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Adult Growth Hormone Deficiency Clinical Management

ABSTRACT

 

The clinical syndrome of GH deficiency (GHD) is characterized by non-specific features including variable presence of decreased mood and general well-being, reduced bone remodeling activity, change in body fat distribution with increased central adiposity, hyperlipidemia, and increased predisposition to atherogenesis. The goal of GH replacement therapy in adults with GH deficiency is to correct the wide spectrum of associated clinical alterations. The estimated prevalence of GHD is approximately 2-3:10,000 population. GHD is caused by structural pituitary disease or cranial irradiation, and usually occurs in the context of additional features of hypopituitarism. Pituitary adenomas are the most important cause of adult-onset GHD followed by craniopharyngiomas, which combined account for 57% of cases. Less common causes are irradiation, head injury, vascular, infiltrative, infectious. and autoimmune disease. Diagnosing patients with GHD should first of all consider who should be tested for GHD, which includes patients at relevant risk with an intention to treat, and second which stimulation test to be used including the proper diagnostic cut-off concentration of GH. The diagnosis of GHD in adults is then usually straightforward. Dosage of h-GH replacement is dependent on age, and gender with adolescents and women usually requiring an increased dosage. The dose titration is monitored by IGF-I concentrations and apart from that a number of organ end points, which may act as ‘biomarkers’ of the treatment effects. This chapter provides an update on GHD including diagnostic pitfalls, and treatment effect, safety, and monitoring.

 

INTRODUCTION

 

The term "midget" as description of a proportionate dwarf was first used in 1816, but it was not until 1912, that Harvey Cushing in “The Pituitary Gland” proposed the existence of a "hormone of growth" promoting skeletal growth in children (1). Growth hormone (GH) or somatrophin was first extracted from cadaveric pituitaries in the late 1950es, and other more metabolic actions of this hormone in humans were described soon after by Maurice Raben (2). The purified hormone was initially only used for the treatment of short stature in hypopituitary children, although Raben already in 1962 described general health improvement after injection of GH in a hypopituitary adult (2). Further, increasing knowledge of GH effects in adults was brought forward by the introduction in 1962 by Utiger et al of a radioimmunoassay for measuring GH in human serum (3).

 

The clinical syndrome of GH deficiency in adults is a consequence of decreased secretion of GH from the anterior pituitary. Until thirty years ago it was widely held that GH deficiency had little pathophysiological consequence despite the previously mentioned earlier anecdotal reports suggesting presence of GH-remediable symptoms of fatigue and decreased general well-being which responded to GH replacement (2). In retrospect, these observations of more than fifty years ago described quite precisely the later well-known classical features of the GH deficiency syndrome. However, the imitated supplies of cadaveric GH and the focus on pediatric usage resulted in delayed further elucidation of the adult GH deficiency state. The measurement of serum GH and the production of recombinant human GH (rhGH) in 1981 made studies of GH concentrations in adults as well as effects on the human body of GH deficiency possible, and clinical studies on replacement with rhGH could begin.

 

The initial pivotal trials of GH replacement therapy in adult hypopituitary patients were published in 1989 (4, 5). Numerous subsequent studies have provided compelling evidence for the existence of a syndrome of adult GH deficiency (6-8). This is characterized by the variable presence of decreased exercise tolerance, decreased mood and general well-being, reduced bone remodeling activity, change in body fat distribution with increased central adiposity, hyperlipidemia, and increased predisposition to atherogenesis. However, it is important to recognize that adult-onset GH deficiency is due to structural pituitary or hypothalamic disease or cranial irradiation for other pathologies and, therefore, usually occurs in the context of additional features of hypopituitarism (9, 10). For this reason, the clinical features attributable to GH deficiency may be compounded by, or directly related to, other pituitary deficiencies. Nonetheless, the fact that GH replacement therapy may favorably alter these clinical features provides considerable surrogate evidence for GH deficiency as a causal factor.

 

Adult GH deficiency is thus a well-recognized clinical entity. It causes abnormalities in substrate metabolism, bone remodeling, body composition, as well as physical, and psychosocial function. Since the mid 80-ies an improvement has been recognized with GH replacement, and this has gradually been incorporated in clinical routine based on the few short-term initial randomized clinical trials, which led to the first international consensus guidelines from Growth Hormone Research Society in 1997 (11) and updated in 2007 (12).

