delivered using either a relocatable or an invasive neurosurgical stereotactic frame. Use of an invasive neurosurgical frame necessitates that the treatment planning and delivery procedures are carried out and completed within a single day. Computerized treatment planning defines the arrangement of the radiation beams, as in SCRT. SRS can be planned either as multiple arcs of rotation, simulating GK SRS treatment, and producing small spherical dose distributions, or as multiple fixed conformal fields. Multiple arc SRS using a linear accelerator, employing multiple isocenters, is a cumbersome and rarely used technique. The use of multiple fixed fields is generally confined to fractionated treatment, although it can also be used for single fraction SRS. Because of the potentially damaging effect of large single fraction radiation doses on normal tissue structures, SRS is only suitable for small pituitary adenomas that are at least 3-5mm away from the optic chiasm.

 

Several dosimetry studies have shown that linear accelerators could deliver the same SRS doses to pituitary tumors as GK, with comparable conformity indices and OAR doses. Linac SRS has the advantage of being available, efficient with a less beam-on time, so could be considered for radiosurgery of pituitary adenomas [32]..

 

Gamma Knife SRS

 

For GK SRS, patients are immobilized in an invasive neurosurgical stereotactic frame. A relocatable non-invasive stereotactic frame has become available, enabling the delivery of hypofractionated stereotactic radiotherapy treatment in addition to SRS, and experience with this system is increasing [33, 34]. GK SRS delivers a single high dose, in a spherical distribution, of 4-18mm diameter. Larger, non-spherical tumors, which represent the majority of pituitary adenomas, are treated by combining several such spherical dose volumes using a multiple isocenter technique. The appropriate number and distribution of isocenters is defined using a 3D computer planning system which also allows for selective plugging of some of the cobalt source positions to enable shaping of the high dose volume envelope. The use of multiple isocenters results in dose inhomogeneity within the target volume, with small areas of high radiation dose (hot spots) in the regions of overlap of the radiation dose spheres. This may lead to radiation damage if critical normal structures, such as cranial nerves, lie within these hot spots. GK SRS is given to doses of 12 - 35Gy to the tumor margin with doses to the optic chiasm and the other cranial nerves in the cavernous sinus limited to 8-10Gy and 16-18 Gy respectively. royal sinus invasion has been reported as a significant predictor of poor outcomes after surgical resection. Different series have shown good local control using GK for positive residuals within the cavernous sinus after surgical resection [35-39].  

 

Although the total dose delivered with fractionated meanings of irradiation is largely consistent within different publications (45-50.4 Gy), the range of dose prescriptions between secretory and non-functioning adenomas treated with single fraction SRS tends to be different. The rationale behind this practice is based on the observation that a more rapid hormone normalization was reported in single studies using higher doses to treat secreting tumors [40, 41]. In absence of a strong radiobiological model and of prospective randomized studies in support, the relationship between dose and endocrine remission warrants further investigation.

 

Robotic Mounted Linac SRS

 

Cyberknife has been used to treat pituitary adenomas using a variety of dose/fractionation regimens, with a tendency to deliver treatment as hypofractionated radiotherapy in 3 to 5 fractions, rather than as single fraction SRS doses.

 

Proton Therapy

 

Proton beams, heavy charged particles with similar radiobiological effectiveness as photons, have been in use at a small number of centers with the relevant facilities since the late 1960s [42, 43]. Proton therapy was initially used in two US centers (Boston, MA, and Loma Linda, CA) and then subsequently in Europe (d’Orsay, France) and Japan (Tsukuba, Japan); these centers have reported the majority of the initial clinical results. The introduction of proton therapy had been underpinned by planning studies demonstrating, in selected cases, improved dose distribution of protons compared with photons.

 

The principal theoretical advantage of proton therapy over photon therapy is the deposition of energy at a defined depth in tissue (the Bragg peak) with little energy deposition beyond that point [44]. These properties make the use of protons appealing for tumors lying in close proximity to critical dose-limiting normal tissues, which is a bar to safe dose escalation using conventional photon radiotherapy, or when a reduction of low dose (the low dose radiation “bath” responsible for the late sequelae of radiotherapy) to the normal brain tissues is of particular clinical evidence, as in children.

 

Current indications for the use of protons within the UK Specialized Commissioning Team include the treatment of craniopharyngiomas and pituitary adenomas up to the age of 24 years old based on theoretical reduction in the possible late side effects of brain radiation, such as second malignancy, neuro-cognitive deficits and cerebrovascular disease [45].

 

Peptide Receptor Radionuclide Therapy (PRRT)

 

PRRT is a form of internal radiation therapy directed to the tumor tissues expressing peptide receptors using gamma emitting radiopharmaceuticals. It is typically used for neuroendocrine tumors; however, it was investigated as a treatment option for aggressive pituitary tumors refractory to other treatment modalities. Different pituitary tumors express somatostatin receptors and show uptake of radiolabeled somatostatin analogues like 68Ga-DOTATATE. The 2018 guidelines of the European Society of Endocrinology listed PRRT as an alternative treatment option for aggressive pituitary tumors refractory to other lines of treatment including temozolomide [46].The treatment doses and the type of nucleotide used varied in the available studies, with only small patient numbers being reported [47, 48].

 

CLINICAL OUTCOMES FOLLOWING PITUITARY RADIOTHERAPY

 

The clinical efficacy of radiotherapy for pituitary adenomas should be assessed by overall survival, actuarial tumor control (progression-free survival, PFS), and quality of life. Few publications focused on quality of life assessment after radiotherapy in pituitary tumors [49-51], while commonly reported endpoints for retrospective studies of radiation treatment for non-functioning pituitary adenomas are local tumor control, and long term morbidity.

 

In patients with functioning pituitary adenomas, the principal endpoint, in addition to PFS and morbidity, is the rate of normalization of elevated pituitary hormone levels. The rate of pituitary hormone decline after irradiation varies with the type of functioning tumor, and the time to reach normal hormone levels is dependent on the initial pre-treatment hormone levels [52]. The appropriate comparative measure for each pituitary hormone is the time to reach 50% of the pre-treatment hormone level, and this should be corrected for the confounding effect of medical treatment.

 

Surrogate endpoints such as ‘tumor control rate’ and the ‘proportion of patients achieving normal hormone levels’ do not, of themselves, provide adequate information on the efficacy of different pituitary irradiation techniques and are potentially misleading [53]. Tumor control rate must be quoted with an indication of the time or duration of follow-up required to achieve the stated level of control. Similarly, the proportion of patients achieving normal hormone levels following treatment is meaningful only when described in terms of the relationship to pre-treatment hormone levels. Due to the use of such surrogate endpoints in published retrospective series, inappropriate and incorrect claims have been made in the literature for superiority of one technique of irradiation over another.

 

Given that the published data on the efficacy of the various available techniques for pituitary irradiation consist entirely of retrospective case-series, the available data inevitably suffer from selection bias. While SCRT is suitable for the treatment of all pituitary tumors, irrespective of size, shape or proximity to critical normal tissue structures, SRS is only suitable for treatment of small tumors away from the optic chiasm. As a result, studies reporting the efficacy of SRS mostly deal with smaller tumors, which are typically associated with lower hormone levels if the adenomas are functioning. Therefore, the reported results of studies of SRS do not necessarily apply to the generality of pituitary adenomas and may give a false impression of greater efficacy if only more favorable cases are treated.

 

THE EFFICACY AND TOXICITIES OF TREATMENT

 

Conventional RT and CRT

 

The efficacy of modern stereotactic pituitary radiotherapy and pituitary radiosurgical techniques must be assessed in the light of the results achieved with standard treatment, which is conventional conformal radiotherapy. Large and mature case series provide data on the long-term effectiveness of CRT in controlling pituitary tumor growth and hormone secretion.

 

TUMOR CONTROL

 

The long-term results following pituitary CRT from case series published in the literature are shown in Table 1 [5-14, 17, 54-66]. The actuarial PFS is in the region of 80%-90% at 10 years and 75%-90% at 20 years [14, 55]. The single largest series of patients with pituitary adenomas treated with conventional fractionated radiotherapy is that from The Royal Marsden Hospital which reported a 10-year PFS of 92% and a 20-year PFS of 88% [8].

Post operative radiotherapy has been reported to provide excellent local control of non-functioning tumors when offered for progressive residual disease with almost no radiological evidence of tumor progression up to 15 years of follow-up [67].

 

ENDOCRINE CONTROL  

 

Fractionated irradiation leads to normalization of excess pituitary hormone secretion in the majority of patients, albeit with some time delay following treatment. For acromegaly, RT achieves normalization of GH/IGF-I levels in 30-50% of patients at 5-10 years, and in 75% of patients at 15 years, after treatment (Table 2) [14, 55]. As the time to normalization of GH levels is related to the pre-treatment GH level, the time to achieve a 50% reduction in GH levels, which takes into account the starting GH level, is in the region of 2 years, with IGF-1 reaching half of pre-treatment levels somewhat after the GH [58, 60].

 

A 10-year follow-up for more than 600 acromegaly patients was published by the Swedish Pituitary Register 2022. It has reported 78% of IGF-1 normalization rate with an annual rate of increased hormonal control of 1.23%. One third of the patients required bi-modality therapy to achieve hormonal control and 5% required triplet therapy i.e. surgical resection, medical treatment and radiotherapy with a trend towards reduced use of conventional radiotherapy doses [68]. 

 

Table 1. Summary of Results of Published Series on Conventional RT for Pituitary Adenomas

Authors

Type of adenoma

Number of patients

Follow-up

(median years)

Actuarial progression free survival (PFS) (%)

Late toxicity (%)

Visual Hypopituitarism

Grigby at al.,1989 [6]

NFA, SA

121

11.7

89.9 at 10 years

1.7

NA

McCollough et al., 1991 [7]

NFA, SA

105

7.8

95 at 10 years

NA

NA

Brada et al., 1993 [8]

NFA, SA

411

10.8

94 at 10 years

88 at 20 years

1.5

30 at 10 years

Tsang et al., 1994 [9]

NFA, SA

160

8.7

87 at 10 years

0

23**

Zierhut et al., 1995 [10]

NFA, SA

138

6.5

95 at 5 years

1.5

27**

Estrada et al., 1997 [56]

SA (ACTH)

30

3.5

73 at 2 years*

0

48**

Rush et al., 1997 [11]

NFA, SA

70

8

NA

NA

42**

Breen et al., 1998 [12]

NFA

120

9

87.5 at 10 years

1

NA

Gittoes et al., 1998 [5]

NFA

126

7.5

93 at 10 and 15 years

NA

NA

Barrande et al., 2000 [57]

SA (GH)

128

11

53 at 10 years*

0

50 at 10 years

Biermasz et al., 2000 [58]

SA (GH)

36

10

60 at 10 years*

0

54 at 10 years

Sasaki et al., 2000 [13]

NFA, SA

91

8.2

93 at 10 years

1

NA

Epaminonda et al., 2001 [59]

SA (GH)

67

10

65 at 15 years*

0

NA

Minniti et al., 2005 [60]

SA (GH)

45

12

52 at 10 years*

0

45 at 10 years

Langsenlehner et al., 2007 [61]

NFA, SA

87

15

93 at 15 years

 

0

88 at 10 years

Minniti et al., 2007 [62]

SA(ACTH)

40

9

78 and 84 at 5 and 10 years*

0

62 at 10 years

Rim et al., 2011 [63]

NFA, SA

60

5.6

96 at 10 years (NFA),

66 at 10 years (SA)

0

76 at 10 years

Kim et al., 2016 [65]

NFA, SA

73

8

98 at 10 years

0

NA

Patt et al., 2016 [66]

SA (GH)

36

4.9 (mean)

89 at 5 years

0

33

NFA, non-functioning adenoma; SA, secreting adenoma; NA, not assessed, ACTH-Cushing, GH- acromegaly, *hormone concentration normalization, **no time specified

 

After RT for Cushing’s disease, urinary free cortisol (UFC) is reduced to 50% of the pre-treatment levels after an interval of 6-12 months, and plasma cortisol after around 12 months [62]. The median time to cortisol level normalization is around 24 months after treatment [62]. The overall tumor and hormone control rates in the reported studies, after a median follow-up of 8 years, are 97% and 74% respectively [64]. Pituitary radiotherapy is rarely used to treat patients with prolactinoma. Occasional patients who fail surgery and medical therapy have been treated with RT, and the reported 10-year tumor and hormone control rates are 90% and 50% respectively [69-71].

 

TOXICITY

 

The toxicity of RT with total treatment doses of 45-50Gy with daily fraction sizes of < 2Gy is low. The principal toxicities reported in studies of CRT are described in Table 1.

 

Hypopituitarism  

 

Hypopituitarism is the most common long-term complication following RT, reported to occur in 30-60 % of patients by 10 years after treatment [8, 9, 14]. Pituitary hormone loss is observed to occur in a characteristic sequence, with GH secretion being affected most frequently, followed by the gonadotrophins, ACTH, and then TSH. Long term follow-up after pituitary irradiation, with intermittent testing for deficiency of all pituitary axes, is therefore an essential part of the post-treatment management of these patients.

 

Visual Pathways Deficit and Other Structural CNS Damage

 

The reported incidence of optic neuropathy resulting in visual deficit following CRT is 1-3% [8, 9]. The occurrence of necrosis of normal brain tissue is almost unknown following pituitary RT, although this complication has been reported to occur in 0.2% of patients [72].

 

Cerebrovascular Disease

 

Pituitary disease is, in itself, associated with increased mortality, principally due to vascular disease [73]. An increased incidence of stroke (relative to the general population) in patients treated with RT for both non-functioning and functioning pituitary adenomas has been reported in a number of retrospective cohort studies [74-77]. Whilst it is has long been known that radiotherapy can lead to vascular injury [78], it is not at present clear how much of the excess stroke risk following RT is attributable to radiotherapy, and how much may be due to other potential causes including the metabolic and cardiovascular consequences of hypopituitarism, the effects of associated endocrine syndromes, and the consequences of surgery.

 

In a retrospective cohort study of 342 patients treated with pituitary surgery and post-operative RT, 31 patients died from stroke after a median follow-up interval of 21 years (range, 2-33) [77] and in all cases the probable location of the stroke lesion was within the irradiated volume. Comparison of stroke patients with matched control patients without stroke drawn from the same cohort showed no significant differences in radiotherapy-dependent variables with the exception of the pre-treatment duration of symptoms of hypopituitarism. This suggests that untreated hormone deficiency may be a significant factor in the pathogenesis of stroke in patients treated for pituitary adenoma, rather than or in addition to treatment with radiotherapy. It is likely that the cause of stroke in patients treated with RT for pituitary adenoma is multi-factorial, and the relative contributions of the various possible contributory factors remains to be determined.

 

Second Brain Tumor

 

Intracranial radiotherapy is associated with the development of second, radiation-induced, brain tumors. The cumulative incidence of gliomas and meningiomas following radiotherapy for pituitary adenomas in retrospective case series is reported to be in the region of 2% at 20 years [77, 79-81]. A large retrospective study of patients who received radiotherapy for pituitary and sellar lesions has shown a relative risk of 3.34 (95% confidence interval 1.06-10.6) for development of malignant brain tumors and 4.06 (95% confidence interval 1.51-10.9) for development of meningiomas in comparison with patients who did not receive radiotherapy. Rates were higher in those treated with radiotherapy at a younger age, and there was no difference in incidence rates between conventional or stereotactic radiotherapy (70).

 

In another large retrospective cohort of more than 3600 patients from six adult endocrinology registries, incidence of secondary brain tumors was compared between irradiated and non-irradiated patients with pituitary adenomas and craniopharyngiomas. The relative risk of secondary brain tumors for irradiated patients was 2·18 (95% CI 1·31-3·62, p<0·0001). Cumulative probability of second brain tumor was 4% for the irradiated and 2·1% for the controls at 20 years. Radiotherapy exposure and older age at pituitary tumor detection were associated with increased risk of second brain tumor [82].

 

Cognitive Deficit

 

Radiotherapy treatment to significant volumes of normal brain in children is associated with subsequent neuro-cognitive impairment [27]. However, the evidence for the effect of radiotherapy treatment to small volumes of brain on neuro-cognitive function in adults is weak [27]. The effect of pituitary radiotherapy on neuro-cognitive function is particularly difficult to discern as this cannot be differentiated from the effect of other treatment interventions, and from the effects of the tumor itself [83-85].

 

A retrospective study of 84 patients following transsphenoidal surgery, of whom 39 received post-operative radiotherapy, compared neuro-cognitive function with a large reference sample, considered to be representative of normal population without pituitary disease. While the pituitary cohort had lower scores on the tests of both memory and executive function in comparison with the reference sample, patients who had received radiotherapy showed no significant difference compared to patients treated with surgery alone [86]. A dosimetric study did not find a correlation between radiotherapy dose to the hippocampus and pre-frontal cortex (brain regions known to be important in memory and executive function) and conformal technique of irradiation with cognitive performance [87].

 

Stereotactic Conformal Radiotherapy (SCRT/FSRT)

 

SCRT achieves tumor control and normalization of pituitary hormone hypersecretion at rates similar to the best reports following conventional RT. Longer duration follow-up is required to demonstrate the presumed lower incidence of long-term morbidity following SCRT compared to conventional RT. The results from reported studies of SCRT are summarized below.

 

TUMOR CONTROL

 

SCRT data for 1166 patients with either non-functioning or functioning pituitary adenomas have been reported in 21 studies to date (Table 2) [14, 17, 55, 64, 88-105]. Analysis of published data up to 2020 shows that, at a corrected median follow-up of 56 months (range 9-152 months), tumor control was achieved in 96% of patients. The 5-year actuarial PFS of 92 patients (67 non-functioning, 25 functioning) treated at The Royal Marsden Hospital was 97% [93]. These results are similar to the results seen in patient cohorts treated with conventional RT (Table 1).

 

ENDOCRINE CONTROL  

 

Detailed data on the rate of pituitary hormone decline are not available, although this is expected to be similar to that seen following conventional RT as the same dose-fractionation is used. In The Royal Marsden case series, 6 of 18 acromegalic patients (35%) had normalization of GH/IGF-I levels after a median follow-up of 39 months [93]. Similarly, in another single center study of 20 patients treated with SCRT, normalization of GH levels was reported in 70%, and local tumor control in 100% after a median follow-up of 26 months [90]. The data available on SCRT for patients with Cushing’s disease are limited. In a small series of 12 patients, control of elevated cortisol was reported in 9 out of 12 patients (75%) after a median follow-up of 29 months [92].

 

TOXICITIES

 

Following SCRT, hypopituitarism has been reported in 22% of patients after an overall corrected median follow-up of 57 months (Table 2). The length of follow-up after SCRT is shorter than reported for the mature cohorts treated with RT. It is likely that the rate of hypopituitarism following SCRT will continue to increase as the duration of follow-up increases particularly as the technique of SCRT generally does not avoid either the hypothalamus or the remaining pituitary gland. Other late complications have been rarely reported after SCRT. While the incidence of treatment-related morbidity with SCRT appears to be low, longer duration follow-up is necessary to detect normal tissue toxicity that may only become manifest at a low frequency many years after treatment.

 

Table 2. Summary of Results on Published Studies on SCRT for Pituitary Adenomas

Authors

Number of patients

Follow-up median (months)

Tumor growth control rate (%)

Late toxicity (%)

Visual  Hypopituitarism

Coke et al., 1997 [88]

19*

9

100

0

0

Mitsumori et al., 1998 [89]

30*

33

86 at 3 years

0

20

Milker-Zabel et al., 2001 [90]

68*

38

93 at 5 years

7

5

Paek et al., 2005 [91]

68

30

98 at 5 years

3

6

Colin et al., 2005 [92]

110*

48

99 at 5 years

2

29 at 4 years

Minniti et al., 2006 [93]

92*

32

98 at 5 years

1

22

Selch et al., 2006 [94]

39*

60

100

0

15

Kong et al., 2007 [95]

64*

37

97 at 4 years

0

11

Snead et al., 2008 [96]

100*

6.7 years

98 and 73 at 10 years for NFA and SA

1

35

Roug et al., 2010 [97]

34*

34

91 (50% hormonal normalization)

-

-

Schalin-Jantti et al., 2010 [98]

30

5.3 years

100

0

23

Weber et al., 2011 [99]

27*

72.4

96

4

8

Wilson et al., 2012 [100]

67

5.12 years

88

2

6

Kim et al., 2013 [101]

76*

6.8 years

97.1 at 7 years

0

48 (one or more hormone)

Kopp et al., 2013 [102]

37

57

91.9

5

43

Liao et al., 2014 [106]

34~

36.8 (mean)

100

0

NA

Minniti et al., 2015 [103]

68

75

97 and 91 at 5 and 10 years

0

26

Puataweepong et al., 2015 [107]

94*

72

95

3

9.6

Diallo et al., 2015 [104]

34*

152 (mean)

97

0

39

Barber et al., 2016 [105]

75*

47.5 (mean)

100

1.5

28

Lian et al., 2020 [108]

113*

36

99

0

28.3

* Case series includes secreting adenomas

 

Radiosurgery (SRS)

 

TUMOR CONTROL  

 

The published results of GK SRS for patients with non-functioning and functioning pituitary adenomas have been summarized in systematic reviews [14, 17, 55, 64] and an update with more recently published studies is given in Table 3 [14, 17, 35, 55, 64, 100, 109-130]. The majority of published reports provide information on tumor ‘control rate’, without specifying a time-frame, and therefore provide little useful information on the efficacy of GK SRS. The summary figure for the actuarial 5-year control rate (PFS) following GK SRS for non-functioning adenomas is 95% at 5 years (few 10-year results are available). This is a lower rate of tumor control than expected following RT & SCRT, particularly when it is considered that only small tumors suitable for GK SRS are treated, compared to that adenoma of all sizes treated with RT, CRT & SCRT.

 

Table 3. Summary of Results of Published Series on SRS for Non-Functioning Pituitary Adenomas

 

Authors

Number of patients

Follow-up median (months)

Tumor control growth rate (%)

Late toxicity (%)

Visual Hypopituitarism

 

Martinez et al., 1998 [109]

14

26-45

100

0

0

 

Pan et al., 1998 [110]

17

29

95

0

0

 

Ikeda et al., 1998 [35]

13

45

100

0

0

 

Mokry et al., 1999 [111]

31

20

98

NA

NA

 

Sheehan et al., 2002 [112]

42

31*

97

2.3

0

 

Wowra et al., 2002 [113]

45

55

93 at 3 years

0

14

 

Petrovich et al., 2003 [114]

56

36

94 at 3 years

4

NA

 

Pollock et al., 2003 [115]

33

43

97 at 5 years

0

28 and 41 at 2 and 5 years

 

Losa et al., 2004 [116]

56

41*

88 at 5 years

0

24

 

Iwai et al., 2005 [117]

34

60

93 at 5 years

0

6

 

Mingione et al., 2006 [118]

100

45*

92

0

25

 

Liscak et al., 2007 [119]

140

60

100

0

2

 

Pollock et al., 2008 [120]

62

63

95 at 3 and 7 years

0

32 at 5 years

 

Kobayashi et al., 2009 [121]

60

>3 years

97

4.3

8.2 worsening

 

Gopalan et al., 2011 [122]

48

80.5

83

9.4

39

 

Park et al., 2011 [124]

125

62

94 at 5 years and

76 at 10 years

1

24 at 2 years

 

Wilson et al., 2012 [100]

51

4.17 years

100

0

0

 

Runge et al., 2012 [123]

61

83

98

0

9.8

 

Starke et al., 2012 [125]

140

4.2 years

97 at 5 and 87 at 10 years

12.8

30.3

 

El-Shehaby et al., 2012 [126]

38

44*

97

0

0

 

Sheehan et al., 2013+ [127]

512

36

95 at 5 years

6.6

21

 

Lee et al., 2014 [128]

41

48

94 at 5 and 85 at 10 years

2.4

24.4

 

Xu et al., 2014 [129]

34

56

73 at 3 years

24

29

 

Hasegawa et al., 2015 [130]

16

98

100

0

6

 

Graffeo et al., 2018[131]

57

48

99

NA

31 at 5years

 

Oh et al., 2018 [132]

76

53.5

96

NA

24.5

 

Cordeiro et al., 2018 [133]

410

51

94.4

NA

34.7

 

Narayan et al., 2018 [134]

87

48.2

90

8.1

20.7

 

Slavinsky P et al., 2022 [135]

 

28

63

94.2

NA

26%

Maldar AN, et al.,2022[136]

63

47

87.3

NA

26% at 5 years

29.7% at 10 years

*Mean follow-up; NA: not available, + multicenter study, 34 patients had prior CFSR

 

ENDOCRINE CONTROL WITH GK SRS

 

The reported endocrine outcomes following GK SRS for acromegaly are shown in Table 4 [14, 36, 40, 55, 64, 109-111, 114, 121, 137-163]. A summary analysis of the published literature up to 2020 shows that -41% of patients achieved normalization of serum GH, after a median follow-up of 46 months. The time to reach 50% of baseline serum GH, reported in only three studies, is in the region of 1.5-2 years with a slower reduction in IGF-I levels [147, 150, 164], which is similar to the rate reported following conventional RT/CRT.

 

Table 4. Summary of Results of Published Series on SRS for GH-Secreting Pituitary Adenomas

 

Authors

Number of patients

Follow-up median (months)

Hormone normalization* (%)

Late toxicity (%)

Visual Hypopituitarism

 

Thoren et al., 1991 [137]

21

64

10

0

15

 

Martinez et al., 1998 [109]

7

26-45

NA

0

0

 

Pan et al., 1998 [110]

15

29

NA

0

0

 

Morange-Ramos et al., 1998 [138]

15

20

20

6

16

 

Lim et al., 1998 [139]

20

26

30

5

5

 

Kim et al., 1999 [165]

11

27

35

NA

NA

 

Landolt et al., 1998 [141]

16

17

50

0

16

 

Mokry et al., 1999 [111]

16

46

31

0

NA

 

Hayashi et al., 1999 [142]

22

>6

41

0

0

 

Inoue et al., 1999 [143]

12

>24

58

0

0

 

Zhang et al., 2000 [144]

68

>12

40

NA

NA

 

Izawa et al., 2000 [145]

29

>6

41

0

0

 

Pollock et al., 2002 [146]

26

36

47

4

16

 

Attanasio et al., 2003 [147]

30

46

23

0

6

 

Choi et al., 2003 [148]

12

43

30

0

0

 

Jane et al., 2003 [149]

64

>18

36

0

28

 

Petrovich et al., 2003 [114]

6

36

100

0

NA

 

Castinetti et al., 2005 [150]

82

49.5*

17

0

18

 

Gutt et al., 2005 [151]

44

22

48

NA

NA

 

Kobayashi et al., 2005 [152]

67

63

17

0

NA

 

Jezkova et al., 2006 [153]

96

54

50

0

26

 

Pollock et al., 2007 [154]

46

63

11 and 60 at 2 and 5 years

0

33 at 5 years

 

Jagannathan et al., 2009 [155]

95

57 *

53

5#

34 (new)

 

Kobayashi, 2009 [121]

49

63

17 (normal or nearly normal)

11

15

 

Wan et al., 2009 [156]

103

60 (minimum)

37

0

1.7**

 

Castinetti et al., 2009 [157]

27

60 (minimum)

42 at 50 months

1.3**

23**

 

Iwai et al., 2010 [158]

26

84

38

0

8

 

Hayashi et al., 2010 [36]

25

36*

40

0

0

 

Erdur et al., 2011 [159]

22

60

55

0

29

 

Sheehan et al., 2011 [40]

130

30

53 at 30 months

0

34

 

Franzin et al., 2012 [160]

103

71

56.9 at 5 years

0

7.8 (new)

 

Liu et al., 2012 [161]

40

72

57.5

0

40 (new)

 

Zeiler et al., 2013 [162]

21

33

30

3.9

13.2

 

Lee et al., 2014 [163]

136

61.5

64.5 and 82.6 at 4 and 8 years

3

33.1

 

Cordeiro et al., 2018 [133]

351

51

NA

NA

38.7

 

Gupta et al.,2018 [166]

25

69.5

28

NA

19.6

Ding et al., 2019 [167]

371

79

59 at 10 years

4

26

 

*mean follow-up; NA not assessed, #3 had previous RT, **whole series

 

A summary analysis of the published literature up to 2020, for patients with Cushing’s disease, shows that 52% achieved biochemical remission (as defined by plasma cortisol and 24-hour UFC level) at a corrected median follow-up of 50 months after SRS (Table 5) [14, 36, 40, 55, 64, 109-111, 114, 121, 138-140, 142, 143, 145, 146, 148, 149, 155-157, 162, 165, 168-178]. The reported time to hormonal normalization ranged from 3 months to 3 years, with no clear difference in the rate of decline of hormone level compared to RT/CRT. The largest single series of GK SRS for Cushing’s disease reported a remission rate of 54%, with 20% of patients who achieved remission subsequently relapsing, suggesting a higher failure rate following GK SRS than following RT/CRT [179].

 

Table 5. Summary of Results of Published Series on SRS for ACTH-Secreting Pituitary Adenomas

 

Authors

Number of patients

Follow-up median (months)

Tumor growth control rate (%)

Hormone normalization*%

Late toxicity

(%)

Visual    Hypopituitarism

 

Degerblad et al., 1986 [168]

29

3-9 years

76

48

NA

55

 

Ganz et al., 1993 [169]

4

18

NA

NA

0

NA

 

Seo et al., 1995 [170]

2

24

100

NA

0

NA

 

Martinez et al., 1998 [109]

3

26-45

100

100

0

0

 

Pan et al., 1998 [110]

4

29

95

NA

0

0

 

Morange-Ramos et al., 1998 [138]

6

20

100

66

0

16

 

Lim et al., 1998 [139]

4

26

NA

25

2

2

 

Mokry et al., 1999 [111]

5

26

93

20

0

2

 

Kim et al., 1999 [165]

8

26

100

60

NA

NA

 

Hayashi et al., 1999 [142]

10

>6

100

10

0

5

 

Inoue et al., 1999 [143]

3

>24

100

100

0

0

 

Izawa et al., 2000 [145]

12

>6

100

17

NA

0

 

Sheehan et al., 2000 [171]

43

44

100

63

2

16

 

Hoybye et al., 2001 [172]

18

17 years

100

83

0

66

 

Kobayashi et al., 2002 [173]

20

60

100

35

NA

NA

 

Pollock et al., 2002 [146]

11

36

85

35

35

8

 

Choi et al., 2003 [148]

9

43

100

55

0

0

 

Jane et al., 2003 [149]

45

>18

100

63

1

31

 

Petrovich et al., 2003 [114]

4

36

NA

50

0

NA

 

Devin et al.,  2004 [174]

35

35

91

49

0

40

 

Castinetti et al., 2007 [175]

40

54

100

42

0

NA

 

Jagannathan et al., 2009 [155]

90

45

96

54

6

22

 

Kobayashi, 2009 [121]

25

64(mean)

100

35

NA

NA

 

Wan et al., 2009 [156]

68

60(minimum)

90

28

0

1.7

 

Castinetti et al., 2009 [157]

18

60(minimum)

NA

50 at 28 months

1.3**

23**

 

Hayashi et al., 2010 [36]

13

36(mean)

97

38

0

0

 

Sicignano et al., 2012 [178]

15

60

97.7

64

NA

12.3

 

Zeiler et al., 2013 [162]

8

35

100

50

3.9

32

 

Sheehan et al., 2013 [177]

96

48

98

70

4

36

 

Marek et al., 2015 [176]

26

78

90.9 at 5 and 10 years

80.7

0

23

 

Cordeiro et al., 2018 [133]

262

51

95.8

NA

NA

26.6

 

Knappe et al., 2020 [180]

119

107

NA

78

NA

NA

 

Gupta et al., 2018  [166]

21

69.5

100

81%

NA

19.6%

*time not specified; NA not assessed

 

In patients with prolactinomas treated with GK SRS the reported time to hormonal response ranged from 5 months to 40 months (Table 6) [14, 40, 55, 64, 109-111, 114, 121, 138-140, 142, 143, 145, 146, 148, 149, 156, 157, 161, 169, 181-186]. At a corrected median follow-up of 43 months (median range 6-60 months), 33% of patients had normalization of serum prolactin concentrations following GK SRS [14]. One study of 35 patients reported a hormonal normalization of 80% after a median of 96 months and a tumor control rate of 97% [184]. There is insufficient information to assess the rate of decline of prolactin following GK SRS in comparison to that following CRT.

 

Table 6. Summary of Results of Published Series on SRS for Prolactin Secreting Pituitary Adenomas

 Authors

Number of patients

Follow-up median (months)

Hormone normalization*%

Late toxicity (%)

Visual        Hypopituitarism

Ganz et al., 1993 [169]

3

18

0

0

NA

Martinez et al., 1998 [109]

5

26-45

0

0

0

Pan et al., 1998 [110]

27

29

30

0

0

Morange-Ramos et al., 1998 [138]

4

20

0

0

16

Lim et al., 1998 [139]

19

26

50

NA

NA

Mokry et al., 1999 [111]

21

31

57

0

19

Kim et al., 1999 [165]

18

27

16

NA

NA

Hayashi et al., 1999 [142]

13

>6

15

NA

5

Inoue et al., 1999 [143]

2

>24

50

0

0

Landolt et al., 2000 [181]

20

29

25

0

NA

Pan et al., 2000 [182]

128

33

41

0

NA

Izawa et al., 2000 [145]

15

>6

16

0

NA

Pollock et al., 2002 [146]

7

26

29

14

16

Choi et al., 2003 [148]

21

43

23

0

0

Jane et al., 2003 [149]

19

>18

11

0

21

Petrovich et al., 2003 [114]

12

36

83

0

NA

Pouratian et al., 2006 [183]

23

55

26

7

28

Jezkova et al., 2009 [184]

35

96

80

NA

NA

Kobayashi, 2009 [121]

27

37(mean)

17

0

0

Wan et al., 2009 [156]

176

60 (minimum)

23

0

1.7

Castinetti et al., 2009 [157]

15

60 (minimum)

46 at 24 months

1.3**

23**

Liu et al., 2013 [185]

22

36

27

-

4.5

Cohen-Inbar et al., 2015 [186]

38

42.3

50

NA

30.3

Ježková et al., 2019 [187]

28

140

82.1

3.6

8.3

 

Early studies of linac based SRS reported results on small numbers of patients, but the available results are broadly equivalent to those reported for GK SRS [17]. In the largest linac based SRS study to date, which included 175 patients with both non-functioning and functioning pituitary adenomas treated using a single dose of 20 Gy, the local tumor control rate was 97% after a minimum of 12 months follow-up [188]. Actuarial 5-year PFS was not reported. Hormonal normalization rates were 47% for GH-secreting adenomas, 65% with Cushing’s disease, and 39% with prolactinomas. The mean time for hormone normalization was 36±24 months. Within the limited follow-up period, 12% developed additional pituitary dysfunction, 3% radiation-induced CNS tissue damage, and 1% radiation-induced optic neuropathy. These results from linac SRS are difficult to evaluate but are broadly similar to those achieved with GK SRS and appear inferior to those obtained with fractionated treatment.

 

TOXICITY

 

In common with other modalities of pituitary irradiation, the most commonly reported complication following GK SRS is hypopituitarism, with a crude incidence ranging from 0% to 66% [14, 55]; the actuarial incidence has not been defined. The expected frequency of visual complications would be low if GK SRS is only offered to patients with a pituitary adenoma at a safe distance from the optic chiasm and nerves (~ 5mm). However, one study in patients with Cushing’s disease reported a 10% incidence of new cranial nerve deficit, with a 6% incidence of optic neuropathy [155]. Similarly, a study reporting results of SRS for prolactinoma noted a 7% incidence of cranial nerve deficit [183]. Although the absolute numbers of patients treated in these studies of GK SRS were small, there is a suggestion that for some patients, possibly with larger tumors, the incidence of optic pathway toxicity with GK SRS is well above what is seen in patients following CRT. Long-term risks of cerebrovascular events and the incidence of second tumors following GK SRS are not yet defined. GK toxicity is expected to be higher when offered after surgical excision rather than as a primary treatment option. In a recently published systematic review and meta-analysis on 1381 patients with pituitary adenomas treated with GK SRS, rates of radiation-induced hypopituitarism were (11.4%) in primary GK compared to (18-32%) in post-operative GK SRS. This highlights the importance of long-term endocrinology follow-up [189].

 

Robotic SRS

 

A small number of retrospective case series on outcomes following CK SRS for pituitary adenomas have been published to date (Table 7) [190-197]. While the published results are comparable to the outcomes achieved with GK SRS, the same criticisms levelled at the GK SRS studies also apply to these early CK SRS series. The duration of follow-up in all the existing CK SRS series is too short to allow meaningful conclusions to be drawn with regard to both efficacy and toxicity outcomes.

 

Table 7. Summary of Results of Published Series on Cyberknife SRS for Functioning & Non-Functioning Pituitary Adenomas

 

Author

Tumor type

Number of patients

Follow-up mean (months)

Tumor Control or Hormone normalization*

(%)

Late toxicity (%)

Visual Hypopituitarism

 

Kajiwara et al., 2005 [190]

14 NFA, 3 PRL, 2 GH, 2 ACTH

21

35.3

95.2TC, 50 HN

4.7

9.5

 

Adler et al., 2006 [191]

12 NFA, 4 GH, 2 ACTH, 1 PRL

19

46

18/19 TC

5.2

NA

 

Roberts et al., 2007 [192]

GH

9

25.4

44.4 HN

0

33

 

Killory et al., 2009 [193]

14 NFA, 4GH, 1 PRL, 1 TSH

20

26.6

100 TC

0

NA

 

Cho et al., 2009 [194]

17 NFA, 3 PRL, 6 GH

26

30

92.3 TC, 44 HN

7.6

0

 

Iwata et al., 2011 [195]

NFA

100

33 median

98 TC

1

4

 

Puataweepong et al., 2015[196]

27 NFA, 7 GH, 5 PRL, 1 ACTH

40

38.5 median

97.5 TC, 54 HN

0

0

 

Iwata et al., 2016 [197]

GH

52

60 median

100 TC, 20.4 HN

0

2.2

 

Plitt et al., 2019 [198]

NFA

53

32.5

98.1 TC

0

1.9

 

Romero-Gameros et al., 2023 [199]

GH

57

48

45.6% HN

0

24.5

                 

TC: Tumor Control; HN: hormone normalization

 

Proton Beam Therapy

 

An early study, published in 1989, of proton beam therapy for pituitary adenomas attempted to compare the effectiveness of this treatment modality to RT/CRT [200]. Follow-up after CRT in 17 patients and after proton therapy in 13 patients found a similar reduction of GH levels in both groups and the small number of patients does not allow for any statistically meaningful comparison. Nevertheless, treatment related side effects, including new hypopituitarism and oculomotor palsies, were more frequent in proton therapy group. Since the efficacy of both pituitary irradiation methods were similar, but proton therapy was associated with a higher incidence of serious side effects, the authors concluded that RT/CRT is the preferred treatment modality [200].

 

In a study from 2006, of 47 patients treated with fractionated proton therapy for both non-functioning and functioning pituitary adenomas reported tumor stabilization in 41 (87%) patients after a minimum 6-month follow-up; 1 patient developed temporal lobe necrosis, 3 developed new significant visual deficits, and 11 developed new hypopituitarism [201]. These are disappointing results suggesting considerably worse outcome both in terms of efficacy and toxicity than seen with photon irradiation.

 

A study of proton beam stereotactic radiosurgery in 22 patients with acromegaly reported normalization of GH in 59% after a median of 42 months. New pituitary deficiency was reported in 38% of patients, but no visual complications were reported [43]. The same group reported on the biochemical response in a larger population of secreting adenomas (74 ACTH-secreting, 50 GH-secreting, 9 PRL-secreting, 8 Nelson’s syndromes, 3 TSH-secreting) treated with the same technique. The study included 27 patients previously irradiated (14 pts) or treated with fractionated proton beam radiotherapy. At a median follow-up of 52 months, 42% of patients did not achieve endocrine control with patients with acromegaly having the longer time to biochemical response (49% at 5 years). The risk of developing hypopituitarism was 62% at 5 years and four patients (3%) experienced post treatment temporal lobe seizures, with associated temporal lobe changes on imaging (1 month to 9 years from proton treatment). [202]).

 

An evidence-based review of proton therapy from ASTRO’s emerging technology committee examined the evidence for proton therapy across multiple tumor sites and concluded that currently available evidence provides only limited indications for proton therapy [203]). The report recommended that robust prospective clinical trials be conducted to determine the appropriate clinical indications for proton therapy. In the present context, the available published reports of proton therapy for pituitary adenoma demonstrate disappointing efficacy and increased toxicity relative to much more readily available photon-based treatment. Also, in dosimetric comparisons, proton beam did not provide superior dose coverage advantage over photon radiation with comparable doses to OARs with both modalities [204]. Therefore, it seems difficult to justify proton therapy to the pituitary outside of the context of a clinical trial.

 

RE-IRRADIATION FOR RECURRENT DISEASE

 

Re-irradiation for progression of pituitary adenoma after previous pituitary radiotherapy is considered to be associated with a high risk of radiation-induced damage due to the presumed cumulative effect of radiation to the optic apparatus, the cranial nerves, and the normal brain tissues. However, re-irradiation using fractionated conventional or stereotactic techniques is feasible, with acceptable toxicity [53], provided that there has been at least a 3-4 year gap following primary radiotherapy treatment to doses below radiation tolerance of the CNS (which is the case for the conventional dose of 45Gy delivered at <1.8Gy per fraction). GK SRS has also been used to re-irradiate small recurrent lesions, particularly if they are not in close proximity to the optic apparatus [205].

 

While the current impression is that late toxicity following pituitary re-irradiation is uncommon, a high incidence of adverse side effects (13% radiation induced optic neuropathy and 13% of temporal lobe necrosis) was reported in a series of 15 patients re-irradiated with both single fraction and fractionated approaches (median time from previous RT 5.8 years) [206]. Nonetheless, there are at present insufficient long-term data to demonstrate the safety of pituitary re-irradiation for recurrent disease, although the use of high precision techniques and fractionation should theoretically reduce late toxicity.

 

With the lack of consensus, variations in the management of pituitary recurrences are discussed in MDT meetings and decisions vary based on expertise and scope of practicing physicians. For example, in a survey study for Canadian neurosurgeons and radiation oncologists, it was observed that physicians newer to practice had a greater tendency to advocate for stereotactic radiosurgery (SRS) or re-resection (54.5% and 36.4%, respectively), as compared to older surgeons who showed a higher propensity (22.2%) to advocate for observation. The presence of cavernous sinus extension encouraged radiation oncologists to offer earlier radiotherapy sooner (61.4%), compared to 40% of neurosurgeons [207].

 

OUTLOOK

 

The techniques of pituitary radiotherapy have gradually evolved over a number of decades with apparent choice between different technologies. All technologies share the aim of concentrating the radiation dose to the tumor with minimal dose to surrounding tissue and the irradiation is given in one, few or many fractions. There has been a lack of randomized comparative studies comparing the techniques to date. Systematic review of case series reported in the literature assessing the efficacy and toxicity provides a reasonably objective assessment of the techniques. While prospective randomized trials would provide the best objective comparative information, the beliefs of practitioners in particular treatment modalities, vested interests in technologies, and general difficulty of conducting studies in diseases with such long natural history make such comparative trials an unlikely prospect. This is compounded by the fact that new radiotherapy technologies continue to be introduced into clinical practice without the need for establishing efficacy as demanded for new drugs. Therefore, controversy will persist with regard to the appropriate and optimal methods for treating pituitary adenomas using radiation, and that all of the treatment modalities described here will continue in clinical use for the foreseeable future despite systematic reviews suggesting that some of the techniques may be less effective and potentially more toxic.