Fig 1. Growth hormone secretion varies throughout life. From: Ho KY et al. (13)

Less well recognized is the fact that the early clinical trials were based on selected groups of patients with very severe hypopituitarism and therefore had a high a priory likelihood of severe GH deficiency, there were few study participants, short-term treatment, and supraphysiological GH doses were calculated based on the experience from childhood GH deficiency. Despite knowledge of the very high influence of age on the secretion of GH (Fig 1) and subsequently on Insulin-like-Growth Factor-I (IGF-I) the initial adult doses in the studies were nevertheless chosen too high (4, 5). Most of the current recommendations and guidelines over the years have thus been based on subsequent retrospective single center experience or data from large surveillance databases run by the pharmaceutical industry as the best surrogates for efficacy and safety of GH therapy of adult GH deficiency (14). The Hypopituitary Control and Complications Study (HypoCCS) compiled data from 5,893 patients on Humatrope® and reported that significant shifts in diagnostic patterns have occurred over 10 years after approval of the adult GH deficiency indication, with a trend to less severe forms of GH deficiency (15). This was further documented in a recent publication from KIMS (Pfizer’s International Metabolic Database) where data compiled over 20 years were retrieved for a total of 6,069 patients with adult-onset GH deficiency and treated with Genotropin® from six countries (Belgium, Germany, Netherlands, Spain, Sweden, and UK). The degree of confirmed GH deficiency became less pronounced and more patients with co-morbidities and diabetes were considered for GH replacement therapy, possibly reflecting increased knowledge and confidence in GH therapy gained with time. Thus, the effects of 1 year of GH replacement were similar over the entry year periods despite changes in the patients’ baseline characteristics (16).

 

Also, less well recognized is the fact that new possible indications for testing and treatment of GH deficiency have emerged and these very likely have a lower a priori likelihood of the disease than the severely hypopituitary patients initially investigated thus challenging the diagnostic criteria laid down for severe GH deficiency. Clinicians are therefore now dealing with other patient populations as, e.g. traumatic brain injury, where neither testing nor treatment efficacy have been scrutinized sufficiently (17) and where current guidelines therefore may fail to apply correctly.

 

This chapter is an update of our chapter from 2017 which was in turn based on the previous chapter on the topic written by John Monson, Antonia Brooke and Scott Akker and the update will describe the diagnostic procedures, as well as the clinical consequences and management of adult patient with GH deficiency. The basic physiology of GH and the pathophysiology of GH deficiency in adults have been dealt with in other Endotext chapters (www.endotext.org).

 

PREVALENCE, INCIDENCE, AND ETIOLOGY OF GH DEFICIENCY IN ADULTS

 

The true prevalence and incidence rate of adult-onset GH deficiency is difficult to estimate with certainty. A reasonable estimate of the prevalence may be obtained from prevalence data for pituitary macroadenomas, which approximate to 1-2:10,000 population (20-22). Addition of cases of childhood-onset GH deficiency persisting into adult life gives an overall prevalence of 2-3:10,000 population. Incidence rates have been assessed in a Danish nationwide study based on registries (23), including 1,823 patients who were divided in males and females with childhood and adult onset GH deficiency, respectively. The average incidence rates were for childhood onset males, 2.58 (95% confidence interval (CI), 2.30-2.88), childhood onset females, 1.70 (95% CI, 1.48-1.96), adult-onset males, 1.90 (95% CI, 1.77-2.04), and adult-onset females, 1.42 (95% CI, 1.31-1.54) all per 100,000, which are slightly higher than previously reported (24, 25). The incidence rate in the Danish study was significantly higher in males compared to females in the childhood onset GH deficiency group and in the adult-onset GH deficiency group in the age ranges of 45-64 and 65+years, while there was no significant gender difference in the 18-44 years age group. The etiology spectrum of GH deficiency is summarized in figure 2.

Figure 2. Congenital and acquired causes of growth hormone deficiency

Pituitary adenomas are statistically the most important cause of adult-onset GH deficiency followed by craniopharyngiomas, which combined account for 57% of cases in the study based on data from KIMS, a multinational, pharmacoepidemiological surveillance database for adult hypopituitary patients receiving GH replacement with Genotropin® (Table 1) (26). Over a decade, there was a decrease in patients enrolled in the surveillance databases with diagnoses of pituitary adenoma (50.2 to 38.6%; P<0.001); craniopharyngioma (13.3 to 8.4%; P=0.005) and pituitary hemorrhage (5.8 to 2.8%; P=0.001); increases in idiopathic GH deficiency (13.9 to 19.3%; P<0.001) and undefined/unknown diagnosis (1.3 to 8.6%; P<0.001) in HypoCCS(15).

 

Table 1. Etiology in Patients with GH Deficiency (from the KIMS database)

Etiology category

Category components

   n

Patient-years

Pituitary adenoma

Non-functioning adenoma

5261

28 065

 

Prolactinoma

 

 

 

Gonadotropinoma

 

 

 

Thyrotropinoma

 

 

Cushing's disease

Cushing's disease

859

4814

Acromegaly

Acromegaly

239

1396

Pituitary atrophy

Congenital

2496

10 535

 

Idiopathic

 

 

 

Empty sella

 

 

Craniopharyngioma

Craniopharyngioma

1562

8392

Benign tumor/lesion

Hamartoma

462

2114

 

Cyst

 

 

 

Meningioma

 

 

 

Schwannoma

 

 

Aggressive tumor  (+hematological neoplasm)

Germ cell tumor

1135

5552

 

Glioma

 

 

 

Chordoma

 

 

 

Sarcoma

 

 

 

Astrocytoma

 

 

 

Ependymoma

 

 

 

Medulloblastoma

 

 

 

Leukemia

 

 

 

Lymphoma

 

 

Miscellaneous etiology

Traumatic brain injury

1969

8189

 

Subarachnoid hemorrhage

 

 

 

Aneurysm

 

 

 

Sheehan's syndrome

 

 

 

Hydrocephalus

 

 

 

Granulomatosis

 

 

 

Histiocytosis

 

 

 

Hypophysitis

 

 

 

Hemochromatosis

 

 

 

Missing etiology

 

 

From: Gaillard et al (26)

 

Irradiation includes both pituitary tumors but also other forms of childhood and adult cranial irradiation. Less common causes of adult hypopituitarism are head injury (27), postpartum ischemic necrosis [Sheehan’s syndrome], pituitary apoplexy, infiltrative diseases, and autoimmune lymphocytic hypophysitis. Traumatic brain injury and subarachnoid hemorrhage are increasingly recognized as a cause of hypopituitarism, in particular GH deficiency, which the recently updated guidelines from American Association of Clinical Endocrinologists and American College of Endocrinology indicated to be one of the most common causes of adult GH deficiency seen in clinical practice (18). Several anti-cancer drugs modulating the immune system and used for antineoplastic purposes may result in hypophysitis with hypofunction including GH deficiency (29, 30), and the list of drugs influencing GH secretion may be increasing, perhaps also including treatment of patient groups with autoimmune diseases.

 

Most cases of adult GH deficiency arise in adulthood, but a proportion of them are suffering from childhood onset GH deficiency thus also including congenital causes. The proportion in each clinical center will depend on referral practice. In the Danish nationwide study 27% of GH deficiency patients were of childhood origin (23). The congenital cases (figure 2) are due to structural lesions such as Rathke’s pouch cysts, pituitary hypoplasia, and midline defects, or to functionally deficient GH biosynthesis and release such as pituitary-specific transcription factors (PROP1, POU1F1, HESX1, LHX3, LHX4), and LEPR or IGSF1. Thus, childhood-onset GH deficiency due to proven genetic defects in GH synthesis is never reversible and therefore does not require retesting prior to treatment on adult indication. The reversibility of isolated idiopathic GH deficiency of childhood is on the other hand well established with normal GH responses on dynamic testing in various series being described in between 30 and 70% of subjects with confirmed GH deficiencies in childhood at completion of linear growth (31-33). Therefore, childhood-onset isolated GH deficiency should always be challenged by rigorous re-evaluation of causes and retesting at completion of final height.

Fig 3. Mean (±SEM) serum GH response to insulin hypoglycemia in normal subjects (▲) and obese subjects before (●) and after (○) weight loss. From: Rasmussen et al (34).

Isolated idiopathic GH deficiency is not accepted as de novo deficiency in adults at this point in time. This is particularly important in the assessment of non-specific symptoms in ageing or overweight persons without additional evidence of pituitary disease; body mass index of >32 kg/m2 is associated with reduced GH reserve on dynamic testing in approximately 30% of patients but this is reversible with weight loss (Fig 3) (34-37). However, combined deficiency of GH and other anterior pituitary hormones, in the absence of structural disease, may be a feature of an evolving endocrinopathy due to deficiencies of the transcription factors PIT-1 or Prop-1. These cases, and possibly also others, may account for some of the patients with isolated GH deficiency developing into multiple pituitary hormone insufficiencies in 6-65% of cases over time (Fig 4) (38-40).

Fig 4. Number of patients with GH deficiency and at least one additional pituitary deficit at baseline who developed central hypothyroidism, hypoadrenalism, hypogonadism or ADH deficiency in relation to years from baseline. From: Klose et al (38)

The sequence of loss of pituitary functions is displayed in Fig 5, demonstrating that GH deficiency usually occurs early in the progression of pituitary insufficiency, at least in pituitary adenomas (10). Normalization of GH but also other deficiencies are sometimes observed after selective adenectomy (41-43).

Fig 5. Sequence of pituitary hormone loss in relation to increasing mass effect from a pituitary tumor. From: Feldt-Rasmussen & Klose (10)

CLINICAL FEATURES OF GH DEFICIENCY IN ADULTS

 

Adult GH deficiency is associated with an extensive array of non-specific symptoms and physical signs, which are nevertheless recognized by experienced endocrinologists to justify their designation as a clinical syndrome (6-8, 44). Typical symptoms and signs are listed in Table 2.