 

Conformal techniques of fractionated pituitary radiotherapy are standard practice, with many centers able to offer the additional accuracy of higher precision radiotherapy previously termed stereotactic but currently part of mainstream high-precision RT. Successful application of high-precision treatment is highly dependent on expertise in accurate target definition using modern MR imaging, on the precision of the immobilization system based on an exhaustive quality assurance program, and on infrastructure particularly in the form of expertise of staff in complex techniques of treatment planning and delivery. It seems most likely that it is the available expertise at all levels of staff in a treatment center that is the principal determinant of the success of pituitary radiotherapy rather than the choice of equipment and the precise treatment technique that is used.

 

SUMMARY

 

Fractionated radiotherapy is an effective treatment for pituitary adenomas, able to achieve excellent disease control and normalization of hormone levels. While the overall safety profile of this treatment modality is favorable, it is not devoid of side effects and it should only be employed when the risks from the disease itself are considered to outweigh the risks from the treatment. The balance of risks should take into account not only the early consequences of the disease and treatment, measured in terms of disease control and immediate morbidity, but also the long-term effects, particularly in terms of the influence of treatment on survival and quality of life, both of which are less well defined.

 

Residual pituitary adenomas, most of which have an indolent natural history, pose little threat to function, unless they lie close to the optic apparatus, or unless they destructively invade adjacent structures, which is an uncommon event. The risks of residual adenoma are therefore often minimal, and in the absence of progression or hormone hypersecretion, there is currently little justification for adjuvant radiation, whether in the form of fractionated or single fraction treatment. However, a policy of postoperative surveillance does require a program of close monitoring, usually in the form of annual MR imaging, and proceeding to timely irradiation if necessary, and certainly well before the need for further surgery. The aim of radiation treatment is to arrest tumor growth without the risks of re-operation.

 

For functioning tumors radiation treatment is generally offered to patients with persistent hormone elevation that is not decreasing at the expected rate following previous intervention of surgery and medical therapy. This usually means persistent hormone elevation in patients with acromegaly, Cushing’s disease, and other functioning adenomas, regardless of how far the actual hormone level is from normal, as the aim in most cases is to achieve normalization. In patients with acromegaly treated with somatostatin analogues, the expense and inconvenience of protracted systemic treatment also warrants early radiation treatment to allow for the withdrawal of medical treatment. The alternative is to continue medical management indefinitely without radiotherapy. It is not clear at present which policy is associated with better long-term survival and quality of life, and this should ideally be the subject of a prospective randomized trial.

 

Current clinical practice is therefore to offer treatment to patients with progressive non-functioning (or functioning) pituitary adenomas considered to be a threat to function, and to patients with functioning pituitary adenomas with persistent hypersecretion. Fractionated radiotherapy, as high-precision IMRT (previously considered as SCRT/fSRT), is the current standard of care for patients requiring radiation treatment for pituitary adenoma. Single fraction radiosurgery can be considered to treat small adenomas away from critical structures in view of the significant risk of radiation-induced damage carried by a high single dose of radiation. Long-term follow-up data are needed to fully evaluate the clinical efficacy of single fraction radiosurgery in comparison with fractionated radiotherapy.

 

ACKNOWLEDGEMENTS

 

MK and NF would like to thank Dr Francesca Solda, Dr Liam Welsh, Dr Thankamma Ajithkumar and Professor Michael Brada who authored previous versions of this review. MK is funded by the NIHR Biomedical Research Centre at University College London Hospitals NHS Foundation Trust and University College London.

 

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Endocrine Testing Protocols: Hypothalamic Pituitary Adrenal Axis

ABSTRACT

 

Abnormalities in the hypothalamic pituitary adrenal (HPA) axis are identified by a careful analysis of both direct and non-stimulated measurements of the hormones as well as provocative tests.  Dynamic testing is useful to determine if elevated levels are suppressible and whether there is sufficient hormone reserve when low levels are measured under stimulation. A combination of all these analyses can distinguish between normal physiology and the consequences of clinical disease in the HPA axis.  While clinical suspicion drives the testing performed, arrival at the correct diagnosis by laboratory testing is crucial for cure of the patient.  Knowledge of the methodologies used in measuring cortisol and ACTH and associated hormones and binding proteins is essential for correct interpretation of the tests.  In this review we compare methodologies available, sensitivity and specificity of the various assays and volumes of sample needed. There are at least 7 different types of dexamethasone suppression testing and they are compared and described in detail. Confirmation of the anatomic source of the hormone is necessary. Petrosal sinus sampling and adrenal vein sampling are reviewed and the clinical indications for each discussed. Finally, once the endocrine diagnosis is reached based on endocrine testing, imaging studies are then reviewed which can confirm the endocrine diagnosis. An abnormality in the HPA axis is a laboratory diagnosis and radiologic imaging is reserved for the last step in the diagnosis of endocrine disease.

 

NONSTIMULATED HORMONE MEASUREMENTS

 

Overview

 

In evaluation of the hypothalamic pituitary adrenal (HPA) axis, static measurement of hormones is seldom useful due to the variable nature of cortisol and ACTH secretion in normal physiological states. In general, if one is suspicious of hypofunction of the HPA axis, then measurement of morning cortisol at 8 am when it is expected to be at its peaks is a good screening strategy. Depending on the result, this might need to be followed by dynamic testing to stimulate either adrenocorticotrophic hormone (ACTH) or cortisol for confirmatory purposes. On the other hand, if one is concerned about Cushing’s syndrome (CS), an overproduction of cortisol or ACTH, then measurement of cortisol should be performed late at night, when it is expected to be at its nadir. Alternatively, one could test cortisol’s response to suppression with dexamethasone.

 

The American Endocrine Society Clinical Guidelines recommend one of the following tests for the initial CS testing: at least two measurements of urinary-free cortisol (UFC), two measurements of late night salivary cortisol (LNSC), 1 mg overnight dexamethasone suppression test (DST) or a longer low-dose DST (1). Cortisol measurement (serum, UFC or salivary) is the end point for each recommended test.

 

Despite recent literature reports describing utility of direct salivary and urine cortisol measurements in CS diagnosis (2-4), most clinicians prefer provocative testing due to the variable nature of cortisol and ACTH secretion in normal physiological states. Cortisol is secreted under the direction of ACTH and follows a diurnal variation, with peak values at 08:00 h and a nadir at 22:00 h. In CS, diurnal variation is lost and PM cortisol level is inappropriately elevated. Superimposed on this diurnal pattern are 8-10 pulsatile peaks released during the course of a 24-hour period. Therefore, depending on the instance when blood is sampled, there can be significant variation in the absolute values of ACTH and serum cortisol. Due to this variability of cortisol and ACTH levels, it may be challenging to distinguish pituitary-dependent Cushing’s disease from pseudo-Cushing’s states. Cunningham et al conducted a study where blood was sampled and cortisol measured every 20 to 30 minutes for 24 hours. The group demonstrated that both circadian and pulse amplitudes of cortisol secretion were decreased in Cushing’s disease (5).

 

This section provides and overview of methodologies commonly used in clinical laboratories for direct determinations of cortisol and ACTH, regardless of whether they are a part of a provocative testing series or direct, non-stimulated hormone assessment.

 

Cortisol

 

Methods currently available for measuring serum cortisol levels include automated immunoassays and liquid chromatography-tandem mass spectrometry (LC-MS/MS).

 

CORTISOL IMMUNOASSAYS (TOTAL CORTISOL)

 

Cortisol immunoassays are widely available, have been in use for a long time, and automated methods provide high throughput with minimal manual sample manipulations. Virtually all immunoassay methods are based on the competitive binding principle, where cortisol from the patient sample and exogenous, labeled cortisol compete for the binding sites available on the anti-cortisol antibody. The major difference between the assays is in the label design and chemistry enabling antibody-antigen binding. All currently available cortisol methods have limit of detection below 1 µg/dL, providing sufficient sensitivity to support interpretation of CS dynamic testing results.

 

A widely recognized disadvantage of immunoassays is a potential of interferences from auto-, anti-animal or heterophilic antibodies. In addition, the older generations of cortisol assays had significant cross-reactivity with other steroids, such as 6-b-hydroxycortisol or prednisolone, due to the use of less specific polyclonal antibody in the assay formulation. However, the majority of current immunoassay methods have transitioned to a more specific monoclonal antibody format, minimizing or eliminating cross-reactivity with other steroids. It should also be noted that some immunoassay vendors use biotinylated antibodies in their assay design. In these instances, biotin may interfere with the assay, causing spuriously elevated cortisol measurement. The presence and magnitude of interference is vendor-specific and the potential of biotin interference should be checked with the laboratory that performs the testing. In general, none of the assays manufactured by Abbott use biotin in reagent formulation, while all assays manufactured by Roche do. The Roche cortisol assay should not be used to measure serum cortisol in a patient taking daily doses of biotin exceeding 5 mg, unless blood is obtained at least 8 hours following the last biotin ingestion.

 

LC-MS/MS CORTISOL ASSAYS

 

The LC-MS/MS assays utilize liquid chromatography to separate cortisol from other serum/plasma components and tandem mass spectrometry to detect and quantify compounds of interest. LC-MS/MS based methods offer superior analytical sensitivity and specificity over immunoassays.

 

Serum Free Cortisol

 

In conditions where CBG concentrations are affected, such as pregnancy or critical illness for example, total serum cortisol may not always reflect the true pituitary-adrenal status. In these cases, assessment of serum free cortisol is preferred. Free serum cortisol concentration are directly measured by separating free serum cortisol fraction using equilibrium dialysis (6) or ultrafiltration (7, 8) followed by cortisol determination, usually performed using LC-MS/MS method. Alternatively, free serum cortisol can be estimated by calculating the ratio of serum cortisol and CBG to obtain serum cortisol index (6).  Although not affected by CBG levels, free cortisol is also secreted in episodic fashion and thus not much more useful than random total serum cortisol levels in assessment of HPA axis functionality.

 

Urinary Free Cortisol

 

Cortisol is excreted in urine in an unbound (free) form and, like free serum cortisol is unaffected by fluctuations in CBG levels. Properly collected 24-hour urine specimens can be used to eliminate fluctuations that would affect serum cortisol levels, due to the pulsatile nature of its release. Therefore, measurement of UFC from 24 hour urine collections has become a valuable diagnostic tool for evaluation of adrenal cortical function and it is one of the first line tests recommended for CS diagnostic testing (1). In the unstressed patient, with normal renal function, elevation of UFC in 24-hour urine specimen is usually sufficient to diagnose CS. A normal result is strong evidence against that diagnosis. Although this test has long been used, its utility in CS diagnosis still remains somewhat controversial. Studies show wide variability in clinical utility of UFC for diagnosis of CS with clinical sensitivity ranging from 53% to over 90% and specificity ranging from 79% to 90% (2, 3, 9). These differences are due to differences in study design, cut-off, and methodology used. Furthermore, in a careful study of normal subjects de Boss Kuil et al found that urinary excretion of free cortisol can differ by as much as 50% between the two consecutive urine collections, while the creatinine values can differ by as much as five fold (10). Since the ratio of free cortisol/creatinine also varies considerably (range 1.0-3.7; median 1.3), intra-variation in urinary cortisol excretion could not be attributed to variation in creatinine excretion. In addition to biological variation, other factors include difficulty in over or under collection of urine. Given such wide discrepancies in reported clinical sensitivity and specificity of UFC measurements and significant intra-individual UFC variability, this test may not be an ideal choice for initial screening of CS.

 

Methodology used for UFC quantitation is the same as for serum cortisol. In terms of specimen collection, an 8:00 AM to the following day’s 8:00 AM collection is desirable. Samples should be refrigerated during collection and, while preservatives are not required, boric acid is usually acceptable. Quantitation of urine cortisol with a more sensitive and specific LC-MS/MS method is generally preferred over immunoassays. Typically, all the LC-MS/MS UFC assays involve a sample pretreatment with an organic solvent which removes the interfering substances. However, some UFC assays immunoassays either do not include this pretreatment step or offer it as an optional step to the user. As a result, UFC reference ranges vary widely between the assay manufacturers, methodologies, and different laboratories. To increase sensitivity, it is recommended that the upper limit of normal for any UFC assay be used as a positive test (5). It would be thus incorrect to make a diagnosis of adrenal insufficiency relying solely on 24-hour urine collections.

 

Salivary Cortisol

 

Late-night (23:00-24:00 h) salivary cortisol (LNSC) is one of the first line tests used to screen for CS. Most studies report high diagnostic sensitivity of this test (80-90%), but there are discrepancies in reported specificities (70-90%), resulting mostly from difference in methodologies and populations studied (2, 3, 11-13) Interestingly, mass spectrometry assays demonstrate high sensitivity, but low specificity (75%) for the diagnosis of CS (11). One potential explanation, as postulated by Raff, is that higher analytical specificity of mass spectrometry actually leads to lower diagnostic specificity, suggesting that cortisol metabolites and precursors picked up by immunoassays may be diagnostically relevant (14). Kannankeril et al recently reported that LNSC has excellent negative predictive value (99.8%) but poor positive predictive value (16.8%) for diagnosis of ACTH-dependent CS (12). Thus, a negative LNSC can be used to rule out ACTH-dependent CS, but complementary tests of adrenal function are needed to establish the diagnosis.

 

Salivary cortisol concentration is not dependent on CBG and could therefore be useful during an ACTH stimulation testing in patients with increased CBG concentrations due to increased estrogen or decreased plasma binding globulins due to critical illness.

 

Similar to UFC, the assay methodology remains the same as serum cortisol with the differences in specimen collection.

 

ACTH

 

ACTH measurements, while subject to the same circadian variability as cortisol (actually it is the variability of the ACTH that is directly responsible for the variability of the cortisol), are not subject to the effects of CBG. Values of ACTH > 100 pg/ml in the setting of possible adrenal insufficiency are usually suggestive of primary adrenal insufficiency, while values >500 pg/ml are diagnostic. Low concentrations of plasma ACTH are not diagnostic, except for the undetectable levels observed in patients with cortisol producing adrenal adenomas. Plasma ACTH concentration is also low in patients taking exogenous steroids.

 

Unlike widely available cortisol assays, the availability of clinical ACTH assays is limited. All currently available methods are immunoassays based on the “sandwich” principle, where two antibodies that recognize different ACTH epitopes are utilized. The first antibody, designated as capture antibody, detects one specific site on ACTH molecule and is used to pull the antigen from the patient’s plasma. The second antibody that detects a different ACTH epitope is then used to “sandwich” the antigen and generate a signal.

 

As is the case with any immunoassay, ACTH assays are susceptible to heterophilic antibody interferences. Several cases have been described in literature where aberrant, falsely elevated ACTH results were inconsistent with clinical picture and lead to unnecessary testing, misdiagnosis, and in some cases surgical interventions. These cases emphasize the importance of interaction between clinicians and the laboratory to identify any interference present and ensure that each patient is appropriately managed (15, 16). In addition, just as is the case with cortisol immunoassays, some vendors use biotinylated antibodies in the capture antibody design. Unlike cortisol, however, biotin interference may result in falsely decreased ACTH levels. The two most commonly used ACTH assays are manufactured by Siemens and Roche. Siemens ACTH assay is not affected by biotin, while the recommendation for Roche ACTH assay is not to use the test in patients ingesting >5 mg biotin daily, unless at least 8 hours had elapsed following the last biotin dose (cf. Roche Elecsys ACTH Package Insert V 12.0, 2020-11).

 

The preferred specimen for ACTH is EDTA plasma. ACTH is heat labile, and if not collected and preserved on ice, will lead to proteolysis, which can reduce the plasma concentration leading to falsely lower values.

 

Miscellaneous Non-Stimulated Measurements

 

CORTISOL BINDING GLOBULIN (CBG)

 

As mentioned earlier, the majority of cortisol (~92%) is bound to CBG, a serum protein. CBG levels increase in pregnancy and patients on oral contraceptives or supplemental estrogen. CBG is decreased in hyperinsulinemic states, nephrotic syndrome, starvation, severe illness, and chronic liver disease. This test is useful for the assessment of unexpected serum cortisol values. It is offered by large reference laboratories and uses a radioimmunoassay method.

 

11-DEOXYCORTISOL (COMPOUND S)

 

This is the immediate precursor of cortisol and is typically increased when ACTH is elevated or in 11 beta-hydroxylase deficiency. The method for 11-deoxycortisol measurement is now available by LC-MS/MS technology and is offered by most reference laboratories.

 

ANTI-ADRENAL ANTIBODIES

 

The measurement of anti-adrenal antibodies has been suggested to be useful in detecting early evidence of adrenal insufficiency, before cortisol values are decreased even in response to stimuli. The only test currently clinically available is a test that detects 21-hydroxylase autoantibodies, which are present in the common autoimmune form of Addison’s disease (17). This test is offered by major reference laboratories and is based on the radioimmunoassay format.

 

CORTICOTROPHIN RELEASING HORMONE (CRH)

 

Serum concentration of CRH is markedly elevated in pregnancy, presumably due to the production of CRH by the placenta. High levels are associated with high levels of CRH binding protein. Although mentioned as useful in the diagnosis of ectopic CRH syndromes, little data is available in this regard. CRH testing is not commonly done and we have not been able to find a commercial laboratory that is currently performing this test.

 

DYNAMIC TESTING

 

Glucocorticoid Deficiency

 

Adrenal insufficiency is a life-threatening disorder and prompt diagnosis is important because adequate hormonal replacement therapy can be lifesaving.

 

Despite that more than 35 years have elapsed since the initial description of the use of the insulin tolerance test (ITT) to diagnose adrenocortical deficiency (18), and more than 200 scientific publications in this area, clinicians today still argue as to which is the most sensitive and specific test to diagnose adrenocortical deficiency. The ITT is still regarded as the gold standard upon which to compare all other tests of HPA axis function. Unfortunately, this test has a considerable spectrum of intra-individual and inter-individual variation (19, 20). Therefore, when comparing other tests to the "gold standard", if the standard is not reliable, how can one determine the effectiveness of the other forms of testing? The problem lies in the ability of a single laboratory to know what the values are for their tests. Therefore, ranges from an ITT test response in normal subjects performed in one laboratory may not be normal for another laboratory. Taking this into account there are some general guidelines that are available for evaluating patients with suspected adrenal insufficiency.

 

PRIMARY ADRENAL INSUFFICIENCY

 

High Dose ACTH Stimulation Test

 

WHEN TO USE THIS TEST: Patients acutely ill in the hospital or clinic who present with signs and symptoms suggestive of primary adrenal insufficiency. Patients who are thermodynamically unstable should be resuscitated with crystalloids and given dexamethasone prior to testing if the diagnosis of primary adrenal insufficiency is being considered.

 

PROCEDURE: An intravenous (IV) line is placed 30 minutes before the test for rapid phlebotomy and to eliminate a temporary rise in cortisol associated with a needle stick. The IV line is to be kept open with 0.9% sodium chloride (NaCl) at a rate of 50 ml/hr. Blood is drawn at 0 min for ACTH (2 ml in a lavender top tube on ice) and cortisol (2 ml in a red top tube). Cosyntropin, 0.25 mg is administered as an IV bolus over 2 minutes. The cosyntropin comes as a lyophilized powder which should be reconstituted with 1 ml of 0.9% NaCl. Thirty min after the injection, blood is obtained from the IV line (2 ml) for cortisol. The same is repeated at 60 min (2 ml) for cortisol.

 

SPECIAL CONSIDERATIONS: The test can be performed at any time of the day. If the patient is receiving hydrocortisone or cortisone acetate, the medication should be held for at least 12 hours prior to testing (if possible). Although the test can be performed while the patient is receiving dexamethasone, there is some cross-reactivity in some assays and cortisol levels may not be accurate. Each laboratory should determine for itself, the effect of dexamethasone on their assay.

 

Patients with known sensitivity to cosyntropin or its preservatives should not have it administered. Oral estrogen use may result in elevation of the total serum cortisol level due to increased corticosteroid binding globulin (21). Patients with albumin <2.5 g/dL may also have a low cortisol level (21, 22).

 

CONTRAINDICATIONS: Hypersensitivity to cosyntropin or any component of the formulation.

 

WARNINGS / PRECAUTIONS: Use with caution in patients with pre-existing allergic disease or a history of allergic reactions to corticotropin. Class C in pregnancy.

 

ADVERSE REACTIONS 1% to 10%: Cardiovascular: Flushing. Central nervous system: Mild fever. Dermatologic: Pruritus. Gastrointestinal: Chronic pancreatitis. <1%: Hypersensitivity reactions

 

DRUG INTERACTIONS: Decreased effect: May decrease the effect of anticholinesterases in patients with myasthenia gravis; nondepolarizing neuromuscular blockers, phenytoin and barbiturates may decrease effect of cosyntropin

 

INTERPRETATION OF RESULTS: Baseline cortisol values <5 µg/dl and ACTH concentrations >100 pg/ml are usually diagnostic of primary adrenal insufficiency. The normal peak cortisol value post stimulation should be an increment no less than 7µg/dl. A peak stimulated cortisol value of >18 µg/dl at 30 min is considered normal. Since 37% of subjects had a peak response to cosyntropin at 30 min and 63% had a peak response at 60 min, both time points are analyzed in all patients and if either the 30 min or 60 min sample reaches the criteria as noted above, the test is considered normal (23).  However, there is some suggestion that new generation cortisol assays may have different cutoff values, but these have not been verified (24). 

 

Free cortisol, instead of total cortisol can be measured using a value of >1.2 µg/dl at 30 or 60 min as a normal result. This can be indicated in patient with albumin levels <2.5 g/dL or those with low cortisol binding globulin.

 

Serum aldosterone can be measured in 0 min, 30 min and 60 min blood samples as ACTH stimulation of the adrenal cortex will also stimulate aldosterone. It has been suggested that a normal aldosterone response to ACTH in the presence of a suboptimal cortisol response is diagnostic of secondary adrenal insufficiency (25).

 

Low dose ACTH stimulation Test

 

WHEN TO USE THIS TEST: Patients with subtle signs of adrenal insufficiency or patients who have been treated with glucocorticoids in whom determination of adrenal reserve is necessary. Patients who have autoimmune disease and may have early adrenocortical insufficiency may be best assessed with this test.

 

PROCEDURE: An intravenous line is placed 30 minutes before the test for rapid phlebotomy and to eliminate a temporary rise in cortisol associated with a needle stick. The IV line is to be kept open with 0.9% NaCl at a rate of 50 ml/hr. Blood is drawn at 0 min for ACTH (2 ml in a lavender top tube on ice) and cortisol (2 ml in a red top tube).

 

Cosyntropin, 1 µg is administered as an IV bolus over 2 minutes. The injection material was prepared according to the method of Dickstein as follows: The cosyntropin was diluted with 50 ml of sterile saline to a stock concentration of 5 µg/ml. Aliquots of 0.2 ml were added into sterile plastic tubes and kept at 4oC for a maximum of 4 months (26). Immediately prior to testing 0.8 ml of saline is added to the tube (final dilution 1 µg/ml) and 1 ml is injected into the patient. Thirty min after the injection blood is obtained from the IV line (2 ml) for cortisol. The same is repeated at 60 min (2 ml) for cortisol.

 

SPECIAL CONSIDERATIONS: Same as for high dose ACTH stimulation test, see above.

 

INTERPRETATION OF RESULTS: This test was originally developed to be more sensitive for diagnosing secondary adrenal insufficiency because it was more of a "physiologic" dose. It is much better at diagnosing secondary adrenal insufficiency than the high dose, although it is not at all recommended in acute or recent hypopituitarism when the intact adrenal glands can still respond normally to any dose of ACTH. Although probably not useful for the initial purpose of secondary adrenal insufficiency, it may be more sensitive at distinguishing milder forms of primary adrenal insufficiency (27). Furthermore, this low dose test was helpful in identifying mild adrenal suppression in asthmatic children being treated with inhaled steroids (28). As noted above, each laboratory should establish their normal values, however in general, a stimulated value at 30 or 60 min greater than 20 µg/dl would be considered normal.

 

A meta-analysis of 30 studies enrolling 1209 adults and 228 children with secondary adrenal insufficiency, evaluating the diagnostic accuracy of high and low dose ACTH stimulation concluded that they have similar diagnostic accuracy. They are both adequate to rule in, but not rule out, secondary adrenal insufficiency

 

SECONDARY ADRENAL INSUFFICIENCY (PITUITARY OR HYPOTHALAMIC)

 

Insulin Tolerance Testing (ITT)

 

WHEN TO USE THIS TEST: Patients in whom pituitary or hypothalamic disease may result in impaired corticotroph (or somatotroph) activity. Patients following pituitary surgery or pituitary radiation can be tested at any time, unlike the ACTH stimulation tests described above which are not useful in the acute setting. A random serum cortisol should be drawn prior to scheduling the test if the value is > 20 µg/dl, the test may not be necessary This test, can be performed in the outpatient clinic, however while relatively safe it requires a trained endocrine registered nurse to be present with the patient during the course of the test.

 

PROCEDURE: A 50 ml vial of 50% Dextrose should be at the patient's bedside in a syringe ready for injection before beginning the procedure.

 

An intravenous line is placed 30 minutes before the test for rapid phlebotomy, to eliminate a temporary rise in cortisol associated with a needle stick, and in order to have IV access for 50% Dextrose in the event of severe hypoglycemia. The IV line is to be kept open with 0.9% NaCl at a rate of 50 ml/hr. Blood is drawn at 0' for cortisol (2 ml in a red top tube) and glucose (1 ml in a gray top tube). Blood glucose is also checked at the bedside with a glucose monitor.

 

Regular (short acting) insulin is administered as an IV bolus at a dose of 0.1 units/kg. Blood is sampled for cortisol and glucose as noted above at 10min, 15min, 30min, 45min, 60min, 90min and 120min. A bedside nurse should monitor the blood glucose more frequently if glucose drops below 60 mg/dl on the glucometer or if the patient complains of neuroglycopenic symptoms, such as fatigue, diaphoresis, hunger, lightheadedness, or nausea. The test should continue until the blood glucose concentration drops below 40 mg/dl.

 

In patients with diabetes on insulin, consideration should be given that they may be insulin resistant. In which case, larger doses of insulin may be given. We usually begin with a single bolus of 0.1 U/kg and then re-bolus with insulin depending on the response to the initial dose (either give the same dose again if there was some response but insufficient, or double the dose if there was only minimal response to blood glucose, or give half the dose if the hypoglycemic response was close to the desired goal). This can be repeated several times until adequate hypoglycemia is reached.

 

Once the response goal of a glucose < 40 mg/dl is reached, patients can be fed a meal such as crackers and orange juice. Blood glucose should be checked at 5min, 10min and 15min post feeding. If there is no increase in glucose or a clinical response within 5min, intravenous glucose should be administered. If no response, then a repeat bolus of glucose is suggested. If no response or IV access is lost, glucagon 1 mg intramuscular can be given.

 

SPECIAL CONSIDERATIONS: The test can be performed at any time of the day, although due to the need for patients to be fasting it is most conveniently done in the morning. If the patient is receiving hydrocortisone or cortisone acetate, the medication should be held for at least 12 hours prior to testing (if possible). Unlike the ACTH stimulation tests, the ITT cannot be performed while the patient is receiving dexamethasone, due to suppression of the hypothalamic pathways necessary to respond to hypoglycemia.

 

In general ITT is not recommended in patients with uncontrolled seizure disorder or significant coronary artery disease.

 

In order to determine if the level of dysfunction is at the hypothalamus or at the pituitary this test is sometimes used in addition to the CRH stimulation test. When the ITT fails to stimulate cortisol, but the CRH test does stimulate it is likely that the patient is having hypothalamic dysfunction.

 

INTERPRETATION OF RESULTS: Serum cortisol should increase within 30 min of the hypoglycemic response to > 20 µg/dl. If the serum cortisol at baseline is 18 ug/dl the test may not be diagnostic. If the baseline serum cortisol is higher than 19 µg, adrenal insufficiency is unlikely. Although the response of cortisol is more reproducible than that of growth hormone in the ITT, intra-subject differences have been reported (20, 30).

 

Metyrapone Testing

 

WHEN TO USE THIS TEST: This test is perhaps the most sensitive to determine whether the HPA axis is intact. Although metyrapone is not generally available from your neighborhood pharmacy, it can be obtained by calling Novartis Pharmaceutical Corp. at 1-800-988-7768 on weekdays. Metyrapone blocks 11-b hydroxylase and results in the inhibition of conversion of 11-deoxycortisol to cortisol. Serum levels of cortisol decrease and concentration of 11-deoxycortisol increases, however 11-deoxycortisol does not down regulate ACTH. Therefore, in a normally functioning HPA axis there is an increase in 11-deoxycortisol. This metabolite can be directly measured in the serum or measured in the urine as 17-OH corticosteroids. This test can help differentiate primary adrenal deficiency from ACTH deficiency. It has a similar diagnostic performance to the ITT and it’s a potential alternative when there is a contraindication to ITT.

 

PROCEDURE: For assessment of adrenal or pituitary insufficiency the test can be performed as an overnight test. Metyrapone is given orally (30 mg/kg body weight, or 2 grams for <70 kg, 2.5 grams for 70 to 90 kg, and 3 grams for >90 kg body weight) at midnight with a glass of milk or a small snack (24). Serum 11-deoxycortisol and cortisol are measured at 8 AM the next morning; it is also recommended to measure plasma ACTH levels (31).

 

SPECIAL CONSIDERATIONS: The concurrent use of glucocorticoids will interfere with the test. Any medications that the patient is taking which increase the P450 enzymes will increase the metabolism and clearance of metyrapone (such as rifampin, phenobarbital, and phenytoin) (32). Similarly, hypothyroidism or hyperthyroidism will affect clearance of metyrapone and the adrenal responsiveness. Therefore, thyroid function tests should be measured prior to performing this test. Measurement of 11-deoxycortisol, like cortisol itself is dependent on CBG and drugs such as estrogens and oral contraceptives will falsely increase the concentrations of 11-deoxycortisol (33).

 

PREGNANCY IMPLICATIONS - Use during pregnancy only if clearly needed. Subnormal response may occur in pregnant women and the fetal pituitary may be affected.

 

LACTATION - Excretion in breast milk unknown/use caution

 

ADVERSE REACTIONS - Frequency not defined. Central nervous system: Headache, dizziness, sedation. Dermatologic: Allergic rash. Gastrointestinal: Nausea, vomiting, abdominal discomfort or pain. Hematologic: Rarely, decreased white blood cell count or bone marrow suppression.

 

INTERPRETATION OF RESULTS: 8 AM serum 11-deoxycortisol concentrations should be >7 µg/dL with serum cortisol less than 5 µg/dL (138 nmol/L), confirming adequate metyrapone blockade. The plasma ACTH concentration at 8 AM should exceed 75 pg/mL (17 pmol/L), confirming that any increases in serum 11-deoxycortisol concentrations are ACTH-dependent, thereby separating primary from secondary adrenal insufficiency (34, 35).

 

Glucocorticoid Excess

 

DEXAMETHASONE SUPPRESSION TEST

 

Measurement of endogenous cortisol production in response to exogenous dexamethasone suppression was the first provocative test and still remains among the most useful tests used for the evaluation of excess cortisol. Dexamethasone, due to its high affinity to the glucocorticoid receptor is a potent inhibitor of ACTH synthesis and release. In addition, most of modern immunoassays for cortisol (both urine and serum) utilize an antibody that does not cross-react with dexamethasone. Therefore, the combination of being able to use relatively low doses and at the same time not interfere with the measurement of cortisol make dexamethasone suppression useful for establishing the presence of a perturbation in the pituitary - adrenal axis and for diagnosing the etiology of hypercortisolism.

 

At least five different tests have been described using dexamethasone, which differ in the dose and timing of dexamethasone treatment and differ in whether there is measurement of urine or serum cortisol or 17-OH-corticostseroids (Table 1). Although the endocrine basis for the tests are in general the same, none are perfect. Confirming the diagnosis of patients with suspected hypercortisolism requires several tests for accurate diagnosis.

 

TABLE 1. Various Dexamethasone Suppression Tests

Dex Supp Test

Dex Dose

Time of Admin

Normal Response

Sens/Spec

Low dose Oral/Night

1 mg

@23:00 x1

<1.8 mcg/dl or <5 mcg/dl

87% / 100%

High dose Oral/Night

8 mg

@23:00 x 1

<50% basal

92% / 100%

Low Dose 2day

0.5 mg

q 6h x 2 days

<10 µg/24h in urine

74-98%/69-100%

High Dose 2 day

2.0 mg

q 6h x 2 days

<50% basal

79% / 100%

Very High dose

8 mg

q 6h x 1 day

<50% basal

74% / 100%

Note: To assure patient compliance and determine whether there is abnormal metabolism of the dexamethasone, serum levels of dexamethasone can be measured. However, this is not a common diagnostic test. Testing can be done by specialized laboratories, such as Esoterix inc. CA. The principle of the assay is RIA after chromatographic sample separation and requires 1 ml of serum sample.

 

All these tests require significant patient participation as the patients are required to self-administer the dexamethasone at inconvenient hours of the day (11PM) or up to 4 times a day. Sampling requires either collection of urine for 24 hours or coming to the physician's office at 8 AM for multiple blood sampling. Drugs that induce hepatic cytochrome P-450 enzymes, such as barbiturates, phenytoin, rifampin, and aminoglutethimide, increase the metabolism of dexamethasone and other steroids. Measurement of serum dexamethasone a few hours after the last dose will help determine if there is abnormal metabolism. All these caveats are in addition to the other problems associated with measurement of cortisol as noted above, including the variable diurnal variation as well as interference with concurrent administration of glucocorticoids, estrogen, or other medications that increase cortisol binding globulin.

 

A popular screening test for confirming hypercortisolism is the overnight 1 mg dexamethasone. A single dose of 1 mg is administered (or 0.3 mg/Kg for children (34) at 11PM and blood is obtained by 8 AM the following morning. The dexamethasone dose is given prior to the diurnal rise in endogenous ACTH release and therefore suppresses the early AM cortisol. A normal response would be a serum cortisol concentration of <1.8 mcg/dl, alternatively a cut point of < 5 µg/dl can be used which will yield more specificity with less sensitivity. If cortisol is >10 µg/dl the likelihood of hypercortisolism is high. The other dexamethasone suppression tests are reviewed in Table VIII. Patients with corticotroph macroadenomas or very active tumors, may have urine free cortisol in excess of 1000 µg/dl which will require higher doses of dexamethasone to confirm suppressibility and/or rule out ectopic ACTH production (36).

 

The two- day low dose dexamethasone suppression test can be used to differentiate Cushing’s syndrome from pseudo-Cushing’s which can present with many of the signs and symptoms associated with hypercortisolism in the setting of other clinical conditions such as depression, alcoholism, PCOS, obesity, and uncontrolled diabetes (37, 38). Dexamethasone 0.5 mg is delivered orally Q6 hours for 48 hours. Serum cortisol is measured 2 hours after the last dose and a cutoff level of <1.4 µg/dl is consistent with pseudo-Cushing’s. Measurement of 24 hour urine excretion of 17-hydroxycorticosteroid and creatinine during the administration of dexamethasone starting at 1200h, has also been suggested with a cut point of 11 umol/day or higher considered positive for Cushing’s syndrome (39). This test however, can misclassify as many as 15% of patients with Cushing’s syndrome and up to 15% of patients with pseudo Cushing’s.

 

The overnight high dose dexamethasone suppression test can help differentiate Cushing’s disease from ectopic ACTH syndrome in patients with ACTH-dependent Cushing’s syndrome. The basis for this differentiation is the fact that ACTH secretion in Cushing’s disease is only relatively resistant to glucocorticoid negative feedback inhibition. Cortisol levels will not suppress normally with overnight 1 mg but will suppress with a higher dose of 8 mg of dexamethasone. Serum cortisol concentration at 8 AM is <5 µg/dL in most patients with Cushing’s disease and is usually undetectable in normal individuals. A more than 50% decrease in cortisol on the day after taking 8 mg dexamethasone supports a diagnosis of Cushing’s disease over ectopic ACTH production. In patients with non-ACTH dependent hypercortisolism, a lack of suppression of cortisol by more than 50% with a low normal ACTH level (5-20 pg/ml) suggests an adrenal etiology.

 

CRH STIMULATION TEST

 

WHEN TO USE THIS TEST: This test is one of the most sensitive to determine if there is an abnormality in the HPA axis and for diagnosing the etiology of hypercortisolism in ACTH dependent Cushing’s.  Although CRH is expensive ($300), when one considers the cost of multiple urine collections and analyses of cortisol as well as the cost of a single MRI of the pituitary (which generally exceeds $1500), CRH is at least cost effective when one considers the overall expense in the evaluation of these patients.

 

PROCEDURE: An intravenous line is placed 30 min before the test for rapid phlebotomy and to eliminate a temporary rise in cortisol associated with a needle stick. Blood is drawn at -15' and 0' for cortisol and ACTH (2 ml in a lavender top tube on ice). CRH is then injected IV at a dose of 1 µg/Kg up to a maximum of 200 µg. Blood is obtained at 15, 30, 60, 90, 120, 180 and 210 min for cortisol and ACTH (2 ml in a lavender top tube on ice).

 

SPECIAL CONSIDERATIONS: The test can be performed at any time of the day, although the initial studies describing the test have been done in the morning.

 

Side effects: The patient may experience slight nausea, metallic taste, urgency to urinate, a change in blood pressure (either increase or decrease), a change in heart rate, headaches, abdominal discomfort, facial flushing, and lightheadedness. These side effects are mild and last for only few minutes. Category C in pregnancy.

 

INTERPRETATION OF RESULTS: The mean ACTH concentrations at 15 and 30 min after CRH should increase by at least 35% above the mean basal value at -15 and 0 min in patients with Cushing's disease, but not in patients with ectopic ACTH secretion. This measure gave the best sensitivity (93%) and specificity (100%) (40, 41).  The best cortisol criterion was a mean increase at 30 and 45 min of 20% or more above mean basal values, which gave a sensitivity of 91% and a specificity of 88%. It should be noted that the criterion for Cushing's disease is based on the presence of hypercortisolism. The CRH test will not adequately differentiate subjects with pseudo-Cushing’s and those with true pituitary dependent Cushing's disease.

 

CRH TEST WITH DEXAMETHSONE

 

WHEN TO USE THIS TEST: Several investigators have found that modifications of the CRH stimulation test can increase further the sensitivity and specificity in the diagnosis of the etiology of Cushing's disease. While the simultaneous use of vasopressin can augment the response to CRH, dexamethasone can be used to suppress all but pathologic responses to CRH stimulation [33]. Without dexamethasone the sensitivity and specificity of the CRH test is 65 and 100%, respectively, while with dexamethasone the CRH test is 100% sensitive and specific. This test is also particularly useful to differentiate true Cushing’s from pseudo-Cushing’s state.

 

PROCEDURE: Dexamethasone, 0.5 mg is self-administered orally by the patient every 6 hours for 2 days, at 6 AM, 12 Noon, 6 PM and midnight. On the morning of the 3rd day an additional dose of dexamethasone is given at 6 AM. The patient arrives at the testing center by 8 AM and an intravenous line is placed 30 minutes before the test for rapid phlebotomy and to eliminate a temporary rise in cortisol associated with a needle stick. Blood is drawn at -15' and 0' for cortisol and ACTH (2 ml in a lavender top tube on ice). CRH is then injected IV at a dose of 1 µg/Kg up to a maximum of 200 µg. Blood is obtained at 15, 30 60, 90 120, 180 and 210 min for cortisol and ACTH (2 ml in a lavender top tube on ice).

 

SPECIAL CONSIDERATIONS: The test can be performed at any time of the day, although it is usually done in the morning.

 

Side effects that the patient may experience are: slight nausea, metallic taste, urgency to urinate, a change in blood pressure (either increase or decrease), a change in heart rate, headaches, abdominal discomfort, facial flushing, and lightheadedness. These side effects are mild and last for only few minutes.

 

Similar to the dexamethasone suppression test, the results should be interpreted with caution in patients taking estrogen therapy as they can present with falsely elevated cortisol levels due to an increase of cortisol-binding globulin. Drugs such as phenytoin, phenobarbitone, carbamazepine, rifampicin and alcohol induce hepatic enzymatic clearance of dexamethasone, mediated through CYP 3A4, thereby reducing the plasma concentration and may be associated with false positive results (42).

 

INTERPRETATION OF RESULTS: A normal response would be a plasma cortisol concentration less than 1.3 µg/dl measured 15 minutes after the administration of CRH.  Values of cortisol greater than 1.3 µg/dl correctly identified all cases of Cushing's syndrome and all cases of pseudo-Cushing's states (100% specificity, sensitivity, and diagnostic accuracy). While this is a general recommendation, each laboratory should confirm based on the sensitivity of the respective cortisol assay. Furthermore, it is important to confirm the serum level of dexamethasone at the time of the blood draw to assure patient compliance with the dexamethasone regimen.  Patients with ectopic ACTH production will have nonsuppressed cortisol and ACTH levels that are not stimulated by CRH.

 

DDAVP STIMULATION TEST

 

WHEN TO USE THIS TEST: This test can be used as part of the workup of ACTH dependent hypercortisolism. It can be used in addition to the CRH stimulation test as studies have shown that the combination of these two tests performs better than either of the tests separately. It can also be performed in lieu to the CRH test in situations in which CRH is not available. The aberrant expression of vasopressin V2 receptor in pituitary ACTH-secreting adenomas is the rationale for the use of the desmopressin test to differentiate corticotroph adenomas (which should respond to desmopressin injection) from ectopic ACTH secreting tumors or pseudo Cushing’s (which should not respond)(43-45).

 

PROCEDURE: An intravenous line is placed 30 minutes before the test for rapid phlebotomy and to eliminate a temporary rise in cortisol associated with a needle stick. Blood is drawn at -15' and 0' for cortisol and ACTH (2 ml in a lavender top tube on ice). DDAVP is then injected IV at a dose of 5 to 10 ug. Blood is obtained at 15, 30, 60, 90, 120, 180 and 210 minutes for cortisol and ACTH (2 ml in a lavender top tube on ice) (45).

 

INTERPRETATION OF RESULTS: No definitive cutoff values have been standardized for the interpretation of this test. The published established criteria for this test have generally been based on studies with small series of subjects. Malerbi et al. proposed a cortisol increase over baseline of 12% to be consistent with diagnosis of Cushing’s disease (46). An absolute ACTH increase over baseline equal or greater than 6 pmol/L yielded higher sensitivity and specificity to differentiate Cushing’s disease from pseudo Cushing’s in a different study. Alternatively the criteria used for the CRH stimulation test can be used in  the interpretation of the results (47).

 

INFERIOR PETROSAL SINUS SAMPLING (IPSS) WITH CRH STIMULATION

 

WHEN TO USE THIS TEST: Once the diagnosis of ACTH dependent Cushing's syndrome has been made based on endocrinologic testing, the next step in the evaluation of such patients should be an MRI of the pituitary to confirm the presence of a pituitary mass. Unfortunately, MRI imaging of the pituitary as a primary diagnostic tool is distinctly unhelpful due to the fact that 10% of all normal individuals may have slight abnormalities of their pituitary and that in many subjects with Cushing's disease, the tumor may be too small to be imaged with MRI scans. However, subjecting a patient to surgical pituitary exploration in the absence of a demonstrable mass is likely to result in an unsuccessful surgery. Furthermore, if previous dexamethasone and/or CRH testing is equivocal, then IPSS should be performed to further confirm the pituitary as the source of the ACTH (34). Although this test is less reliable in lateralizing the ACTH source (i.e., left versus right), than it is in confirming that the ACTH is central in origin, it can rule out ectopic ACTH production by a tumor (although ectopic CRH secreting tumors would be difficult to distinguish from true Cushings' disease based on IPSS). Simultaneous measurement of prolactin in the central samples can normalize the data if there is any difference in the location of the catheters (48).