 

Table 2. Typical Symptoms and Signs of the Adult Growth Hormone Deficiency Syndrome

Body composition

·       increased body fat, particularly central adiposity

·       decreased muscle mass

·       decreased muscle function

Cardiovascular and metabolism

·       decreased sweating and poor thermoregulation

·       decreased insulin sensitivity and increased prevalence of impaired glucose tolerance

·       increased total and LDL cholesterol and Apo B. Decreased HDL cholesterol

·       accelerated atherogenesis

·       a variable decrease in cardiac muscle mass

·       impaired cardiac function

·       decreased exercise capacity

·       decreased total and extracellular fluid volume

·       increased concentration of plasma fibrinogen and plasminogen activator inhibitor type I

Bones

·       decreased bone mineral density, associated with an increased risk of fracture

Quality of Life

·       depressed mood

·       reduced concentration

·       increased anxiety

·       fatigue

·       lack of energy levels

·       low self-esteem

·       increased sick days

·       social isolation

·       lack of positive well being

 

Body Composition and Heart

 

GH deficiency is characterized by substantial changes in body composition with increments in total fat, percentage fat, and particularly visceral fat mass (45-52). Methodologies employed for this purpose have included dual energy X-ray absorptiometry (DEXA) (53), bioelectrical impedance (6-8), CT scan of specific body parts, or the simple measurement of the ratio of waist to hip circumference (52-56) (Table 2) and there is complete concordance among all studies which have examined these aspects in hypopituitary adults. Importantly, although the prevalence of obesity is increased in hypopituitary adults, the increment in visceral fat is also evident in those patients who are non-obese (45). In parallel with changes in fat mass, lean body mass is reduced. The latter may explain the reductions in muscle strength (57-59) and exercise tolerance, which have been documented in adult GH deficiency. The degree to which lean body mass is reduced is difficult to determine because of the reduction in total body water which is also evident in the GH deficiency state; body composition measurements, particularly bioelectrical impedance, may overestimate changes in lean body mass as a consequence of alterations in tissue hydration. Furthermore, the reduction in extracellular water, which is compounded by reduced total body sodium in GH deficiency, may be a major factor underlying the reported reductions in exercise capacity (60-64). To this may be added the effect of reduced left ventricular mass and function which have been described in a number of studies (65-75), although some of these studies on cardiac function in GH deficiency have been less clear.

 

Glucose Metabolism

 

In contrast to GH deficiency occurring in children, adult GH deficiency is associated with relative insulin resistance (45, 76-79) and an increased prevalence of impaired glucose tolerance and diabetes mellitus (76). The adverse changes in insulin sensitivity are predictably most obvious in obese patients but are also evident in hypopituitary patients with normal body mass index in whom the inverse relationship between insulin sensitivity and central fat mass, which characterizes the 'metabolic syndrome' is clearly seen (45, 76-79). It is therefore likely that the changes in insulin sensitivity observed in adult GH deficiency are due predominantly to increases in central fat mass. Interestingly, adult subjects with lifetime congenital untreated isolated GH deficiency have reduced β-cell function, no evidence of insulin resistance, and a higher frequency of impaired glucose tolerance (79).Thus, lifetime, untreated isolated GH deficiency increases insulin sensitivity, but impairs β-cell function, and does not provide protection from diabetes (79, 80). It has been postulated that changes in body composition and particularly fat mass might be a consequence of unphysiological glucocorticoid replacement. Against this is the fact that the doses of glucocorticoid replacement used in primary adrenal failure, which are similar to those used in hypopituitarism, are not associated with abnormalities of body composition. However, local tissue exposure to either endogenous or exogenous cortisol may be different in secondary as opposed to primary adrenal failure. The GH/IGF-I axis is now recognized to be an important modulator of the activity of the enzyme 11b hydroxysteroid dehydrogenase Type 1 (11bHSD1) (81). This isoenzyme acts as a predominant reductase, particularly in liver and adipose tissue, increasing the net conversion of inactive cortisone to the active cortisol. The activity of the enzyme is decreased by GH and, as a consequence GH deficiency is associated with a shift in the equilibrium set point in favor of cortisol. It is therefore possible that the increase in central adiposity, which characterizes the GH deficiency state, could be compounded by enhanced exposure to cortisol within adipocytes; hepatic metabolism might be perturbed by a similar mechanism. These mechanisms would tend to increase serum cortisol concentrations in patients receiving hydrocortisone replacement, which is quite often supraphysiological doses, but not in patients with intact ACTH reserve in whom negative feedback would determine maintenance of stable circulating cortisol concentrations. However, GH is also a negative determinant of serum cortisol binding globulin and therefore comparisons of serum total cortisol concentrations between GH deficient and GH replete states are not valid.

 

Atherosclerosis Risk Factors- Lipids and Hypertension

 

Adult GH deficiency is associated with an increase in total cholesterol, LDL-cholesterol and apolipoprotein B (4-8, 82, 83). A modest decrement in HDL-cholesterol has also been described in some studies. These changes are evident in both sexes and are quantitatively greater in women. Despite GH deficiency related sodium and water depletion, an increased prevalence of hypertension in adult hypopituitarism has been documented and may be related to a reduced activity of nitric oxide synthase, and consequent increased peripheral vascular resistance, as a result of GH deficiency. The changes in lipoprotein metabolism, body composition, insulin sensitivity, and peripheral vascular resistance indicated above would predict increased atherogenesis in the GH deficiency state. Indeed, several studies have reported an increase in ultrasonographically determined intima-media thickness and plaque formation in large arteries of patients with adult-onset GH deficiency as well as in adults with childhood-onset disease (84, 85).

 

Bone Mineralization

 

Decreased bone mineral density is a recognized phenomenon in adult hypopituitary patients (53, 82, 86-92) and is associated with an increased fracture risk (Fig 6) (92-96). Measurements of markers of bone formation and bone resorption are consistent with a low bone turnover state in GH deficiency. Deficits in bone mineral content and density are more striking in adults with childhood-onset GH deficiency and this is likely to be a consequence of failure to achieve genetic potential peak bone mass either because of inadequate GH replacement in childhood or its early cessation at the time of slowing of linear growth (86). Failure to achieve peak bone mass has important implications for the future development of osteoporosis and fracture risk. In the study by Lange et al (96), it was found that patients with idiopathic childhood onset GH deficiency, who at retest in adulthood did not have GH deficiency according to adult criteria, had reduced serum IGF-I and BMD/BMC compared to controls. This observation was also made in the patients who did have persistent GH deficiency in adulthood. The findings may reflect the fact that the present diagnostic criteria for adult GH deficiency (i.e., response to the ITT) do not reflect the clinical consequences of disordered GH-IGF axis in childhood onset GH deficiency young adults who were treated with GH in childhood. Alternatively, despite seemingly adequate GH treatment in childhood an optimal peak bone mass in adolescence may never have been reached in either of the groups. Noteworthy, IGF-I levels correlated with clinical signs of the adult GH deficiency syndrome. The situation in hypopituitarism is further complicated by the frequent accompaniment of gonadal steroid deficiency, often of unknown duration, which has a documented effect on the BMD (97). In addition, glucocorticoid replacement for primary adrenal failure is associated with modest reductions in bone mineral density, but over-replacement in hypopituitary patients does accelerate bone loss (98). Thus, glucocorticoid over-replacement may increase the prevalence of vertebral fractures in patients with untreated GH deficiency. However, treatment of GH deficiency seems to protect the skeleton from the deleterious effects of glucocorticoid overtreatment in hypopituitary patients. Along the same line, data suggest that the characteristics of patients in the various diagnostic groups of hypopituitarism depend on the primary disease which resulted in GH deficiency, and that the clinical expression of GH deficiency does not differ between the groups. Patients with previous hypercortisolism showed more long-term effects of their disease, such as diabetes mellitus, hypertension, and fractures (99), and patients with former Cushing’s disease have more fractures (100). Furthermore, Lange et al reported abnormal bone collagen morphology and decreased bone strength in rats with isolated GH deficiency (101), which might provide a co-explanation for the increased fracture rate in GH deficiency. Whether similar conditions are present in patients with GH deficiency needs further study, but results from a human study of muscle and tendon biopsies from patients with GH deficiency or acromegaly indicated a collagen-stimulating role of local IGF-I in human connective tissue and add to the understanding of musculoskeletal pathology in patients with either high or low GH/IGF-I axis activity (102).

Fig. 6. Comparisons of the prevalence of (A) all fractures in the EVOS (European Vertebral Osteoporosis Study) participants and in KIMS participants over the age of 60 years and (B) all fractures in naïve and non-naïve KIMS patients and of fractures of the radius in naïve and non-naïve and in patients with adult onset (AO) and childhood onset (CO) disease. From: Wüster et al (92)

Nonetheless, available evidence indicates that qualitatively similar changes in bone mineral density are found in adult-onset isolated GH deficiency as in panhypopituitarism, therefore supporting a role for GH deficiency in the pathogenesis. Furthermore, these abnormalities in bone metabolism and bone density are favorably influenced by GH replacement (see later).