 

It is recommended that active hypercortisolism is confirmed by measuring a 24-hour UFC or overnight UFC the day preceding IPSS. Misleading results have been reported when this test is performed “out of cycle” in patients with cyclical Cushing’s.

 

PROCEDURE: This test is done in conjunction with a skilled interventional neuroradiologist. It is important that the endocrinologist is personally present in the room during the procedure so that assurance can be made that the proper blood tests were drawn at the specified times. The patient is brought to the angiogram suite without sedation. A large bore IV line is placed in an antecubital fossa (to be certain there is access to peripheral blood sampling and CRH injection). Catheters (5 French) are placed in the femoral veins and threaded under fluoroscopic guidance to the inferior petrosal sinus. Injection of IV contrast confirms proper placement of the catheters.

 

Patients are on constant, pulse, blood pressure and oxygenation monitors during the course of the procedure. Test tubes are prechilled in ice and labeled so that during the rapid sampling period, blood can be placed in the tubes without delay.

 

It is recommended to routinely obtain 4 baseline measurements at -15, -10, -5 and at 0 minutes. This allows for practice allowing proper coordination between the radiologists drawing blood from the IPSS and the individual drawing blood from the brachial vein. Appropriate amounts of blood should be removed to discard the dead space of the catheter (this varies depending on the size of the catheter used). 2 ml of blood is obtained in lavender top vacutainer tubes on ice for measurement of cortisol (on peripheral samples); ACTH and prolactin (on central samples).

 

At 0' CRH is then injected as described above for the peripheral CRH test. Alternatively, a combination of CRH and 10ug of desmopressin can be used, especially if the patient has had a negative response to a prior CRH test. If CRH is not available, IPSS can also be performed with desmopressin alone per the protocol described above. Blood is then sampled from both central and peripheral lines at 2', 5' 10' and 15'. After the 15' time point and right before the IPSS catheters are removed, repeat fluoroscopic localization of the catheters should be performed to confirm that there was no displacement during the sampling. However, sampling on peripheral blood may continue as described in the CRH test discussed above.

 

SPECIAL CONSIDERATIONS: The test can be performed at any time of the day, although it is usually done in the morning.

 

Side effects that the patient may experience are: slight nausea, metallic taste, urgency to urinate, a change in blood pressure (either increase or decrease), a change in heart rate, headaches, abdominal discomfort, facial flushing, and lightheadedness. These side effects are mild and last for only few minutes.

 

Patients greater than 300 pounds in weight may not be able to be supported by the standard fluoroscopic table. Furthermore, such large patients may have an abdominal pannus that precludes reasonable access to the femoral veins. In such instances the IPSS can be performed via catheters placed in the antecubital vein with the patient immobilized in the sitting position.

 

Strokes have been reported in the literature as a potential complication (36). To minimize this possibility, it is recommended that the catheters remain in the petrosal sinus for no more than 30 min.

 

Freeze/thawing can decrease the ACTH concentration (see above); therefore, we recommend that the samples be brought to the endocrine lab and analyzed within 24 hours with the plasma separated and kept on ice during this time. If the analysis is not possible within 24 hours, the samples should be aliquoted and frozen to minimize the amount of freeze/thawing.

 

INTERPRETATION OF RESULTS: Plasma ACTH values are normalized to the prolactin value in order to correct for possible different localization of the catheters, or movement of the catheters during the study. The post CRH ACTH/Prolactin value of the central catheters should be >2.1 fold the ACTH/Prolactin value of the peripheral sample. In most cases of pituitary dependent Cushing’s, the increase is > 5.0-fold. A central to peripheral ACTH gradient higher or equal to 2 before CRH administration or higher or equal to 3, 10 min after CRH infusion is considered diagnostic of a pituitary source of ACTH (Cushing's disease). Lateralization would mean that the ratio of the left to right side is >2.0. Frequently the ratio criteria can be met without the need for CRH stimulation, however, the diagnostic accuracy increases from 86% to 90% with CRH (37).

 

The workup of ACTH dependent Cushing’s to differentiate Cushing’s disease from ectopic ACTH source can be quite challenging and often times requires combination of different dynamic testing in addition to imaging that often ultimately led to costly and invasive diagnostic procedures such as IPSS to be able to establish an accurate diagnosis. A retrospective study involving 167 patients with Cushing’s disease and 27 patients with ectopic Cushing’s found that using thresholds of a cortisol increase >17% with an ACTH increase >37% during CRH test and a cortisol increase >18% with an ACTH increase >33% during desmopressin test, the combination of both tests gave 73% sensitivity and 98% PPV of Cushing’s disease. The PPV was 100% in patients with positive response to both tests, with a negative pituitary MRI and whole-body CT scan. The NPV was 100% in patients with negative response to both tests, with negative pituitary MRI and positive whole body CT scan. This combination of dynamic tests with imaging studies is proposed as an accurate, cost-effective diagnostic strategy for the workup of ACTH depended Cushing’s that might minimize the need for IPSS which can be invasive, costly and unavailable in all institutions (43)

 

ADRENAL VEIN SAMPLING

 

WHEN TO USE THIS TEST: Patients diagnosed with ACTH independent Cushing’s and found to have bilateral adrenal tumors on imaging pose a particular challenge to the clinician. The differential diagnosis in these cases includes unilateral cortisol secreting adenoma (or carcinoma) with contralateral non-functioning cortical adenoma, bilateral cortisol secreting adenomas, macronodular adrenal hyperplasia, and primary pigmented nodular adrenocortical disease. Adrenal vein sampling measuring cortisol can be very helpful in this scenario and give valuable information to elucidate the proper diagnosis and guide therapy.

 

PROCEDURE: This test is done in conjunction with a skilled interventional radiologist under sedation. The procedure is usually performed early morning after an overnight fast on the second day of either a low dose (0.5 mg orally every 6 hours) or high dose (2 mg orally every 6 hours) of dexamethasone administration. This eliminates the probability of endogenous ACTH secretion causing interference with the interpretation of autonomous adrenal gland cortisol secretion. The adrenal veins can be catheterized by the percutaneous femoral vein approach, the position of the catheter tip should be verified by venogram. Concentrations of cortisol and aldosterone should be measured in blood obtained from both adrenal veins and the external iliac vein (for the detection of peripheral venous concentrations) (49).

 

SPECIAL CONSIDERATIONS: Potential complications include thrombosis with subsequent infarction or hemorrhage adrenal insufficiency and hypertensive crisis, however these are rare (48).

 

The aldosterone concentrations are usually much higher on the right adrenal vein compared to the left, this is presumably due to the anatomy differences and the catheter proximity to the right adrenal medulla. For this reason, although plasma epinephrine is measured to confirm success of adrenal vein catheterization, it cannot be used to correct for blood sample dilution between the 2 adrenal veins. There have been few case reports in which aldosterone has been used for side-to-side dilution differences, however whether it can be used for this purpose remains unclear (49, 50).

 

INTERPRETATION: Catheterization of each adrenal vein can be considered successful if plasma aldosterone concentration in the adrenal vein exceeds peripheral venous concentration by more than 100 pg/ml. An adrenal-to-peripheral venous cortisol gradient greater than 6.5 can be considered consistent with a cortisol secreting adenoma. Lateralization can be determined by measuring the side-to-side cortisol gradient (high-side to low-side). A ration of 2.3 or greater is consistent with autonomous cortical secretion from predominately 1 adrenal gland (49).

 

IMAGING STUDIES IN THE HPA AXIS EVALUATION

 

The evaluation of the HPA axis function should always be approached through biochemical measurements. With few exceptions, imaging studies provide no information about hormonal function but can be very useful for the localization of tumors or lesions. Once a biochemical diagnosis of either deficiency or excess of glucocorticoid production has been established, imaging studies can complement and assists the hormonal evaluation, providing valuable information about etiology, prognosis, and management.

 

Pituitary Imaging

 

In the vast majority of cases of ACTH dependent Cushing’s syndrome (CS), the source of ACTH is in the pituitary (Cushing’s Disease), so performing imaging studies of the pituitary gland in this scenario to try to localize a tumor is appropriate. However given the high incidence of non-functioning pituitary adenomas in the general population (up to 10%) (51) and the increasing sensitivity of the high resolution imaging modalities available that can lead to false positive results, it is important to perform a thorough dynamic testing evaluation of each case and consider inferior petrosal sinus sampling if appropriate (see section above), before committing a patient to pituitary surgery. Adrenocorticotropic pituitary tumors represent about 10% of all pituitary tumors (52) and  ACTH-secreting adenomas are most commonly microadenomas (<1cm). In cases of macroadenoma, assessment of extrasellar extension including chiasmatic compression and cavernous sinus involvement is imperative (53).

 

The other scenario in which pituitary imaging is indicated and can be useful in the evaluation of the HPA axis function, is in patients diagnosed with secondary adrenal insufficiency who have no history of recent exogenous glucocorticoid exposure or any other clear explanation for the clinical presentation. In these cases, a mass lesion disrupting the HPA function should be suspected, especially if the patient presents with deficiencies of other pituitary hormones and/or elevated prolactin, as isolated adrenal insufficiency from a non-functioning tumor affecting the pituitary is very rare.

 

PITUITARY MRI

 

Magnetic resonance imaging (MRI) is the mainstay of pituitary assessment. MRI is more sensitive than computed tomography (CT) in detecting corticotroph adenomas, but still detects only about 50% of these tumors (54) and has a false positive rate of 12-19% (55, 56)]. Standard pituitary imaging protocols typically include thin-section (2 or 3 mm) of T1-weighted (w) spin echo sequences (SE) performed both in coronal and sagittal planes through the pituitary fossa, which are repeated after administration of intravenous gadolinium contrast medium, associated with a T2-weighted sequence in the coronal plane (57, 58). High spatial detail can be achieved by using thin slices, a fine matrix size and a small field of view focused on the pituitary (58). The classic MR features of a corticotroph adenoma include a less than 1 cm focal area of lesser enhancement on T1-w images following contrast administration, hyperintense or hypointense on T2-w images as compared with the normal pituitary gland, remodeling of the pituitary sella floor and deformity of the gland contour (59). Acquiring dynamic sequences in the first 1-2 minutes after contrast injection can increase the sensitivity (60), but this technique has not been unequivocally demonstrated to improve the usefulness of MR in Cushing’s (61). The use of three-dimensional (3D) spoiled gradient recalled acquisition in the steady state (SPGR) sequence allows for superior soft tissue contrast compared to conventional spin echo sequences, this technique can be further optimized with thin-slice imaging (<1mm) (58).  Compared to T1-w SE sequence, SPGR has been reported to increase sensitivity but also has a higher false positive rate (62, 63).

 

PITUITARY CT SCAN

 

Pituitary computed tomography (CT) scanning is less sensitive than MRI for the detection of pituitary adenomas (64)and it is usually reserved for those patients who cannot safely undergo brain MRI. Acquisition of 1 mm (or less) axial sections through the pituitary fossa with coronal reconstructions can be helpful in the assessment of macroadenomas (57). It is also very helpful preoperatively in patients planned for transsphenoidal pituitary surgery to delineate the bony anatomy (65)

 

Adrenal Gland Imaging

 

There are a couple of scenarios in which adrenal gland imaging plays a role in the evaluation of the HPA axis. It is indicated and particularly important in the evaluation of patients diagnosed with ACTH independent CS, which is most commonly caused by adrenocortical adenomas or carcinomas and less frequently bilateral micronodular and macronodular hyperplasia. It can also be considered in cases of primary adrenal insufficiency. Tumors in the adrenal are fairly common in humans, they have been found to be present in 3% of autopsies performed in persons older than 50 years of age (66) and have been reported to be incidentally discovered in up to 5% of cross-sectional abdominal imaging carried out for unrelated problems (67). Most of these incidentally found adrenal tumors are nonfunctioning, 10 to 15% secrete excess amounts of hormones (68) of these, adrenocortical tumors are the most common. On the basis of imaging characteristics alone, no distinction can be made between a benign hyperfunctioning and a non-functioning adenoma, and this can only be differentiated based on clinical and biochemical diagnosis. Adrenal carcinoma represents <10% of adrenal tumors, 30 to 40% of these are hyperfunctioning in adults (69).  There are multiple important imaging characteristics that can help differentiate benign adrenal adenomas from pheochromocytomas, adrenocortical carcinomas and metastasis, like percentage of lipid content, tumor size, homogeneity, border regularity, presence of calcifications, invasion of surrounding tissue, and lymph node enlargements (Table 2).

 

ADRENAL CT SCAN

 

Unenhanced thin- section CT scan followed by contrast-enhanced examination is the cornerstone of imaging of adrenal tumors. Unenhanced CT is important to provide density measurements of lesions (70). The rich intracytoplasmic fat in adenomas results in a low attenuation on nonenhanced CT. The Hounsfield (HU) scale is a semiquantitative method to measure radiograph attenuation. If an adrenal mass measures <10 HU on unenhanced CT, the likelihood that it is a benign adenoma is nearly 100% (71).  However up to 30% of benign adenomas might not contain large amounts of lipid and present with higher HU on nonenhanced CT scan. This is when measuring the contrast washout on delayed images is very useful. Ten minutes after the administration of contrast, an absolute medium washout of more than 50% has been reported to be close to a 100% sensitive and specific for benign adenoma (72). Non-adenomas include metastases, pheochromocytomas and carcinomas.

 

Adrenal carcinomas usually appear as a unilateral mass, >4 cm in size with an inhomogeneous appearance due to necrosis, hemorrhage, fibrosis, and calcification. Careful assessment of the draining venous structures is essential on imaging, together with identification of direct infiltration of adjacent viscera (57).

 

ADRENAL MRI

 

When lesions cannot be characterized adequately with CT, MRI evaluation (with T1 and T2-weighted sequences, chemical shift and fat-suppression refinements) can be sought. Adrenal adenomas usually show low homogeneous signal on T1-weighted images and a signal intensity equivalent or higher than the liver on T2-weighted images. Chemical shift imaging will readily identify the lipid rich adenomas with signal loss on the out-of-phase sequences (73). This loss of signal can be measured using the adreno-splenic-ratio (ASR) and the signal intensity index (SII). An ASR ratio of <70% has been shown to be highly specific for adenomas and has a 78% sensitivity. Using the SII, a minimum of 5% signal loss characterizes an adrenal adenoma with accuracy of 100% [61]. MRI can also be particularly useful to evaluate for local and distant invasion of adrenocortical carcinomas.

 

Primary pigmented nodular adrenocortical disease is a rare cause of Cushing’s syndrome that has a female predilection and may be familial or associated with Carney complex. On imaging the adrenal glands may appear normal or minimally hyperplastic with multiple, usually <5 mm, unilateral or bilateral benign cortical nodules. The adrenal nodules are macroscopically pigmented; they demonstrate a lower T1 and T2 signal intensity on MRI compared to surrounding atrophic cortical tissue. When nodules are 1-2 cm in size, there might be atrophy of the intervening cortex, which helps distinguish this condition from ACTH- dependent hyperplasia (57).

 

Another rare cause of Cushing’s syndrome is ACTH-independent macronodular adrenal hyperplasia, which has a male predilection. The imaging appearance of the adrenal glands is striking with massive bilateral adrenal enlargement, nodularity. and distortion of adrenal contour. Nodules can measure 1 to 5.5 cm. On MRI they are hypointense relative to liver on T1-w images and hyperintense or isointense in T2-w images. On chemical shift imaging, nodules lose signal intensity on out-of-phase due to their high lipid content (57).

 

OTHER ADRENAL IMAGING MODALITIES

 

Patients that harbor adrenal masses, which are not adequately characterized by CT or MRI, can be further evaluated with functional nuclear medicine modalities that include single photon emission computed tomography (SPECT) scintigraphy with various radionuclide tracers, and positron emission tomography (PET) scintigraphy with various radionuclides.  PET images provide a higher spatial resolution compared to SPECT (70).

 

PET scan with either Fluorodeoxyglucose (FDG) or 11C-metomidate (MTO) can be useful in selected cases to differentiate benign adrenal adenomas from adrenocortical carcinomas. An elevated uptake on the FDG scan correlates with high metabolic activity and raises the suspicion for malignancy (74) with high sensitivity and specificity (75). Limitations of this technique include physiological excretion of FDG into renal inflammatory system and high metabolic uptake in inflammatory and infectious processes as well as in benign pheochromocytomas, leading to false positive results (64). Metomidate is an inhibitor of 11 beta-hydroxylase (CYP11B1) and aldosterone synthetase (CYP11B2), and based on this property its use can help differentiate tumors of adrenocortical origin from non-cortical lesions. Originally developed as a PET imaging agent radiolabeled with 11C, more recently it has been labeled with 18F and 123I, allowing SPECT and SPECT/CT imaging (76).

 

Integrated or “fused” PET-CT imaging allows to combine CT attenuation measurements with the intensity of FDG uptake, as described by the standardized uptake value (SUV), improving the performance of either imaging technique alone (77).

 

Scintigraphy with Iodine-131-Iodomethyl-19-norcholesterol (NP 59) is a functional nuclear medicine imaging modality that can be used to differentiate adrenal cortical adenomas from carcinomas. This is a labeled cholesterol analogue that specifically binds to low-density lipoproteins and after receptor-mediated uptake it is stored in the adrenocortical cells (70).  NP 59 uptake is regulated by ACTH and suppressed by dexamethasone, concentrating in hyperfunctioning cortisol and aldosterone secreting adenomas and showing low uptake in adrenocortical carcinomas because of the inefficient concentration of radiotracer by malignant tissue (78).

 

Other Imaging Modalities for Ectopic Cushing’s

 

Patients diagnosed with ACTH dependent Cushing’s whose biochemical dynamic tests suggests an ectopic source, pose a special challenge to the clinician. In 12 to 20% of these patients, the source remains undiscovered despite repeated biochemical and radiological investigations (55).

 

In the setting of ectopic ACTH production, imaging studies play a crucial role in trying to identify the source of the tumor causing the disease and guide management and prognosis. The optimal imaging study to detect these tumors has not been defined. CT, MRI, PET scan, 111In-pentetreotide (OCT) scintigraphy at conventional or higher radionuclide doses, as well as newer molecular imaging techniques like 131I/123-metaiodobenzylguanidine (MIBG), 18F-fluoro-2-2-deoxyglucose-positron emission tomography (FDG-PET), 18F-fluorodopa-PET (F-DOPA-PET), 68Ga-DOTATATE-PET/CT or 68Ga-DOTATOC-PET/CT scan (68Gallium-SSTR-PET/CT) are complementary and have been shown to be useful in different scenarios with variable sensitivity and specificity (79-83). For the most part at least two different imaging modalities are needed to establish a diagnosis and sometimes, repeated imaging over several months is required to identify the source. The choice of imaging modalities is guided by the sensitivity of the procedure balanced with the risk of false-positive findings (72).

 

A good approach is to start by obtaining images of the chest, since most ACTH-secreting tumors are located in this area. The most common causes are bronchial carcinoid tumors and small cell lung cancer. Other sources of excess ACTH production include neuroendocrine tumors of the thymus, bowel and pancreas, medullary carcinoma of the thyroid, pheochromocytomas, and mesotheliomas.

 

CT of the chest, abdomen and pelvis with intravenous contrast medium injection is the most commonly used initial imaging test performed and is very useful in many cases. In patients with equivocal CT imaging findings, MRI can be useful, particularly for tumors within the abdomen. It is recommended to follow CT and MRI imaging with a functional imaging modality, being OCT scintigraphy the most widely used. Functional imaging reduces false-positive results because it relies on the specific properties of tumor cells, not just their anatomic characteristics. However, tumors lacking the relevant receptor can have false negative results (83). Site-specific differences occur and different imaging modalities might have higher sensitivity and specificity depending on this. A recent systematic review showed that FDG-PET can be very sensitive in the detection of neuroendocrine tumors with high proliferation index, particularly in the pancreas. This review also showed that 68Gallium-SSTR-PET/CT had a 100% sensitivity but this is an imaging technique that has limited availability and was only performed in a minority of the patients in their series (80).

 

Table 2. Imaging Characteristics of Adrenal Tumors

Characteristic

Adenoma

Carcinoma

Pheochromocytoma

Metastasis

Size

<4 cm

>4 cm

Variable

>4 cm

Shape

Round

Irregular

Round

Irregular

Border

Smooth

Irregular

Well delineated

Irregular

Laterality

Unilateral

Unilateral

May be bilateral or unilateral

May be bilateral

Appearance

Round, homogeneous

Inhomogeneous with central necrosis. May have calcifications

Cystic and hemorrhagic changes.

Inhomogeneous

Vascularity

Normal

Increased

Increased

Increased

Growth rate

Slow (1 cm/year)

Fast (>2 cm/year)

Slow (0.5-1 cm/year)

Variable/Fast

Lipid content

Lipid rich or poor

Lipid poor

Lipid poor

Lipid poor

CT attenuation

 

<10 HU unenhanced.

>50% absolute washout.

>20 HU unenhanced.

<50% absolute washout.

>20 HU unenhanced.

<50% absolute washout.

>20 HU unenhanced.

<50% absolute washout.

MRI

Isointense with liver in T1 and T2-w.

Chemical shift

Hypointense compared to liver on T1-w

High to intermediate signal on T2-w

High signal intensity on T2-w

Hypointense compared to liver on T1-w

High to intermediate signal on T2-w

FDG-PET-CT

Low SUV

High SUV

Variable SUV

High SUV

Other

 

Evidence of invasion or metastasis

 

History of prior cancer

 

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The Diabetic Foot

ABSTRACT

 

Diabetic foot ulcers (DFU) are associated with significant impairment of quality of life, increased morbidity and mortality, and are a huge drain on health care resources. In Western countries, the annual incidence of foot ulceration in the diabetic population is around 2%. DFUs develop as a consequence of a combination of factors, most commonly peripheral neuropathy (loss of the gift of pain), peripheral arterial disease (PAD), and some form of unperceived trauma. Recent studies emphasize the very high prevalence of foot ulceration in people with diabetes on dialysis as a consequence of end-stage renal disease. The mortality in this patient group is higher than for most forms of cancer. All patients with diabetes should have an annual screen to identify their foot ulcer risk status: those with any risk factors require specific foot care education as well as regular contact with a health care professional, usually a podiatrist. DFUs should heal if there is an adequate arterial inflow, infection is aggressively managed, and pressure is removed from the wound and its margins. In the management of plantar neuropathic ulcers, offloading is critical and all efforts must be made to enhance patient understanding of the need for offloading. Antibiotic usage should be guided by clinical signs of infection and microbiologic analysis of deep tissue specimens: evidence now exists to show that oral antibiotics are equally efficacious as intravenous in treating most cases of osteomyelitis in the diabetic foot. Most adjunctive therapies have little evidence to support their use although recent trials suggest efficacy for a number of topical therapies including LeucoPatch (3C patch) and sucrose octasulphate; and negative pressure wound therapy has also been shown to be helpful in certain cases. There is currently no indication for hyperbaric oxygen usage, whereas recent studies suggest that topical oxygen therapies help wound healing. Charcot neuroarthropathy (CN) should be easily preventable: most important is to treat any neuropathic patient with a warm swollen foot as having CN until proven otherwise.

 

INTRODUCTION

 

At the beginning of the 21st Century, diabetic foot problems, although eminently preventable, represent one of the commonest causes of hospital inpatient admission in Western countries. In 2005, the International Diabetes Federation realized the global importance of diabetic foot disease and chose to focus their campaign during the whole year on raising awareness with a worldwide campaign to “put feet first” and highlight the common problem of amputation amongst diabetic patients throughout the world. To coincide with World Diabetes Day 2005 (November 14, birth date of Frederick Banting), the Lancet elected to dedicate a whole issue to diabetic foot problems (1).

 

In this chapter, the global term “diabetic foot” refers to the variety of pathological conditions that might affect the feet in patients with diabetes. Foot ulcers are defined as lesions involving a skin break with loss of epithelium: they can extend into the dermis and deeper layers sometimes involving bone and muscle. Amputation is defined as “the removal of a terminal, non-viable portion of the limb”. The lifetime risk of a person with diabetes developing a foot ulcer (DFU) has been estimated to be as high as 34 % (2).

 

The suffering of affected individuals and the cost of DFUs are both equally staggering. Those individuals with DFUs usually have other complications of diabetes including nephropathy: data from the UK and the USA confirmed that the outlook for those people with foot complications who are on dialysis is very poor with a high mortality risk (1-3). Data from our group confirm that those people with diabetes who have had an amputation and who are on dialysis have a 75% two-year mortality; the majority of these were of cardiovascular etiology. Data such as these are worse than most malignant diseases, with the possible exception of lung and pancreas. There is therefore an urgent need for preventative strategies to reduce the incidence of foot complications amongst those with diabetes. With respect to costs, in 2008 Rogers et al (4) reported that in the US $18 billion was spent on the care of DFUs and US $11.7 billion on lower extremity amputations. More recently, data from the UK in 2019 suggest that a conservative estimate of the annual cost of diabetic foot problems exceeds UK £900 million which represents approximately 1% of the total budget of the National Health Service (5).

 

The importance of regular diabetic foot care in very high-risk patients is emphasized by an observational study from Arizona where the State decided to remove routine podiatry from high-risk patients to reduce their health budget. This led to an annual saving of US $351,000 but the cost of this action measured by increased hospitalization, length of stay, and amputations was $16.7 million (6).

 

This chapter will include a discussion on the epidemiology of foot problems including foot ulceration, amputations, and Charcot neuroarthropathy (CN). The etiopathogenesis will then be described and aspects of management of neuropathic, neuroischemic, and infected DFUs considered. The question of how to address primary and secondary prevention of diabetic foot problems will then be discussed followed by a section on Charcot neuroarthropathy. For more detailed discussion, the reader is referred to review articles on these topics (2,7-9).

 

EPIDEMIOLOGY OF THE DIABETIC FOOT

 

The study of the epidemiology of diabetic foot disease has been beset by numerous problems relating to both diagnostic tests used, and population selected. However, there is little doubt that foot complications are common. In the UK, the North West Diabetes Foot Care Study (a community-based study of over 15,000 people) reported that the annual incidence of foot problems amongst the population with diabetes was just under 2% (10), with similar results having been reported from the Netherlands. Similarly, when discussing amputations, the figures vary widely again due to diagnostic criteria as well as regional differences. It must be remembered that many individuals at diagnosis of type 2 diabetes have significant neuropathy: in the United Kingdom Prospective Diabetes Study, for example, 13% of patients at diagnosis had neuropathy of sufficient severity to put them at risk for foot ulceration (7).

 

With respect to ethnicity, studies from the UK suggest that foot ulcers and amputations appear to be less common in Asians of Indian sub-continental origin and Afro-Caribbean men. In contrast, reports from the USA suggest that amputation rates are more common amongst African-Americans with diabetes than amongst white Americans. Similarly, ulceration is much more common in Hispanic Americans and native Americans than in non-Hispanic whites (2). More recently, reviews have confirmed the importance of healthcare inequities in diabetic foot disease: race, ethnicity, socioeconomic status, and geography are powerful mediators of risk for DFU and lower-extremity amputation (2,11).

 

ETIOPATHOGENESIS OF DIABETIC FOOT ULCERATION

 

The foot does not break down spontaneously and in this section, the many warning signs that the feet are at risk of breakdown will be discussed. This was recognized by Elliott Joslin almost 90 years ago when he stated that “diabetic gangrene is not heaven-sent but is earth-borne” (12). It was previously believed that neuropathy, vascular disease, and infection were the main causes of ulceration: it is now recognized that infection occurs as a consequence of ulceration, and is not a cause thereof. There are many contributory factors to foot ulceration, the most important of which are diabetic neuropathy and peripheral arterial disease (PAD). These and other causative factors are listed in table 1.

 

Table 1. Risk Factors for Foot Ulceration

Peripheral neuropathy
Somatic
Autonomic

Peripheral arterial disease
Proximal and/or distal disease

Past history of foot ulcers/amputation

Other long-term complications
End-stage renal disease (especially on dialysis)
Post-transplant (including pancreas/kidney transplant)
Visual loss

Plantar callus

Elevated foot pressures

Foot deformity

Edema

Ethnic background

Poor social background

More common contributory factors shown in bold

 

Diabetic Neuropathy

 

Although the association between both somatic and autonomic neuropathy and foot ulceration has been recognized for many years, it is only in the last 20 years that prospective studies have confirmed these assumptions (2,8,10). It has been reported that the risk of developing the first foot ulcer is seven-fold higher in those with moderate to severe sensory loss compared with non-neuropathic diabetic individuals (13). Additionally, poor balance and instability as a consequence of loss of proprioception have been confirmed and are also likely contributory factors not only to foot ulceration, but also to Charcot neuroarthropathy (CN) (2,7,14,15).

 

Sympathetic autonomic neuropathy in the lower extremity leads to reduced sweating and dry skin that is prone to crack and fissure, and as well, in the absence of PVD, to increased blood flow, arterio-venous shunting, and the warm foot.

 

As will be discussed later, simple clinical tests may be used to identify the high-risk neuropathic foot (16). Most important in the identification of the high-risk neuropathic foot is good clinical observation and removal of the shoes and socks, with careful inspection of the feet as part of the routine follow up of all patients with diabetes.

 

Peripheral Arterial Disease (PAD)

 

A two-center study of causal pathways to foot ulceration reported that peripheral ischemia was a causal component in the pathway to ulceration in 35% of cases (17). In many Western countries, there has been an increase in the percentage of foot ulceration in which ischemia is a contributory factor (18). It is well recognized that patients with diabetes are more prone to distal arterial disease, which may be associated with a poorer outcome.

 

A detailed discussion of PAD in diabetes is outside the scope of this chapter and readers are directed to reviews on this topic (1920). A large follow-up study from Australia has confirmed that the strongest predictors of development of PAD in type 2 diabetes include microvascular complications (particularly macroalbuminuria and photocoagulation for retinopathy (21)).

 

Other Risk Factors

 

Of all the risk factors for foot ulceration (table 1), the most important is a past history of ulceration and/or amputation (2). In some series, the annual recurrence rate is up to 50%.

 

Other Long-term Complications

 

Those with other late complications particularly nephropathy, have an increased ulcer risk. Visual disturbance as a consequence of retinopathy is a confirmed risk factor; it is easy to understand why this should be. Those patients with sensory loss, particularly large fiber dysfunction, have poor balance and rely on vision as a secondary protective factor. Thus, those who have had for example extensive laser therapy and also have loss of proprioception, are at great risk of foot injury particularly when walking on uneven surfaces and in the hours of darkness.

 

A strong association between end-stage renal disease and foot ulceration has been emphasized in a number of studies. The temporal association between the start of dialysis treatment and foot ulceration was first confirmed by Game et al (22). A study comprising patients from both the US and the UK subsequently reported a very high prevalence of foot pathology in patients on dialysis, with 46% of patients having past or present foot ulceration and 18% were already amputees (23). The same group later confirmed that being on dialysis is an independent risk factor for foot ulceration in patients with diabetes (3,24). As noted above, preliminary data from the same group suggests that those patients who have already undergone amputation and who are on dialysis have a two-year mortality of up to 75%.

 

It must also be remembered that patients post-renal transplant or even post-simultaneous pancreas-kidney (SPK) transplant remain at very high risk of developing foot complications. There have been a number of reports of both foot ulceration and Charcot neuroarthropathy occurring in patients post-SPK (25). Theoretically, such subjects are “non-diabetic” but they remain at high risk because they invariably have a dense sensorimotor and autonomic peripheral neuropathy. They should remain under annual review and be coded as ‘diabetes in remission’.

 

Plantar Callus

 

Plantar callus forms under weight-bearing areas as a consequence of the dry skin (autonomic neuropathy), insensitivity, and repetitive moderate stress from high foot pressures. Callus itself acts as a foreign body and can cause ulceration in the insensate foot.

 

Elevated Foot Pressures

 

Numerous studies have confirmed the contributory role that abnormal plantar pressures play in the pathogenesis of foot ulceration (127). Most studies used sophisticated techniques such as pedobarography to assess foot pressures, but these are not required in day-to-day clinical practice.

 

Foot Deformities

 

A combination of motor neuropathy, cheiro-arthropathy, and altered gait pressures is thought to result in the “high-risk” neuropathic foot with clawing of the toes, prominent metatarsal heads, high arch, and small muscle wasting.

 

Demographics

 

In Western countries, the male sex has been associated with a 1.6-fold increased risk of foot ulcers (10). There is an increased risk of foot ulceration with increasing age and duration of diabetes.

 

Psychosocial Factors

 

There have been a few studies of psychosocial factors in the pathway to foot ulceration and it appears that patients’ behavior is not driven by the abstract designation of being “at risk”; it is driven by patients’ perception of their risk (26) . Thus, if a patient does not believe or understand that a foot ulcer lies on the path from neuropathy to amputation, are they likely to follow educational advice on how to reduce neuropathic ulcers? Moreover, a prospective study has confirmed that depression predicts first, although not recurrent, diabetic foot ulcers (27) .

 

THE PATHWAY TO FOOT ULCERATION IN DIABETES

 

As discussed and outlined in Figure 1, the pathway to ulceration is indeed complex and involves an interaction of numerous factors. Whereas none of the factors listed in the last section will alone result in ulceration, it is the interaction and combination of risk factors working together that leads to skin breakdown. In the prospective study of Reiber et al, 63% of all foot ulcers resulted from a combination of neuropathy, deformity, and trauma: in Western countries, the commonest cause of trauma is ill-fitting footwear (17). It must be remembered that as those with neuropathy have reduced sensory input, they will commonly be unable to feel the fit of a shoe until the pressure from the shoe is quite high. Thus, people with neuropathy frequently choose shoes that are too small. All such individuals should be advised to have their feet measured prior to the purchase of any “off the shelf” footwear.

 

Other simple examples of two risk factors working together in the pathway to ulceration are neuropathy and mechanical trauma (a common scenario is a neuropathic individual with a foreign body in the shoe), neuropathy and thermal trauma (holidays are particularly dangerous), and neuropathy and chemical trauma (such as inappropriate use of over-the-counter chemical corn treatments which should never be used in those with neuropathy).

 

In summary, whereas neuropathy was present in four out of five cases of new foot ulcers in the Reiber study (17), as noted above, the combination of neuropathy and ischemia is becoming more common in Western countries, and neuro-ischemic ulcers are the commonest type seen in 2023 in diabetic foot clinics.

 

FOOT ULCERATION

 

DFUs are common, associated with much morbidity and even mortality but should be eminently preventable. It used to be believed that diabetic foot ulcers were difficult to heal: this is not true: a foot ulcer will heal if it is permitted to do so and this requires attention to three factors-

A That there is adequate arterial inflow to the foot.

B That any infection is appropriately and aggressively managed.

C That all pressure is removed from the wound and its margins.

 

 

Figure 1. Pathways to Diabetic Foot Ulceration.

 

Despite increased knowledge of the pathogenesis and treatment of diabetic foot ulcers in recent years, it is still the third point, offloading the wound, that is poorly adhered to by health care professionals. Many forget that those with a neuropathic or neuroischemic ulcer have “lost the gift of pain”. That pain is a gift which is only realized when it is lost, as first described by Dr Paul Brand when studying leprosy (28). However, before going into more detail on management, it is important to classify wounds appropriately in order to guide therapeutic management.

 

CLASSIFICATION OF DIABETIC FOOT WOUNDS

 

Accurate and concise ulcer description and classification systems are required to improve multidisciplinary collaboration and communication, as well as for aiding treatment choices. For many years, the Meggitt-Wagner grading system was regarded as the gold standard. One problem with this system is that the ischemic status of the wound is not included. Thus, a number of new classification systems for diabetic foot wounds have been proposed and validated over the last 20 years. A commonly used system in the United States is the University of Texas Wound Classification System (29). This incorporates the Meggitt-Wagner grades but also enables the practitioner to stage the wound with respect to the presence or absence of infection and/or ischemia (Figure 2). In a comparative prospective study across two Centers, one in the UK and one in the US, the University of Texas Classification System was shown to be superior to the Meggitt-Wagner system at predicting outcomes (30). However, this study also showed that the traditional Meggitt-Wagner system was itself generally accurate in predicting outcomes.

 

Most recently, the WIFI (Wound Ischemia, Foot Infection) classification was introduced and is the most commonly used today in the USA, particularly in vascular clinics. This was developed and validated as a method to assess three variables – the wound, level of ischemia and the presence and severity of foot infection – to predict the risk of amputation (Figure 3)

 

Figure 2. The University of Texas Wound Classification System.

Figure 3. WIFI system. Wound, Ischemia, and Foot Infection (WIfI) Classification of Limb Threating diabetic foot disease, tissue loss, ischemia, and infection frequently overlap. However, one is frequently more dominant than the other at different times in the life cycle of an acute-on-chronic event. Here, the amount of tissue loss, ischemia, and foot infection can be ordinally graded to help predict outcome and assist in communicating a plan of action. aA higher score on the WIfI scale is associated with lower extremity amputation and morbidity and can be used to determine the need for revascularization. WIfI scores of 1, 2, 3, and 4 were associated with 1-year amputation rates of 0%, 8%, 11%, and 38%, respectively. Figure from JAMA 2023 Jul 3;330(1):62-75 with permission.

 

EVALUATION OF THE DIABETIC FOOT ULCER

 

Clinical evaluation of the foot wound should include a detailed description of the site, size, and depth of the wound. The neuropathic and vascular status of the wound should then be assessed (for details see below). In general, neuropathic ulcers typically occur in the warm but insensate foot, often under pressure bearing areas, and are surrounded by callus. In contrast, ischemic wounds tend to occur in the cool, poorly perfused foot, and are often at lateral fifth metatarsal head regions or the medial first metatarsal head regions. In a predominantly ischemic wound, callus tissue is uncommon. In a neuroischemic wound, the morphology will depend upon the predominance of each of these two pathologies. The correct identification of the degree of ischemia is of the utmost importance when evaluating a wound. If the foot is cool with impalpable pulses, then non-invasive Doppler ultrasound studies are indicated. Conventional methods of assessing tissue perfusion in the peripheral circulation may not be entirely reliable in patients with diabetes. For example, the Ankle Brachial Pressure Index, which is routinely used to screen for PAD in individuals without diabetes, may well be falsely elevated in the those with diabetes because of medial arterial calcification. Toe pressure indices may therefore be more reliable.

 

Peripheral Arterial Disease

 

A detailed discussion of vascular procedures is outside the scope of this review, although any person being considered for radiological or surgical procedures will require arteriography. Care must be taken in the use of certain contrast media in patients with chronic renal disease. A detailed discussion of the use of bedside investigations to diagnose PAD in people with diabetes is provided in the recently published guidelines by Fitridge et al (31).

 

Is Infection Present?

 

The correct diagnosis of infection in the diabetic foot wound is critical as it is often the combination of untreated infection and PAD that lead to amputation in the diabetic foot. A systematic review that was updated in 2020 still recommend that the diagnosis of infection requiring treatment is a clinical one (32). However, appropriate tissue specimens should be sent to the microbiological laboratory for culture and sensitivity. Superficial swabs are of little use: deep tissue specimens or if osteomyelitis is suspected, bone biopsies are recommended (32) .

 

A high index of suspicion for the presence of osteomyelitis is essential when assessing the diabetic foot wound. The “probe to bone” (PTB) is often used to diagnose osteomyelitis although there has been much discussion about its accuracy. A systematic review concluded that the PTB test can accurately diagnose osteomyelitis in high-risk patients, and rule out osteomyelitis in low-risk patients (33).

 

Role of Plain X-Ray in Diagnosing Osteomyelitis

 

The plain radiograph remains the commonest first radiological investigation of an acutely presenting diabetic foot problem. Despite this, it may be dismissed because of relatively low sensitivity for acute osteomyelitis, with literature over the last 10 years concentrating on CT scanning, MR scanning, and nuclear medicine studies (particularly Gallium Citrate, labelled leucocyte scans and recently PET, PET-CT, SPECT-CT and PET-MR). These latter studies are of limited availability and are expensive, and some carry a high radiation burden. They have their own sensitivity and specificity problems and may not be available in a timely manner. The initial sensitivity of the plain radiograph for acute osteomyelitis is improved by serial studies at one to two-week intervals, during which time therapy for presumed osteomyelitis may be instigated for clinical reasons and whilst awaiting the results of further “high tech” imaging (if still required). The plain radiographic findings could then be considered of high sensitivity and specificity, but with a two-week lag, both for diagnosis and for response to treatment. Appropriate clinical information for the reporting radiologist must include that the patient is diabetic, whether the foot is neuropathic, whether an ulcer is present and if so, its precise anatomical location, and whether it probes to bone. The radiologist should be aware that most sites of acute osteomyelitis in the diabetic foot occur in the floor of an ulcer that probes to bone and that if the foot is neuropathic there may be acute fractures without a history of trauma or acute Charcot neuroarthropathy may be present.

 

Whilst periosteal reaction is an early feature of osteomyelitis, it is not commonly seen around the small bones of the foot, and if present, is most often seen around metatarsals, and may be due to fracture rather than osteomyelitis.

 

The hallmark plain radiographic feature of osteomyelitis in the diabetic foot is focal loss of bone density, almost invariably adjacent to the floor of an ulcer. Whilst sometimes described as bone destruction, it is initially bone de-mineralization that causes this appearance, which can reverse on successful treatment, with radiographic re-appearance of the apparently destroyed bone (Figure 4). Obtaining the radiographic view most likely to demonstrate the bone in the floor of an ulcer is therefore an important consideration, often overlooked now that requests are electronic and radiographic views are selected from limited drop-down menus. For example, toe-tip ulcers and ulcers on the dorsum of the inter-phalangeal joints require lateral toe views - best obtained using dental radiographs if available; the inferior surfaces of metatarsal heads are best demonstrated on sesamoid views; the heel requires both lateral and axial views. As a general rule, radiographs tangential to the bone surface at the site of suspected osteomyelitis are ideal, in addition to the standard radiographs of the region. A dedicated team of radiographers familiar with these requirements will improve the relevance and quality of the resultant radiographs.

 

Plain radiology remains an important investigation in the diagnosis and management of diabetic foot osteomyelitis, but it needs to be of high quality, with appropriate views, and regularly repeated to fulfil its potential.

 

Figure 4. Acute presentation with an ulcer at the tip of the great toe, probing to bone. The terminal phalangeal tuft does show some irregularity (left panel). B) two weeks later there is marked bone demineralization consistent with osteomyelitis (middle panel). C) After 2 months of treatment there has been partial remineralization of the bone but with an underlying pathological fracture (right panel).

 

MANAGEMENT OF DIABETIC FOOT ULCERS

 

The principles of management of different types of foot ulcers will be discussed in brief in this section. The University of Texas Wound Classification System (Figure 2) will be used throughout.