 

Quality of Life

 

Decreased psychological well-being and quality of life (QoL) are recognized as particularly important for patients with GH deficiency and from the patients' perspective they have arguably become the major indication for GH replacement therapy. In some countries such as UK, decreased QoL is a needed symptom of a certain quantitative level as measured by validated GH deficiency questionnaires before even considering testing and treatment for GH deficiency according to National Institute for Health and Care Excellence or NICE (103). QoL is also related to a number of other features of GH deficiency. Thus Chikani et al. found subnormal anaerobic capacity, which independently predicted stair-climbing capacity and QoL in adults with GH deficiency. The authors concluded that GH regulates anaerobic capacity, which determines QoL and selective aspects of physical function (Fig 7) (104).

Fig 7. Relationship between stair-climb performance and anaerobic power (A) and VO2max (B), and between daily step counts quantified by pedometry and anaerobic power (C) and VO2max (D) in the combined groups of 13 adults with GHD (●) and matched normal subjects (○). LBM, lean body mass; VO2max, maximal oxygen consumption. From: Chikani et al (104)

QoL issues have been examined using various generic measures including the Nottingham Health Profile and the Psychological General Well Being Schedule (105-108). These instruments determine various aspects of health-related and needs-based quality of life and the most prevalent findings from various studies have been deficits in the domains of mood, anxiety, and social interaction. In one of the studies the Nottingham Health profile was adapted to a 9-year follow-up study of adults with untreated GH deficiency. During this 9-year study, small but significant declines in health were observed in GH-deficient adults who remained untreated. By contrast, the patients who received GH continuously experienced improvements in energy levels while all other areas of QoL were maintained. The beneficial effects of GH on QoL are therefore maintained with long-term GH replacement and obviate the reduction in QoL seen over time in untreated GH-deficient adults (106). Although these findings are readily apparent in many patients with adult-onset GH deficiency, it has proven more difficult to discern similar phenomena in patients with childhood-onset disease. This may be due to at least two factors. Firstly, standard generic quality of life instruments may be insensitive in the investigation of young people and secondly, there may be a major element of psychological adaptation or decreased expectation when the condition has commenced early in life. In an attempt to improve the reproducibility of studies of QoL in adults with GH deficiency, questionnaires have been developed which focus on those symptoms, which are most frequently documented in hypopituitary adults during extended open interviews.

 

One such instrument, which is now widely used for the baseline and longitudinal follow-up of patients, is the Quality-of-Life Assessment in Growth Hormone Deficient Adults (QoL-AGHDA) (107-111), which is also the one required by NICE. This is a needs-based instrument consisting of 25 questions with a yes/no answer format and the final score is obtained by summating all the positive responses; a higher score, to a maximum of 25, denotes poorer quality of life. The questionnaire has been shown to be reproducible in a variety of languages and satisfies Rasch analysis criteria for unidimensionality, construct validity, and hierarchical ordering of items (108).  In the long-term KIMS study surprisingly, QoL-AGHDA scores increased, indicating worsening of QoL across the entry year periods(16). This possibly reflected a patient selection bias, due to the change in the underlying etiology of GH deficiency: for example, the increase in the proportion of patients with traumatic brain injury or other less defined diagnoses may affect QoL. Alternatively, patients with poor QoL were more likely to receive GH treatment (15).     

 

Mortality

 

Over the past decades it has been increasingly recognized that hypopituitarism is associated with premature mortality. Studies in Sweden and the UK have demonstrated a two-to-three-fold increase in standardized mortality ratio, most striking in women (112-115). Specific pituitary pathologies, especially craniopharyngioma, may convey an increased mortality rate, which is likely to be independent of specific hormonal deficiencies (114). However, bearing in mind the numerical preponderance of pituitary macroadenomas as the cause of hypopituitarism, the overall findings from these studies favor an increase in morbidity and mortality from macrovascular disease and, in one of the Swedish studies, predominantly cerebrovascular disease (113). The increase in cardiovascular mortality in the initial Swedish study (116) was paralleled by a reduction in deaths from malignant disease in males but this has not been a definite feature of subsequent observations.

 

Much debate surrounds the mechanism for increased prevalence of vascular disease. These patients were replaced with glucocorticoids, thyroxine, and in some cases gonadal steroids, which prompted the conclusion that untreated GH deficiency was the major causal factor (117). However, this interpretation assumed that replacement of adrenal and thyroid deficiency was optimal and must also take into account that estrogen deficiency may not have been replaced. In fact, replacement, particularly with hydrocortisone, was often supraphysiological (118-120), while thyroxine replacement was more likely underdosed (10, 120-123), and estrogen is often not replaced in females of the fertile age (124). Recent clinical practice has rectified this mistake and consequently hydrocortisone doses are now significantly lower and thyroxine doses significantly higher than when the original mortality data were collected. Anecdotally, a recent paper on lifelong untreated isolated GH deficiency due to a mutation in the GH releasing hormone (GHRH) receptor gene found no alteration of longevity in this highly selected genetic background (125).Nonetheless, the fact that untreated GH deficiency, in the context of varying degrees of hypopituitarism, is associated with an adverse cardiovascular risk profile provides circumstantial evidence for a causative role for GH deficiency to mediate increased rates of vascular disease (45, 54, 77, 84, 85).

 

DIAGNOSTIC PROCEDURES

 

GH is secreted in a pulsatile fashion with serum measurements varying between peaks and troughs, the latter falling below the assay detection limit of conventional radioimmunoassays. For this reason, a diagnosis of GH deficiency cannot be made by measurement of baseline serum GH concentration although a single serum GH measurement taken fortuitously at the time of a secretory peak may serve to exclude GH deficiency. Therefore, the diagnosis of GH deficiency is dependent on the demonstration of a subnormal rise in serum GH in response to one or more dynamic stimulation tests. Many diagnostic tests have been developed for GH deficiency, most of them for patients with established hypothalamo-pituitary disease with a high a priori test outcome for deficiency. The same tests are now also used for diagnosing GH deficiency in a number of other potential patient populations raising high risk of misuse and wasting of resources. Further, the technical performance of hormone assays is highly variable among different laboratories(126). Thus, diagnosing patients with GH deficiency should first of all consider who should be tested for GH deficiency, the validity of the chosen stimulation test including the proper diagnostic cut-off concentration of GH, and the availability of local resources and expertise. As stated in the 2019 ACCE/ACE paper, cases with no suggestive history such as hypothalamo-pituitary disease or cranial therapy i.e., cases with a low pretest probability or low a priori likelihood of GH deficiency (18), GH stimulation testing should not be performed.

 

The recommendations for stimulation testing of patients for adult GH deficiency are provided in the guidelines mentioned in Fig. 8 (11, 12, 18, 19). Noteworthy all guidelines mention the patients eligible for testing as having either hypothalamo-pituitary pathology, verified GH deficiency in childhood, or have had intracranial irradiation. Options include the insulin tolerance test (ITT), glucagon test, and combinations of arginine and GH releasing hormone (GHRH) or GH secretagogues. Recently, the macimorelin test was approved for the diagnosis of adult GH deficiency (127).

Fig 8. Guideline recommendations for whom to test for GH deficiency.

Fig 9. Plasma human growth hormone (HGH) and blood glucose concentrations after insulin administered intravenously. (PAR, a hypophysectomized patient; other patients, normal). From: Roth et al (128)

The first description of stimulation of GH upon hypoglycemia was published already in 1963 (128) (Fig 9), and the insulin stimulation test (ITT) is still considered the ‘gold’ standard stimulation test for GH deficiency.

 

The ITT is the best validated test, and  has been demonstrated to distinguish reliably between GH responses in patients with structural pituitary disease and those of age matched controls across the adult age range (Fig 10A) (129). A variety of serum GH cut off points have been used to define GH deficiency. However, an international consensus (convened by the Growth Hormone Research Society) has defined severe GH deficiency in adults as a peak response to ITT of <3 µg/L (11).

 

It is essential that the ITT is carried out in dedicated units under strict supervision by experienced staff and it is contraindicated in patients with epilepsy and/or ischemic heart disease. The ITT may have a questionable reproducibility, probably due to low degree of robustness to everyday life as it strongly depends on pre-test events as well as on the patient (130, 131). Further, the ITT holds a certain risk especially in inexperienced hands (132), although it is quite safe in experienced centers (133).

                          

A particular advantage of insulin and glucagon testing is the simultaneous assessment of the adequacy of ACTH reserve. Combinations of GHRH and either arginine, pyridostigmine (or GH secretagogues) are the most potent stimuli of GH secretion and normative data for these tests have been set to define GH deficiency (28, 134-136). These tests appear to be reliable and practical, with few contraindications and the GHRH + arginine test may eventually replace ITT as the diagnostic test of choice (134, 137) in European countries. However, peak GH in response to these tests as well as to the glucagon test is highly affected by BMI, and thus BMI related cut off levels are mandatory (135).

 

Choice of stimulation test may be quite difficult, and the evidence from studies is variable. Furthermore, GHRH is not available in USA, which has prompted reassessment of the use of the glucagon as alternative test when ITT is contraindicated (18, 138-141). However, the diagnostic accuracy of the glucagon stimulation test is unclear especially in patients who are overweight. Recently, the macimorelin test showed promising good overall agreement with the ITT at the same cut point, and seemed unaffected by BMI, age, and sex (127), and is now considered a good alternative.