 

Neuropathic Plantar Ulcers (UT 1A, 1B, 2A, 2B)

 

As noted above, neuropathic ulcers tend to occur under pressure areas, particularly at the plantar surface of the forefoot. Other recognized sites include the dorsal areas of the toes, particularly the distal inter-phalangeal joint if there is clawing of the toes. In patients with marked deformities such as those caused by Charcot neuroarthropathy, ulcers may occur at other pressure points, particularly in the plantar mid-foot due to, for example, a dropped cuboid bone. When lecturing on the management of neuropathic diabetic foot problems, one is often asked “what can one put on the wound to heal it?”. The answer is invariably that one should be asking “what should one take off the foot to help heal the ulcer?”. Thus, the management of a plantar neuropathic foot ulcer that is not infected is firstly sharp debridement of the ulcer down to bleeding healthy tissue with removal of all callus tissue over the wound and the edge, and secondly, the removal of pressure from the wound while the person is walking. Pain sensation normally protects wounds from further damage causing the non-neuropathic individual to limp. Any subject with a plantar ulcer who walks into the clinic without limping must, by definition, have loss of pain sensation. A neuropathic individual with a plantar ulcer will therefore walk on the ulcer as there is no warning symptom to inform him or her otherwise. Techniques for removing pressure include the use of casts (either removable or irremovable), boots, half shoes, sandals and felted foam dressings. The total contact cast (TCC) is regarded as the gold standard. Studies that randomize patients to an irremovable TCC, a removable cast walker (RCW), or other offloading devices invariably confirm that healing is fastest in the irremovable device (2,7). Although RCWs and irremovable casts (such as the TCC) offload equally well in the gait laboratory, the irremovable device is always associated with more rapid healing in clinical practice. The problem is that those with neuropathic foot ulcers have lost the sensory cue that tells them not to walk on their active ulcer. Studies suggest that individuals are compliant with wearing the offloading RCW during the day, but feel that home is safer and therefore tend to put slippers on, or even walk barefoot at home. A subsequent trial has confirmed that if the RCW is rendered irremovable by wrapping with scotch cast for example, then the outcome is that there is no difference in healing rates between the TCC and the RCW rendered irremovable (34) . Most people with simple neuropathic foot ulcers (UT grades 1A, 2A, 1B, 2B) generally heal in less than three months although of course this does vary with ulcer size. There is no contraindication to casting neuropathic individuals with mild foot infections (UT grades 2A, 2B). It is recommended that after the wound is healed, offloading should continue for a further four weeks to enable the scar tissue to firm up.

 

Wound dressings are important to keep the ulcer clean, but the placement of a large dressing on a wound may lead the person to a false sense of security by believing that dressing an ulcer is curative. Nothing could be further from the truth in the neuropathic ulcer. Unfortunately, there is little evidence from randomized controlled trials (RCTs) that any dressing is superior to another. Indeed, Jeffcoate et al (35)  randomized people to one of three dressings and could find no difference in outcome according to dressing used: the only difference was in cost. Thus, without an evidence-base, there is no indication to use some of the newer more expensive dressings.

 

Neuro-ischemic Ulcers

 

A neuro-ischemic ulcer is one occurring in a foot of a person who has both a neuropathic deficit and impaired arterial inflow: these would be classified UT 1C, 2C in the absence of infection, or 1D, 2D or 3D in the presence of infection. Such individuals warrant full vascular investigation as described above, and referral to the vascular surgery team. The principles of treatment are similar to those for neuropathic ulcers, and it has been confirmed that offloading can safely be used in non-infected neuro-ischemic ulcers under a weight-bearing area. However, antibiotics should be used if there is any suspicion of infection and casting only used with extreme caution in such cases (36). There is now evidence that one dressing, sucrose octasulphate, can improve the healing rates of neuroischemic ulcers in diabetic patients (for further details, see below under adjunctive treatments). With respect to the effectiveness of revascularization of the ulcerated foot in those with neuro-ischemic lesions, results showed that major outcomes following endovascular or open bypass surgery were similar amongst studies (37).

 

Management of Diabetic Foot Infections

 

Appropriate wound debridement and offloading together with antibiotics are important in the management of the infected neuropathic foot ulcer, although there are few data from randomized trials to guide the prescriber (32). There is however no evidence that clinically non-infected neuropathic ulcers warrant treatment with antibiotics. With respect to the choice of antibiotic therapy, the reader is directed to the helpful 2012 Infectious Diseases Society of America Clinical Practice Guideline (38).  Commonly used broad-spectrum antibiotics include Clindamycin, Cephalexin, Ciprofloxacin, and the Amoxycillin – Clavulanate potassium. Oral antibiotics usually suffice for mild infections, whereas more severe infections including cellulitis and osteomyelitis require intravenous antibiotic usage initially. Care should also be taken to optimize glycemic control, as hyperglycemia impairs leucocyte function.

 

The above statements on antibiotics refer to initial treatment: after starting with such broad-spectrum antibiotics, when the results of cultured deep tissue specimens are available, antibiotic therapy should be targeted at the likely primary infective organisms. Finally, with respect to duration of antibiotics, there are no data available from randomized trials to help guide the practitioner. Antibiotics should be continued until clinical signs of infection have resolved, but there is no indication to continue antibiotics beyond this period of time and certainly no indication to continue until the wound has healed. A recent review has identified the challenges facing us due to the increasing threat of multidrug-resistant pathogens (39) .

 

Osteomyelitis

 

Diagnosis of osteomyelitis has been discussed above both relating to the PTB test and also the use of plain radiographs. Although the treatment of osteomyelitis has traditionally been surgical, there is increasing evidence from case series and a RCT, that osteomyelitis localized to one or two bones, such as digits, may successfully be treated with antibiotics alone (40, 41). A randomized trial from Spain showed that antibiotics alone were not inferior to localized surgery (41). Again, with respect to duration of antibiotic therapy for osteomyelitis, there is no evidence-base to guide us though a recent trial suggests that six weeks’ antibiotic therapy for non-surgically treated diabetic foot osteomyelitis may be sufficient: traditionally, up to three months has been recommended (42). Lastly, many were surprised to read the results of the OVIVA (Oral Vs Intravenous Antibiotics) study (43) which randomized patients with osteomyelitis to oral vs intravenous antibiotics and showed no superiority of either delivery modality. These observations will certainly challenge the approach to osteomyelitis management in the future. A detailed updated review on infection management has been published by the American Diabetes Association in 2020 (44) .

 

Adjunctive Treatments

 

Adjunctive therapies are those which might be considered for complex diabetic foot wounds which fail to heal after 8-12 weeks of standard of care as discussed in the above sections. In recent years, many new such therapies, including skin substitutes, oxygen and other gases, products designed to correct abnormalities of wound biochemistry and cell biology associated with impaired wound healing, applications of cells, bioengineered skin and others, have been proposed to accelerate wound healing in the diabetic foot. Some years ago, an internationally conducted systemic review concluded that there was little published evidence from appropriately designed clinical trials to justify the use of such newer therapies (45).

 

However, there has been a renaissance in diabetic foot care with many RCTs of new therapies published since 2018 including topical therapies and oxygen-based treatments (46). A number of well-designed RCTs were published in 2018. The first proven therapy for neuro-ischemic ulcers, sucrose octasulfate dressings, was reported in the Explorer study (47). In the active group, 48% of wounds were closed after 20 weeks compared to 30% in the control dressing group (p<0.002). In the same issue of Lancet Diabetes Endocrinology, Game and colleagues reported the positive effect of the Leucopatch (3C Patch) device (a disc containing autologous platelets, leucocytes and fibrin) when applied to the surface of hard-to-heal foot ulcers (48).

 

Although, as noted above, the International Working Group on the Diabetic Foot (IWGDF) systematic review in 2016 (45) could not support the use of many of the therapies outlined above, this had changed by 2020 when three trials of placenta-derived products were considered (49). Although none was blinded, these were judged to be of low risk of bias as outcomes were assessed in a blinded manner. The first studied a cryo-preserved amniotic membrane allograft (50), the second an umbilical cord product (51), and the third a dehydrated amniotic membrane allograft (52): each showed significantly faster healing in the active treated group versus standard of care. Further details of all these studies referred to above can be found in the most recent American Diabetes Association (ADA) compendium on evidence-based management of complex diabetic foot wounds (53).

 

Hyperbaric and Topical Oxygen in the Diabetic Foot

 

HBO has been promoted as an effective treatment in diabetic foot wounds over many years (8). However, early RCTs have been criticized because of the small numbers of patients enrolled, and methodological and reporting inadequacies. A well designed and blinded RCT was conducted in Sweden some years ago suggesting the benefit of HBO in chronic neuro-ischemic infected foot ulcers with no possibility of revascularization (54). More recently, there have been two negative studies including a large retrospective cohort trial (55) and a multi-center Canadian study that showed no benefits of HBO whatsoever in any patient group (56). Thus, at present, the use of HBO in any diabetic foot wound has few data to support its efficacy and the multi-center trial from the Netherlands was also negative (57). The use of HBO in diabetic foot wounds was the topic of a recent debate (58).

 

There has been increasing interest in the use of topical oxygen-based therapies in wound healing in recent years. Whereas the latest studies of HBO have been negative, there have been interesting developments in the use of devices delivering topical oxygen. There is now evidence that both continuous (59) and cyclical (60) topical wound therapy may improve wound healing rates. A number of more recent studies now support the use of cyclical topical oxygen therapy (TWO2) (53) including some ‘real world’ data (61) and a number of meta-analyses and systematic reviews, the most recent of which has just been published (62). Thus, there is a body of evidence to support the use of TWO2 in the management of hard-to-heal diabetic foot ulcers that fail to respond to standard of care.

 

Negative Pressure Wound Therapy (NPWT)

 

The application of NPWT is believed to accelerate healing through reducing edema, removal of exudate, increased perfusion, self-proliferation, and the formation of granulation tissue (63). RCTs have suggested efficacy in rates of wound healing and reduced amputations, with the application of NPWT in both post-surgical and non-surgical chronic non-healing ulcers (64,65). A systematic review confirmed that there was some evidence to support the use of NPWT in post-operative wounds (49).

 

 ADA Standards of Care and IWDGF Guidelines 2023

 

The ADA publishes its standards of care and clinical practice guidelines each January in Diabetes Care. In 2023 (66), those adjunctive therapies for foot ulceration recommended and supported by level A evidence (based on large, well-designed randomized controlled trials or well-done meta-analyses of randomized controlled trials) included: negative-pressure wound therapy, placental membranes, bioengineered skin substitutes, several acellular matrices, autologous fibrin and leukocyte platelet patches, and topical oxygen therapy. The IWDGF guidelines are renewed every four years, and in 2023, for adjunctive therapies for foot ulceration, recommended, with variable levels of strength and certainty of evidence, that the following might be considered (67): - regular sharp debridement (strength of recommendation: strong), sucrose-octasulfate impregnated dressings, hyperbaric oxygen in neuro-ischemic or ischemic diabetes-related foot ulcers, topical oxygen therapy, the autologous leucocyte, platelet and fibrin patch (Leucopatch or 3C Patch), placental derived products and Negative Pressure Wound Therapy (only as an adjunct therapy to standard of care for the healing of postsurgical diabetes-related foot wounds).

 

CHARCOT NEUROARTHROPATHY (CN)

 

Charcot neuroarthropathy, although uncommon, is a potentially devastating late complication of diabetic neuropathy (68). Although the exact mechanisms resulting in the development of CN remain unclear, much progress has been made in our understanding of the etiopathogenesis of this disorder over the last two decades. CN occurs in a well-perfused foot with both somatic and autonomic neuropathy: the patient presenting with acute CN tends to be slightly younger than is usual for those presenting with foot ulcers. A history of trauma may be present though may be missed because of the severe sensory loss. Although, in its pathogenesis, there are many unanswered questions, improved understanding in recent years of the role of inflammatory pathways might lead to new pharmacologic approaches in the acute phase of the condition. The outcomes in terms of management of CN have been generally poor because of ignorance that leads to delayed diagnosis.

 

Most important in the management of this condition is recognition of the acute Charcot foot. Any patient with known neuropathy who presents with a warm, swollen foot of unknown causation should be presumed to have acute CN until proven otherwise. Contrary to earlier reports, many patients may present with painful, difficult to describe symptoms in the affected foot despite significant neuropathy.

 

In its early stages, all investigations may be normal, including the foot x-ray. The role of the radiologist in the diagnosis of acute and chronic CN is discussed in the next section.

 

Role of Radiologist in in Diagnosing CN

 

As with acute osteomyelitis (see above), the initial radiographs in acute CN may appear (almost) normal, though it is common for soft tissue swelling to be present and radiographically visible, usually over the dorsum of the foot. It is consequently imperative that both the clinician and the radiologist are aware of the possibility of this condition being present. The first more specific radiographic feature is bone demineralization, usually subchondral or periarticular, around the joint(s) involved by the acute CN process (in contrast to acute osteomyelitis, where it is related to the ulcer location). Focal peri-articular fractures may then develop (Figure 5). If CN is suspected, despite non-diagnostic initial radiographs, then the options are to treat as acute CN (see below) and perform serial radiographs at one-to-two-week intervals until the diagnosis is confirmed or no longer clinically suspected, or treat similarly whilst arranging urgent radiological investigation with a more sensitive test (whilst repeating the radiographs if the further tests are delayed). CT scanning may show small avulsion fractures around midfoot articulations that are invisible on plain radiographs, with minimal increase in the sensitivity and specificity over the plain radiograph, but MR scanning (to include fat suppressed sequences) is better, demonstrating soft tissue edema, bone marrow edema and/or ligamentous disruption. If the MR scan shows no marrow signal abnormality in the foot, acute CN is unlikely. Where the appearances or clinical presentation are complex, with both osteomyelitis and acute CN being suspected, Indium labelled white cell scans and PET/CT have a role, though both can be false positive for osteomyelitis in the presence of acute CN. In infection, MR may demonstrate soft tissue abscesses or sinus tracks that may extend to the (infected) bone surface.

 

In chronic inactive CN, plain radiographs demonstrate the features of joint distension, destruction, dislocation, disorganization, debris, increased bone density (sclerosis) and deformity. On MR scanning, marrow edema of acute CN is replaced by low signal from sclerosis of the bone. Acute osteomyelitis superimposed on chronic CN produces a mixed picture requiring careful clinical-radiological review.

 

Diagnosis of acute Charcot neuroarthropathy remains a synthesis of high clinical awareness, clinical findings and radiological findings. The latter should always include serial plain radiography and, where necessary, MR scans.

 

An overview of imaging in the Charcot foot is available online (69).

 

Figure 5. Acute Charcot neuroarthropathy. There is widening of the interosseous distance between the medial cuneiform and 2nd metatarsal (arrowheads), indicating disruption of the Lis-Franc ligament and a subtle flake fracture fragment (arrow).

 

Management of Charcot Neuroarthropathy

 

The treatment of CN depends upon the stage during which it is diagnosed. The essence of treatment in the acute phase remains non-weight bearing immobilization in a total contact or below-knee cast. Duration of treatment will depend upon response and it is recommended to continue casting until the temperature differential between the active and non-affected foot is down to approximately 1.5°C. As for the foot ulcer, it is recommended that treatment in a cast be continued for up to 4 weeks after the temperature differential has settled. At present, there are no proven medical or pharmacological approaches other than casting that have been shown to improve outcome. The management of advanced CN with bone deformity requiring reconstructive surgery is beyond the scope of this chapter and the reader is referred to a detailed review (70).

 

PREVENTION OF FIRST AND RECURRENT ULCERS

 

Prevention will only be successful with the early identification of those patients who have risk factors for foot ulceration. In the 1990s, the concept of the “annual review” was developed, and all those with diabetes should, at whatever stage, be screened for evidence of complications at least annually. The principle aim of such a review is to identify those with early signs of complications and institute appropriate management to prevent progression. The “Comprehensive Diabetic Foot Examination” (CDFE), was developed by a taskforce of the American Diabetes Association (ADA) that was charged with describing what should be included in the annual review for those at risk of foot complications (16). As noted above, the most important aspect of the annual foot review is the removal of shoes and socks with very careful inspection of both feet including between toes. Many neuropathic feet can be identified by this simple clinical observation, looking for features such as small muscle wasting, clawing of the toes, prominence of the metatarsal heads, distended dorsal foot pains (a sign of sympathetic autonomic neuropathy), dry skin, and callus formation. The key components of the diabetic foot annual examination are displayed in table 2.

 

The ADA Taskforce recommended that for evidence of neuropathy, that the perception of pressure using the 10g monofilament should be used at four sites in each foot (16). An additional test which might include a vibrating 128 Hz tuning fork or others outlined in table 2 should also be used to confirm any abnormality.

 

For the vascular assessment, foot pulse palpation is most important. Again, as noted above, the ankle brachial index may be falsely elevated in many people with diabetic neuropathy and therefore listening to the Doppler signal may be more helpful as may be a more detailed non-invasive vascular assessment.

 

More recently, other simple devices for clinical screening have been described. The simplest of all is the “Ipswich Touch Test” developed by Rayman et al in Ipswich, UK. This test simply assesses the ability of the patient to perceive the touch of a finger on the toes (71). The Vibratip which is a battery-operated disposable vibrating stylus can also be used to assess vibration sensation (72), and this has the advantage of using a forced-choice methodology. Both of these tests have been validated in clinical studies (71, 72).

 

Table 2. Key Components of the Diabetic Foot Exam. Adapted from Boulton (16)

Inspection
Evidence of past/present ulcers?
Foot shape?
Prominent metatarsal heads/claw toes
Hallux valgus
Muscle wasting
Charcot deformity
Dermatological?
Callus
Erythema
Sweating
Dystrophic nails

Neurological
10g monofilament at 4 sites on each foot + 1 of the following:
Vibration using 128 Hz tuning fork
Pinprick sensation
Ankle reflexes
Vibration perception threshold

Vascular
Foot pulses
Ankle Brachial Index, if indicated
Doppler wave forms, if indicated

 

Prevention of Diabetic Foot Ulcers

 

Surprisingly, there is no evidence from RCTs to confirm the efficacy of preventative foot care education either in the prevention of first foot ulcers or of recurrent foot ulceration (73). This, however, should be interpreted as lack of evidence rather than evidence of no effect. For those patients with no foot ulcer history found to have any of the risk factors listed above or in table 2, they require education in foot self-care and regular podiatric attention.

 

With respect to secondary prevention, a RCT that looked at the effect of a foot care education program in those with a history of foot ulcers could provide no evidence that such a program of targeted education led to clinical benefit when compared to the usual care (74). It seems likely that those with a history of foot ulcers have such predominant physical abnormalities (e.g., foot deformity, loss of sensation, etc.) that education alone in self-foot care management is insufficient to prevent recurrent ulceration. It may be the combination of foot care education and an intervention that the individual can perform may be more effective. Lavery and colleagues, in studies supported by other RCTs demonstrated in an RCT that patients with a history of neuropathic foot ulcers who were randomized for self-foot temperature monitoring did demonstrate a reduced recurrent ulceration rate. All patients in the active group received foot care education and were provided with a skin thermometer which they used twice a day to check the temperatures of both feet. Those patients who discovered increased unilateral foot temperatures were advised to stop walking and see their health care professional. In the active group there was a highly significant reduction in recurrent foot ulceration (75): however, not all subsequent studies have confirmed this observation (76).

 

Important in the prevention of foot complications in diabetes is the team approach: members of the team commonly include the diabetes specialists, orthopedic and vascular surgeons, podiatrists, nurse educators, physiotherapists, pedorthists, and others. A study from one district in the UK was able to confirm a 62% reduction in major amputations over an 11-year follow-up period: this decrease occurred after the establishment of such a multi-disciplinary diabetic foot care team (77).

 

One of the impacts of the recent Covid-19 pandemic has been an explosion in the use of telemedicine and remote monitoring in the care of the diabetic foot (78). A number of studies are currently ongoing looking at “smart technology” in the prevention of recurrent diabetic foot ulcers. These include the use of sensors in socks or shoes to detect pressure change and also various devices to measure differentials in skin temperature: each of these might alert patients in the pre-ulcerative phase with the hope of preventing the actual ulcer from developing. It has now clearly been confirmed that a temperature differential of 2.2C between the feet using remote at home monitoring in patients at high risk of plantar ulceration is a strong predictor of ulcer development (79). Similarly, intelligent pressure sensing insole systems can reduce the incidence of plantar ulcers in those with a past history of ulceration (80). However, face to face consultations remain crucial in the screening for PAD and neuropathy in people with diabetes.

 

The Foot in Remission

 

As a recurrence is so common after the healing of neuropathic or neuro-ischemic foot ulcers, it has been suggested that those with a history of foot ulcers should be described as having “a foot in remission” rather than healed. This might better communicate risk of recurrence not only to the patient, but also other healthcare professionals (8). It is hoped that, as in cancers, aggressive treatment during the active disease together with a focus on improving care in “remission” can help to maximize patients’ function and of course improve quality of life (8,26) .

 

CONCLUSIONS

 

Although there has been much progress in our understanding of the etiopathogenesis and management of diabetic foot disorders over the last 30 years, much of what we use in clinical practice today still lacks an evidence-base. This is particularly true for example for dressings. The International Working Group on the Diabetic Foot has reported on the details required in the planning and reporting of intervention studies in the prevention and management of diabetic foot lesions (81). Details of the necessary trial design, conduct, and reporting should be taken into account when assessing published studies on interventions in the diabetic foot. Most important of all however in the management of patients with diabetic foot disorders, is to remember that the patient has frequently lost the “gift of pain” that protects most of us from developing significant foot problems but, when absent, can lead to devastating consequences.

 

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Osteoporosis and Bone Fragility in Children

ABSTRACT

 

Childhood is a unique time during which individuals accrue bone rapidly, and peak bone mass is achieved early in the third decade of life. Several factors may adversely influence bone accrual, including primary skeletal disorders as well as secondary causes of low bone density such as specific endocrinopathies, altered weight-bearing, and certain medications. Pediatric osteoporosis is defined by both: 1) a clinically significant fracture history; and 2) a low bone mineral density (BMD). Pragmatically, the diagnosis of osteoporosis is indicated by a BMD Z-score < -2.0 and a clinically significant fracture history, defined as two or more long bone fractures by age 10 years, or three or more long bone fractures at any age up to 19 years. Additionally, the finding of one or more vertebral non-traumatic compression fractures is diagnostic of osteoporosis independent of BMD. Notably, the diagnosis of pediatric osteoporosis should not be made based on densitometric criteria (i.e., DXA) alone. As childhood osteoporosis has several potential underlying etiologies, evaluation requires a careful assessment by a clinician with expertise in the possible mechanisms that may be contributing to the increased skeletal fragility. Both non-pharmacologic therapies as well as bone-active medications, such as bisphosphonates, increase bone mass and may lower the risk of fracture. The development of novel therapies that may restore physiologic anabolic bone activity in children with insufficient bone accrual from various causes has the potential to improve care for pediatric patients with osteoporosis. Prospective data acquisition to inform treatment strategies for primary prevention of fracture in children with osteoporosis, as is done in adult populations, is urgently needed to prevent the significant morbidity of fracture in this vulnerable population.

 

INTRODUCTION

 

Childhood and adolescence are unique time periods during which individuals accrue bone rapidly, and peak bone mass is only achieved early in the third decade of life. Several congenital or acquired factors may adversely influence bone accrual, including primary skeletal disorders, or secondary causes of low bone density such as delayed puberty, endocrinopathies, altered weight-bearing, and certain medications.

 

Pediatric osteoporosis is defined by both: 1) a clinically significant fracture history; and 2) a low bone mineral density (BMD). Pragmatically, the diagnosis of osteoporosis is indicated by a BMD Z-score < -2.0 and a clinically significant fracture history, defined as two or more long bone fractures by age 10 years, or three or more long bone fractures at any age up to 19 years. Additionally, the finding of one or more non-traumatic vertebral compression fractures is diagnostic of osteoporosis independent of BMD. Notably, the diagnosis of pediatric osteoporosis should not be made based only on densitometric criteria (i.e., DXA) (1).

 

ETIOLOGIES

 

Primary Causes of Low Bone Density or Osteoporosis

 

Genetic diversity overall accounts for 60-70% of the variability in bone mass, and numerous genes have been associated with bone density in genome-wide association studies and whole genome sequencing analyses (see Table 1). These include genes in the WNT signaling pathway (such as LRP4, LRP5, SOST, WNT4, WNT16, WLS), the osteoprotegerin-Receptor Activator of Nuclear factor Kappa-Β Ligand (RANKL) pathway (such as OPG, RANKL, RANK), TGFβ signaling (TGFBR3), mesenchymal stem cell differentiation pathway, endochondral ossification pathway (such as RUNX2), the pathway of collagen synthesis (such as COL1A1 and COL1A2) and other genes such as ESR1, CCDC170 (located adjacent to ESR1), VDR, and CALCR (2, 3). Further, several bone density associated loci have been associated with fracture risk, including FAM210A, SLC25A13, MEPE, SPTBN1, DKK1, LRP5, SOST, and  EN1(2-4).

 

In general, conditions that impair bone or connective tissue development can result in low bone density and increased fracture risk. Monogenic disorders leading to low bone density or osteoporosis include the various types of osteogenesis imperfecta, which are discussed in another chapter of Endotext (5) and will not be covered here. Marfan syndrome, caused by mutations in the gene coding for fibrillin-1 (FBN1), is a connective tissue disorder inherited in an autosomal dominant fashion. In addition to abnormalities in blood vessels, ligaments, muscles, and heart valves, the condition is associated with low bone density at multiple sites, particularly after adjusting for the taller height of these individuals, and with reduced bone accrual during adolescence, especially at the femoral neck (6-8). Similarly, certain forms of Ehlers-Danlos syndrome are associated with low bone density, such as those that result from mutations in COL5A1, COL5A2 and COL3A1 (8).  One study of adults with classical or hypermobility Ehlers-Danlos syndrome reported lower bone density, altered bone quality (as assessed by the trabecular bone score), and increased prevalence of morphometric vertebral fractures compared with controls (32% vs. 8% in controls) (9). Another study has reported lower bone density and strength estimates in individuals with hypermobile Ehlers-Danlos syndrome and generalized joint hypermobility spectrum disorder compared to controls (10). Other studies have reported similar data (11, 12). 

 

Low bone density is also observed in patients with homocystinuria with reported low bone density Z-scores in 38% of patients in one study (13) and lysinuric protein intolerance (14-16). High homocysteine levels have been demonstrated to have deleterious effects on osteoblasts and osteoclasts, to increase oxidative stress, disrupt cross-linking of collagen molecules, and increase levels of advanced glycation end products, all of which can reduce bone strength (17). Further, low lysine concentrations are related to growth failure and low bone density (18, 19).

 

Osteoporosis-pseudoglioma syndrome (OPPG) is a condition caused by homozygous or compound heterozygous inactivating mutations in the gene coding for low density lipoprotein related protein 5 (LRP5) (18-20). Wnt ligand binds to the Frizzled/LRP5 complex to activate the canonical Wnt signaling pathway and increase bone formation. Thus, inactivating mutations in LRP5 lead to severe juvenile osteoporosis. The condition is also associated with congenital vision loss that typically manifests in infancy and is a consequence of a spectrum of conditions ranging from phthisis bulbi to vitreoretinal dysplasia. Heterozygous carriers can have low bone density for age and gender norms, but do not demonstrate the eye findings (20, 21). 

 

Hypophosphatasia is a consequence of both recessive and dominant mutations in ALPL, the gene that codes for tissue nonspecific alkaline phosphatase (TNSALP), which is necessary for breaking down inorganic pyrophosphate in bone to enable bone mineralization (22). Reduced mineralization can lead to skeletal defects, altered growth plates resembling rickets, low bone density, and impaired cementum mineralization resulting in early loss of teeth. There are six major forms of hypophosphatasia ranging in severity from very severe (often associated with perinatal demise), to an infantile, juvenile, and adult form, to a very mild form that involves only the teeth (odontohypophosphatasia) and a rare form with normal ALP levels called pseudohypophosphatasia. The severity of the condition depends on the amount of ALP activity that results from the gene mutation.

 

Other primary conditions associated with fragility fractures but without low bone density include McCune-Albright syndrome, osteopetrosis, and pycnodysostosis (mutations in the gene coding for cathepsin-K). As these conditions are rarely associated with pediatric osteoporosis, they are not discussed further here.

 

Secondary Causes of Low Bone Density or Osteoporosis

 

NUTRITIONAL AND MALBSORPTIVE

 

Deficient Intake of Calcium and Vitamin D:

 

Insufficient intake of calcium and/or vitamin D can result in suboptimal bone mineralization, and the associated secondary hyperparathyroidism has the potential to cause deleterious effects on bone. However, data are conflicting regarding the impact of calcium or vitamin D deficiency and their replacement on bone mineral content (BMC) and BMD. One systematic review of dairy intake or calcium supplementation in children and adults 1-25 years old concluded that these measures provide no beneficial effect on bone mineralization or fracture risk (23). A meta-analysis of 21 randomized controlled trials (RCTs) found no significant change in total body BMC in those randomized to supplemental dairy or calcium alone regardless of baseline intake; however, the study did find an increase in whole body BMC in children with low baseline calcium intake who received high doses of dietary calcium supplements or dairy products with or without vitamin D supplementation (24). Another meta-analysis of 19 RCTs reported a small favorable effect on total body BMC and upper limb BMD with calcium supplementation, but no effect at the lumbar spine or femoral neck (25). A more recent meta-analysis of 15 RCTs and three non-randomized studies did find a positive impact of calcium supplementation on femoral neck BMD in children (26). Calcium supplementation has also been reported to have a beneficial effect on bone strength estimates in prepubertal and early pubertal children (27). Of note, maternal calcium supplementation during pregnancy has not been demonstrated to benefit offspring BMD even when baseline intake was low (28).  Overall, data suggest a possible small effect of dietary calcium or dairy supplementation on bone outcomes when baseline intake is low, with greatest effects at the whole body and femoral neck.

 

Similarly, data for the effects of vitamin D deficiency and supplementation are mixed, but overall suggest some effect on bone outcomes. One study reported that baseline 25-hydroxyvitamin D (25OHD) levels predict prospective changes in lumbar spine BMD over the next three years in peripubertal Finnish girls (29), and a case control study of 150 African American children 5-9 years old reported that those with forearm fractures were more likely to be vitamin D deficient (30). In Chinese adolescents, 25OHD levels 20-37 nmol/L (8-15 ng/mL) in girls and 33-39 nmol/L (13-16 ng/mL) in boys are reported to have positive effects on bone outcomes (31). The impact of race is interesting, with dark skinned children typically having lower 25OHD levels than light skinned children, but higher BMD measures. Further, data suggest that vitamin D supplementation in dark skinned (but not light skinned) children living in northern latitudes positively impact femoral neck BMC (32). Some data (but not all) suggest that maternal vitamin D status may predict offspring BMD, with low maternal 25OHD levels being concerning for low peak bone mass in their children (33). However, a meta-analysis of vitamin D supplementation during pregnancy and infancy reported no impact on subsequent bone health (34).

 

Conditions of Low Energy Availability or Energy Deficit

 

Conditions such as anorexia nervosa and the female athlete triad (Triad)/relative energy deficiency in sports (RED-S) are known to be associated with low BMD, reduced bone strength, and increased prevalence of fractures (35, 36), even in adolescents. Anorexia nervosa in both male and female adolescents is associated with low BMD (35, 37-39), and reduced bone accrual in adolescent girls with anorexia nervosa (40) raises significant concerns regarding peak bone mass acquisition. Young oligo-amenorrheic athletes have lower BMD than eumenorrheic athletes at the femoral neck and hip and lower strength estimates at the distal tibia; they also have lower spine BMD and lower strength estimates at the radius than non-athletes (41-43). Factors contributing to impaired bone outcomes include lower lean mass, lower BMI, hypogonadism, low levels of insulin like growth factor-1 (IGF-1), relatively high cortisol levels, and alterations in levels of appetite regulating hormones that also have an impact on bone health,  (such as insulin, leptin, peptide YY and oxytocin) (37, 44).

 

Conditions of Malabsorption

 

Conditions such as celiac disease, inflammatory bowel disease, cystic fibrosis, and biliary atresia are associated with malabsorption of essential nutrients, including vitamin D, that are important for optimizing bone health.

 

Celiac disease is associated with low BMD (45) and an increase in fracture risk (46). One meta-analysis reported that a lifetime history of bone fractures was twice as common in those with celiac disease versus controls, and that a baseline history of celiac disease is associated with a 30% increase in any fracture and 69% increase in spine fracture (46). The impact of celiac disease on bone health is related to a decrease in BMI and lean mass (in those who have poor weight gain or a decrease in body weight following diagnosis), malabsorption with reduced bioavailability of calcium and vitamin D, secondary hyperparathyroidism, an increase in intestinal production of inflammatory cytokines (IL-1β, IL-6 and TNF-α), and because of antibodies that may bind to bone tissue transglutaminase (47, 48). The institution of and adherence to a gluten free diet mitigates most of these factors.

 

Inflammatory bowel disease results in low bone mass in 30-50% of patients, who also demonstrate reduced rates of bone accrual during the adolescent years, resulting in compromised peak bone mass (49). Data for fractures are conflicting, with studies in children reporting modest to no increase in long bone fractures while studies in adults report a 32-40% increase in fracture risk (50-52); asymptomatic vertebral fractures are often missed in retrospective studies based on self-report. Some studies (but not all) report a higher risk of impaired bone health in children with Crohn’s disease (53, 54) compared to those with ulcerative colitis, likely because the former more commonly affects areas of the intestine responsible for absorption of vital nutrients and is more likely to be associated with use of glucocorticoids, but data are conflicting in this regard (55-57). In general, children with Crohn’s disease are most likely to present with growth and puberty delay. There are also conflicting data regarding whether or not bone compromise is more likely in boys (vs. girls) with inflammatory bowel disease (55, 57, 58).

 

In addition to malabsorption of vital nutrients, factors that contribute to low bone density and impaired bone accrual in inflammatory bowel disease include low BMI and reduced lean mass, associated pubertal delay and hypogonadism, poor nutritional intake, reduced physical activity, active inflammation (cytokine secretion by activated T-cells, and increased IFN-γ and TNF-α, which may inhibit osteoblastic activity and active osteoclasts both directly and via RANK ligand), and chronic use of glucocorticoids, which have anti-inflammatory effects (which helps with the condition) but affect bone metabolism at multiple steps (52-55, 59, 60). In general, the severity of disease correlates with the extent of bone compromise.

 

Cystic fibrosis results in low bone density in 30-60% of individuals with the condition, associated with increased fracture risk in adults (61, 62). A 100-fold increase in vertebral fractures and a 10-fold increase in rib fractures has been reported in adults with cystic fibrosis (61), and this can be problematic, as poor bone health can result in non-eligibility for a lung transplant in certain centers (63). Many factors contribute to low bone density including reduced BMI and lean mass when associated with low body weight, low levels of IGF-1, pubertal delay and hypogonadism, malabsorption of fat-soluble vitamins (including vitamins D and K), insufficient protein intake in diet, fecal calcium losses, secondary hyperparathyroidism, physical inactivity, increased secretion of inflammatory cytokines (IL-1β, IL-6 and TNF-α), chronic use of glucocorticoids, and direct effects of chloride channel defects (64-66).

 

Biliary atresia is also associated with malabsorption of fat-soluble vitamins, including vitamin D, and therefore, the condition can result in low bone density, which correlates with the severity of liver disease and jaundice (67, 68).

 

CONDITIONS OF REDUCED MECHANICAL BONE LOADING (INCLUDING DISUSE OR IMMOBILIZATION

 

Mechanical loading leads to a reduction in sclerostin secretion from osteocytes, the mechanosensors of bone, and increased signaling along the canonical Wnt pathway with an increase in bone formation (69). There are data to suggest that an optimal nutritional status and estrogen levels are permissive for these effects of mechanical loading on bone (70). Meta-analyses have demonstrated beneficial effects of bone loading activity on bone in children, particularly in the pre- and early pubertal years (71, 72). Therefore, conditions of reduced mechanical loading are associated with impaired bone accrual and low BMD. Similarly, the pull of muscle on bone is known to have bone anabolic effects. During periods of muscle disuse and prolonged immobilization, in addition to reduced osteoblastic activity (from increased production of sclerostin), there is an activation of osteoclastic bone resorption. Thus, conditions associated with hypotonia, spinal cord injury, spina bifida, muscular dystrophy, spinal muscular atrophy (SMA), and severe burns are associated with impaired bone accrual and low BMD in children and adolescents.

 

Patients with cerebral palsy (particularly those with limited ambulation) have low bone density and increased fracture risk associated with reduced mechanical loading of the skeleton, muscle wasting, suboptimal nutrition, and also vitamin D deficiency or impaired metabolism from concomitant use of certain anti-epileptic drugs (73-75). Studies have demonstrated that the severity of cerebral palsy predicts the severity of low BMD Z-scores in this condition (76, 77).

 

Duchenne and other muscular dystrophies are associated with reduced muscle mass, muscle strength, and muscle function resulting in low bone density and increased fracture risk (75, 78-82). Concomitant glucocorticoid therapy also impacts bone deleteriously, although amelioration of the underlying condition through glucocorticoid use may mitigate these effects to some extent (83). In one study, 53% of patients with Duchenne muscular dystrophy treated with deflazacort had vertebral fractures over a nine-year period (84). Another study has reported a 16-fold increased risk of fracture in patients taking daily deflazacort (85). Vamorolone, a dissociative steroidal anti-inflammatory drug, holds promise for use in this condition without significant bone effects (86). Studies have also reported impaired calcium metabolism and vitamin D status as well as high IL-6 levels in Duchenne muscular dystrophy, which could also contribute to impaired bone health (75, 79, 80, 87). Similarly, spinal muscular atrophy (SMA) is associated with low bone density and increased fracture risk (88-91). Low bone density in patients recovering from burns (92) is consequent to immobilization, muscle wasting, increased release of inflammatory cytokines that active osteoclastic activity and increase bone turnover, and low 25OHD levels (93). In one study, 27% of children with severe burns had low bone density Z-scores (92).

 

ENDOCRINE CONDITIONS

 

Many hormones have a direct impact on osteoblast and osteoclast activity (Figure 1); thus, a disruption in these hormone systems can have deleterious effects on bone.

Figure 1. Regulation of Bone Formation and Resorption. Osteoblasts are the primary bone-forming cells. Osteoblast anabolic activity is stimulated by testosterone and growth hormone and inhibited by cortisol and hyperglycemia. Osteoclasts mediate bone resorption. Thyroid hormone, parathyroid hormone, and inflammatory cytokines increase bone resorption, while estradiol inhibits osteoclast function. Osteocytes embedded within the bone matrix secrete sclerostin which inhibits osteoblast function; mechanical loading decreases sclerostin production thereby “releasing the brake” on osteoblast activity. Calcium deficiency, often as a result of vitamin D deficiency, leads to poorly mineralized bone matrix as well as secondary hyperparathyroidism.

 

Hypogonadism

 

Conditions of hypogonadism (Table 1) are associated with low bone density and impaired bone accrual given the critical role of the gonadal hormones on bone (70). Estradiol has anti-resorptive effects through its effects on the RANK-RANK-ligand-osteoprotegerin system. Estradiol also inhibits secretion of sclerostin, which otherwise inhibits the canonical Wnt signaling pathway and therefore osteoblast action, and also inhibits osteoclastic action (94). Testosterone has both direct bone anabolic and anti-resorptive effects, and also affects bone through its aromatization to estradiol. It increases periosteal bone apposition, while decreasing endosteal bone resorption, which collectively accounts for the larger size and thicker cortices of the male adult skeleton (70). During puberty, the rising levels of estradiol and testosterone are critical for adolescent bone accrual (95), and hypogonadism is therefore associated with reduced bone accrual, low bone density, and an increased risk of fracture (96, 97).

 

Hypercortisolemia

 

Chronic administration of glucocorticoids for underlying inflammatory or other conditions (such as inflammatory bowel disorders, chronic arthritis, Duchenne muscular dystrophy, renal conditions including post-transplant patients, and connective tissue disorders), and endogenous hypersecretion of cortisol (ACTH dependent or independent) can cause low bone density and increase the risk for fracture (98). Excessive exposure to glucocorticoids has multiple deleterious effects on bone. It inhibits osteoblastic activity (through direct effect on osteoblast precursors and stimulation of apoptosis of mature osteoblasts and osteocytes), reduces mechanosensing ability through its osteotoxic effects, increases osteoclast activity by decreasing osteoprotegerin and increasing RANK-ligand secretion from osteoblasts, impairs calcium absorption from the gut, impairs the renal handling of calcium, has an inhibitory effect on the growth hormone (GH)-IGF-1 axis, and leads to reduced muscle mass, impaired collagen formation, and suppression of the HPG axis (98, 99).

 

Importantly, hypercortisolemia is associated with increased fracture risk (particularly of the spine) independent of low BMD, related to the dose and duration of therapy (99). Low bone density can become evident within 3-6 months of therapy and improves in the first year after stopping glucocorticoids (particularly after the first six months). One study in children receiving glucocorticoids for three years for rheumatic disease reported an unadjusted vertebral fracture incidence rate of 4.4 per 100 person-years, and a 3-year incidence proportion of 12.4% (100). The highest annual incidence was in the first year, and every 0.5 mg/kg increase in glucocorticoid dose was associated with a doubling of fracture risk. Of concern, 50% of the fractures were asymptomatic and would have been missed without a lateral spine x-ray (100).  Importantly, recovery of vertebral shape and height appears possible in children affected in the pre- or early pubertal years and is unlikely in those who are mid to late pubertal (99, 101).

 

Chronic, Untreated Hyperthyroidism

 

Chronically high thyroid hormone levels, including at initial diagnosis of Graves’ disease, can lead to increased bone resorption and low BMD, particularly at cortical sites (102-104). An increase in IL-6 levels has been associated with this condition and contributes to increased bone resorption (105). Subclinical hyperthyroidism, as seen in survivors of pediatric differentiated thyroid carcinoma receiving levothyroxine at doses that suppress TSH (but with thyroid hormones levels still in the normal range), does not appear to have major negative effects on bone (106), indicating that high levels of thyroid hormones, but not suppressed TSH, account for the deleterious effects on bone in patients with hyperthyroidism.

 

Hyperparathyroidism

 

Primary hyperparathyroidism is rare in children and adolescents (and mostly associated with conditions such as MEN1 and MEN2), but secondary hyperparathyroidism occurs in conditions of hypocalcemia and vitamin D deficiency, and both secondary and tertiary hyperparathyroidism may be associated with chronic renal disease. The latter is discussed in a later section of this chapter. Chronic hyperparathyroidism causes increased bone resorption and results in low BMD, and the forearms (and primarily cortical sites) are involved to a greater extent that other parts of the body in this condition, with relative sparing of the spine (107).

 

Growth Hormone Deficiency and Resistance

 

Both GH and IGF-1 have multiple effects on bone. GH increases levels of osteoprotegerin, stabilizes the canonical Wnt signaling pathway, increases muscle mass and bone growth, while also stimulating local and hepatic IGF-1 secretion. The latter also stabilizes the canonical Wnt signaling pathway to activate osteoblasts, stimulate bone growth and an increase in muscle mass, increases 1-α hydroxylase activity, thus increasing intestinal absorption of calcium and phosphorus, increases tubular reabsorption of phosphorus, and increases RANK ligand activity. Thus, conditions of GH deficiency and resistance are at risk for low BMD. Adults with GH deficiency in the KIMS database had a 2.7 times higher fracture risk than the general population (108), and other studies have also reported an increased fracture risk in this population (109). However, a higher risk of fractures has not been observed in children with GH deficiency who received GH replacement therapy (110). Further, areal BMD in children with GH deficiency is often no longer low after adjusting for body size (111). Quantitative computed tomography studies have reported normal volumetric BMD, lower cortical thickness, and no differences for trabecular structure in children with GH deficiency vs. controls (112).  In conditions of undernutrition, an acquired state of GH resistance and low levels of IGF-1 contribute to low rates of bone accrual and low BMD (113).

 

Poorly Controlled Diabetes

 

While studies are still in the process of examining the effects of diabetes on bone in children, data seem quite clear that poorly controlled diabetes is associated with low BMD (114-117). This has been linked to low IGF-1 levels secondary to hypoinsulinemia resulting from poor diabetes control, increased markers of oxidative stress, and increased secretion of inflammatory cytokines (118).

 

CHRONIC MEDICAL CONDITIONS

 

Chronic inflammatory states such as inflammatory bowel disorders, connective tissue disorders, chronic arthritis and other inflammatory states are associated with low BMD for multiple reasons, including increased release of proinflammatory cytokines, which activate osteoclastic activity, chronic use of glucocorticoids and possibly some degree of undernutrition. Many of these conditions have been covered in previous sections.

 

Systemic Mastocytosis

 

Systemic mastocytosis is associated with low bone density in adults (119, 120), and BMD in these patients correlates with tryptase levels, mast cell proportion in bone marrow biopsies, and duration since diagnosis (119). Data are lacking in children.

 

Leukemia and Other Malignancies

 

Infiltrative conditions such as leukemia and other malignancies is associated with low bone density. Low bone density in patients with malignancy is a consequence of poor nutrition, malabsorption and diarrhea, vitamin D deficiency and associated hyperparathyroidism, release of inflammatory cytokines, chronic use of glucocorticoids, the effects of chemotherapy (gonadal failure, a direct suppressive effect of alkylating agents on bone marrow, and bone toxicity of high-dose methotrexate), as well as a direct effect of radiation therapy on osteoblasts. Pediatric acute lymphoblastic leukemia (ALL) is a known cause of low bone density and osteoporotic fractures (121-123). One study reported a cumulative fracture incidence of 32.5% for vertebral fractures and 23% for non-vertebral fractures in children with ALL over a six-year period, with 39% of children with vertebral fractures being asymptomatic (123). Vertebral reshaping occurred in younger children, but persistent vertebral deformity was noted in about 25%, particularly in older children and those with more severe vertebral collapse.

 

Beta-Thalassemia and Sickle Cell Disease

 

A large proportion of children with beta-thalassemia are reported to have low bone mass or bone density with reduced bone accrual compared to controls, regardless of transfusion and chelation regimens (124-126). One study reported BMC Z-scores of ≤ -2 in 61% of adolescents with beta-thalassemia (124). Another study reported that 82% and 52% of children and adolescents with transfusion dependent beta-thalassemia had low BMD Z-scores at the spine and the hip, respectively (125). Other studies, however, have reported much lower rates of low BMD in these children. Overall, nutritional status is a major determinant of bone outcomes in this condition.  Similarly, sickle cell disease in children and young adults has been associated with low bone density (127, 128), even after height adjustment (129), related to puberty, hip osteonecrosis, chronic pain, and hemoglobin values (129). Many of these children also have low calcium intake and low serum concentrations of 25OHD (127). Other predictors of low BMD include a low BMI, male sex, delayed puberty, and low serum zinc concentrations (128, 130).

 

Chronic Kidney Disease

 

Chronic kidney disease is a major risk factor for low BMD and fractures because of the associated secondary or tertiary hyperparathyroidism, hyperphosphatemia, reduced mineralization (reduced 1-α hydroxylase), increased cytokines such as TNF-α, and chronic use of glucocorticoids (131-133).

 

IATROGENIC CAUSES

 

Certain medications can also contribute to low bone density in children and adolescents. Antiepileptic medications such as phenytoin, primidone, phenobarbital, and carbamazepine impair vitamin D metabolism by stimulating hepatic microsomal cytochrome P450 enzymes, causing vitamin D deficiency, secondary hyperparathyroidism, and low BMD (134). Data also suggest that antiepileptic drugs may inhibit the cellular response to parathyroid hormone (PTH). Further, use of valproic acid has been associated with increased osteoclast activity and low BMD in some studies. In contrast, newer antiepileptic medications such as lamotrigine and topiramate have not been associated with impaired vitamin D metabolism or low bone density.

 

As already discussed, chronic glucocorticoid use has several deleterious effects on calcium absorption, retention, and osteoblast and osteoclast function. Methotrexate and certain antiviral drugs have also been demonstrated to contribute to impaired bone health. Further, medications that suppress the hypothalamic-pituitary-gonadal axis such as GnRH analogs and depo medroxyprogesterone acetate are associated with low BMD. Lastly, radiation therapy is known to have direct deleterious effects on osteoblasts.

 

LIFESTYLE FACTORS  

 

Cigarette smoking is believed to be a risk factor for low bone density (135), although it is difficult to sort out the effects of smoking on bone versus the contribution of risk factors common among smokers, which include a low BMI, greater intake of alcohol, lower levels of physical activity, and poor diet. The longer the duration of smoking and the greater the number of cigarettes consumed, the greater the risk of fracture. Further, healing following a fracture is slower in smokers than non-smokers, and complications during the healing process are more common in smokers. Even exposure to secondhand smoke has been related to suboptimal bone outcomes. Women who smoke often produce less estrogen and tend to enter menopause earlier, which would also contribute to increased bone loss. Further, levels of cortisol and free radicals are higher in smokers, which may also contribute, and nicotine and free radicals are toxic to osteoblasts. Importantly, quitting smoking does reduce the risk of low bone density and fractures. However, it may take several years to lower a former smoker’s risk.

 

Additionally, alcohol is deleterious to bone when consumed in excess (136); more than two alcoholic drinks per day are associated with low bone density, and may be related to decreased absorption of calcium, increased concentrations of cortisol and PTH, lower levels of estrogen, and alcohol per se is toxic to osteoblasts. Reduced bone density and impaired bone quality contribute to increased fracture risk (137).

 

Table 1. Causes of Low Bone Density or Osteoporosis

PRIMARY CAUSES OF LOW BONE DENSITY OR OSTEOPOROSIS

Osteogenesis imperfecta (COL1A1, COL1A2, IFITMF5, SERPINF1, CRTAP, LEPRE1 and other genes)

Marfan syndrome (FBN1)

Ehlers Danlos syndrome (COL5A, COL3A, non-monogenic forms)

Homocystinuria (CBS, MTHFR, MTR, MTRR, and MMADHC genes)

Lysinuric protein intolerance (SLC7A7)

Osteoporosis pseudoglioma syndrome (LRP5)

Idiopathic juvenile osteoporosis

Hypophosphatasia (ALPL)

Others

Other Primary Conditions Associated with Fragility Fractures but Without Low Bone Density

Polyostotic fibrous dysplasia (GNAS1)

Osteopetrosis (LRP5, CLCN6, CA2, others)

Pycnodysostosis (CTSK)

SECONDARY CAUSES OF LOW BONE DENSITY OR OSTEOPOROSIS

Nutritional and Malabsorptive Conditions

• Deficient intake of calcium and vitamin D

• Conditions of low energy availability or energy deficit (e.g., anorexia nervosa, Female Athlete Triad/Relative Energy Deficiency in Sports (RED-S))

• Conditions of malabsorption (e.g., celiac disease, inflammatory bowel disease, cystic fibrosis, biliary atresia)

Conditions of Reduced Mechanical Bone Loading (Including Disuse or Immobilization)

• Cerebral palsy

• Spinal cord injury

• Spina bifida

• Muscular dystrophy

• Spinal muscular atrophy

• Severe burns

• Conditions of prolonged immobilization

Endocrine Conditions

• Hypergonadotropic hypogonadism:

O     Primary ovarian insufficiency

O     Primary testicular insufficiency

•  Hypogonadotropic hypogonadism:

O     Isolated or combined pituitary hormone deficiencies (genetic and acquired causes)

O     Hyperprolactinemia

O     Functional hypothalamic amenorrhea (conditions of energy deficit, chronic stress)

O     Medications (e.g., depot medroxyprogesterone acetate, GnRH analog therapy)

• Hypercortisolemia:

O     Iatrogenic from prolonged use of glucocorticoids for underlying chronic conditions*

O     Endogenous: adrenal, pituitary and ectopic tumors

• Hyperthyroidism (chronic untreated)

• Hyperparathyroidism

• Growth hormone deficiency and resistance

• Diabetes (particularly when poorly controlled)

Chronic Medical Conditions

• Chronic inflammatory states**

• Mastocytosis

• Infiltrative conditions (e.g., leukemia and other malignancies)

• Thalassemia and sickle cell disease

• Chronic kidney disease

Iatrogenic

• Antiepileptic medications

• Glucocorticoids

• Methotrexate

• Antiretroviral drugs

• Depot medroxyprogesterone acetate

• GnRH analogs

• Radiation therapy

Lifestyle factors

smoking and chronic alcohol use

*Examples: Duchenne muscular dystrophy, inflammatory bowel disorders, chronic arthritis, renal conditions including post-transplant patients, connective tissue disorders, leukemia and other malignancies

**Examples: Inflammatory bowel disease, chronic arthritis, connective tissue disorders, nephrotic syndrome

 

EVALUATION

 

History and Physical Exam

 

Initial evaluation includes a thorough medical history, with special attention to aspects that may adversely affect bone health such as chronic immobility or oncology treatments; medication history, with a focus on past and current medications that may adversely influence bone health, such as glucocorticoids, anti-epileptic drugs, and hormonal contraception; pubertal history, dependent upon age; and family history of recurrent fractures, pre-menopausal osteoporosis, and bone disorders.

 

Additionally, a bone health assessment should include the following: 1) fracture history, including mechanism of injury (e.g., traumatic, fall from a standing height, etc.), treatment (e.g., cast, surgery, and if any complications such as prolonged healing); 2) dietary intake of calcium-rich foods, with quantification of the typical servings per day of dairy, and any supplementation of calcium and vitamin D, including type of supplementation (e.g., calcium carbonate, cholecalciferol, etc.) and dosages; 3) physical activity including sports, dance, gym class, physical therapy, and time in stander, as applicable.

 

The physical exam should be comprehensive and include a thyroid and pubertal exam, palpation of the spine, and assessment for hyper flexibility and any physical restrictions (i.e., contractures).

 

Laboratory Studies

 

Dependent upon the degree of clinical concern for osteoporosis or increased bone fragility, determined by the history, next steps could include assessment of bone mineral density by DXA, laboratory studies, and additional testing. If the bone fragility history is equivocal, it is reasonable to start with a DXA and perform additional evaluation if there is demonstrated low BMD. However, if the history is strongly suggestive of osteoporosis or increased bone fragility, the next steps are typically DXA and laboratory evaluation (see Table 2). It is helpful to assess calcium, magnesium, phosphorus, alkaline phosphatase, 25OHD, PTH, screening for celiac disease, and creatinine. Urinary calcium and creatinine ratio (spot) can be helpful to assess calcium status and there is an increased risk of hypercalciuria in non-ambulatory patients. Rarely, bone turnover markers, such as bone formation markers osteocalcin and bone specific alkaline phosphatase and the bone resorption marker c-telopeptide, may be helpful, if there is a clinical concern for a low bone turnover state. Also, 1,25-dihydroxyvitamin D (1-25OHD) is not routinely assessed, but is helpful if there is a clinical concern for a disorder of vitamin D metabolism. Additional biochemical assessments should be considered on a case-by-case basis. Notably, for all laboratory assessments, it is important to have pediatric reference ranges, and pubertal specific (i.e., Tanner stage) reference ranges when applicable, in order to properly interpret values.

 

Imaging Studies

 

EVALUATION OF BONE MINERAL DENSITY

 

DXA is the clinical gold standard for measuring BMD (138). The current International Society for Clinical Densitometry (ISCD) pediatric guidelines for optimal bone densitometry assessments include: for 4-15 years old total body less head and lumbar spine; 16 years and older lumbar spine and hip (1). By age 15 years, the skeletal landmarks at the hip that guide positioning are well-developed and enable the replication of positioning. In adolescent patients, it may be useful to perform a transition scan around 16 years old, including total body less head, lumbar spine, and hip, as this will enable assessment of interval change at two skeletal sites. The current ISCD pediatric guidelines suggest measurement of hip BMD in the school-age child if lack of weight-bearing and skeletal fragility are concerns. In certain clinical scenarios, it may be useful to obtain a distal lateral femur or forearm scans, such as in patients with neuromuscular disorder with impaired mobility (139). Distal lateral femur scans can be very informative in non-ambulatory patients. Forearm scans can be useful in patients who are unable to hold still, those with significant contractures, and in patients with orthopedic hardware that precludes scans of other skeletal sites.

 

It is helpful to assess interval change enabling evaluation of bone accrual and comparison of Z-scores over time (i.e., did they increase, remain the same, or decrease). The shortest interval usually assessed is one year, and dependent upon the clinical situation, it may be prudent to reassess after two years or longer, especially if it would not change clinical management. From a practical standpoint, insurance typically requires DXA scans to be performed at least one year apart (> 365 days from last DXA scan), but all scanning sites should be covered and are determined by medical necessity.

 

DXA is interpreted via areal BMD (g/cm2) calculated Z-scores which are age, sex, and ancestry matched and based on pediatric normative data (140). A Z-score less than -2.0 SD is low, and between -1.0 to -2.0 SD is considered borderline low and may be of clinical significance in patients with risk factors for increased bone fragility. Notably, in pediatrics, the diagnosis of osteoporosis requires both: 1) a clinically significant fracture history, which is defined as at least two long bone fractures in children less than 10 years old, at least three long bone fractures by 19 years old, or any vertebral fractures; and 2) low bone density, with BMD Z-scores < -2.0, assessed by DXA.

 

However, as a two-dimensional projected area of a three-dimensional structure, DXA is affected by bone size. For this reason, pediatric DXA derived areal BMD is affected by bone size and smaller bones may have an artifactually lower BMD Z-score. To take this into account, the BMD Z-score can be adjusted for height (i.e., height for age Z-score) in those with short stature (https://zscore.research.chop.edu/calcpedbonedens.php) or, in certain scenarios, adjusted for bone age if a patient has delayed puberty but is not short (141).

 

DXA only assesses bone mass and density and does not fully capture all factors contributing to bone fragility, such as volumetric BMD (g/cm3), bone microarchitecture (e.g., trabecular vs. cortical bone), bone quality, or bone strength. Additional research modalities allow for the assessment of bone microarchitecture, quality, and strength, such as peripheral quantitative computed tomography (pQCT), high resolution pQCT, and trabecular bone score (TBS), a measure of bone quality of the lumbar spine which correlates to bone microarchitecture. There are recently published pediatric TBS reference ranges (142). However, there are few pediatric normative data for these alternative modalities, currently limiting their use to primarily the research setting.

 

ASSESSING FOR COMPRESSION FRACTURES

 

It is important to evaluate the patient for compression fractures in patients with low bone density and clinical concern, such as back pain or unexplained decrease in physical activity. If there is acute concern for compression fractures, initial evaluation should include spine x-rays, typically two-view anteroposterior and lateral radiographs. If imaging is consistent with compression fracture(s), there should be prompt evaluation by orthopedics and endocrinology, as the disease course can be positively affected with appropriate treatment.

 

Vertebral fracture assessment (VFA) is an additional spine assessment that can be performed concurrently with DXA to assess for spine vertebral fractures. It is commonly used in adults but has only recently been utilized in children (143). Advantages of VFA over spine radiographs include lower radiation dose, logistics (done at the same visit as DXA), and lower cost. There is emerging evidence that it is useful to screen for vertebral fractures with VFA in high-risk pediatric populations, such as those with Duchenne muscular dystrophy and osteogenesis imperfecta.

 

RADIOGRAPHY

 

Radiographs (i.e., x-rays) do not quantify bone mass and are not a good screening tool for low bone mass. However, if radiographs are performed for other indications, such as a clinical concern for fracture or related to another medical evaluation, when there is at least 30-40% bone loss, there are typical findings, such as bone demineralization, gracile bones, and thin cortex. If there is radiographic concern for low bone mass, with concurrent risk factors for suboptimal bone accrual, this should be further evaluated with a DXA to quantify BMD. Radiographs can be useful to assess for specific findings in several bone disorders including rickets, which is a consequence of under-mineralization of bone in growing children; skeletal dysplasias, which are often diagnosed based on radiographs; osteopetrosis, with over-mineralization of bone; and osteogenesis imperfecta, of which several types have a substantial number of wormian bones on skull radiograph.

 

Consultative Services

 

Additional consultations may be required, depending upon the specific underlying etiology of the patient’s low bone density. For many patients, especially those who are underweight, intolerant of cow milk-based foods (i.e., milk protein allergy), or have an eating disorder, working closely with a nutritionist to ensure adequate caloric intake and calcium-rich foods is very useful. Patients with mobility challenges, such as hypermobility and non-ambulatory patients, often benefit from working with physical therapy. Dependent upon the suspected underlying disease, additional evaluation by other subspecialists, such as a geneticist or gastroenterologist, may be helpful.

 

Table 2. Laboratory and Imaging Evaluation for Increased Bone Fragility and Osteoporosis

Laboratory Studies

Standard Evaluation

calcium with albumin, magnesium, phosphorus, alkaline phosphatase, 25-hydroxyvitamin D, parathyroid hormone, tissue transglutaminase with IgA, creatinine

Consider*

genetic testing for osteogenesis imperfecta and possibly other genetic disorders (dependent upon family history), TSH/fT4, pubertal assessment (FSH, LH, estradiol, testosterone), bone turnover markers (osteocalcin, bone specific alkaline phosphatase, c-telopeptide), 1,25-dihydroxyvitamin D, erythrocyte sedimentation rate and c-reactive protein (if known or suspected chronic inflammatory disease), urine calcium and creatinine ratio (spot)

Imaging Assessments

Standard Evaluation

DXA – sites dependent upon age and logistics**

Consider*

Screening lateral spine x-rays in high-risk patients, VFA in high-risk patients, skull x-ray if concern for osteogenesis imperfecta, skeletal survey if concerned for skeletal dysplasia

* Consider additional assessment on a case-by-case basis

** See text for details regarding recommended sites

 

TREATMENT

 

Non-Pharmacologic Interventions to Optimize Bone Mineral Density and Bone Strength

 

CALCIUM AND VITAMIN D

 

Calcium is a critical component of bone, necessary for the formation of hydroxyapatite which confers strength to the bone matrix (144). Calcium is a threshold nutrient, meaning that once adequate intake is achieved to maximize calcium retention, further intake does not provide additional benefit to bone health (145). The optimal calcium intake for any individual depends on several factors: these include vitamin D status, given that vitamin D stimulates gut absorption of calcium, as well as other dietary factors such as sodium and protein intake which can alter renal calcium excretion (146). In addition to impairing skeletal mineralization, dietary calcium insufficiency may cause a secondary hyperparathyroidism, promoting bone resorption and phosphate excretion, further decreasing bone density. The United States National Academy of Sciences guidelines provide a Recommended Dietary Allowance (RDA) of calcium which is anticipated to meet the needs of 97.5% of the healthy population (Table 3) (147).

 

Table 3. Recommended Daily Intake of Calcium and Vitamin D by Age

Age

Calcium intake (mg)

Vitamin D intake (IU)

0-6 months

200

400

7-12 months

260

400

1-3 years

700

600

4-8 years

1000

600

9-18 years

1300

600

19-50 years

1000

600

 

1-25OHD, the active metabolite of vitamin D, is critical for optimal gastrointestinal absorption of calcium. Vitamin D sufficiency is assessed by circulating concentrations of 25OHD, though there is some controversy regarding the 25OHD threshold which reflects sufficiency. The Institute of Medicine (IOM) has defined sufficiency as 25OHD ≥ 20 ng/mL (147), based largely on bone biopsy evaluation of unmineralized osteoid accumulation (148), while other guidelines recommend a target of 30 ng/ml (149). To achieve these serum concentrations, the IOM recommends daily intake of 400 IU in the first year of life, and 600 IU from ages 1-70 years (Table 3). However, individual patients may require higher intakes to achieve vitamin D sufficiency, including those with malabsorptive conditions such as cystic fibrosis and inflammatory bowel disease (150, 151). In addition, individuals with obesity have a smaller incremental increase in 25OHD concentration with supplemental vitamin D and may require 2000 IU daily or more to achieve target serum concentrations (152).

 

For children on high-dose glucocorticoid therapy for underlying inflammatory or oncologic disease, several specific effects on calcium and vitamin D metabolism must be considered. Glucocorticoids can directly inhibit the gut absorption of calcium via decreased expression of epithelial calcium channels (153). In addition, glucocorticoids can inhibit the synthesis of 1-25OHD and accelerate the catabolism of vitamin D metabolites (154). Therefore, these patients may require higher than typical intake of calcium and vitamin D, which should be guided by monitoring circulating concentrations of 25OHD and PTH.

 

Studies of calcium supplementation in healthy children suggest that increases in BMD may be limited to prepubertal children and in those with low baseline calcium intake, again supporting the model of calcium as a threshold nutrient (155, 156). Long-term follow-up studies indicate that the effect of calcium supplementation wanes after discontinuation of the intervention (25, 157-160). Similarly, a meta-analysis of pediatric vitamin D supplementation studies indicated only modest effects on BMD which were limited to those with a baseline 25OHD <14 ng/mL (161). One follow-up study showed a loss of effect on BMD three years after completion of the supplementation intervention (162). These data suggest that, for children at risk for low calcium intake or low circulating vitamin D metabolites, optimization of these factors should be an ongoing process.

 

PHYSICAL ACTIVITY

 

Mechanical loading of the skeleton via high-impact physical activity promotes bone acquisition in growing children (71). Several observational studies have shown an association of childhood physical activity with increased BMD (163-167), with effects that persist into young adulthood (168, 169). A meta-analysis of RCTs confirmed a significant though small effect of physical activity on measures of bone mass, with increased responsiveness in pre-pubertal participants (170). Interestingly, this analysis also revealed a positive association of calcium intake with bone mineral content and density, suggesting that calcium enables or synergizes with the effects of weight-bearing (171, 172). Among healthy children, a threshold force of approximately 3 times the force of gravity, such as experienced during running or jumping, seems to be required to stimulate bone formation (173). Importantly, physical activity is beneficial even in healthy children with a high genetic risk for low BMD (174).

 

The role of weight-bearing activity in children with underlying musculoskeletal disease is less well-studied. Small studies of children with cerebral palsy have shown efficacy of increasing time of use in a stander (175) and a physical therapy program (176) to improve BMD. Whole-body vibration (WBV) has been studied in children with several conditions (177) including cerebral palsy (178-182), Duchenne muscular dystrophy (183-185), osteogenesis imperfecta (186, 187), and Down syndrome(188). Synthesis of the results of these studies is challenging due to methodological variation in the magnitude and frequency of vibration as well as the length of treatment sessions. In general, among children with cerebral palsy, WBV appears to have positive effects on bone density and bone strength estimates, while data are conflicting or limited in other conditions. 

 

Pharmacologic Intervention

 

WHOM TO TREAT WITH BONE ACTIVE MEDICATIONS

 

Selection of appropriate pediatric patients for pharmacological intervention is not straightforward (189). Unlike in adults, for whom low BMD alone suffices to confer a diagnosis of osteoporosis, the diagnosis of osteoporosis in children requires evidence of skeletal fragility, defined as multiple long-bone fractures or a vertebral compression fracture (190). Current evidence-based guidelines for the use of pharmacotherapy do not recommend prophylactic use of pharmacotherapy given the absence of robust prospective data enabling estimation of fracture risk in vulnerable children (191). This differs from guidelines for osteoporosis management in adults, in whom primary prevention of fracture is a goal (192). Given that, particularly in children with progressive neuromuscular disease, a single fracture can lead to permanent loss of ambulation (193, 194), further research to better define which pediatric patients may benefit from prophylactic therapy is urgently needed. Indeed, in certain particularly high-risk patients, such as those with spinal muscular atrophy (SMA), clinicians may choose to treat in advance of a patient meeting pediatric osteoporosis criteria (195).

 

Conversely, some children who fulfill criteria for osteoporosis may not warrant pharmacotherapy. Children with secondary causes of osteoporosis which may be transient, such as an inflammatory disease that responds to treatment, or glucocorticoids that are discontinued, have the potential to repair BMD losses as well as to spontaneously heal vertebral fractures. As an example, in a cohort of children with Crohn’s disease, initiation of anti-TNF-alpha therapy led to significant increases in BMC and BMD Z-scores over 12 months, indicating “catch-up” bone accrual (196). A study of fractures among children with acute lymphocytic leukemia (ALL) demonstrated that, while the cumulative incidence of vertebral compression fracture over 6 years was 33%, complete healing with restoration of normal vertebral shape was observed in 77% of those with fractures. Predictors of healing included younger age (mean 4.8 vs 8.0 years) and number and severity of fractures (123). Lower cumulative glucocorticoid doses may also correlate with greater chance of spontaneous healing in children with inflammatory disease (101). The decision whether or not to initiate pharmacotherapy thus depends on a careful weighing of each child’s individual clinical history and anticipated course of disease (189).

 

BISPHOSPHONATE TREATMENT

 

For children at high risk of fracture, bisphosphonates are the best-studied and most widely used pharmacologic treatment. Bisphosphonates are non-hydrolysable analogs of pyrophosphate that bind tightly to hydroxyapatite crystals and inhibit osteoclast-mediated bone resorption (197). Once embedded in bone, bisphosphonates are retained in the pediatric skeleton for several years, as evidenced by detectable urinary concentrations up to eight years after administration (198). Bisphosphonates are available in both oral and intravenous formulations. The bioavailability of oral bisphosphonates is extremely low, and there is significant intraindividual skeletal retention of bisphosphonates, which depends in part on endogenous bone turnover and renal function (199).

 

Table 4. Selected Bisphosphonates: Dosing and Examples of Pediatric Uses

Bisphosphonate

Administration

Typical Dosing Regimen

Use in Pediatrics

Alendronate

PO

5-10 mg daily(200) or 35 mg weekly(201)

·  Osteogenesis imperfecta(200, 202-204)

·  Glucocorticoid induced osteoporosis(205, 206)

·  Duchenne muscular dystrophy(207, 208)

·  Cerebral palsy(209)

·  Cystic Fibrosis(210)

·  Acute lymphoblastic leukemia(211)

·  Spinal cord injury(212)

·  Transplant(213)

Risedronate

PO

2.5-5 mg daily(214) or 15-30 mg once weekly(215)

·  Osteogenesis imperfecta(214-216)

·  Duchenne muscular dystrophy(217)

·  Cerebral palsy(218)

·  Non-ambulatory children(219)

 

Pamidronate

IV

9 mg/kg year, given as 0.25-1 mg/kg daily for 3 days every 2-4 months(220)

·  Osteogenesis imperfecta(204, 221, 222)

·  Glucocorticoid induced osteoporosis (223)

·  Cerebral palsy(224-226)

·  Acute lymphoblastic leukemia(227)

·  Idiopathic juvenile osteoporosis(228)

·  Burns(229)

 

Zoledronic acid

IV

0.05-0.1 mg/kg year, every 3-12 months(230, 231)

·  Osteogenesis imperfecta(230, 232-235)

·  Glucocorticoid induced osteoporosis(236)

·  Duchenne muscular dystrophy(237)

·  Cerebral palsy(238, 239)

·  Rett syndrome(239)

 

Neridronate

IV

2 mg/kg every 3-6 months(240)

·  Osteogenesis imperfecta(240, 241)

·  Osteoporosis pseudoglioma syndrome(242)

 

Early studies of bisphosphonate therapy in children focused on those with osteogenesis imperfecta. Treatment with both oral and intravenous formulations leads to significant increases in BMD at both the hip and spine (200, 214, 215, 243-245). Subsequent studies in other conditions including cystic fibrosis and glucocorticoid induced osteoporosis showed similar increases in BMD with bisphosphonate use (205, 210). This is a non-trivial result, given that skeletal fragility in osteogenesis imperfecta, as in most pediatric conditions, is not mediated by accelerated bone resorption. A primarily anti-resorptive medication thus does not address the underlying cause of low BMD. However, trans-iliac biopsy data demonstrate that bisphosphonate therapy in children leads to increases in cortical width, via modeling-based bone formation at the periosteal and endocortical surfaces (246). In addition, trabecular BMD increases via an increase in trabecular number but not in thickness. This effect is hypothesized to be due to a greater retention of primary trabeculae after new bone formation and subsequent incorporation into secondary spongiosa (246).

 

While the beneficial effects of bisphosphonates on bone density are well-documented, effects on the more critical outcomes of fracture and associated morbidities are less clear and almost exclusively limited to the osteogenesis imperfecta population (see Endotext chapter on osteogenesis imperfecta for details). In adults, data from a recent individual patient data meta-regression of osteoporosis trials revealed significant and strong correlations between increases in BMD and fracture risk reduction (247). Whether this result generalizes to growing children is uncertain. Small observational studies and randomized controlled trials suggest that bisphosphonates may reduce the incidence of vertebral fracture in glucocorticoid-treated children (101, 237, 248). Data regarding anti-fracture efficacy in other conditions including cerebral palsy is lacking (238).

 

The choice of which bisphosphonate to use, as well as the optimal dosing regimen and length of treatment, is challenging due to a limited number of trials as well as their relatively small size. Some studies suggest that intravenous (IV) agents may be more effective at promoting vertebral fracture healing (249), though a head-to-head study of alendronate vs. pamidronate in children with osteogenesis imperfecta showed no difference in BMD accrual, suppression of bone turnover markers, or fracture incidence (250). A major consideration is the risk of pill esophagitis with oral bisphosphonates, which is exacerbated by the presence of gastrointestinal reflux, leading to the recommendation that patients should swallow pills only with water and remain upright for at least 30 minutes after administration. Given the significant challenge this poses to many children with osteoporosis due to an underlying neuromuscular or other chronic disease, IV bisphosphonate therapy is often the most practical choice. Dosing regimens vary both by underlying condition and between institutions; typical dosing regimens are noted in Table 4.

 

How long to continue therapy once initiated is also not well-defined. Because growing children accrue new bone via modeling-based growth, intermittent dosing regimens result in new bone not being exposed to bisphosphonates. This leads to the classic “zebra-lines” seen on x-rays of children treated with IV bisphosphonates (251). Concern has arisen that the junction between regions of treated and non-treated bone may be at particularly high risk of fracture (252, 253). For children with primary osteoporosis, continuation of therapy until the completion of growth is thus typically recommended. Monitoring of BMD, via DXA, as well as careful assessment of fracture incidence both by history and spine imaging can guide the maintenance phase of therapy which may require decreases in the dose or frequency of administration (252, 253). In children with secondary osteoporosis in which the underlying condition has resolved or is well-controlled, discontinuation of treatment with close monitoring may be appropriate (191).

 

Short-term Adverse Effects of Bisphosphonates

 

Because the skeleton functions as a reservoir for calcium as well as phosphate, anti-resorptive therapy can lead to short-term hypocalcemia and hypophosphatemia, which typically presents in the first 1-3 days after infusion though may have a more delayed onset (234, 254, 255). While often asymptomatic, due to the possibility of symptomatic hypocalcemia requiring IV calcium infusion, it is critical to mitigate this risk by ensuring vitamin D sufficiency (i.e., 25OHD > 30 ng/mL) and optimization of oral calcium intake via diet or supplementation starting the night prior to infusion and continuing for the following 5-10 days. Due to the higher risk of electrolyte abnormalities with the first dose, a 50% reduction is commonly employed (256). Acute phase reaction characterized by myalgia, bone pain, fever, nausea, and headache is seen in 20-80% of patients following the first IV infusion (255-258) and can typically be managed with anti-pyretic, analgesic, and anti-nausea medication as needed.

 

Particular care must be taken with patients on glucocorticoid therapy who may have iatrogenic central adrenal insufficiency and may thus require stress-dose glucocorticoid treatment to provide 24-hour glucocorticoid coverage as well as careful anticipatory guidance about the risk of adrenal crisis in this setting. As bisphosphonates are renally cleared, it is critical to assess renal function in children prior to administration to prevent nephrotoxicity. For children with underlying musculoskeletal disease, serum creatinine may not be an accurate reflection of renal function, and measurement of cystatin C as an alternative assessment of renal function should be performed (259). While concerns about bisphosphonates interfering with fracture healing have been raised, this has not been borne out by evidence except in the special case of iatrogenic injury via osteotomy (260).

 

Other Adverse Effects of Bisphosphonates

 

In adults, particularly at the high doses used in malignancy, bisphosphonates have been reported to cause several rare but serious adverse events including atypical femoral fracture (AFF) and osteonecrosis of the jaw (ONJ). An AFF is a low-trauma, transverse fracture of the subtrochanteric femur, typically preceded by prodromal pain (261). While such fractures have been seen in children with osteogenesis imperfecta, this may reflect the natural history of the disease and not be related to bisphosphonate use (262, 263). Case reports of AFFs in bisphosphonate-treated children with other conditions including idiopathic juvenile osteoporosis (264) and SMA (195), suggest that anticipatory guidance regarding the possibility of AFF and early symptoms should be offered to patients. Several case-finding series have not identified bisphosphonate associated ONJ in children (265, 266). Several cases of an osteopetrosis-like phenomenon have been reported in children exposed to bisphosphonates; in all cases, these were at substantially higher bisphosphonate doses than are typically prescribed to children (267, 268). Finally, possible teratogenicity of bisphosphonates, particularly given their prolonged retention in and release from the skeleton has been raised as a potential concern. However, a case series of twenty one women exposed to bisphosphonates just prior to conception or during pregnancy did not demonstrate any concerning signal of fetal harm (269).

 

OTHER AGENTS

 

Denosumab is a humanized monoclonal antibody against RANKL, a critical factor for osteoclast differentiation and activation. As such, similar to bisphosphonates, denosumab is a potent anti-resorptive medication. The effective half-life of denosumab is much shorter than bisphosphonates, and a major clinical challenge in its use is the “rebound effect,” specifically an increase in bone turnover markers above pre-treatment baseline levels and a significant increase in vertebral fractures after discontinuation in adults (270, 271). In several case reports of denosumab use in children, this rebound can present as severe hypercalcemia within just several weeks following the previous dose (272-276). Given these considerations, denosumab is currently used only sparingly in pediatric populations with specific indications including osteogenesis imperfecta type 6 (277, 278) and giant cell tumors (279-281).

 

Given that most pediatric osteoporosis stems from insufficient bone accrual (i.e., decreased bone formation), the use of anabolic rather than anti-resorptive agents may offer better efficacy (282, 283). Sclerostin is an endogenous inhibitor of the canonical wnt-β-catenin signaling pathway, and romosozumab, an anti-sclerostin antibody, has been approved for women with post-menopausal osteoporosis (284, 285). An alternative sclerostin antibody, setrusumab, has been investigated in a phase 2 trial of adults with osteogenesis imperfecta (286), and pediatric studies of both antibodies in osteogenesis imperfecta are ongoing (Clinicaltrials.gov: NCT05768854, NCT05125809, and NCT04545554).

 

Teriparatide, the c-terminal portion of PTH, is also approved for post-menopausal osteoporosis and has potent osteoblast-stimulating activity. Until recently, the United States FDA included a black box warning about increased risk of osteosarcoma in patients treated with teriparatide based on pre-clinical models. While phase 4 data have not confirmed an excess risk in clinical patients and this black box warning was removed in 2020, persistent FDA guidance to avoid teriparatide in patients with open epiphyses has limited its use. A recent small study of adolescent boys with Duchenne muscular dystrophy suggested decreased fracture incidence with teriparatide and no significant adverse events (287). Most patients in this study were treated for two years and then transitioned to an anti-resorptive therapy to prevent the loss of BMD observed after discontinuation of teriparatide in adults (288, 289).

 

CONCLUSIONS

 

Childhood osteoporosis has several potential underlying etiologies, requiring a careful assessment by clinicians with expertise in the numerous mechanisms which can contribute to skeletal fragility. Both non-pharmacologic therapies as well as bone-active medications such as bisphosphonates increase bone mass and may lower the risk of fracture. The development of novel therapies that can restore physiologic anabolic bone activity in children with insufficient bone accrual of various causes has the potential to improve care for pediatric patients with osteoporosis. Prospective data acquisition to inform treatment strategies for primary prevention of fracture in children with osteoporosis, as is done in adult populations, is urgently needed to prevent the significant morbidity of fracture in this vulnerable population.

 

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  239. Wiedemann, A., et al., Annual Injection of Zoledronic Acid Improves Bone Status in Children with Cerebral Palsy and Rett Syndrome. Calcif Tissue Int, 2019. 104(4): p. 355-363.
  240. Gatti, D., et al., Intravenous neridronate in children with osteogenesis imperfecta: a randomized controlled study. J Bone Miner Res, 2005. 20(5): p. 758-63.
  241. Maines, E., et al., Children and adolescents treated with neridronate for osteogenesis imperfecta show no evidence of any osteonecrosis of the jaw. J Bone Miner Metab, 2012. 30(4): p. 434-8.
  242. Celli, M., et al., Clinical and biochemical response to neridronate treatment in a patient with osteoporosis-pseudoglioma syndrome (OPPG). Osteoporos Int, 2017. 28(11): p. 3277-3280.
  243. Adami, S., et al., Intravenous neridronate in adults with osteogenesis imperfecta. J Bone Miner Res, 2003. 18(1): p. 126-30.
  244. Gatti, D., et al., Intravenous bisphosphonate therapy increases radial width in adults with osteogenesis imperfecta. J Bone Miner Res, 2005. 20(8): p. 1323-6.
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I agree w/ Madhu. Also, I think, in general, people are doing less of a PE, so this is a reminder

 

Carney Complex

ABSTRACT

 

Carney complex (CNC) is a rare dominantly inherited syndrome of multiple neoplasias combined with cardio-cutaneous manifestations. Approximately 70% of index cases have a familial history, while the remaining 30% have a de novo germline mutation. Hitherto, two loci have been principally involved in the genetics of CNC: the CNC1 gene, located on 17q22-24, which is coding the regulatory subunit (R1a) of the protein kinase A (PRKAR1A) and is responsible for 2/3 of cases, whereas the putative “CNC2” gene at the 2p16 locus has not been identified as yet. As most of the identified PRKAR1A mutations are nonsense and lead to a lack of detectable mutant protein, no genotype-phenotype correlations are generally observed. Cutaneous lesions (lentigines, nevi, and myxomas), although with minimal clinical impact, are the most common and occasionally specific findings, assisting early diagnosis. Cardiac myxomas show an atypical presentation and contribute substantially to mortality. Among several associated endocrine neoplasias, Primary Pigmented Nodular Adrenal Dysplasia is the one most frequently observed, followed by thyroid nodules, somatomammotrope adenomas, and testicular tumors. The diagnosis is principally set by 12 major clinical criteria and 2 supplemental criteria, including molecular testing and family history. Molecular testing, which has a mutation detection rate of approximately 60%, cannot currently be recommended for all patients. If testing is performed and a mutation is detected, genetic screening is recommended for first-degree relatives. Surveillance for all the manifestations of CNC should be performed at least annually, starting in infancy. As CNC is generated by a constitutional genetic defect, no etiologic therapy is available yet. The therapeutic approach should target each clinical manifestation and treat accordingly.

 

INTRODUCTION - HISTORICAL OVERVIEW

 

Carney complex (CNC - Online Mendelian Inheritance in Man 160980, 608837) is a dominantly inherited syndrome of multiple neoplasias combined with cardiocutaneous manifestations. The neoplastic lesions are both endocrine (adrenal, pituitary, thyroid, testicular tumors) and non-endocrine (myxomas, schwannomas). The skin lesions are divided into two major types: a) pigmented such as lentigines and blue nevi that can be observed on the face, neck, and trunk and b) not pigmented such as cutaneous myxomas (1) (Figure 1).

Figure 1. Spotty pigmentation of the face. With permission http://ugen.nichd.nih.gov.

This syndrome was first described by J. Carney in 1985, as “the complex of myxomas, spotty pigmentation, and endocrine overactivity”. In the original study, 40 patients were included, and a familial distribution was reported in 10 of them. Additional evidence for unifying this coexistence of otherwise rare conditions in an inherited clinical entity was the young age at presentation and the unusual type of involvement of most affected sites, which tended to be multicentric (heart and skin) and bilateral in paired organs (adrenal, breast, and testis) (2). One year later Carney reported observations consistent with Mendelian dominant inheritance of the syndrome (3) that in the meanwhile was designated as “Carney complex” (CNC) by Bain (4). This new entity included patients manifesting cardiocutaneous lesions, previously diagnosed as LAMB (lentigines, atrial myxoma, mucocutaneous myxoma, blue nevi) (5) and NAME (nevi, atrial myxoma, myxoid neurofibroma, ephelides) (6).

 

In 1996, linkage analysis studies by Stratakis et al. (7) demonstrated a locus potentially linked to CNC on chromosome 2p16, in proximity to the gene encoding proopiomelanocortin and the DNA-mismatch repair genes hMSH2 and hMSH6. However, the syndrome was later shown to be genetically heterogeneous (8), and in 1998, a second possible locus located on chromosome 17q2 was detected (9). In 2000, two different research teams demonstrated that germline mutations in the gene coding the alpha regulatory subunit (R1a) of protein kinase A (PKAR1A) located on the locus 17q22-24 were responsible for several phenotypes of CNC (10,11). More recently, mutations of other genes, which encode the catalytic subunit α or β of the PKA, and phosphodiesterases 11A and 8B have been reported in CNC patients (1).

 

Nowadays, diagnosis of the syndrome is feasible in clinically asymptomatic patients by commercially available molecular genetic assays and next-generation sequencing techniques. Notably, Carney’s complex should not be confused with Carney’s triad, a completely different entity consisting of the triad of gastric leiomyosarcoma, pulmonary chondroma, and extra-adrenal paraganglioma.

 

EPIDEMIOLOGY AND INHERITANCE

 

Carney’s complex is a rare disease and the majority of cases have been registered by the NIH-Mayo Clinic (USA) and the Cochin Center (Paris, France) consortium (12,13). Approximately 70% of individuals diagnosed with CNC have a familial history, while the remaining 30% present as a de novo germline mutation. In large series, a predilection of female over male gender has been observed (63% vs. 37% respectively), whereas there is no apparent predilection concerning ethnicity (14).

 

CNC is inherited as a dominant trait, although transmission through a female affected parent is almost 5-fold more frequent than the male. A possible explanation for this discrepancy might be the fact that male patients often harbor Large Cell Calcified Sertoli Cell Tumors (LCCSCT), which may hamper fertility (15). Moreover, data from animal models correlate haploinsufficiency at the PRKR1A gene locus with male infertility, independently of LCCSCT (16). The median age of diagnosis is 20 years; however, in many cases, a diagnostic delay of decades is reported. In general, the penetrance of CNC is 70%-80% by the age of 40 years, as clinical manifestations accumulate during the lifespan. The maximum number of affected generations reported in one kindred is 5 (9).

 

MOLECULAR GENETICS AND PATHOPHYSIOLOGY

 

 Hitherto, two loci have been principally involved in the genetics of CNC: 17q22-24 and 2p16.

 

CNC1 Gene

 

The CNC1 gene, located on 17q22-24, is 21 kb long and contains 11 exons, coding the regulatory subunit (R1a) of the protein kinase A (PRKAR1A), a protein of 384 amino acids (17). Protein Kinase A (PKA) is an enzyme involved in G protein-coupled intracellular pathways and serves as a mediator of c-AMP actions promoting cell metabolism, proliferation, and apoptosis. Its quaternary structure consists of 4 peptide chains that form a tetramer of two regulatory (R) subunits, each bound to one catalytic (C) subunit (18). So far four subtypes of regulatory (RIα, RIβ, RIIα, and RIIβ) and four subtypes of catalytic subunits (Cα, Cβ, Cγ, and Prkx) have been identified. A corresponding gene is coding each R (PRKR1A, PRKR1B, PRKR2A, PRKR2B) and each C subunit (PRKACA, PRKACB, PRKACG, PRKX) respectively (19). When c-AMP binds to the regulatory subunits, their conformation is altered, causing the dissociation of each active C subunit from the dimer with the corresponding R subunit. The free catalytic subunits then phosphorylate serine and threonine residues of proteins critical to the activation of downstream processes, such as cAMP response-binding protein (CREB) (Figure 2).

 

Figure 2. The G protein-coupled intracellular pathways and the defect in CNC patients: PRKAR1A mutations result in deficient / inefficient regulatory subunits, resulting in constitutional activation of C subunits (http://prkar1a.nichd.nih.gov).

 

Heterozygous inactivating mutations of PRKAR1A have been detected in more than 70% of affected individuals. Interestingly, in patients presenting with Cushing's syndrome (CS) this frequency rises to about 80%. (20). Up to date, 140 different PRKAR1A mutations have been registered at the CNC consortium database (http://prkar1a.nichd.nih.gov), and they are distributed among the 11 exons of the PRKAR1A gene, showing a predilection for exons 2, 3, 5 and 7, which are more often mutated, whereas exon 1, is non-coding and rarely mutated.  Most of them are family or patient-specific; however, certain hot-spot mutations have been identified such as the  c.709- 7del6 in intron 7, c.491-492delTG in exon 5, and c.82C > T in exon 2 (21).

 

The penetrance for CNC due to PRKAR1A mutations is higher than that encountered in CNC due to other genetic defects, reaching 98% (12). The vast majority of mutations (83%) lead to a premature stop codon (nonsense) and thus, short mutant mRNAs that are eliminated by selective degradation, a phenomenon known as nonsense-mediated mRNA decay (NMD) (17). The result is a lack of detectable mutant protein and a reduction of RIα protein levels by 50%. The rest of the mutations (17%) result in the expression of an altered protein (missense) that may be associated with more severe phenotypes (22). Large PRKAR1A deletions have also been detected in a proportion of CNC patients, who also express a more severe phenotype with unusual features. These deletions are more prominent (21.6%) among patients negative by conventional Sanger sequencing, rendering array-based studies necessary for diagnostic confirmation of such cases (23). The structure of the PRKR1A gene and the location of detected mutations are shown in Figure 3.

 

Figure 3. Schematic presentation of the PRKR1A gene and detected mutations in relation to their exon location.

 

Germline haploinsufficiency of PRKAR1A leads to a deficiency of the R1a subunits, which in turn results in enhanced intracellular signaling by PKA due to unhindered activation of the catalytic (C) subunits, as evidenced by an almost 2-fold greater response to c-AMP in CNC tumors and cell lines (24,25). How this PKA overactivity leads to tumor development has not been fully elucidated. According to previous studies, PKA-enhanced activity may trigger pathways that favor cell proliferation as the upregulation of D-type cyclins (26) or activation of the mTOR pathway (27). Recent studies in adrenocortical cell lines have confirmed the accumulation of cyclin D1 and further suggest Bcl-xL upregulation, which is associated with resistance to apoptosis (28). Consistent with the Knudson two-hit model of hereditary tumorigenesis, PRKAR1A haploinsufficiency (first hit) has been considered as a predisposition for tumorigenesis, which when combined with loss of heterozygosity (LOH) at 17q22- 24 (second hit), may lead to the development of tumors in CNC patients (29). Interestingly, tumors that do not present inactivation of the remaining wild-type allele have also been described, implying that the coexistence of PRKAR1A haploinsufficiency with defects of other tumor suppressor genes or proto-oncogenes may act synergistic for tumorigenesis (30). Accordingly, activating somatic mutations of the beta-catenin gene (CTNNB1) have been detected in adrenocortical tumors of CNC patients, carriers of a PRKAR1A mutation (31).

 

These findings were supported by experiments on Prkar1a +/- knockout mice, the genotypic animal model of Carney’s complex. These mice were developed by inserting an antisense transgene for Prkar1a exon 2 and present with many of the manifestations of CNC, such as adrenocortical hyperplasia with cortisol hypersecretion, thyroid follicular neoplasia non-pigmented schwannomas and bone lesions (32). On the contrary, mice with complete loss of Prkar1a were not viable as this genotype leads to early embryonic demise due to failure of heart tube development (33). Eventually, the development of thyroid and pituitary cell tumors as well as heart myxomas was achieved by inducing tissue-specific complete ablation of Prkar1a (34,35). Moreover, mice double heterozygote for Prkar1a and Trp53 or Rb1 developed more sarcomas and grew more, and larger pituitary and thyroid tumors compared to the single Prkar1a heterozygotes (36).

 

Other Loci

 

Approximately 30% of the families affected with CNC are not related to defective PRKAR1A. The putative “CNC2” gene located at the 2p16 locus is linked to the majority of them; nevertheless, it has not yet been identified. These patients present with a milder phenotype, they are diagnosed later in life and are usually sporadic cases. Initial studies demonstrated amplification of a 10 Mb region at the 2p16–23 locus in PRKAR1A-negative CNC patients. Moreover, somatic alterations of the 2p16 region have been reported in CNC tumors which are usually gene amplifications, whereas, tumor-specific LOH has not been a consistent feature of CNC2 (37). These data suggested that the gene located at 2p16 is a potential oncogene that may code a PKA catalytic subunit.

 

Recently, alterations of PRKACA and PRKACB resulting in a gain of function of the catalytic subunits α and β of PKA respectively, have been associated with components of CNC (38,39). Similarly, inactivating mutations of the phosphodiesterase 11A (PDE11A) gene (located at 2q31.2) and PDE8B, which result in augmented cAMP signaling, have been demonstrated in isolated PPNAD patients (40,41), while CNC patients present a high frequency of PDE11A sequence variants (42).

 

GENOTYPE AND PHENOTYPE CORRELATIONS

 

 Efforts have been made to relate specific phenotypes to corresponding genotypes. A study analyzing 353 patients and 80 different genotypes demonstrated that individuals carrying a PRKAR1A mutation tended to present manifestations earlier and were more likely to have pigmentary disorders, myxomas, and thyroid as well as gonadal tumors. Mutations located in exons were more often associated with acromegaly, myxomas, lentigines, and schwannomas, while intronic mutations had a less serious phenotype  (21). As most of the identified PRKAR1A mutations are nonsense and lead to a lack of detectable mutant protein due to NMD, no genotype-phenotype correlations are expected to be seen. However, specific hot-spot mutations show some genotype-phenotype correlation, such as c.709-7del6, which is associated with the development of PPNAD and c.491-492del, which is frequently associated with cardiac myxomas, lentigines, and thyroid tumors. Regarding those few missense mutations that lead to the expression of a mutant protein, they are related to more severe forms of CNC syndrome, suggesting that NMD may play a protective role against the deleterious effects of mutant products (43).

 

CLINICAL MANIFESTATIONS

 

Carney’s complex is a constellation of clinical manifestations that shows significant variability between patients, even among members of the same family. Some of these features are quite specific, like PPNAD, while others are not, such as thyroid nodules or blue nevi (1). The maximum number of conditions reported to be present together in a single patient is five. Skin disorders are the most common, followed by cardiac myxomas and PPNAD (44,45). These data are summarized in Table 1.

 

Table 1. Clinical Manifestations of CNC

 

A

B1

B2

Adrenal

 

 

 

·       PPNAD

26.0

54.3

57.1

·       Possible PPNAD

 

 

11.4

Cardiac myxoma

53.0

18.6

22.9

Skin

 

37.1

60.0

·       Lentigines

77.0

30.0

55.7

·       Skin myxomas

33.0

14.3

20.0

·       Blue nevi

 

11.4

17.1

Pituitary

 

 

 

·       Certain hypersomatotropism

10.0

8.6

18.6

·       Possible hypersomatotropism

 

-

30.0

Multiple thyroid nodules or carcinoma

5.0

7.1

11.4

Testicular calcifications/LCCST

33.0

20.0

35.0

Breast

 

 

 

·       Benign lesions

3.0

 

42.0

·       Myxomatosis

 

2.0

0

·       Adenoma

 

4.0

0

·       ACR 2-3

 

n/a

0

·       Carcinoma

 

6.0

10.0

Schwannomas

10.0

 

 

·       Confirmed by histology

 

4.3

4.3

·       Suspected

 

0

5.7

Osteochondromyxomas

 

 

 

·       Confirmed by histology

 

2.9

2.9

·       Suspected

 

0

2.9

  1. A) at the time of presentation among 338 patients from an older study (44) and B) from a recent prospective study including 70 patients at the time of presentation (B1), and after three years of follow-up (B2); (45)

 

Most often clinical signs appear in the teen years and early adulthood, with a median age of diagnosis at 20 years of age, while, evidence of the disease, especially cutaneous lesions, can be found even in newborns. During infancy, the most common tumors encountered are cardiac and cutaneous myxomas, as well as PPNAD, while LCCSCT and thyroid nodules appear somewhat later. Acromegaly is clinically evident during the third and fourth decade of life, while cardiac myxomas are equally distributed during the life span (46).

 

The average historic adjusted life expectancy of CNC patients has been reported to be 50-55 years, principally due to individuals who succumb from early cardiovascular sudden death: complications due to cardiac myxoma (myxoma emboli, cardiomyopathy, cardiac arrhythmia, surgical intervention) comprise the major factor of mortality for CNC patients (43). Other less important factors are metastatic or intracranial PMS, thyroid carcinomas, and metastatic pancreatic and testicular tumors (1,44).

 

Cutaneous Pigmentary Disorders

 

These lesions may appear either as multiple lentigines or as blue nevi. They may be present at birth; however, they acquire their typical intensity and distribution around puberty when they increase in number and appear anywhere on the body. Typically, they fade after the fourth decade, although they have been reported in individuals as old as 70 years. Occasionally café au lait spots and depigmented lesions may also be observed (47).

 

LENTIGINES

 

They are the most common cutaneous manifestation of CNC patients (70-75%) and usually present as multiple small (0.2 to 2 mm) brown to black macules that can practically appear on any part of the body with areas of confluence and foci of deeper pigmentation. They are typically located around the orifices of the body, such as on the vermilion border of the lips, on the eyelids, ears, and the genital area (Figure 1). Macroscopically, lentigines are flat, poorly circumcised macules, though in African- Americans, they may be slightly raised, similar to nevi. They may look like solar lentigines; however, they differ as they develop predominantly in areas that have not been exposed to sunlight (e.g., genitalia) and do not change with sun exposure. Histologically, the hyperpigmentation of CNC lesions is associated with melanocytic hyperplasia and hypertrophy, rather than increased melanin production as observed in solar lentigines (47).

 

BLUE NEVI

 

These are larger lesions (up to 8 mm), blue to black, and dome-shaped. They are less common than lentigines but still represent the second most frequent skin manifestation in CNC. They may be multiple with a variable distribution. Histologically, they may present features of epithelioid, junctional, or even compound nevi. Epithelioid blue nevi, currently known as Pigmented Epithelioid Melanocytomas, comprise a class of uncommon melanocytic tumors of intermediate malignancy, which may frequently present lymph nodes metastasis but rarely disseminate to distantorgans (48).

 

Myxomas

 

CUTANEOUS MYXOMAS

 

The skin myxomas present as non-pigmented subcutaneous nodules with a smooth surface and may look white, flesh-colored, opalescent, or pink (Figure 4). They are generally asymptomatic and appear up to the fourth decade. Myxomas can emerge on the face and trunk, while typical sights in CNC are the eyelids (the most common site), external ear canal, and nipples. Less common sites of myxoma formation include the oropharynx (tongue, hard palate, and pharynx) and the female genital tract (uterus, cervix, and vagina). Interestingly, hands and feet are preserved (47). Clinical diagnosis is quite difficult as they are often confused with common “skin tags” and other overgrowths, thus histological confirmation is usually required. Lesions can be localized to the upper dermis and subcutis and consist of polygonal to stellate dermal fibroblasts scattered singly or in non-encapsulated clusters against an abundant basophilic myxoid matrix (2). Although cutaneous myxomas have minimal impact on the clinical course of CNC, their recognition is crucial since they are the most specific manifestation of CNC and may herald the presence of a potentially fatal cardiac myxoma (49)

 

Figure 4. Cutaneous myxoma on the right flank of a CNC patient. With permission from Dermatology Online Journal 2004; 10 (3): 11.

 

CARDIAC MYXOMAS

 

Although these tumors are benign, they are responsible for the majority of deaths (>50%) related to CNC mainly due to cardiovascular complications. In a recent prospective study of 319 CNC patients, 42.6% developed cardiac myxomas and the mean age at diagnosis was in the 3rd decade of life, occasionally presenting as early as at 4 years. The risk of developing cardiac myxomas was elevated among patients already presenting thyroid lesions or breast myxomas. They can develop in any cardiac chamber, with a predilection in the left atrial septum, while they may be multiple and recurrent, therefore, their resection cannot guarantee a permanent cure. Almost half of the patients harboring a cardiac myxoma will experience recurrence, and the risk is increased among women, lasting up to 20 years after the initial detection (49). Of notice, the detection of an apparently sporadic cardiac myxoma should alert the physician, as CNC-associated myxomas represent a significant proportion (7%) of these rare tumors. However, there are significant differences between cardiac myxomas in CNC and their sporadic counterparts regarding their epidemiology, distribution, and biological behavior. Sporadic myxomas emerge most commonly in middle-aged women and are almost exclusively localized at the left atrial aspect of the interatrial septum, at the fossa ovalis. In addition, most of them are cured by surgical resection and do not recur (50).

 

Heart myxomas typically present with a triad of symptoms: a) Symptoms related to myxoma embolization (e.g., stroke, peripheral artery occlusions), b) Heart failure due to reduced cardiac output (complete occlusion of a valvular orifice can lead to sudden death) c) Constitutional symptoms (emaciation, recurrent fevers) probably related to production of cytokines [e.g., interleukin (IL-6)], by the tumor (51). Their size ranges from a few millimeters to 8 cm in diameter and can be partially calcified. They can be depicted sonographically as isoechoic (compared with the heart wall) masses inside the cardiac chambers. They can be studied further with magnetic resonance imaging (MRI), where they appear as hyperintense lesions on T2-weighted images (52). Histologically, the tumors have a gelatinous or hemorrhagic appearance and arise from a population of multipotent subendocardial mesenchymal precursor cells (53)

 

BREAST MYXOMAS (MYXOID FIBROADENOMAS)

 

These lesions are observed in about a fifth of women with Carney complex and are generally considered benign breast tumors. They usually occur in females after puberty and can be multicentric as well as bilateral (Figure 5). Their size ranges from 2mm to 2cm in diameter and may be pink or white with a mucoid appearance. Physical examination of the breast is indicative of diffuse nodularity without dominant masses. Nipple discharge, breast skin abnormalities, or sentinel lymphadenopathy are not features of breast myxomas (54). Histologically, breast myxomas appear as lobulated mesenchymal lesions, characterized by accumulations of large amounts of ground substance in the lobules, as well as in the interlobular stroma. The tumors may or may not be encapsulated (2).

 

Figure 5. Breast multiple myxomas in a patient with Carney complex. Mammogram (A), shows typical dense breasts in a younger woman with no evidence of tumor. However, in the fat-suppressed magnetic resonance image (B) shown on the right, the presence of multiple small myxomas is clearly seen. With permission http://ugen.nichd.nih.gov.

 

When detected in mammography, they appear as well-defined, non-calcified, isodense, or hypodense lesions. Occasionally, they may have an irregular contour, a worrisome finding that warrants fine-needle aspiration (FNA), even in proven CNC patients. However, the imaging modality of choice is MR mammography as it has greater sensitivity compared to ultrasonography or conventional mammography. The number of myxoid lesions depicted with this technique is usually numerous (more than 58 per breast in a case) and shows a homogeneous increase of the signal intensity, a situation characteristic of CNC, also referred to as “breast myxomatosis” (52).

 

OSTEOCHONDROMYXOMAS

 

Osteochondromyxomas or Carney bone tumors are rare myxomatous tumors of the bone that principally affect nasal sinuses and long bones. They have been described in a few cases (1-5%) and exhibit benign behavior; however, they can occasionally cause bone erosion and extend into soft tissues (55). Radiologically they can present as osteolytic lesions with aggressive periosteal new bone formation or as an expansive bone area with mixed sclerotic and lucent regions). These lesions often get the characteristic appearance of “ring sign”, which is evident in plain radiographs, computed tomography, and MRI and are quite specific for CNC (56). Complete resection of the tumor is usually curative. Experiments in rodents demonstrated the osteoblastic origin of the lesion and that the knockdown of PRKAR1A disrupts the differentiation of osteoblasts (56,57).

 

Endocrine Tumors and Overactivity

 

PPNAD (PRIMARY PIGMENTED NODULAR ADRENAL DYSPLASIA) PPNAD

 

This is the endocrine disorder most frequently observed in individuals with CNC. It bilaterally affects the adrenal glands and, according to recent data, can cause clinically overt Cushing’s Syndrome in more than 50% of patients with CNC (45). However, autopsy studies have provided histological evidence that PPNAD is present in almost every CNC individual (2). In 12% of the CNC patients, isolated PPNAD is the only manifestation. A bimodal age distribution is observed: a first peak occurs during infancy, while a second one that includes the majority of cases takes place between the second and third decade of life. The median age at diagnosis is 34 years and it is predominantly observed in females (sex ratio 2.4:1) (44). Histologically, the adrenal cortex is dominated by small pigmented micronodules with an average size of less than 10mm (Figure 6). Although not encapsulated, the nodules are sharply demarcated from the remainder of the cortex and most of them appear to originate deep in the cortex almost at the level of the medulla. A brown-pigmented substance, lipofuscin, is contained in many of the tumor cells and is responsible for the characteristic color of the lesions. Interestingly, tumor cells stain positively for neuroendocrine markers (e.g., Synaptophysin), while normal cortical cells don’t (58). Internodular cortical atrophy is typical, thus the overall weight of the adrenal gland remains more or less normal (2).

 

Figure 6. Macroscopic and CT-scan findings in primary pigmented nodular adrenocortical disease (PPNAD). A: Macroscopic appearance of the adrenal gland where multiple pigmented micronodules are evident at the cut surface. B: Adrenal CT scan revealed a micronodule on the external limb of the left adrenal (see red arrow). Copyright © 2006 Bertherat; licensee BioMed Central Ltd.

 

Radiological and scintigraphic findings are not specific, since the adrenals may appear bilaterally or unilaterally enlarged but in most cases, they appear normal (59). Computed Tomography (CT) is the most appropriate examination for depicting adrenal lesions in PPNAD. Particularly, images obtained with a slice thickness of 3 mm or less, before and after intravenous (IV) injection of contrast are preferable as they might reveal subtle contour irregularities and the presence of hypodense spots that correspond to small, pigmented nodules. The characteristic picture is that of “beads on a string” (52). The type of hypercortisolism observed in this disorder is that of ACTH-independent adrenal hyperfunction. However, demonstrating cortisol overproduction can be challenging because it may develop progressively over the years. Moreover, intermittent, or cyclic forms of hypercortisolism have been reported (60). Clinical manifestations are non-specific and similar to those observed in patients with Cushing syndrome (CS) of other etiologies (central obesity, hypertension, myopathy), with a predisposition to osteoporosis. A 6-day Liddle’s test (low dose dexamethasone for 2 days followed by high dose dexamethasone for 2 days) has been used for the distinction of PPNAD from CS caused by other primary adrenal disorders (61). A paradoxical increase of UFC and/or 17-hydroxysteroids of more than 50% on the second day after high-dose dexamethasone administration is indicative of PPNAD. However, recent reports have argued against the utility of Liddle’s test by demonstrating low sensitivity (39%) and specificity (45). Initial screening with overnight dexamethasone suppression test and urine free cortisol is suggested instead.

 

Notably, reports from independent groups describe the development of adrenocortical cancer (ACC) in the context of CNC (62,63). In both reports, the patients carried PRKAR1A mutations and ACC developed on the background of PPNAD. This observation together with previous reports of benign macronodules (between 1 and 3.5 cm) in adrenal glands affected with PPNAD implies a continuum of tumorigenesis from adrenal hyperplasia to benign nodules, and then cancer, associated with alterations in other tumor suppressor genes apart from PRKAR1A (64).

 

GROWTH HORMONE (GH)-SECRETING PITUITARY ADENOMAS (ACROMEGALY)

 

Clinically evident acromegaly due to a pituitary GH-secreting tumor has been observed in approximately 10-12% of patients with CNC, whereas, gigantism, resulting from excessive GH secretion prior to puberty, is quite rare (44). Data from a recent prospective study, raise this figure to 18%, with a median age at diagnosis 34.5 years (45).

 

The usual underlying pathology is a solitary pituitary adenoma, while cases of multiple adenomas or even diffuse somatomammotrope hyperplasia, a possible precursor of GH-producing adenomas, have been demonstrated in CNC patients (65) as well as in specific Prkr1a knockout mice (66). Pituitary adenomas usually stain positively for both GH and PRL and are occasionally accompanied by mild hyperprolactinemia (67). However, almost a third of CNC patients present asymptomatic disturbances of the somatotroph axis, without meeting the diagnostic criteria of acromegaly, even without pituitary MRI findings (45).

 

THYROID NODULES

 

Seventy-five percent of CNC patients present with thyroid nodules, most of them being benign, non-toxic follicular adenomas. Thyroid nodules usually appear during the first ten years of life in CNC patients. Occasionally, patients (~3%) present with papillary or follicular carcinoma, particularly after a long history of multiple thyroid adenomas (21). In contrast to experimental data and what is observed in CNC patients with adrenal and pituitary tumors, thyroid nodules do not appear to have a predilection for hyperfunction (68).

 

TESTICULAR TUMORS

 

These tumors are of three types: A) Large Cell Calcifying Sertoli Cell Tumors (LCCSCT), B) Leydig cell tumors, and C) adrenocortical rest tumors. So far, the two latter types have been observed only in patients in whom LCCSCT had already been diagnosed.

 

LCCSCTs are observed in 20-50% of affected CNC males at the time of presentation, however, most males will develop such tumors in their adult life (21,45). These tumors are rarely observed in sporadic forms (<1% of testicular tumors), however, they are common in syndromes such as CNC and Peutz-Jeghers, where they are often multicentric and bilateral. They are almost always benign; malignancy has been rarely reported, particularly in tumors exceeding 6 cm in diameter. Nevertheless, their local expansion results in the replacement and compression of the normal testicular tissue (69). Occasionally (25%), LCCSCT may be hormone-producing and demonstrate increased P-450 aromatase expression (15). LCCSCT often presents as rock-hard and non-tender testicular masses and in ultrasonography, they appear as heterogeneous lesions of increased echogenicity with large areas of calcification (70). Macroscopically they are well-demarcated, yellow, and calcified tumors. Clinically, these hormone-producing tumors may cause sexual precocity in young males with low gonadotropin levels, as well as gynecomastia that may result from aromatase overactivity. Typically, fertility is impaired due to obstruction of the seminiferous tubules (16).

 

Leydig cell tumors and adrenocortical rests are both steroid-producing tumors and macroscopically are quite similar, characterized by a brownish hue and relatively soft texture. Leydig cell tumors may show malignant behavior, thus radical resection has been typically recommended. On the contrary, adrenal rests are benign lesions that do not require resection but can lead to recurrent Cushing’s syndrome after adrenalectomy (71). The histological distinction between these two types of tumors can be difficult and a useful feature is the detection of crystalloids of Reinke that are present solely in Leydig cell tumors. However, these crystalloids are not a constant finding. In such case, testicular vein sampling can be helpful, as it may demonstrate cortisol gradient between peripheral and testicular venous blood.

 

OVARIAN LESIONS

 

Eight to 14% of female patients with CNC may present with ovarian lesions, either cystic or solid tumors of the ovarian surface epithelium, such as serous cystadenomas and teratomas. The percentage of ovarian lesions rises up to 60% in autopsy series (72). Ovarian cysts are usually clinically insignificant, whereas, tumors may progress, occasionally, to ovarian carcinoma, particularly in the elderly.

 

Psammomatous Melanotic Schwannomas

 

Psammomatous Melanotic Schwannomas (PMS) are encapsulated tumors of the peripheral nerve sheath and are observed in less than 10% of individuals with CNC, usually in the fourth decade of life (21). Other hereditary syndromes that may present with PMS are neurofibromatosis and isolated familial schwannomatosis. Schwannomas in CNC are heavily pigmented and present frequently with calcifications and multicentricity. Their dark, brownish pigmentation is attributed to elongated spindle-shaped Schwann cells with melanogenic potential. Calcifications are encountered in a laminated form called psammomas and may be accompanied by hemorrhage and necrosis (73). PMS can develop anywhere in the central and peripheral nervous system; however. the most frequent locations are the nerves of the gastrointestinal tract and the paraspinal sympathetic chain (28% of cases). Other sights involved are the chest wall with involvement of the adjacent ribs and the trigeminal ganglion.

 

The initial presentation is usually characterized by local compression; whenever located in the gastrointestinal tract or within soft tissues they may evoke pain and discomfort. If they develop in the spine they may present as radiculopathy. Schwannomas are among the most difficult tumors to treat, especially when they emerge around nerve roots along the spine, a location that makes excision not feasible. In addition, in rare cases (10%), they can be malignant and then often metastasize to the lungs, liver, or brain (74). Unfortunately, there is a paucity of effective treatments for metastatic PMS. Promising results have been recently published for the combination of the check-point inhibitor Nivolumab along with concurrent external beam radiotherapy (75).

 

OTHER MANIFESTATIONS

 

Apart from the major clinical manifestations, there are many other features suggestive of CNC, however, they are not present in a constant manner to set the diagnosis (44). These features are listed in Table 2.

 

Table 2. Findings Suggestive or Possibly Associated with CNC, but Not Diagnostic for the Disease.

1. Intense freckling (without darkly pigmented spots or typical distribution).

2. Blue nevus, usual type (if multiple).

3. Café-au-lait spots or other "birthmarks".

4. Elevated IGF-I levels, abnormal OGTT, or paradoxical GH responses to TRH testing in the absence of clinical acromegaly.

5. Cardiomyopathy.

6. Pilonidal sinus.

7. History of Cushing’s syndrome, acromegaly, or sudden death in extended family.

8. Multiple skin tags and other skin lesions; lipomas.

9. Colonic polyps (usually in association with acromegaly).

10. Hyperprolactinemia (usually mild and almost always in association with clinical or subclinical acromegaly).

11. Single, benign thyroid nodule in a young patient; multiple thyroid nodules in an older patient (detected by ultrasonography).

12. Family history of carcinoma, in particular of the thyroid, colon, pancreas, and ovary; other multiple benign or malignant tumors.

 

Breast ductal adenomas are benign tumors of the mammary gland ducts that may also develop in the context of CNC and can be multiple and bilateral as well. Coexistence with breast myxomas can be observed (54). They are palpable, painless masses that usually appear near the areola and can produce bloody nipple discharge. Radiologically their appearance varies from well-delineated and spherical to completely irregular lesions and they always contain calcifications (52). These calcifications may be coarse (typically benign) or microcalcifications, which are often encountered in adenocarcinomas. Moreover, a possible association between CNC and breast cancer has been demonstrated in the most recent prospective study, affecting up to 13.5% of female patients at an unusually young age (<50 years) (45). Consequently, the differential diagnosis is difficult, and FNA is always recommended.

 

Other tumors reported in around 2,5-4,5% of CNC patients are pancreatic neoplasms including acinar cell carcinoma, adenocarcinoma, and intraductal pancreatic mucinous neoplasia (45,76). In addition, CNC is associated with increased detection of liver lesions, including hepatocellular adenomas, carcinomas, and fibrolamellar carcinomas (77,78).

 

DIAGNOSIS

 

The diagnosis of CNC is principally set by clinical criteria and can be confirmed by molecular testing, which has a mutation detection rate of approximately 60-70%. Genetic testing currently can only be recommended either as an adjunctive test for individuals who meet the clinical criteria or for the detection of affected members of families where the index case harbors a known mutation, in order to avoid unnecessary medical surveillance of non-carriers (1).

 

The following clinical criteria were initially proposed in 1998, were revised in 2001, and have not been modified since then. They yield a sensitivity of nearly 98%. They include 12 clinical manifestations that set the major criteria for diagnosis, as well as 2 supplemental criteria regarding molecular testing and family history. At least two major criteria need to be present to establish the diagnosis of CNC and their occurrence has to be confirmed either biochemically, histologically, or by imaging as indicated. In the presence of one supplemental criterion, a single clinical manifestation is sufficient to establish the diagnosis (44).

 

Major Criteria

 

Skin pigmentation disorders

  1. Spotty skin pigmentation with a typical distribution (vermilion border of the lips, conjunctiva, and inner or outer canthi, vaginal and penile mucosa)
  2. Blue nevus, epithelioid blue nevus (multiple)*

Myxomas

  1. Cutaneous and mucosal myxomas*
  2. Cardiac myxomas*
  3. Breast myxomatosis* or fat-suppressed magnetic resonance imaging findings suggestive of this diagnosis
  4. Osteochondromyxoma*

Endocrine tumors / Overactivity

  1. Primary pigmented nodular adrenal dysplasia (PPNAD)* or a paradoxical positive response of urinary glucocorticosteroids to dexamethasone administration during Liddle’s test
  2. Acromegaly due to GH-producing adenoma or evidence of excess GH production
  3. Large-Cell Calcifying Sertoli Cell Tumor (LCCSCT)* or characteristic calcification on testicular ultrasonography
  4. Thyroid carcinoma* or multiple, hypoechoic nodules on thyroid ultrasonography, in a young patient

Miscellaneous

  1. Psammomatous Melanotic Schwannoma*
  2. Breast ductal adenoma*

* histologically confirmed

 

Supplemental Criteria

  1. Affected first-degree relative
  2. Inactivating mutation of the PRKAR1A gene

 

MANAGEMENT

 

So far, no evidence-based monitoring schedule has been established for CNC; however, clinical work-up for all the manifestations of CNC should be performed at least once a year in all patients, and asymptomatic known mutation carriers, should start in infancy.

 

Surveillance

 

Prepubertal children should be screened as follows:

  • Cardiac ultrasound should start as soon as the diagnosis is made, based either on clinical or genetic grounds, and be performed at least once a year thereafter. In patients with a history of cardiac myxoma, screening should be more frequent, optimally every 6 months, due to the increased risk of recurrence (49).
  • Patients should undergo an initial thyroid ultrasound within the first decade of age, and then repeated according to findings.
  • Screening for the other manifestations should be performed in patients under 5 years of age only by clinical examination. Especially for males, testicular ultrasonography is recommended at the initial evaluation and if microcalcifications are present it should be repeated yearly. Regarding ovarian and breast imaging of female patients, these may be deferred until after puberty (1).
  • Pubertal staging and growth rate should be monitored as pediatric patients with CNC may present with failure to thrive, a possible outcome of various CNC components, such as Cushing’s syndrome due to PPNAD or hepatic involvement (79). On the other hand, the presence of a functional LCCSCT may be associated with growth and maturation acceleration.

 

In post-pubertal adolescents and adults, the following investigations should be performed at initial diagnosis and annually thereafter, including screening for:

  • Cardiac myxomas by echocardiography, which if positive, should be repeated bi-annually. The possibility of first occurrence decreases with age and is exceptional after the age of 50 (49).
  • PPNAD by measurement of urinary free cortisol, ACTH, and overnight suppression with 1 mg Dexamethasone, followed by a formal Low Dose Dexamethasone Test if abnormal. If this suggests cortisol hypersecretion, the diagnosis may be supported by a 6-day Liddle’s test and an adrenal CT scan.
  • Acromegaly by measurement of serum GH, PRL, and Insulin-Like-Growth-Factor I (IGF I). In case of abnormal findings, confirmation of GH hypersecretion with an oral glucose suppression test (OGTT) and imaging of the pituitary region with MRI is suggested.
  • Thyroid nodules by ultrasonography and further evaluation with FNA as needed, according to the relevant guidelines for the general population.
  • LCCSCT in males by testicular ultrasound, especially when small-sized calcifications are found. Follow-up may be less frequent than annual due to the slow progression of these tumors (45)
  • PMS with spine MRI once at baseline and thereafter when clinical signs suggest the presence of this tumor.
  • Breast myxomas as well as ductal adenomas in females should be screened and followed up in the context of screening for breast cancer including self-examination, clinical evaluation, mammography, and ultrasound, starting earlier than in the general population, maybe earlier than the age of 40 (45). In the case of findings, MRI of the breast is more sensitive in mapping the lesions (52).
  • Ovarian lesions by transabdominal ultrasonography during the first evaluation. The test should be repeated due to the low risk of ovarian malignancy (72).

 

Treatment

 

As CNC is generated by a constitutional genetic defect, no etiologic therapy is available yet. The therapeutic approach should target each clinical manifestation and treat accordingly.

  • Cardiac myxomas require surgical removal. However, due to the high recurrence rate, re-operation is usually indicated (49)
  • Cutaneous and mammary myxomas may be surgically removed, mainly for cosmetic and/or diagnostic purposes.
  • Regarding PPNAD, bilateral adrenalectomy has been typically suggested if overt Cushing’s syndrome is evident. Some institutions though have reported treatment with a low dose regimen (0,5-4 g daily) of O,p'-dichlorodiphenyldichloroethane (Mitotane) (80,81) with long term effects; however, the possible significant adverse events of such an approach should be considered.
  • LCCSCT has been traditionally treated with orchiectomy; however, the fact that these tumors often occur bilaterally and are grossly benign has raised an issue to consider treatment options that might preserve fertility. Such an approach is testicular-sparing surgery, followed by strict monitoring of growth and pubertal staging and administration of anti-estrogen drugs in case of recurrence (82). Alternatively, successful treatment of prepubertal gynecomastia and growth acceleration by exclusively using aromatase inhibitors has been reported; however long-term efficacy and safety data are still lacking (83). Similarly, management of Leydig tumors, which often present as small non-palpable testicular lesions, tends to change with the implementation of advanced imaging modalities (magnetic resonance, contrast-enhanced ultrasonography, strain elastography) which may allow a more conservative approach, including surveillance and testis-sparing surgery (84)
  • Pituitary adenomas should be removed by transsphenoidal or transcranial approach, according to their size and extension as in sporadic tumors. Alternatively, long-term medical treatment can be offered.
  • Thyroid nodules should be evaluated and treated surgically according to current guidelines.
  • PMS: surgery to remove primary and/or metastatic lesions.

 

Genetic Counseling

 

Genetic analysis may be suggested for CNC index cases, taking into consideration the fact that the mutation detection rate of PRKR1A testing with standard sequencing is at present approximately 60%. Therefore, a negative test does not exclude CNC in an individual who meets clinical criteria. In such cases, copy number variant (CNV) analysis by comparative genomic hybridization (CGH) and/or PRKAR1A gene deletion testing may be suggested to rule out a PRKAR1A defect. Currently, genetic diagnosis may be assisted by NGS techniques. If all testing for PRKAR1A defects is negative, screening for other candidate genes or loci, including the PRKACA, PRKACB and the phosphodiesterase 8 and 11 genes has been suggested.

 

In those cases where a mutation is detected, genetic screening (specific sequencing) is recommended for first-degree relatives (parents, siblings, and offspring). In case of a positive test, mutation carriers should undergo the same follow-up and management as that suggested for CNC patients. The first cardiac ultrasound should be performed at the same time as the molecular testing.

 

Genetic counseling should include the following general information:

  • If a parent of the index case is affected, the risk to his siblings is 50%. On the contrary, in case of a de novo mutation, this risk falls to approximately 1%.
  • Each child of an individual with CNC has a 50% chance of being affected.
  • Fertility may be impaired in males with CNC. Contrary to male patients, CNC is not specifically associated with female infertility and successful pregnancies and deliveries of female CNC patients have been reported (85).
  • Most tumors of CNC are in general benign except for thyroid nodules and schwannomas; however, they are associated with significant morbidity. Prenatal testing is available by chorionic villous sampling (CVS) at approximately ten to 12 weeks of gestation or amnioparacentesis at 15-18 weeks of gestation. Pre-implantation genetic diagnosis (PGD) is available for PRKAR1A mutation carriers and in conjunction with in-vitro fertilization allows the selection of disease-free embryos for implantation.

 

FUTURE PERSPECTIVES

 

Although remarkable progress has been made since CNC was first described, several issues need to be answered. There are still CNC families that do not carry a PRKAR1A gene mutation and cannot be assigned to CNC2 either. The CNC2 gene located at the 2p16 locus remains to be determined.

 

Researchers put efforts in the search for a more specific therapy for CNC. An older study demonstrated that 8-Cl-adenosine (8-Cl-ADO), a cAMP analog was able to, inhibit in vitro the proliferation induced by G protein-coupled receptors (86); however, no further research has been published on this substance. Moreover, PRKAR1A haploinsufficiency has been shown to induce cyclooxygenase-2 (COX2) activation and prostaglandin E2 (PGE2) overproduction, a disorder that has been associated with the abnormal proliferation of adult bone stromal cells (ABSCs) seen in osteochondromyxomas of CNC patients (87). Experimental administration of celecoxib, a COX2 inhibitor, in mice with PKA defects decreased PGE2 and associated proliferation of ABSCs, resulting in a substantial reduction of bone tumor growth and improved organization of cortical bone that was adjacent to the tumor. Based on the same principle, experiments with celecoxib on adrenocortical cell lines and in a mouse model of PPNAD demonstrated in vitro and in vivo reduction of steroid secretion and cell proliferation (88). Recent advances in genomics and pharmaceutical technologies are promising for timely diagnosis and “etiologic” cure of this syndrome.

 

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Monitoring Technologies – Continuous Glucose Monitoring, Mobile Technology, Biomarkers of Glycemic Control

ABSTRACT

 

It is recognized that traditional measures of glucose control (such as hemoglobin A1c [A1C]) provide little information regarding the need for day-to-day changes in therapies. While intermittent self-monitored blood glucose (SMBG) provides additional information with which to make treatment decisions, significant barriers to its use exist, such asinconvenience and lack of timely and regular feedback. Furthermore, important information regarding glucose trends may be missed. Continuous glucose monitoring (CGM) has become increasingly reliable and has demonstrated efficacy in terms of improving A1C, reducing hypoglycemia, and improving the time in target glucose range. Incremental progress continues to be made toward a fully functional artificial pancreas, of which CGM will play a vital role. As more and more data are presented to patients and providers, it has become increasingly paramount that the data are organized in a standardized way and that communication of data is streamlined using patients’ mobiledevices where available and within the existing clinic infrastructure. Systems that provide immediate feedback to patients and decision support tools for patients and providers have demonstrated superior outcomes compared to routine SMBG alone. Alternate markers of glucose control may provide complementary information about glucose control and long-term prognosis. This chapter will review the latest evidence for use of professional and personal CGM, mobile glucose monitoring approaches, and biomarkers of glycemic control.

 

INTRODUCTION

 

The current technology for monitoring of glucose levels has been well established since the 1980′s. This practice is beneficial to patients with diabetes from both a clinical and an economic standpoint when used optimally. Knowledgeof the glucose levels that are measured can allow a patient to select an appropriate dose of insulin or implement dietary or other lifestyle changes to regulate their glucose levels. Expert groups provide recommendations for glucose targets, including A1C, self-monitored blood glucose (SMBG), and interstitial glucose (1,2). Although targets vary, expert groups recommend individualization based upon risk of hypoglycemia, polypharmacy, comorbidities, and other characteristics that may affect long-term benefit and individual patient characteristics. The ADA has expanded recommendations for assessing overall glucose levels to include the A1C or CGM metrics such as % Time in Range(TIR, the % of time spent 70-180 mg/dl), or the Glucose Management Indicator (GMI), which is an estimate of A1C that is derived from a 14-day CGM report for routine assessment of glucose levels (1).

 

The landscape of glucose monitoring technologies is expanding and rapidly changing. For a full review of glucose monitoring technologies, the reader is referred to one of many excellent reviews referenced throughout this chapter. Several trends are emerging in glucose monitoring and will be reviewed in more detail in this chapter:

 

  • CGM: This practice is becoming more widely established as evidence supporting its use has accumulated. The data available through CGM can permit significantly more fine-tuned adjustments in insulin dosing and other therapies than spot testing from self-monitoring of blood glucose (SMBG) can CGM technologies forautomatic collection of data have spurred interest in noninvasive glucose monitoring as an additional tool for obtaining information about glucose levels.
  • Closed loop control (CLC): Also known as an “artificial” or “bionic” pancreas, this technology links CGM withautomatically controlled insulin The first steps toward CLC are now in use.
  • Mobile Technology and Decision Support: In recent years, increasing connectivity between glucose monitoringtechnologies and mobile devices has facilitated ongoing improvements in self-care and communication of data.
  • Alternate Markers of Glucose Control: Finally, the use of additional analytes besides glucose is still being established.

 

This chapter analyzes the technology, benefits, and problems with the use of intermittent SMBG and CGM, mobile technology and decision support, and alternate biomarkers of glycemic control.

 

CONTINUOUS GLUCOSE MONITORS

 

CGM measures glucose levels (typically interstitial glucose) continuously and updates the glucose level display every 5 minutes. Most CGMs consist of 1) a monitor to display the information (in some cases, this is the patient’s mobile device), 2) a sensor that is usually inserted into the subcutaneous tissue, and 3) a transmitter that transmits the sensor data to the monitor. Previously, all devices were approved for adjunctive use only due to limitations in accuracy; in this case patients must still perform fingerstick glucose monitoring in order to guide therapy and perform calibrations. However, in 2016, the FDA approved the use of the Dexcom G5 as the first CGM for stand-alone use.Newer technologies have eliminated the requirements for calibration of CGM with a fingerstick glucose. The accuracy of all commercially available CGMs is still the lowest in the hypoglycemic range, which is where the need for sensitivity and specificity is great in terms of serving as an alarm for hypoglycemia.

 

CGM can provide both retrospective as well as real-time information to detect: 1) hypoglycemic and hyperglycemic excursions; 2) predict impending hypoglycemia; and 3) wide fluctuations in glucose levels, also known as glycemicvariability. 24-hour telephone support is available for all FDA approved CGM devices. Use of CGM can help both thepatient and their medical provider make fine tune adjustments to medication therapy and provide insight to the patient on behavioral changes to achieve glycemic control. Additionally, current efforts to link CGM measurement with automatically controlled insulin delivery, has progressed incrementally toward a fully functional artificial pancreas.Systems can be divided according to their intended use as professional CGM (which is a clinic-owned device and provides either retrospective or real-time glucose data) and personal CGM (which is patient-owned and provides real-time glucose data).

 

PROFESSIONAL CGM

 

Professional CGM describes CGM data that are obtained via healthcare provider owned equipment. It does not necessarily provide the glucose results in real time, but downloads the readings after they have been collected, similar to a 24-hour cardiac Holter monitor that provides information about cardiac rhythms after they have occurred. This allows the health care provider to obtain relatively unbiased glucose patterns during typical everyday life. The Endocrine Society recommendations state that professional CGM may be of benefit in adults with diabetes to detectnocturnal hypoglycemia, dawn phenomenon, postprandial hyperglycemia and to assist in management of diabetes therapies (3). Professional CGM is more readily reimbursed than personal CGM, but interpretation of both personal and professional CGM reports by qualified healthcare professionals may be reimbursed on a monthly basis.

 

Some personal CGM systems can be operated in a blinded fashion in order to provide professional glucose data. These systems will be discussed in more detail later (see “Personal [Real-time] Continuous Glucose Monitoring”). The first device for reading blood glucose levels continuously was a professional CGM that was approved by the FDA inJune 1999. This device was the Continuous Glucose Monitor System (CGMS) manufactured by Medtronic MiniMed (Medtronic Diabetes, Northridge, CA) (4). Since then, newer models have shown improvements in accuracy and patient acceptance. In a meta-analysis of 22 articles, professional CGM resulted in a greater reduction in A1c(-0.28%, 95% CI -0.36% to -0.21%, P < 0.00001) as well as TIR (5.59%, 95% CI 0.12 to 11.06, P = 0.05) compared to usual practice (5).

 

FreeStyle Libre Pro

 

The FreeStyle Libre Pro utilizes the same sensor as the Libre personal CGM. The Libre is factory calibrated andtherefore does not require self-monitored blood glucose calibrations. This may be a potential advantage since capillary blood glucose testing is subject to various system and user errors, which in addition to the physiologic lag time between blood and interstitial glucose (which is magnified in the postprandial period) could contribute to CGM error. Itcollects up to 14 days of glucose readings, which are recorded every 15 minutes. The glucose sensor is fully disposable and a single reader is used to activate and scan multiple devices, allowing multiple patients in one office to undergo the procedure simultaneously. Reports are obtained through the LibreView website, which offers a secure cloud-based system, or the FreeStyle Libre desktop reporting software. Reports provide daily patterns, an assessmentof glucose variability and hypoglycemia risk, a daily glucose report, and an overall snapshot report.

 

The overall MARD (Mean Absolute Relative Difference which is calculated by averaging the absolute values of relative differences between CGM measurement results and corresponding comparison method results) for the FreeStyle Libre is 11.4%, 86.7% of readings were in Zone A of the Consensus Error Grid analysis, and 99.7% of results were in Zones A and B (6). It is important to note that sensor accuracy is lower on day 1 and in thehypoglycemia range (MARD 20.3% for values <72 mg/dl in one study) (7). Accuracy improves and remains steady over the 14-day wear period. The Libre utilizes glucose oxidase in a “direct signaling” approach that is not dependenton oxygen and minimizes interference by other substances, such as acetaminophen, which may falsely elevated readings on other devices.

 

Dexcom Professional

 

The Dexcom G6 Pro was approved by the FDA in March 2018 and is available in blinded or unblinded mode depending upon whether the goal is to observe glucose patterns without intervention, to provide immediate feedback to educate and inform patients about their medications and behaviors, or to facilitate decisions about pursuingpersonal CGM. The sensor, transmitter, and receiver are essentially identical to the personal Dexcom G6 system and features expedited startup time and no calibration. The device measures interstitial glucose levels every 5 minutes and is approved for 10 days of use. The device is downloaded using Dexcom CLARITY, a web-based software program that is also used to download and review personal data.

 

Analysis of Retrospective Data

 

Data from all CGM devices can be studied retrospectively after downloading (8). It is recommended that diet, activity, symptom, and insulin data are collected during professional CGM to assist with interpretation, either via patient diary,direct entry of events into the device, or use of an accompanying app, depending on the system. Three time periods should be analyzed. These are:

 

  • Overnight: Out-of-target overnight glucose levels can be modified by adjusting the basal insulin dose.
  • Pre-prandial Period: Out-of-target pre-prandial glucose levels can be modified by adjusting the previous meal bolus, meal, or exercise pattern.
  • Post-prandial period: Out-of-target postprandial glucose levels can be modified by adjusting the immediate meal bolus, meal, or exercise pattern.

 

In certain special situations, targets may need to be adjusted. Other important elements of a professional CGM analysis are shown in Table 1. An example of a patient who used CGM is presented in Figure 1. The CGMdemonstrated high glucose levels from 6:00 PM to 11:00 PM post-supper and low glucose levels from 12:00 AM to 2AM. Recognition of these patterns allowed appropriately timed treatment interventions.

 

Table 1. Elements of Professional Continuous Glucose Monitoring Analysis

Overall Control

Mean Glucose

Glucose Variability (Standard Deviation, Coefficient of Variation)

Daily Detail

Diurnal Patterns: dawn phenomenon, overnight Meal effects

Correction Exercise effects

Other patterns (work days vs. weekend, menstrual cycles)

Hypoglycemia

Precipitating factors

Corresponding meter glucose (recognition)

 

 

Ambulatory Glucose Profile

 

The ambulatory glucose profile (AGP, Figure 2) is a standardized reporting format for glucose data that was developed by an expert panel of diabetes specialists and sponsored by the Helmsley Charitable Trust and is customized for insulin pumps or injection therapy (9). The universal report is intended to simplify and facilitate interpretation of otherwise complex and lengthy reports with varying terminology. It is anticipated that a standardized report would “help clinicians develop expertise in CGM use, enhance quality of care through enhanced pattern recognition, improve practice efficiencies with minimal disruption of workflow, and engage patients, thereby reinforcing consistent use of CGM technology.” A single page report that the medical team can view and file into a patient’s electronic medical record and that can be used as a shared decision-making tool with people with diabetes wasconsidered to be of great value in the report of the 12th International Conference on Advanced Technologies & Treatments for Diabetes (ATTD 2019) (10). The AGP is currently employed by many reporting systems and consists of 3 components:

 

  • Statistical Summary, which utilizes standard metrics and terminology to summarize the number of values,percentage of values, and time in target, above target, and below target, as well as an assessment of glucose variability.
  • Modal day report which collapses data from days or weeks to a single day in order to identify patterns by time of day. Data are presented graphically as 5 distribution curves, representing the median, interquartile range, and10th to 90th percentiles, on the backdrop of target range.
  • Daily View, which facilitates review of within day

 

Composite Metrics

 

As a measure of the quality of glycemia, the time in range (TIR), similar to the A1C is limited in its assessment of hypoglycemia. Multiple composite metrics have thus been reported (11). However, the use of multiple metricsincreases complexity and is subject to issues with collinearity. The Glycemia Risk Index (GRI) is a composite metricthat was developed using input from 330 clinical experts who analyzed 14-day tracings from 225 adults with diabetes (12). GRI more heavily weights very high or very low glucose values and correlates with clinician rankings more closely than TIR or time below range (%time < 70 mg/dl, TBR) alone.

 

Figure 2. Ambulatory Glucose Profile for Insulin Pumps.
Glucose Statistics: Metrics include mean glucose, estimated A1C, glucose ranges, coefficient of variation and standard deviation.
Glucose Profile: Daily glucose profiles are combined to make a one-day (24-hour) picture. Ideally, lines would stay within grey shaded area (target range).
Orange: median (middle) glucose line.
Blue: area between blue lines shows 50% of the glucose values.
Green: 10% of values are above (90% top line) and 10% are below (10% bottom line). Insulin Profile Graph: Shows basal insulin pump settings over a 24-hour period.
Bolus Insulin Graph: Combines all bolus insulin doses into one graph to make a one-day (24-hour) picture. Each box on the graph covers 60 minutes of doses.
Orange: median (middle) dot.
Blue: shaded box shows 50% of the bolus dosages in the hour.
Green: lines above and below the shaded box (whiskers) show how many of the bolus dosages per hour were between 75 - 90% and between 10 - 25%.

 

PERSONAL REAL-TIME CGM (RT-CGM) OR INTERMITTENTLY SCANNED CGM (IS-CGM)

 

RT-CGM devices not only display the current glucose every few minutes, but may also alert the patient for impending (projected alert) or actual (threshold alert) hyperglycemia or hypoglycemia or rate of change in glucose. Bycomparison, is-CGM requires patient interaction with the device to obtain readings but may still provide alerts for hypoglycemia or hyperglycemia. While few head to head studies are available, some studies suggest greater reduction in hypoglycemia and improvement in TIR with RT-CGM compared to is-CGM in persons with type 1 diabetes (13,14), even up to 24 months (15).

 

Over time, accuracy with RT-CGM and is-CGM has improved substantially (16,17,18). In fact, some devices, including the Dexcom and Freestyle Libre are approved for stand-alone use, meaning that under specified conditions, the device may be used to make treatment decisions without confirmatory blood glucose measure. However, the user will still experience a tradeoff between a high alarm sensitivity and specificity for detecting hypoglycemic events, particularly where glucose levels are changing rapidly (Figure 3). Current and recent glucose levels, trend information,and a visual alarm are all presented so that a patient can predict future low or high glucose excursions. Using this information will allow the patient to take actions to spend more time in the euglycemic range and less time in the hypoglycemic or hyperglycemic ranges. This potential decrease in glycemic variability will not necessarily be reflected in an improved A1C value, which reflects mean glycemic levels.

 

Figure 3. Tradeoffs between emphasis on high sensitivity compared to emphasis on high specificity in a hypoglycemic alarm that is part of a continuous glucose monitor.

 

Evidence- Type 1 Diabetes

 

Studies may be divided according to background therapies (insulin pump or injection therapy).

 

STUDIES UTILIZING EITHER INSULIN PUMP OR INJECTIONS AS BACKGROUND THERAPIES

 

  • The seven-country GuardControl Study was the first randomized controlled trial to ever demonstrate a statisticallysignificant improvement in A1C levels with the use of RT-CGM (19). The Guardian RT was used either continuously or biweekly for three months and both regimens were compared to control treatment which did not include use of CGM. At one month and at three months the continuous users had significantly lower A1C levelsthan the controls. The biweekly users had intermediate improvement which did not reach statistical significance compared to the outcomes in the control group.
  • In 2008, the Juvenile Diabetes Research Foundation Continuous Glucose Monitoring Study Group evaluated 322 adults and children with type 1 diabetes (either injection or insulin pump therapy) and A1C 7-10% who wererandomized to either RT-CGM or usual care (20). RT-CGM was associated with a 53% reduction in A1Ccompared to usual care (p<0.001), but was only significant among subjects over age 24 due to lack of consistent use in younger patients. Hypoglycemia was infrequent and was not different between groups.
  • In 2011, 120 children and adults with type 1 diabetes on insulin pump or injection therapy and A1C <7.5% wererandomly assigned to RT-CGM (Freestyle Navigator—not available in the US) or masked CGM every other week (21). The time spent in hypoglycemia was reduced over 50% at 26 weeks, and patients spent more time in 70-180 mg/dl range.
  • In the IMPACT trial, 241 adults with type 1 diabetes with an A1C less than or equal to 7.5% were randomly assigned to Freestyle flash glucose monitoring (described in more detail under “Overview of Stand-Alone Personal CGM systems”) vs. SMBG. In this group 68% of the patients were treated with multiple daily injections and 32% with CSII. The amount of time spent in hypoglycemia was decreased by nearly 90 minutes per day (P<0.0001) when patients had access to CGM data (22). It must be noted that this technology does not provide real-time alerts for impending hypoglycemia or hyperglycemia and data are accessed via a hand-held device on Ina small study of patients with hypoglycemia unawareness or recent severe hypoglycemia, RT-CGM more effectively reduced the time spent in hypoglycemia compared to flash glucose monitoring (23).
  • The CITY study was a randomized study among 153 adolescents and young adults with type 1 diabetes. CGM resulted in a -0.37% greater reduction in A1C compared to usual care (p=0.01) (24). In this study, only 68% of participants used CGM at least 5 days per week in month 6, which is significantly lower than studies reported inadults (25). However, this is more than twice that reported in the pivotal JDRF study of 2008 (20). Moreover, this study utilized an earlier generation CGM which required twice daily calibration; thus, it is possible that newer technologies may support greater persistence with use.
  • Among 203 older adults (median age 68) with type 1 diabetes randomized to CGM or usual care, CGM resulted in less hypoglycemia at 26 weeks (estimated treatment difference 27 minutes/day, p<0.001) as well as modest improvement in A1C (estimated treatment difference -0.3%, p<0.001) (26). The improvement in hypoglycemia was sustained over 52 weeks, at which point CGM use was still >90% (27).

 

STUDIES UTILIZING INSULIN PUMP THERAPY AS BACKGROUND

 

  • In the largest study to date, the STAR3 study, 485 adults and children with A1C 4-9.5% were randomized to sensor-augmented pump therapy (Medtronic Paradigm Revel) or multiple daily injections per day (28). Sensor-augmented pump therapy resulted in better A1C reduction with between-group difference of 0.6%, p<0.001.Hypoglycemia did not differ between groups, but only short-term CGM data were available for comparison and patients with a history of severe hypoglycemia were excluded.

 

STUDIES UTILIZING INJECTION THERAPY AS BACKGROUND

 

  • In 2016, a 6-month randomized controlled trial, the DIAMOND study, compared RT-CGM (using Dexcom G4system) versus SMBG in 158 patients with type 1 diabetes on multi-dose injection therapy and demonstrated a significantly lower A1C (between group difference 0.6%, p<0.0001), decrease in hypoglycemia (43 minutes vs. 80 minutes per day, p=0.0002) and less glucose variability with RT-CGM compared to SMBG. This study did not address hypoglycemia frequency in the two groups (25).
  • The GOLD trial studied 161 patients with type 1 diabetes receiving multiple daily injections with either RT-CGM (Dexcom G4) or standard care in a random order cross-over trial. The mean difference in A1C was 0.43% (p<0.001), favoring RT-CGM. One subject in the CGM group compared to 5 subjects in the standard care group experienced a severe hypoglycemic event. The percentage of time spent in hypoglycemia numerically favored the CGM group but statistical analyses were not presented. There was a significant reduction in standard deviationand MAGE (measures of glucose variability). Overall well-being, diabetes treatment satisfaction, and fear of hypoglycemia improved (29).
  • In the FLASH-UK study, 156 participants with type 1 diabetes were randomized to intermittently scanned glucosemonitoring or usual care (30). The intervention group had a significantly greater reduction in HbA1 (adjusted treatment difference -0.5%, p<0.001), higher % TIR, and lower % TBR.
  • A randomized controlled trial among 104 adults with type 1 diabetes found that intermittently scanned glucose monitoring improved A1c (estimated treatment difference 0.3% [95% CI, 0.0%-0.6%; P = 0.04) and TIR but not TBR compared to blood glucose monitoring (31).

 

META-ANALYSES

 

A Cochrane review and another meta-analysis found modest A1c reductions, particularly among patients who were not using insulin pumps, patients under age 18, and among patients with lower adherence (32). The results were heavily influenced by the STAR3 trial, and the JDRF study did not report a difference between pump users and patients using multiple dose injection therapy. Severe hypoglycemia rates did not differ. However, the quality of most studies was limited due to small sample size, lack of blinding, and lack of sufficient data to compare hypoglycemia rates. Meta-analyses may be hampered by the inclusion of studies with obsolete technology or lack of consideration for the intended use of the device in the study (33,34). In another meta-analysis, studies that specifically enrolled patients at risk for hypoglycemia and used blinded CGM to assess it did show improvement in hypoglycemia (35).

 

More recently, a meta-analysis of 21 studies published between 2011-2020 encompassing 2149 individuals with type 1 diabetes revealed that CGM led to a significant reduction in A1C by 0.23% (p=0.0005), with larger treatment effect at higher baseline A1C (>8%), and no effect on severe hypoglycemia or DKA (36). However, the meta-analysis did not report CGM derived metrics such as TIR or TBR or clinically significant hypoglycemia. In a 2023 meta-analysis of 22 randomized controlled trials that included participants with type 1 diabetes, there was an overall improvement in A1c,TIR and TBR (37). Reduction in A1C was limited to nonadjunctive devices but all devices resulted in improvement in TIR.

 

PATIENTS WITH HYPOGLYCEMIC UNAWARENESS

 

Many older studies specifically excluded patients with a history of severe hypoglycemia or were underpowered todetect significant hypoglycemia. Recent studies have examined the use of RT- CGM in patients with hypoglycemiaunawareness, which is a risk factor for severe hypoglycemia (events requiring outside assistance to treat).

 

  • In the HypoCOMPaSS trial, 96 patients with a history of hypoglycemia unawareness determined by the GOLD Score of at least 4 or more were randomly assigned in a 2x2 factorial design to insulin pump or injection therapy, both with access to a bolus insulin calculator, and either RT-CGM (Medtronic Continuous Glucose Monitoring System) or SMBG. All patients had diabetes education with a goal toward hypoglycemia avoidance (38). Theresults demonstrated a similar reduction in severe hypoglycemia and improvement in hypoglycemia unawareness and fear of hypoglycemia without a significant treatment interaction between insulin or glucose monitoring interventions. Treatment satisfaction was higher with insulin pump compared to injection therapy but similar between RT-CGM and
  • The IN CONTROL trial evaluated patients with Type 1 diabetes and hypoglycemia unawareness receiving either injection or insulin pump therapy in a crossover study comparing RT-CTM (Medtronic Paradigm Veo system with a MiniLink transmitter and an Enlite glucose sensor) or SMBG (39). Hypoglycemia was significantly reduced with RT-CGM compared to SMBG (including a 9.8% reduction in events <70 mg/dl and 44% reduction in events <40 mg/dl). Severe hypoglycemic events were significantly reduced but hypoglycemia unawareness was unchanged.
  • In a smaller study of 52 adults with type 1 diabetes and problematic hypoglycemia, immediate randomization to CGM was more effective for preventing severe hypoglycemia (39% fewer events, p<0.05) than a dedicated hypoglycemia avoidance education program alone (40). CGM also lead to greater reduction in A1c (treatment difference -0.47%, p<0.05), but impaired awareness was restored in 31% of both groups, supporting the conceptthat CGM assists in earlier recognition and treatment of impending hypoglycemia as opposed to effecting fundamental change in counterregulatory responses.

 

Differences between studies may be explained by differences in populations and the technologies utilized. In the InCONTROL study, contact with patients was less frequent, sensor use was greater (89 vs. 57% in HypoCOMPaSS) and there were no insulin adjustment protocols. Therefore, more studies are needed to understand the potential role of background therapy, other technologies, and clinical support.

 

PATIENT REPORTED OUTCOMES

 

Generic Quality of life scores generally do not improve with RT-CGM but treatment-specific measures, such asdiabetes distress, hypoglycemic confidence, fear of hypoglycemia and to a lesser extent, measures of convenience, efficacy and performance, may be improved (28,41,42).

 

Evidence- Type 2 Diabetes

 

In patients with type 2 diabetes, even in patients not on insulin, RT-CGM may act as a motivator and positive influence for patients to improve lifestyle. The change in behavior can potentially lead to better glycemic control and weight loss(43). Moreover, periodic (every 3 months) short- term (14 day) use of real-time CGM may be sufficient to achieve andmaintain clinically relevant improvements in A1c in this population (44).

 

  • In 2012, Vigersky et al. randomized 100 patients with type 2 diabetes on basal insulin and anti-hyperglycemic agents into either a group that used real-time RT-CGM intermittently (2 weeks on, 1 week off) or a group that recorded SMBG four times per day for 12 weeks. At 12 weeks, they found a statistically significantly greater reduction in A1c by 1.0% in the CGM group compared to 5% reduction in the SMBG group. The effect persistedup to the 40-week follow-up, 0.8% and 0.5% reduction in A1c in the RT-CGM versus SMBG group respectively (45).
  • In 2017, Beck et al conducted a randomized study to evaluate benefit of RT-CGM use in 158 patients with type 2 diabetes with mean A1C of 8.5% treated using multiple daily injections (46). Over a 24-week period the A1C decreased to 7.7% in the RT-CGM group compared to 8% in the group with usual care (mean difference -0.3%,p=0.022). RT-CGM derived hypoglycemia and quality of life did not differ.
  • The Dexcom MOBILE study assessed patients with type 2 diabetes on basal insulin randomly assigned to the Dexcom G6 or usual care for 8 months and reported a significant reduction in A1C, improved TIR andhypoglycemia (47). This was accomplished without an appreciable change in insulin or other medication use, indicating that CGM improves glucose levels by facilitating behavioral changes. Moreover, subsequent discontinuation of CGM for 6 months resulted in loss of about half of the improvement in TIR (48). Moreover, the benefit was similar in older (≥65 years old) vs. younger adults (49).
  • In a 10-week study of 101 patients with type 2 diabetes on multiple daily injections of insulin, patients randomized flash glucose monitoring (Freestyle Libre) had greater A1C reduction (-0.82 vs -0.33%, p=0.005), found their treatment to be significantly more flexible and were more likely to recommend it to others (50).
  • Among 141 adults with type 2 diabetes treated with insulin or sulfonylurea and recent myocardial infarction, thoserandomized to intermittently scanned glucose monitoring had significantly less TBR (-80 minutes, 95% CI -118, -43 minutes) at 90 days, but marginal difference in A1c or TIR, and the intervention was reported to be cost-effective (51).
  • In a randomized trial of 116 adults with type 2 diabetes using non-insulin therapies, intermittently scanned glucose monitoring in combination with diabetes self-management education demonstrated superior A1c reduction at 16 weeks (treatment difference 0.3%, 95% CI 0 to 7%, p=0.048), larger increase in TIR (9.9%, p<0.01), and greatersatisfaction compared to education alone (52).

 

Real World Outcomes

 

  • In a study of over 29,000 pediatric patients with type 1 diabetes in the Type 1 diabetes Exchange Registry or the German/Austrian DPV Initiative, pediatric CGM use was associated with lower mean A1C regardless of insulindelivery modality (pump or injection) (53).
  • In a study of 106 UK hospitals incorporating 16,427 participants, 1241 with repeated TIR data, improvements inTIR were associated with improvement in hypoglycemia unawareness and diabetes related Moreover, TIR>70% was associated with reduced resource utilization (hospital admissions for hypoglycemia or hyperglycemia, paramedic visits, and severe hypoglycemia (54).
  • In the Swedish National Diabetes Registry that included 14,372 adults with type 1 diabetes, intermittently scanned glucose monitoring was associated with a small (0.11%, p<0.0001) reduction in A1C after 15-24 months and reduction in severe hypoglycemic episodes (OR 0.79, 95% CI 0.69-0.91) (55).
  • Using the French national claims database, a total of 74,011 patients with type 1 or type 2 diabetes initiatedintermittently scanned glucose monitoring and over 98% persisted with the device at 12 months (56). Following initiation of the device, patients had a 39-49% reduction in hospitalizations for acute complications and a 32-40%reduction in diabetes-related Moreover, the reduction in hospitalizations persisted after 2 years (57).
  • In Belgium, a study of 1913 adults with type 1 diabetes were studied before and after nationwide reimbursement of intermittently scanned continuous glucose monitoring (58). Following the policy change, treatment satisfaction improved, there was a significant reduction in admissions for acute complications (severe hypoglycemia orketoacidosis), and there were fewer absences from work.
  • Among 41,753 patients with insulin requiring diabetes in an integrated health care delivery system, 3806 patientsinitiated CGM, which was associated with a greater reduction in A1C (adjusted treatment difference 0.40%, p<0.001), emergency department or hospitalization for hypoglycemia (adjusted difference -2.7%, p=0.001), areduction in number of outpatient visits and an increase in telephone visits (59). However, there was no difference in hospitalizations for hyperglycemia or ketoacidosis.
  • In a Medicare supplemental and commercial claims database study of 2463 patients with type 2 diabetes on multiple injections of insulin/day, intermittently scanned CGM was associated with a reduction in acute diabetes events (HR 0.39, 95% CI 0.30-0.51) and all cause hospitalizations (HR 68, 95% CI 0.59-0.78) at 6 monthscompared to the 6 months prior to initiation (60).

 

Recommendations

 

Patients should be adequately informed of the benefits and limitations of this technology, particularly with respect to the role for SMBG. At a minimum, structured education programs encompassing concepts such as carbohydrate counting and active insulin time (insulin on board) should be completed prior to considering RT-CGM, and payers mayrequire that patients demonstrate that they can reliably and consistently perform SMBG (61). Several expert groups have issued guidance in the use of RT-CGM.

 

  • In 2016, the Endocrine Society, co-sponsored by The American Association for Clinical Chemistry, the American Association of Diabetes Educators, and the European Society of Endocrinology, published guidelines for use ofinsulin pumps and CGM. The guidelines recommended RT-CGM in adults with type 1 diabetes and any A1C who are willing and able to use the devices nearly daily. The panel suggested short-term intermittent use for patientswith type 2 diabetes (not requiring prandial insulin) who had an A1C ≥7% and are willing and able to use the device (3).
  • The American Diabetes Association (ADA) Standards of Care recommend CGM in adults with type 1 diabetes andthose with hypoglycemia unawareness or frequent hypoglycemia (Table 2a). Among pediatric patients, the ADAnotes that CGM may reduce missed school days with regular usage (1).

 

Table 2a. ADA 2023 Recommendations for CGM

Group

Recommendation (Level of Evidence)

 

Real-time CGM

Intermittently Scanned CGM

 

Adults

Youth

Adults

Youth

MDI or CSII

insulin use

Should be offered (A)

Should be offered(B-T1D,

E-T2D)

Should be offered(B)

Should be offered (E-

T1D)

 

Should be used as close to daily as

possible (A)

Should be scanned frequently, at

least every 8 hours (A)

Basal insulin use

A

NA

C

NA

All

·       Devices are recommended for individuals or caregivers who can use the devices safely

·       The choice of device should be individualized based on patient centered factors.

·       People should have uninterrupted access to supplies to minimize gaps in monitoring (A)

·       Periodic RT-CGM, intermittently scanned CGM, or professional CGM

can be helpful where continuous use is not possible (C)

Diabetes and

pregnancy

CGM can help to achieve A1C targets in pregnancy when used as an

adjunct to pre- and postprandial SMBG (B)

A=Clear evidence from well-conducted, generalizable randomized controlled trials that are adequately powered;B=Supportive evidence from well-conducted cohort studies; C= Supportive evidence from poorly controlled or uncontrolled studies; E=expert consensus.

T1D=type 1 diabetes, T2D=type 2 diabetes, SMBG=self-monitored blood glucose

 

Table 2b. AACE Recommendations for CGM by Methodology

Method

Background/Therapy

Evidence*

BEL*

Grade^

RT-CGM

•       Problematic hypoglycemia

•       Lifestyle and other factors should also be considered

Low- Intermediate

1

B

isCGM

•       Newly diagnosed T2D

•       Non-hypoglycemic therapies

•       Motivated to scan device several times/day

•       Low hypoglycemia risk, desire for more data

Low/Expert Opinion

4

D

Diagnostic/ professional CGM

•       Newly diagnosed T2D

•       problematic hypoglycemia, but no access to personal CGM

•       non-insulin therapies as an educational tool

•       Trial use

Intermediate

1

B

Intermittent CGM

persons …who are reluctant or unable to commit to routine CGM use.

Intermediate

1

C

* Level of Evidence:

  • High (1) = randomized controlled trial (RCT) or meta-analysis of RCT
  • Intermediate (2) = meta-analysis including nonrandomized studies, network meta-analysis, nonrandomizedcontrolled trial, prospective cohort, case control, cross-sectional, hypothesis driven epidemiologic, open label extension, post-hoc analysis
  • Weak (3) = discovery/exploratory, economic, consecutive case series, case report, safety/feasibility, high impact basic research
  • None (4) = consensus, position, policy, guideline, any highly flawed study, lower impact basic science

BEL=best evidence level

^Grade is based upon evidence level, recommendation qualifiers, subjective factors, and consensus

 

Table 2c. AACE Recommendations for CGM—Patient Characteristics

Background/Therapy

Evidence rating

BEL

Grade*

3+ injections/day or CSII

High

1

A

Frequent/severe or nocturnal hypoglycemia or unawareness

Intermediate-High

1

A

Children/adolescents with T1D

Intermediate-High

1

A

Pregnant, 3+ injection/day

Intermediate-High

1

A

Gestational DM on insulin

Intermediate

1

A

Gestational DM no insulin

Intermediate

1

B

T2D, on insulin

Intermediate

1

B

* Level of Evidence:

  • High (1) = randomized controlled trial (RCT) or meta-analysis of RCT
  • Intermediate (2) = meta-analysis including nonrandomized studies, network meta-analysis, nonrandomizedcontrolled trial, prospective cohort, case control, cross-sectional, hypothesis driven epidemiologic, open label extension, post-hoc analysis
  • Weak (3) = discovery/exploratory, economic, consecutive case series, case report, safety/feasibility, high impact basic research
  • None (4) = consensus, position, policy, guideline, any highly flawed study, lower impact basic science

BEL=best evidence level

^Grade is based upon evidence level, recommendation qualifiers, subjective factors, and consensus

 

The 2021 American Association of Clinical Endocrinologists recommendations for use are summarized in Table 2band 2c. These include all adults and children with type 1 diabetes, especially those with severe hypoglycemia or hypoglycemia unawareness, and all patients with type 2 diabetes on multiple insulin injections, basal insulin, or sulfonylureas who are at risk for hypoglycemia (2).

 

In 2017, the Advanced Technologies & Treatments for Diabetes (ATTD) Congress organized an international consensus panel, consisting of physicians, researchers, and individuals with diabetes to analyze the existing literature and to provide guidance for utilizing, interpreting, and reporting CGM data (62). This was updated in 2019 (Table 3 and 4). These recommendations are supported by recent data from the DCCT demonstrating that a 10% reduction in time in target glucose range derived from 7-point self-monitored glucose profiles is associated with a 40% reduction in risk of microalbuminuria and a 64% reduction in risk of incident or progressive retinopathy (63).

 

Table 3. CGM-Based Targets for Different Diabetes Populations

Glucose Range

%Time in Range

 

Non-Pregnant Patients

Type 1 and Type 2 Diabetes

Older/High Risk Diabetes

>250 mg/dl (13.9 mmol/L)

<5%

<10%

>180 mg/dl (10 mmol/L)*

<25%

<50%

70-180 mg/dl (3.9-10 mmol/L)

>70%

>50%

<70 mg/dl (3.9 mmol/L)**

<4%

<1%

<54 mg/dl (3.0 mmol/L)

<1%

 

 

Pregnant Patients

Type 1 Diabetes

Gestational and Type 2 Diabetes #

>140 mg/dl (7.8 mmol/L)

<25%

-

63-140 mg/dl (3.5-7.8 mmol/L)

>70%

-

<65 mg/dl (3.5 mmol/L)

<4%

-

<54 mg/dl (3.0 mmol/L)

<1%

-

*Includes time >250, **Includes time <54 mg/dl, #Insufficient data

 

Table 4. Summary of ATTD Recommendations for CGM

Limitations of A1C

CGM should be utilized when there is a discrepancy in A1C and other measures of glucose control.

CGM should be utilized to assess hypoglycemia and glucose variability.

Guiding management and assessing outcomes

CGM should be considered for patients with type 1 diabetes and insulintreated type 2 diabetes who are not achieving targets or those with hypoglycemia.

All patients should receive training education regarding how to interpret andrespond to their data, utilizing standardized programs with follow-up.

Performance

No accepted standard exists for CGM system performance. However, a mean absolute relative difference ≤10% provides little additional benefit forinsulin dosing.

Definition and assessment of hypoglycemia

Clinical classification

Level 1: 54-70 mg/dl with or without symptoms

Level 2: <54 mg/dl with or without symptoms (clinically significant)

Level 3: cognitive impairment requiring external assistance for recovery

Quantification using CGM

% of values or time below a given threshold (54 or 70 mg/dl) Number of events (defined as CGM readings persistently below threshold for at least15 min. with recovery defined as persistent readings over the threshold forat least 15 min.) over a given reporting period)

Glycemic Variability

Coefficient of Variation should be the primary measure

Time in Range

The % time in hyperglycemia, hypoglycemia, and target range should

be reported.

CGM Metrics

Standardized reporting using the AGP and integration into electronic health records is recommended.

Key metrics:

·         Number of days worn (14 days recommended)

·         % time CGM is active (70% of data from 14 days recommended)

·         Mean glucose

·         Glucose Management Indicator

·         Glycemic variability (%CV, target <36%)

·         % Time in Range (TIR): 70-180 mg/dl (3.9-10.0 mmol/L)

%Time Above Range (TAR): 181-250 mg/dl (10.1-13.9 mmol/L), and >250 mg/dl (>13.9 mmol/L)

·         %Time Below Range (TBR): 54-69 mg/dl (3.0-3.8 mmol/L), and

<54 mg/dl (3.0 mmol/L)

 

Also, in 2017 the ADA and the European Association for the Study of Diabetes published a joint statement providing recommendations for systematic improvements in clinical use and regulatory handling of CGM devices (64).

 

Hospital Use

 

CGM is not currently approved for use in the hospital setting. However, during the COVID-19 pandemic, the FDA announced that it would not object to their use in an effort to support reduction in use of personal protective equipmentand risk of exposures to staff. Thus, there has been increasing interest in their use. Moreover, an increasing number of patients are using these devices in the ambulatory setting and want to continue their use in the hospital. Recent randomized trials support the use of CGM on the hospital wards, where it has been shown to be safe, and may reduce the frequency of hypoglycemia (65,66). In the ICU, there is concern that CGM may be less accurate due to factors such as edema, hypoperfusion, and acidosis but preliminary studies suggest use of CGM in conjunction with periodic point of care (POC) blood glucose (BG) within well-established protocols is safe and may reduce the need for POC BG (67).

 

In 2020, the Diabetes Technology Society sponsored a panel of experts in inpatient diabetes management to reviewthe evidence for us of CGM in the hospital (68). The panel agreed that CGM had the potential to improve clinicaloutcomes, particularly for patients who are unable to communicate signs or symptoms of hypoglycemia, but use is limited by lack of data demonstrating accuracy (particularly in the hypoglycemic range or in case of diabetic ketoacidosis, poor perfusion, or acetaminophen use) and clinical utility, and a lack of decision support systems, including infrastructure for communicating results to care teams and to the electronic medical record. The panelagreed that patients who are admitted with personal CGM devices should be allowed to continue use of such devices under the condition that they are able to self-manage the devices on their own and are followed by an endocrinologist or experienced practitioner who is specifically trained in their use. In particular, the panel advised implementing institutional policies that recommend continued capillary or blood glucose monitoring, ensuring that CGM data are not used for inpatient insulin dosing (since no CGM device is FDA approved in the inpatient setting), and requiring patients to sign safety waivers which illustrate the potential risks and benefits of continued use. Devices must beremoved for any MR or CT imaging. The panel made the specific recommendations for clinical care including:

  • Consider use of CGM to reduce exposures (such as for point of care glucose) and need for personal protective equipment in persons with highly contagious diseases.
  • Barring use in the setting of highly contagious disease, CGM values should be confirmed with point of care (POC) glucose prior to making treatment decisions.
  • Hospitals should develop implementation plans which include a process map, protocol, provider/staff/patient education and order sets.
  • Providers should recognize CGM pattern caused by compression of the device, which can cause a falsely low value.
  • Providers should ensure patients are not taking medications or supplements that can interfere with CGM.
  • Nurses should be adequately trained on use of CGM, inspect the insertion site every shift, and set expectations that POC values are still necessary to support ongoing use of CGM (typically every 6 hours).
  • Hospitals need to develop security protocols, data storage, visualization tools, and integration within the electronic medical record to support the use of CGM.
  • Hospitals need to identify CGM values in the electronic medical record to distinguish values from blood glucose values.
  • Hospitals need to adopt the Unique Device Identifier (UDI) to track devices in the electronic medical record.

 

Limitations of Use

 

It should be emphasized that most prospective randomized controlled trials enroll highly motivated patients. In the real-world setting, there are concerns about limited resources for training, and less motivated patients may be overwhelmed with the additional data, particularly where complex algorithms are required. Nevertheless, in the Type 1 Diabetes Exchange Registry, CGM use increased from 7% in 2010-2012 to 30% in 2016-2018, and rose more than 10-fold in children (69). A1C levels were lower in CGM users compared to nonusers. While CGM use has improved substantially over time, more than half of respondents cited cost or insurance coverage as a significant barrier to use (70). Moreover, disparities in prescribing patterns and implicit bias have been described (71,72,73). Modifiablereasons for avoiding use include the hassle of devices (47%) and aversion to having a device attached to the body (35%). Skin reactions and/or difficulty with adhesion are well known and are an important cause of discontinuation (74). Methods of addressing this barrier such as use of barriers, overlay patches, or topical antihistamines and corticosteroids have been described but additional research is needed (75).

 

In a multi-national study of 263 patients, persistent sensor use for 12 months was only 30% (76). Improvement in A1C was associated with higher A1C at baseline, older age, and more frequent sensor use. Diabetes related hospital admissions were reduced following the initiation of sensor augmented pump therapy and fear of hypoglycemia improved. In the 6-month follow- up phase of the JDRF-CGM trial, RT-CGM was initiated in the control group in a manner that more closely approximates clinical practice (77). Investigators found a significant reduction in CGM use inall age groups over time. However, increasing sensor use was associated with A1C reduction. It is likely that adherence will improve as technologies improve.

 

Other limitations include possible interference with acetaminophen, ascorbate, and other active agents in glucose-oxidase based electrochemical sensors. They are also dependent on both the sensitivity and specificity on the enzyme availability on the electrode surface. There are well known delay artifacts due to the time lag between glucose concentration in the interstitial fluid and blood glucose. These time ranges, often between 5 and 10 minutes, are not crucial to analyzing retrospective data, but can be critical when CGM is indicated for real-time decision making (78).

 

Daily Use

 

Patients must be aware that sensor readings can deviate from actual blood glucose measurements, particularly during rapid glucose changes such as that which occurs post-meal or during exercise. Calibration, where necessary, should not be performed when trend arrows indicate rapid swings in glucose. While systems are becoming more reliable, patients may need to verify sensor readings before taking action such as meal boluses or treatment of hypoglycemia depending on the device, even if a device is approved for nonadjunctive use.

 

Alarm thresholds should be set in order to maximize patient compliance, keeping in mind that the sensitivity fordetecting hypoglycemia decreases as the threshold is reduced below 70 mg/dl. Conversely, specificity improves to amuch smaller degree at lower thresholds, and thus false alarms may not be reduced substantially.

 

Several algorithms have been published that provide specific guidance to patients for responding to trend arrows and alarms and are summarized below. All algorithms are complex and are not integrated within bolus calculators ofexisting insulin pumps. Therefore, they should only be implemented in patients who have demonstrated anunderstanding of CGM technology, including lag times between CGM and BGM, calibration procedures, alerts andtrend arrows, as well as understanding of insulin action time and the risks of insulin stacking. In one small study, trend arrows were accurate approximately 79% of the time outside of mealtime windows (30 minutes before and 120 min after carbohydrate intake) but this dropped to ~60% within mealtime windows (80). Thus, algorithms are not intended for use post-meal. The use of automated insulin delivery systems should increase safety and efficacy and reduce the complexity of the trend arrow approach.

 

  • The algorithm by Jenkins et al. provides tiered recommendations that are based upon the meter glucose and sensor trend arrows (81). In addition, the algorithm advises patients how to review downloads of the data periodically (weekly) and make adjustments. Patients who were randomly assigned to sensor augmented pump with the algorithm had lower A1C and reported better quality of life at 16 weeks compared to patients who did not get the The effect on quality of life persisted at the 32-week follow-up, and was associated with A1Creduction. Importantly, patients who received the algorithm at 16 weeks after initiating sensor augmented pump did not benefit.
  • The DirecNet study algorithm (for use with the Navigator system) recommended that patients increase or decreasethe meal + correction bolus by 10-20% based upon the rate of change and provided specific instructions for responding to alarms (82). Algorithm use was high in the first 3 weeks but dropped off by week 13, despite increasing insulin self- adjustments, possibly as patients became more independent over time.
  • Subsequent methods recommended adjustment of only the correction insulin dose by the amount needed to cover a glucose level that is incrementally higher or lower than the current glucose, based upon the trend arrow (83,84).
  • Klonoff and Kerr proposed a more straightforward correction dose (in 5-unit increments), based upon the trend arrow and the patient’s insulin sensitivity (85).
  • A consensus statement facilitated by the Endocrine Society provides expert guidance on the use of trend arrows for making treatment decisions (86). The guidance recommends adjustment of boluses pre-meal and no sooner than 4 hours post-meal in 0.5-unit increments based upon the trend arrow and the patient’s sensitivity. The statement recommends no additional treatment within 2 hours of a previous meal bolus, and correction bolus using the bolus calculator or usual correction dose only in the 4 hours after a meal. Similar expert guidance has been developed for the Freestyle Libre system (87).
  • A more recent adaptation of the Endocrine Society guidance incorporated pre-meal glucose levels in addition to theinsulin sensitivity (88) and a small randomized study demonstrated it was more effective than the incorporation of insulin sensitivity alone, particularly among insulin pump patients (89).

 

Overview of Stand-alone Personal RT-CGM and IS-CGM Systems

 

The first RT-CGM (Guardian, MedtronicR) was approved in 2004. Since then, additional models and other devices have entered the market, and accuracy and patient satisfaction have improved. Several personal continuous glucosemonitors have been approved by the US Food and Drug Administration (FDA) for use in the United States or carry CE marking for use in Europe and are currently on the market (Table 5). For a full review of regulatory requirements for glucose monitoring devices, the reader is referred to one of several excellent reviews (90).

 

Table 5. Comparison of Subcutaneous Continuous Glucose Monitoring Devices

 

 

 

Calibration required

Confirmatory Fingersticks requiredprior to

treatment

 

 

Real-time alerts

 

 

Sensor Life (days)

 

 

Warm-up (hrs)

 

Removefor MRI, CT

diathermy

 

 

Acetaminophen interference

Dexcom G5

Y

N

Y

7

2

Y

Y

Dexcom G6

N

N

Y

10

2

Y

N

Dexcom G7

N

N

Y

10

0.5

Y

N

Medtronic

Guardian 3

 

Y

 

Y

 

Y

 

7

 

2

 

Y

 

Y

FreeStyle Libre

14 day

 

N

 

N

 

N

 

14

 

1

 

Y

 

N

FreeStyle Libre 2

N

N

Y

14

1

Y

N

FreeStyle Libre 3

N

N

Y

14

1

Y

N

Eversense

(surgical implant)

 

Y

 

N

 

Y

 

180

 

NA

 

Y

 

No

 

GUARDIAN CONNECT

 

The Guardian Connect utilizes the Medtronic Guardian Sensor 3, the Guardian Connect transmitter, and the GuardianConnect app to transmit data via Bluetooth every 5 minutes to the user’s smart phone or device (initially only available on iOS devices) via the Guardian Connect App on smartphones and via CareLink personal and professional software. A separate receiver is not available with this system. Data can be shared with others remotely, and SMS messages can be sent in times of hypoglycemia. The system is only approved for adjunctive use and at least 2 daily fingerstick calibrations are required.

 

DEXCOM G6

 

The Dexcom CGM utilizes a glucose oxidase sensor at the tip of a wire that is implanted in the subcutaneous space. The data are transmitted wirelessly and are displayed on a separate receiver (personal smartphone or device specificreceiver). The Dexcom G6 has a sensor life of 10 days, no longer requires calibrations, and minimizes interference by acetaminophen. G6 is also associated with a smartphone app that allows the patient to log activity, set reminders or alarms, and physically see their glucose levels and trends throughout their time wearing the device. The Dexcom CLARITY Diabetes Management Software organizes and presents the patient’s blood glucose data. Dexcom SHARE app allows users to share data with up to 10 other individuals.

 

DEXCOM G7

 

The Dexcom G7 features a 60% smaller size (the size of 3 stacked quarters) vs. the G6, is fully disposable, and has a shorter 30-minute warm up time and a 12-hour grace period to replace completed sensors. The overall MARD was reported to be 8.2% with the abdomen and 9.1% on the arm (17). Consistent with previous studies, accuracy is lower at lower sensor glucose, higher glucose rate of change, and on day one of wear.

 

FREESTYLE LIBRE 14 Day

 

The sensor utilizes Wired Enzyme™ technology in which the enzyme and mediator are co- immobilized on the sensor. It offers factory calibration, and therefore nearly eliminates the need for fingerstick monitoring. However, patients are still advised to perform SMBG whenever an alert appears on the reader display (which occurs when the glucose isrising or falling rapidly) or whenever the glucose value does not fit the patient’s symptoms. The reader contains a built-in meter for this purpose. The sensor is FDA approved for 14 days of use. The system is not approved for use in children under age 18, or during pregnancy or in persons requiring hemodialysis. The Libre has minimized the interference by acetaminophen which is present in other devices but interference from other substances such as ascorbic acid or aspirin may be possible. The Libre 14 day differs from other CGM devices in that the system does not alert the user for glucose values surpassing a high or low threshold. In addition, glucose values are not automatically made available to the user but are easily and instantly accessed by scanning the sensor with a handheld reader or theassociated app FreeStyle LibreLink. However, this product may be attractive option for patients who are averse to the hassle imposed by other RT-CGM devices. Glucoses are measured every minute and recorded every 15 minutes. Data can be accessed using the reader or downloaded to LibreView cloud based online management system, or using the FreeStyle Libre desktop software. The MARD is reported by the manufacturer to be 9.7% overall, and as with other CGM devices, less accurate on day 1 of wear and in hypoglycemia range (91).

 

FREESTYLE LIBRE 2

 

The FreeStyle Libre 2 system offers real-time alerts for high or low glucose values and improved accuracy, approved for ages 4 years and older (92). However, users must continue to scan the device to obtain glucose readings.Moreover, similar to the Libre 14 day, the sensor memory is only 8 hours and glucose data are lost if the sensor is scanned less frequently.

 

FREESTYLE LIBRE 3

 

The FreeStyle Libre 3 is even smaller than other devices (the size of 2 stacked pennies), does not require scanningunlike older models, but does require the use of a compatible smartphone. The bluetooth range is improved from 20 to 33 feet. Accuracy is improved compared to the Libre 2, with an overall MARD of 9.2% in adults and 9.7% in children (16).

 

EVERSENSE

 

The Eversense system (Senseonics) is a 90-day implantable sensor that uses fluorescent technology to sendmeasures via a rechargeable transmitter which rests just above the skin to a smartphone app titled Eversense NOW (93). In a pivotal clinical study of 71 patients with type 1 and type 2 diabetes, there were no device-related serious adverse events, and the MARD was 11.1%, with over 99% of samples in clinically acceptable error zones A and B of Clarke Error Grid Analysis (94). One study reported interference with tetracycline and mannitol, but not with acetaminophen or ascorbic acid (95). The Eversense XL CGM system consists of a 180-day implantable sensor thathas been shown to have acceptable safety and accuracy with an overall MARD of 9.1% (96). This option may be particularly useful for patients with privacy concerns, physical disability, needle phobia, allergies or other difficulty with adhesion, or activities or professions that may be barriers to external wear (97).

 

Sensor Augmented Pumps

 

To date the largest A1C reductions have been observed when sensors are initiated with insulin pump technology. In the observational (nonrandomized) COMISAIR study, patients initiating CGM (with or without insulin pump) achieved significantly larger reductions in A1C (-1.2%) compared to subjects initiating insulin pump alone (-0.6%) or remaining on injections alone (- 0.3%) (98). There was no difference in outcomes between the DexCom G4 and Enlite sensor.

 

A reduction in time spent in hypoglycemia was observed only in patients using CGM (8% vs 6%, p<0.001).

 

STEPS TOWARDS AN ARTIFICIAL PANCREAS

 

Until recently, RT-CGM technology has operated completely independently of insulin delivery. By combining continuous basal insulin delivery during fasting periods with discrete bolus doses of insulin at mealtimes, insulindelivery can be crafted to mimic the natural pattern of pancreatic insulin release. An artificial pancreas consists of: 1) an automatic and continuous glucose monitor; 2) an implanted continuous insulin delivery system; 3) a control processor to link the insulin delivery rate to the glucose level; and 4) a signal to send the glucose level to the body surface for continuous display onto a monitor. Limitations to full implementation include sensor accuracy and lag time, inadequate onset and offset of currently available rapid acting insulin analogs, meal challenges, and changes in insulinsensitivity due to circadian rhythms, exercise, menstrual cycles, and intercurrent illness (99). However, even incremental advances improve glucose control without increasing the complexity of decision-making on the part of the patient. These include:

  • Low glucose (threshold) suspend: the insulin pump suspends when the glucose decreases below a pre-set value.
  • Suspend before low: insulin pump suspends when hypoglycemia is
  • Hybrid closed loop: insulin delivery increases or decreases based upon the sensor glucose value but meal boluses are still required.
  • Closed loop control: fully closed loop delivery without the need for meal boluses
  • Dual hormone systems: these are hybrid closed loop or closed loop control systems that utilize glucagon or other peptides (such as amylin) in an effort to more closely mimic the physiology of the endocrine pancreas.

 

The long-term safety, efficacy, cost, and cost-effectiveness of an artificial pancreas are still largely unknown at this time. However, the urgency of this technology is demonstrated by the #WeAreNotWaiting movement, which has given rise to home-grown, crowd-sourced, patient driven systems that utilize existing devices which are linked by open-source software, such as Open Artificial Pancreas System, and Loop. Recently Tidepool Loop received FDA approval (100). A retrospective observational study of patients with Type 1 diabetes demonstrated lower mean glucose, higher time in target range, and less time in hypoglycemia using Open Artificial Pancreas Systems (OpenAPS) compared to sensor augmented pump use alone (101). In general, open-source systems carry safety concerns, particularly among less tech-savvy patients, in the absence of regulatory approval (102). However, the healthcare provider can providesafety recommendations as well as a back-up plan in case of system failure (103). The reader is referred to one of several reviews as a detailed review is beyond the scope of this chapter (104,105).

 

Threshold Suspend

 

Progress is expected toward a fully functional closed loop system in incremental steps. The first step toward a fully automated “artificial pancreas” is the low glucose suspend feature, which is now available. The Medtronic 530Gsystem, containing the Veo insulin pump and Enlite sensor, is the first sensor augmented pump with low threshold suspend and uses the same sensor as the more recent 630G system. The Enlite sensor accuracy is significantly improved over the previous Sof-sensorR, with a MARD of 13.6% when used with the 530G (106). The Enlite is also one-third of the size of Sof-sensor and the filament is 38% shorter. The Enlite sensor may be worn up to six days. The low threshold suspend SmartGardTM technology suspends the pump for up to two hours in the event of sensor detected hypoglycemia in which the user does not respond to the alarm. Prior to suspension, a “siren” sounds which is distinct from other high or low alerts, and the suspension can be overridden at any time. The MiniMed Connect mobile accessory sends sensor data to an app on a mobile device where data can be viewed (available only with the 530G system). A study that enrolled 247 patients with type 1 diabetes and documented nocturnal hypoglycemia to sensor-augmented pump with or without a low-glucose threshold-suspend feature demonstrated similar A1C between groups at 3 months but lower frequency of nocturnal hypoglycemia (107). Similar findings were demonstrated in an Australian study of 95 patients, in which the incidence rate ratio for hypoglycemia was 3.6 (95% CI 1.7-7.5, p<0.001) (108). There were no reports of DKA in either study.

 

Suspend Before Low

 

The next incremental step in closed loop systems is the suspend before low feature, currently available in theMedtronic 640G (approved only in Europe) and the 670G systems. This feature automatically suspends insulin delivery 30 minutes before a low glucose threshold is predicted and resumes delivery once the glucose recovers, without alerting the patient. In a 6-month randomized study of 154 children and adolescents with type 1 diabetes, the 640G system reduced the time spent in hypoglycemia from 2.6 to 1.5% without causing a change in A1C (109). The t:slim X2 Insulin Pump incorporates Basal IQ technology with predictive low glucose suspend using the Dexcom G5 or G6 sensor. In a randomized cross-over study of 103 participants with type 1 diabetes age 6-72 years of age, predictivelow glucose suspend resulted in a 31% reduction in time spent in hypoglycemia < 70 mg/dl without a change in meanglucose or time in hyperglycemia (110).

 

Hybrid Closed Loop (HCL)

 

This step refers to sensor glucose driven automatic adjustment of basal insulin with or without additional auto boluses,and still requires the patient to bolus for meals. In a recent consensus statement, an ideal candidate for automated insulin delivery systems (103):

  • Is technically capable of managing a pump, has basic carbohydrate counting skills, and is able to implement a back-up plan (including the use of manual injections).
  • Has realistic expectations of system In particular, several situations that are unique to HCL are worth emphasizing:
    • Bolusing: pre-blousing approximately 15 minutes prior to meals is critical to maintain In many systems,delayed boluses not only cause early postmeal hyperglycemia but also precipitate delayed hypoglycemia as the system has already begun to augment insulin delivery in response to hyperglycemia.
    • Exercise management: Similarly, carbohydrate loading prior to exercise while using HCL systems will only stimulate insulin delivery and thus is recommended that users implement other means for management such as setting a higher target, typically with a designated exercise mode, or exiting to manual mode with temporarybasal insulin reduction or temporary suspension of the pump.
    • Hypoglycemia management: HCL users typically need fewer carbohydrates (about half) to manage hypoglycemia since the pump has generally already suspended insulin delivery based upon glucose trends.
  • Has adequate support, including diabetes education, insurance coverage, and caregiver or other social support where relevant.
  • Has the ability to transmit data to the healthcare
  • Is mentally and psychologically able to implement AID

 

On the other hand, there does not appear to be an ideal threshold A1c for determining candidates for HCL therapy, asthose with lower A1c may benefit by reducing TBR and those with higher A1c benefit from reductions in hyperglycemia without the perceived risk of ketoacidosis traditionally attributed to initiation of insulin pump therapy (111). Thus, less ideal candidates may obtain the greatest benefit in terms of achieving glycemic targets.

 

HCL demonstrates improvements in a range of glycemic outcomes and may confer psychological benefits as well.Most studies have enrolled patients with type 1 diabetes. More data are needed for special populations including type 2 diabetes, especially those with very high insulin requirements, pregnancy, acute illness, steroid use, renaldysfunction, and persons in assisted living facilities (112).

 

As with CGM, it is important to evaluate these systems in the real-world setting, where user experience can differ from that of the highly controlled and supportive research environment. Cost and insurance hassles, as well as user wear issues are the most commonly reported barriers to use of any diabetes related device. These barriers contribute todiabetes distress and depressive symptoms which can impede self-management behaviors (70,112). HCL systems improve glucose control but may also introduce additional alarms or alerts which are needed for safety (such as threshold alerts for hyperglycemia or hypoglycemia or HCL mode exits due to insulin delivery exceeding the system’s guardrail) or ongoing functionality such as calibration of the CGM (113). Newer systems have attempted to address many of these barriers through improved algorithms or other features (Table 6). Devices differ considerably with respect to algorithms used for insulin adjustment and a number of other features (Table 6) (114,115,116). There are few head-to-head studies comparing the efficacy and safety of available HCL systems. Details of select systems are presented next.

 

MEDTRONIC 670G

 

The first system to gain FDA approval is the Medtronic 670G, which adjusts basal insulin delivery every 5 minuteswhen in auto mode. This system utilizes the Guardian sensor 3, which offers enhanced sensor accuracy, with an overall MARD of 9.64% (117). The system was associated with a reduction in A1C from 7.4 to 6.9% and there were trends in improvement of time in target range and hypoglycemia in a non-randomized study of 124 patients with type 1 diabetes (118). A subsequent randomized trial of 151 adults and children demonstrated a significant reduction in A1c and TBR compared to insulin pump without CGM (119). There are few studies addressing long-term use however. In a 1-year prospective observational study of 84 patients, 28% stopped using auto mode by 3 months, and 33% discontinued by 12 months (120). The most common reasons for discontinuation included sensor issues (62%) and difficulty obtaining supplies (12%), fear of hypoglycemia (12%), and preference for injections (8%) or sports (8%). In astudy of 92 youth, 30% discontinued HCL, typically between 3 and 6 months after initiation, due to issues such asdifficulty with calibrations, alarms, and extra time needed for operation (121).

 

MEDTRONIC ADVANCED HYBRID CLOSED LOOP (AHCL) SYSTEM (780G)

 

This HCL system is approved for use in Europe and features substantially reduce frequency of alerts, improved time in auto mode, remote software updating, an adjustable target setting as low as 100 mg/dl and enable users to view data via an app on mobile devices (122). In a single arm study of 157 adolescents and adults the 780G system resulted in nearly 95% time in automated mode with 1.2 exits per week, improved A1C, TIR, and TBR (123). In a randomized study of 82 persons with type 1 diabetes using multiple injections per day and isCGM, AHCL resulted in improvements in A1C (-1·42%, 95% CI -1·74 to -1·10; p<0·0001) and TIR, but no difference in hypoglycemia (124). There was an improvement in treatment satisfaction, fear of hypoglycemia, and similar diabetes quality of life. By comparison in a randomized study of 41 participants with type 1 diabetes who were naïve to both CGM or insulin pump technologies, AHCL also resulted in improvements in TBR (125). In a real-world study of 3211 youth (<age 15 years) and 8874 individuals >age 15 years, ACHL demonstrated >90% treatment persistence over 6 months (126). The ACHL system was reported to have better glucose monitoring treatment satisfaction but similar diabetes distress, technology attitudes, and fear of hypoglycemia compared to the 670G system (127).

 

TANDOM CONTROL-IQ

 

This system utilizes a t:slim X2 insulin pump with a calibration-free Dexcom G6 sensor (128). In a 6-month trial of 168 patients (age 14-71) randomized 2:1 to hybrid closed loop vs. sensor augmented pump alone, the % time in target 70-180 mg/dl was increased by 11% more in the hybrid closed loop group compared to sensor augmented pump(p<0.0001), with improvements in hypoglycemia, mean glucose and A1c. Moreover, real-world outcomes among 1435 persons with type 1 diabetes included reduced impact of diabetes on life, improved device related treatment satisfaction, and improved emotional well-being (129).

 

OMNIPOD 5

 

The Omnipod 5 is a HCL system that uses the Omnipod DASH platform (130). In a single arm study, the Omnipod 5 demonstrated a reduction in A1C of 0.38%, increase in TIR of 9.3% and decrease in TBR of 1.6% (131).

 

Table 6. Comparison of Hybrid Closed Loop Systems

 

Medtronic 670G/770G

Medtronic780G

Tandem T:Slim with Control IQ

Omnipod 5

iLet BionicPancreas

Insulin delivery

Tubing

Tubing

Tubing

Tubeless (pod)

Tubing

CGM

Guardian 3

Guardian 4

Dexcom G6

Dexcom G6

Dexcom G6

Reservoir capacity(unit)

300

300

300

200

180

Calibration needed

Yes

No

No

No

No

Supplies

DME

company

DME

company

DME company

Pharmacy

To be determined

Control via smartphone

Dataviewable from Smartphone

Data viewablefrom Smartphone

Smartphone bolus

Compatible smartphone controller

No

Algorithm initiation

48 hours in manualmode to estimate

TDI

48 hours in manual mode to

estimate TDI

Weight and TDI entry with maximumdelivery of 50% TDI over 2 hr

TDI estimated from programmed

basal rates

Weight entry

Bolus automation

No

Yes, every 5 minutes

up to 1 auto-correction bolus//hr if glucose predicted >180 mg/dl

No

unknown

Other inputs

CIR, AIT

Unable to overridebolus dose

CIR, AIT

CIR, ISF, AIT is fixedat 5 hours

CIR, ISF, AIT

Boluscalculator uses CGM rate of change

“Usual for Me”, “More”, or“Less” customized by

meal

Extended bolus

No

No

Yes, up to 2 hr

No

No

Algorithm adjustment

Every 6 days

Every 6days

TDI used to scalebasal changes

Every 3 days with pod change

Continuously or based on

change in entered weight

Target

120 mg/dl

100, 110,

120 mg/dl

112.5-160 mg/dl

110, 120, 130,

140, 150 mg/dl, customizableby time of day

100, 110, 120,

130 mg/dl, customizable by time of day

Exercise

Temp target 150 mg/dl for

2-12 hour

Temp target 150 mg/dlfor

2-12 hour

Exercise target 140-160 mg/dl—cannotprogram duration

Sleep mode: target 112.5-120 mg/dlwithout auto-correction bolus, programmable

Target 150 mg/dl, “less aggressive”,for 1-24 hr

None

Safety mode*

Yes, for 670/770G

results in forced exits from HCL

Yes, exits to Safe Basal up to 4hours (5.7 vs. 1.7

x/week with 670G) (130).

Not applicable(defaults to basal rate settings)

Yes, forced exits “rare”

Yes, BG-run mode uses manuallyentered BG upto 72 hours, forces switch to

alternate therapy.

PID=proportional integral derivative (system with continual change in response to error between actual and targetvalues). MPC=model predictive control (dynamic reference model serves as a basis. TDI=total daily insulin dose,CIR=carbohydrate to insulin ratio, AIT=active insulin time, ISF=insulin sensitivity factor. *Safety mode provides amechanism to ensure insulin delivery in case of loss of sensor input or threshold for insulin delivery guardrail is reached.

 

Closed Loop Systems (CLC)

 

Additional steps toward closed loop control (CLC) insulin delivery require algorithmic insulin adjustments, whicharguably present additional safety concerns. Overnight CLC insulin delivery is relatively straightforward, whereas post-meal control and exercise effects remain the most challenging of events to manage. Until recently, most randomized studies have been small and reported only short-term outcomes, often in controlled settings.

 

ILET BIONIC PANCREAS

 

The iLet Bionic pancreas was approved by the FDA in 2023. This insulin pump is initiated using the patient’s body weight and requires meal announcements (designated as small, medium, or large) but not formal carb counting and thus represents an incremental step toward a fully closed loop insulin pump. In A 13-week multi-center randomized study of 219 participants with type 1 diabetes demonstrated a greater reduction in A1c with the iLet bionic pancreas (-0.5%, [95% CI -0.6 to -0.3; P<0.001) but no difference in hypoglycemia compared to standard care (132).

 

OTHER SYSTEMS

 

Systems have utilized single hormone (rapid acting insulin only) or dual hormone (both fast- acting insulin analog and glucagon to imitate normal physiology) as directed by a computer algorithm (Figure 4) (133). At this time, there areinsufficient data demonstrating the superiority of one system or algorithm compared to others. The three most common algorithms are:

  • Model Predictive Control (MPC): predicts future glucose levels and adjusts insulin delivery in response.
  • Proportional Integral Derivative (PID): calculates the deviation of glucose from target to determine insulin delivery.
  • Fuzzy Logic (FL): mimics insulin dosing based upon clinical

 

A meta-analysis of 40 randomized studies (35 studies using insulin alone and 9 dual hormone studies) including 1027participants with type 1 diabetes demonstrated a significant increase in % time in target range (70-180 mg/dl, weighted mean difference 9.6%, 95% CI 7.5-12%), as well as less time in hypoglycemia or hyperglycemia, regardless of type of system (134). In another meta-analysis of 24 studies and 585 participants (7 studies using dual-hormone therapy and 20 studies of insulin only) reported greater improvement in time in target with artificial pancreas systems (12.6%, 95% CI 9.0-16.2, p<0.0001), and greater improvement with dual hormone compared to single hormone systems (135). Another meta-analysis of studies with at least 8 weeks duration confirmed these findings (136). A systematic review and meta-analysis of 25 studies in 504 children demonstrated superior %TIR with CLC and bi-hormonal systems vs. single hormone systems (137).

 

Figure 4. Dual hormone Closed Loop Control system.

 

MINIMALLY INVASIVE AND NON-INVASIVE GLUCOSE MONITORS

 

Continuous hypoglycemia detection systems using current sensing technology must be either implanted (fully or partially, either subcutaneously or into a blood vessel). Implantation is more secure, but may be associated with biocompatibility problems or local irritation. Less invasive methods may be categorized as minimally invasive or noninvasive. Minimally invasive techniques extract fluid (tears or interstitial fluid) while noninvasive technologies do not.

 

Minimally invasive methods include electrical, nanotechnology, and optical approaches while noninvasive techniquesrely on some form of radiation without the need to access bodily fluids. Noninvasive methods frequently incorporate electric, thermal, optical, or nanotechnology methods for detection. Many noninvasive devices under development are aimed for non- continuous monitoring as they often require controlled surroundings including factors such as light, motion and temperature.

  • Optical approaches utilize reflective, absorptive, or refractive properties of infrared and optical bands of the light spectrum to detect glucose. Pure optical methods under development utilize Raman and Near infra-red spectroscopy.
  • Thermal methods detect glucose via the far-infrared band of the spectrum and provide noninvasive approaches for glucose monitoring.
  • Electric methods use electromagnetic radiation, currents, or ultrasound approaches to detect dielectric properties of Reverse iontophoresis has been employed with early minimally invasive approaches while bioimpedance spectroscopy has been used in recent noninvasive approaches.
  • Nanotechnologies aim to miniaturize existing technologies, including fluorescence and surface plasmon resonance (SPR) approaches (138).

 

Few devices (other than interstitial CGMs discussed above) have demonstrated high levels of accuracy recommendedby expert groups, though several have been approved by CE or FDA (139).

 

MOBILE TECHNOLOGY AND DECISION SUPPORT

 

It has become increasingly clear that the isolated use of glucose monitoring technologies without a specific plan toaddress the data provides minimal benefit, particularly among patients with type 2 diabetes or who are not using insulin (140). In order for glucose monitoring to provide the most benefit, patients and providers must be able to easilyobtain and communicate the data. Data must be organized in such a way that patterns can be identified, and patients must receive feedback at the point of care. The widespread use of mobile devices provides opportunities for data collection, analysis, and communication of results with health care providers as well as facilitates digital or remote clinical models of care (141). Finally, as healthcare providers are inundated with more data and spend increasingamounts of time using electronic medical records, it has also become paramount that devices and or reports from the devices communicate or interface with these systems (142).

 

Hurdles to wider implementation of mobile technology include the lack of usability (both for patients, as well as providers who may be expected to review and act upon reports), safety, efficacy (including long-term adherence), and cost-effectiveness studies (143). The lack of data is in part due to the rapidly changing technology itself, which rendersthe technology obsolete by the time a vigorous clinical trial is conducted and published. The fee for service model is amajor barrier to adapting many glucose monitoring technologies, which often require frequent feedback and treatment adjustments, efforts that are not reimbursed without an actual office visit. Finally, cyber security is a big concern for all medical devices, especially for devices that are controlled by a smartphone (144).

 

Device Downloading, Connectivity, and Interoperability

 

Manual recording of glucose data is fraught with inaccuracies (145). Most monitors can be downloaded, via a tethering cable or wireless connection, either by the patient or healthcare provider. Each glucose monitoring devicegenerally works with its own proprietary management software. However, several programs (Tidepool,Glooko/Diasend, Carelink by Medtronic, Accu- chek) are capable of downloading and organizing data for multiple different devices (146).

 

Reports are standardized across all device downloads, facilitating efficient and actionable patient and healthcare provider review. These programs also facilitate population health and telehealth strategies (discussed below). The Nightscout Project is a crowd sourced application that provides a free mobile technology platform for patients whowant to access their devices in real time on any mobile device (147). Recent data suggest that retrospective weekly review of data is associated with improved TIR (148,149) as well as patient reported outcomes including confidence in avoiding hypoglycemia, overall well-being and diabetes distress (150).

 

Direct connectivity of blood glucose or CGM levels to cell phones or other devices not only improves data integrity but may also simplify the assimilation of glucose levels with other data such as insulin use, carbohydrate intake, andactivity levels for the purpose of facilitating insulin dose adjustments in real time or retrospectively. Cell phone connectivity may also improve communication with providers. A few meters with direct cellular capability are available.

 

Devices with direct cellular or Bluetooth connections may be paired with apps that facilitate collection, communication, and analysis of a variety of data and provide tools for education (such as nutrition information) at the point of care.

 

Currently, both the Tandem t:slim X2 and Insulet’s Omnipod 5 System are FDA approved for remote blousing via a cell phone app (151,152). A regulatory pathway has been developed for alternate controller enabled (ACE) infusion pumps which can be operated in conjunction with interchangeable components, particularly CGMs (153). In 2019, theFDA approved the first such devices (Tandem t:Slim X2 and Omnipod DASH system).

 

Diabetes Apps

 

A variety of stand-alone smart phone applications that support glucose monitoring are also available. Most provide information and track data (usually manually entered), some allow insulin or carbohydrate documentation, facilitate carbohydrate or calorie counting, promote weight loss, track or promote physical activity, enhance medication adherence, and use motivational or self-efficacy approaches, and a few provide an insulin dosing calculator. Simple apps provide information or tracking functions while more sophisticated approaches incorporate gaming theory and machine learning approaches that learn from the user’s previous experiences to optimize interactions. Apps have shown limited magnitude and sustainability of effect due to a variety of factors, including user fatigue, require continuous data entry (e.g., most apps do not connect directly with a glucose meter), and lack of integration with the health care team. Moreover, most apps have not been evaluated by the FDA or other regulatory agencies. Data privacy is also a concern, as no federal regulations currently prevent app developers from disclosing data to third parties. Most apps (81% in one survey of Android apps) do not have privacy policies, and of those that do, 49% share user data with third parties (154). Expert groups have developed policy or guidance statements to improvestandardization and functionality (155,156,157).

 

Efficacy

 

While the data are still evolving with respect to mobile diabetes applications, several systematic reviews and meta-analyses demonstrate modest (~0.5%) reductions in A1C in persons with type 2 diabetes, especially among younger patients, apps that provide healthcare provider feedback, or had other features including wireless entry of data (158,159,160,161). The Agency for Healthcare Research and Quality published a systematic review of comparative effectiveness studies assessing apps or programs available through a mobile device for the purpose of diabetes self-management (162). For type 1 diabetes, 6 apps were identified, 3 of which were associated with improvement in A1c, 2 of which were associated with improvement in hypoglycemia. Five apps for patients with type 2 diabetes were identified, 3 of which were associated with improvement in A1c. Efficacy is variable, in part because app features vary but also because apps are often studied as part of a multi-component intervention, making it difficult to assess individual elements, particularly the effect of additional health care provider support. Other researchers have focusedon identifying standard evidence-based features that should be included in diabetes apps, such as education, glucose monitoring, and reminders (163,164).

 

Usability

 

In a systematic review of 20 studies, only one third of the 20 apps met the authors’ health literacy standards (165).Usability was measured in 7 studies through satisfaction surveys from patients and experts, and ranged from 38-80%. The most common usability problems were multi-step tasks, limited functionality, and poor system navigation. While many apps are rated high quality for performing a single task, most do not address diabetes self-management tasks comprehensively (166) or otherwise do not function properly (165,167).

 

Decision Support

 

The use of pattern management software improves health care provider efficiency and accuracy in identifying needed therapeutic adjustments (168,169). Software programs provide graphs or charts and may in some cases provide dosing advice, either for the healthcare provider or directly to the patient.

 

Insulin Dosing Calculators

 

Insulin dosing calculators have been used for years as a means of incorporating glucose measures into routine practice, largely in concert with continuous insulin infusion pumps. While numerous apps have become available forbolus insulin calculation and basal insulin titration, it is important to note that only a few have been formally evaluated and approved by regulatory agencies. In addition, many still require manual data entry, few integrate within existing electronic medical records, and published evidence for efficacy is limited (170). All approved insulin calculators or dose titration apps require a prescription or need to be set up by a healthcare provider. Many such apps operate in conjunction with connected meters and insulin pens, which are subject to regulatory oversight and long-term support (171). Such support ensures safety and that software is updated to address any problems with operation and device compatibility. The functionality of connected pens ranges from insulin tracking functions, including insulin on board calculations and reminders to smart insulin pens which feature bolus dose calculators and more advanced decisionsupport such as dose titration and coaching features (172). A full review of insulin dosing apps is beyond the scope of this chapter.

 

Bolus calculators are known to substantially improve dosing accuracy and glycemic control in outpatients with type 1 diabetes (173,174,175). Bolus calculators might be particularly helpful for patients with poor numeracy. A number of stand-alone smart-phone apps for bolus insulin calculation have been developed but safety and efficacy remain a concern (176,177). Though algorithms typically incorporate the current glucose level, active insulin time, and carbohydrate intake, some do not account for activity or illness. Applications that improve the accuracy of carbohydrate counting, which is a major source of error (regardless of educational level), are desirable (178). Reports from connected pens provide insight into missed or altered insulin doses and when integrated with CGM data can alsofacilitate the evaluation of timing of boluses.

 

Likewise, basal insulin calculators have been developed to recommend ongoing adjustments in therapy, either fortitration or for mealtime insulin calculations. Unfortunately, efficacy and safety studies are not currently available for most apps. Most basal insulin titration apps account only for fasting glucose measures and not overnight trends.

 

Although there are a plethora of apps available, the ultimate choice should be individualized to the needs of thepatient. Those patients only needing a resource that assists with carbohydrate counting can be referred to common apps like MyFitnessPal or Calorie King. For glucose monitoring, apps that require manual entry of data should beminimized as they are not likely to be utilized long-term. Universal platforms that can download multiple devices can increase clinic efficiency. Where possible, patients should be invited to directly link with their clinic. This is particularly useful for telehealth visits. Smart insulin pens provide assistance with insulin dosing and can also be downloaded using some universal platforms.

 

Integration within the Electronic Health Record (EHR)

 

The major limitation of patient generated data is that it does not integrate within the EHR in a meaningful way. Someopportunities exist with the integration of Apple Health Kit and Samsung S-Health which can transmit data from a variety of apps but this process requires multiple steps and can be cumbersome (179,180). Recently, a consensus report from the Integration of Continuous Glucose Monitoring Data into the Electronic Health Record (iCoDE) project was published, setting standards for integration of CGM data within the EHR (181). Under these standards, data would be accessed by placing an order in the EHR. This would generate a notice to the patient via email or electronic message to obtain consent for sharing data. Once approved, standardized report is uploaded to the EHR. Importantly,none of these mobile health tools replace frequent patient contact and feedback (182).

 

BIOMARKERS OF GLYCEMIC CONTROL

 

Hemoglobin A1c (A1C)

 

A1C is the best biomarker indicator of glycemic control over the past 2-3 months due to strong data predicting complications (1,2). In addition, the American Diabetes Association has recommended its use for the diagnosis of diabetes (1).

 

Hemoglobin A1c refers to the nonenzymatic addition of glucose to the N-terminal valine of the hemoglobin beta chain. Assays are based upon charge and structural differences between hemoglobin molecules (183,184). Therefore, variants in hemoglobin molecules may lead to analytic interferences. It should be noted that some homozygous hemoglobin variants (HbC or HbD, or sickle cell disease) also alter erythrocyte life span and therefore, even if theassay does not show analytic interference, other methods of monitoring glycemia should be utilized, as A1C will be falsely low. Individual assay interferences are available at the National Glycohemohemoglobin Standardization Program website: www.ngsp.org (185). Several commercial home monitoring kits are also available (186). The two reference methods used to standardize A1c levels are 1) HPLC and electrospray ionization mass spectrometry or 2) a two- dimensional approach using HPLC and capillary electrophoresis with UV-detection (187). A brief summary of assay methods is described below.

 

  • HPLC methods utilize the fact that glycated hemoglobin has a lower isoelectric point and migrates faster than otherhemoglobin As such it has variable interference with hemoglobinopathies that alter the charge of the molecule (such as HbF and carbamylated Hb), but these may be revealed through individual inspection of the chromatograms.
  • Boronate affinity methods are based upon glucose binding to m-aminophenylboronic acid and measures glycation on the N-terminal valine on the beta chain but also glycation at other sites. There is minimal interference from hemoglobinopathies but this assay is not widely available.
  • Immunoassays make use of antibody binding to glucose and N-terminal amino acids on the beta chain and therefore may be affected by hemoglobinopathies with structural changes at these sites, including HbF but notHbE, HbD, or carbamylated Some newer assays have attempted to correct for these interferences.
  • Enzymatic methods lyse whole blood, releasing glycated N-terminal valines which are detected using achromogenic reaction and are not affected by hemoglobin

 

An Organization with links to governmental regulatory agencies, the National Glycohemoglobin Standardization Program (NGSP) (<http://www.ngsp.org/news.asp >), evaluates every laboratory and home test for A1C, sets accuracy standards, and certifies which methods meet their standards (188). The trend in industry is for monitors to become increasingly more accurate and the trend in regulatory organizations is to require increasing accuracy for ongoing certification.

 

A1C is an analyte found within red blood cells, comprised of glycated Hemoglobin. The glycation gap (formerly known as the glycosylation gap) (GG), based on fructosamine measurement, and the Hemoglobin Glycation Index (HGI), based on mean blood glucose, are two indices of between-individual differences in glycated hemoglobin adjusted forglycemia. GG is the difference between the measured A1C test and the A1C test result predicted from serum fructosamine testing based on a population regression equation of A1C on fructosamine (189). and HGI is the difference between the measured A1C test and A1C results predicted from the mean blood glucose level (calculated from self-monitored blood glucose tests) based on a population regression equation of A1C tests on mean blood glucose levels (190). These two indices are consistent within an individual over time and reflect an inherent tendency for an individual’s proteins to glycate (191,192). Patients with high GG and HGI indices might have falsely high A1C test results and might also be at increased risk of basement membrane glycosylation and development of microvascular complications. Whether between-individual biological variation in Hemoglobin A1c is an independent risk factor, distinct from that attributable to mean blood glucose or fructosamine levels, for diabetic microvascular complications is controversial (193).

 

Because the A1C test is supposed to reflect the mean level of glycemia, attempts have been made to correlate thiswidely-accepted measure with empirically measured mean blood glucose levels. In 2008, the A1c-Derived Average Glucose (ADAG) study compared A1C and continuous glucose monitoring derived mean glucose and 7-point glucose profiles among 507 patients with type 1 and type 2 diabetes and without diabetes from 10 international centers to derive an estimated average glucose (eAG) from A1C levels using the following equation: eAG(mg/dl) = (28.7* A1C)-46.7 (Table 6).

 

Table 6. A1C and Estimated Average Glucose

A1C (%)

eAG (mg/dl)

eAG (mmol/l)

5

97

5.4

6

126

7.0

7

154

8.6

8

183

10.2

9

212

11.8

10

240

13.4

11

269

14.9

12

298

16.5

 

Several lines of evidence support this disconnect from a tight correlation between mean glycemia and A1C levels. First, improvements in mean glycemia may not necessarily be reflected by improvements in A1C in intensively treated patients (194). A1C does not reflect short-term changes in glucose control, and therefore can be misleading wherethere have been recent changes in the clinical condition. In addition, glucose fluctuations, compared to chronic sustained hyperglycemia, have been shown to exhibit a more specific triggering effect on oxidative stress and endothelial function (195,196). Glycemic variability cannot be assessed by a global measure of mean glycemia, such as A1C, but requires multiple individual glucose values, such as what can be obtained from continuous glucose monitoring or from seven-point- per-day (or greater) self-glucose testing. Third, A1C does not permit specific adjustments in therapy, particularly among patients requiring insulin titration. Finally, A1C reliability may be affected by several conditions that alter red blood cell lifespan and its use in these circumstances can be misleading. Acomparison of the features and limitations in glucose markers is presented in Table 7 (197,198,199).

 

Table 7. Comparison of Markers of Glycemic Control

 

Biomarker mechanism

Interval of time reflecting glucose

control

Cautions/Interferences

A1C

Hemoglobin glycation

3 months

Hemoglobinopathy (↑/↓*)

Decrease in RBC survival (hemolysis, splenomegaly, pregnancy, drugs) (↓)

Increase in RBC survival (Erythropoietin, iron replacement) (↑)

Transfusion (↓)

Fructosamine

Protein glycation

2 weeks

Conditions resulting in hypoproteinemia (severe cirrhosis, nephrotic syndrome, enteropathy) (↓)

High dose Vitamin C, severe hyperbilirubinemia/uremia/ hypertriglyceridemia (↑)

1,5-AG

Renal clearance

1 week

Chronic kidney disease (stage 4, 5) (↓)

Glucosuria (pregnancy, renal tubular disorders SGLT2 inhibitors) (↓)

Advanced cirrhosis (↓)

High soy diet (↑)

*Assay-dependent

 

Ethnic differences in A1C have also been reported (200). For example, recent data from the Type 1 Diabetes Exchange demonstrates a 0.4% higher A1C at a given mean glucose among black patients compared to whitepatients with type 1 diabetes, but no effect of race on glycated albumin or fructosamine (201). However, NHANES data do not demonstrate an effect of ethnicity on the association between A1C and retinopathy (202). Data from the ARIC study demonstrated that A1C, fructosamine, glycated albumin, and 1,5-AG were consistent with residualhyperglycemia among blacks compared to whites, and the prognostic value for incident cardiovascular disease, end stage renal disease and retinopathy were similar by race (203). It should be noted that the range of available A1C was relatively narrow in NHANES and ARIC, and further data across an expansive range is needed. In relation to CGMs, utility of A1C is further enhanced when used as a complement to glycemic data measured by CGM (10). Other biomarkers are becoming more widely used, however, A1C remains the most common biomarker. Other measures of average glycemia such as fructosamine and 1,5-anhydroglucitol are available, but their translation into average glucose levels and prognostic significance are not as clear as for A1C (1).

 

Fructosamine

 

A short to medium-term marker (reflecting the average glucose control over the past few weeks) may be useful for determining control over a period of days to weeks since A1C does not reflect recent changes in glucose control. Alternate markers may also be useful in patients with discrepant A1C and self-monitored blood glucose readings as well as patients with other hematologic conditions known to affect A1C. Fructosamine is a term that refers to a family of glycated serum proteins and this family is comprised primarily of albumin and to a lesser extent, globulins, and to an even lesser extent, other circulating serum proteins. No product exists for home use that measures serum fructosamine. A home blood fructosamine monitor, Duet Glucose Control System, was marketed in the early 2000′sand then withdrawn from the market. No subsequent home fructosamine test has been available since then. Randomized controlled trials have reported inconsistent effects of frequent monitoring on A1C lowering, possibly due to differences in execution of therapeutic interventions (204,205). Serial monitoring of short-term markers may also facilitate timely elective surgery in patients whose procedure is delayed due to an elevated A1C. In a recent study, fructosamine was a better predictor of post-operative complications in patients undergoing primary total joint arthroplasty (206).

 

GLYCATED ALBUMIN

 

The largest constituent of fructosamine is glycated albumin. Several investigators and companies are developing portable assays for glycated albumin to assess overall control during periods of rapidly changing glucose levels. In these situations, an A1C test may change too slowly to capture a sudden increase or decrease in mean glycemia. The components of the necessary technology appear to be in place to build a commercial instrument for home testing of glycated albumin. However, there is no randomized controlled trial showing that the measurement of glycated albumin improves outcomes. In the ARIC study, fructosamine, glycated albumin, and 1,5-AG were associated with incident diabetes, even after adjustment for baseline A1C and fasting glucose. In the ARIC study, both fructosamine and glycated albumin predicted incident retinopathy and nephropathy, even after adjusting for A1C (207). However, in adults with severe chronic kidney disease, none of the markers, including A1C, fructosamine, or glycated albumin were very highly correlated with fasting glucose, and there did not appear to be an advantage of one marker over another (208). In addition, baseline glycated albumin and fructosamine were associated with cardiovascular outcomes over a 20-year follow-up period after adjusting for other risk factors, but the overall magnitude of associations was similar to A1C (209). In the Diabetes Control and Complications Trial (DCCT), glycated albumin had a similar association with retinopathy and nephropathy as A1C, but the combination of both markers provided even better prediction (210). Short-term markers are also of interest for use in pregnancy, where glucose levels are changing more quickly than can be reflected by A1C. Unfortunately, glycated albumin does not predict gestational diabetes more effectively than A1C or fasting glucose (211). However, other preliminary data suggests that glycated albumin may be a better predictor of pregnancy complications than A1C (212).

 

1,5-Anhyroglucitol

 

The aforementioned biomarkers for measuring glycemic control, (A1C, fructosamine, and glycated albumin) only reflect mean levels of glycemia. These measures can fail to portray hyperglycemic excursions if they are balanced by hypoglycemic excursions. Plasma 1,5- anhydroglucitol (1,5-AG) is a naturally occurring dietary monosaccharide, witha structure similar to that of glucose (Figure 5). This analyte has been proposed as a marker for postprandial hyperglycemia (213). An automated laboratory grade assay named Glycomark is approved in the U.S. for measuring 1,5-AG as a short-term marker for glycemic control. A similar laboratory assay has been used in Japan. During normoglycemia, 1,5-AG is maintained at constant steady-state levels because of a large body pool compared with the amount of intake and because this substance is metabolically inert. Normally, 1,5-AG is filtered and completely reabsorbed by the renal tubules. During acute hyperglycemia when the blood glucose levels exceed 180 mg/dl, whichis the renal threshold for spilling glucose into the urine, serum 1,5-AG falls. This fall occurs due to competitive inhibition of renal tubular reabsorption by filtered glucose. The greater the amount of glucose in renal filtrate (due to hyperglycemia), the less 1, 5-AG is reabsorbed by the kidneys. The 1,5-AG levels respond sensitively and rapidly torises in serum glucose and a fall in the serum level of this analyte can indicate transient elevations of serum glucose occurring over as short a period as a few days. Measurement of 1,5-AG can be useful in assessing the prior 1-2 weeks for: 1) the degree of postprandial hyperglycemia; and 2) the mean short-term level of glycemia. This assay might prove useful in assessing the extent of glycemic variability that is present in an individual with a close-to-normal A1C level, but who is suspected to be alternating between frequent periods of hyperglycemia and hypoglycemia. In such a patient, the 1,5-AG level would be low, which would indicate frequent periods of hyperglycemia, whereas in a patient with little glycemic variability, the 1,5-AG levels would not be particularly depressed because of a lack of frequent hyperglycemic periods. In the ARIC study, 1,5-AG was associated with severe hypoglycemia after adjustmentfor other variables, an observation which is consistent with the role of 1,5-AG in reflecting glycemic variability, a known risk factor for hypoglycemia (214).

 

Longitudinal data from the ARIC study showed that 1,5-AG was associated with ESRD over a 19-year follow-up period, but the relationship was no longer significant after adjusting for glucose control with other markers (215). Among participants with diabetes and A1C <7%, each 5 mcg/mL decrease in 1,5-AG was associated with an increase in dementia risk by 16%, and at A1C >7%, there was also a significant association over a median 21-year follow-up period (216). There was also an association of 1,5-AG and cardiovascular outcomes in ARIC, which persisted, thoughwere attenuated after adjusting for A1C (217). Therefore, it is not yet clear whether 1,5-AG, as a measure of glucoseexcursions, provides incremental value beyond A1C for predicting long-term complications.

 

Figure 5. Structure of glucose (left) and 1,5-anhydroglucitol (right).

 

CONCLUSIONS

 

Many new types of technology are increasingly being developed and applied to fight diabetes and its complications. New technologies will improve the lives of people with diabetes by measuring glucose and other biomarkers of glycemic control and linking glucose levels with insulin delivery to improve the lives of people with diabetes.

 

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