Fig 10. Results of tests of GH deficiency in normal (○) and hypopituitary patients (●). From: Hoffman et al (129)

As a result of an age related increase in somatostatinergic tone, spontaneous GH secretion declines by approximately 14% per decade of adult life but this does not alter substantially the response to dynamic tests of GH reserve and the same cut-off GH concentrations can be used across the age range (142). However, several tests pose more risks in elderly individuals (e.g., ITT, glucagon) compared to the young (141, 143), and older people are more likely to be obese with a high waist circumference. They are therefore more at risk of getting a false positive test outcome (144, 145), at least if not lowering the cut-off GH concentration. In general, to avoid misdiagnosing hypopituitary patients with GH deficiency, the importance of using local laboratory assay and test specific cut-off concentrations cannot be overemphasized (28, 146-149).

 

Severe obesity may decrease the GH response to insulin hypoglycemia to levels suggestive of GH deficiency but this is a completely reversible phenomenon if weight loss is achieved (Fig 3) (34). Body composition is by far the most important factor that needs to be considered when GH responses are evaluated and waist corrected GH-responses may be superior to BMI-corrected cut-offs (130). However, regarding the impact of BMI or waist circumference on GH-responses, further studies are needed to establish cut-off values also considering age, sex and ethnicity. Glucocorticoid therapy, including substitution therapy, probably reduces GH-responses to the GHRH + arginine test in line with the PD–GHRH test (150). Failure to recognize the impact of obesity on stimulated GH secretion may result in a false positive diagnosis of GH deficiency (28, 34, 37, 149, 151) and it is now standard practice that the diagnosis should be made in conjunction with evidence of structural pituitary disease and/or the documentation of additional pituitary hormone deficiencies. The latter provide robust support for a diagnosis of GH deficiency because of the increasing probability of GH deficiency in the presence of one (c.80%) or more (c.90%) additional pituitary trophic hormone deficiencies (152, 153) (Fig 11). Sadly, one publication (154) documented that many centers do not comply with recommendations, since the percent of patients meeting recommended test-specific cut points varied from 32 to 100%, depending on the stimulation test used. There was no mentioning of laboratory or assay specific cut-off concentrations. The study thereby highlights the need for continued education regarding treatment guidelines for adult GH deficiency, including the testing procedures.

Fig 11. Likelihood of GH deficiency related to number of pituitary hormone deficiencies other than GH deficiency. From: Sönksen PH et al. (155)

GH secretory reserve may also be assessed by measurement of serum concentrations of the GH-dependent peptides IGF-I, IGF binding protein 3 (IGFBP3) and the acid labile subunit of the ternary complex (ALS). Of these, IGF-I is the most sensitive marker of GH action and provides a reliable test of GH reserve in childhood-onset disease. Its diagnostic value for GH deficiency is limited by the fact that between 30 and 40% of individuals with severe GH deficiency of adult-onset will demonstrate a serum IGF-I concentration in the low part of the normal age related reference range (116). Nonetheless, in the absence of liver dysfunction or malnutrition, which may secondarily reduce IGF-I generation, and if determined in the appropriate clinical context of pituitary disease and hypopituitarism, a decreased serum IGF-I provides a strong confirmatory indication for GH deficiency (129).

 

Testing of patients with suspected non-classical causes of hypopituitarism is much more challenging, since most available evidence of diagnostic reliability has been based on patients with structural hypothalamo-pituitary pathology, genetic causes of GH deficiency, documented GH deficiency in childhood, or brain irradiation. In recent years there has been considerable focus on etiologies previously considered rare causes of hypopituitarism. Published series of hypopituitarism in traumatic brain injury  and subarachnoid hemorrhage suggested prevalence rates up to 25-50% (17, 156, 157), and both traumatic brain injury  and subarachnoid hemorrhage were subsequently highlighted in the guidelines as new indication for GH testing (12, 19). Still it is notable that the large majority of these patients had isolated deficiencies and in particular isolated GH deficiency (27). Acknowledging the many aforementioned caveats for the diagnosis of GH deficiency these cases may have been strongly overemphasized also because most data were based on only single testing. The fairness of such concerns was evident in a Danish study showing a low concordance of repeated testing for GH deficiency in TBI (Fig 12) (28), which underlines the importance of stringent testing including a second confirmatory test in patients with low a-priory likelihood of GH deficiency. This approach is consistent with the ACCE/ACE 2019 guidelines (18).

Fig 12. The prevalence of insufficient test responses in the total cohort (A) and in the subgroup undergoing dual testing (B). A, Prevalence of insufficient test responses to either ITT or PD-GHRH/GHRH-arg (i.e., combined tests) in the total cohort of TBI patients (black columns) and healthy controls (white columns), respectively, as defined by either local or guideline-derived cutoffs. Whiskers indicate the 95% CI. GHD was more frequently diagnosed in TBI patients tested by a combined test as compared with ITT, and even more so if guideline cutoff values were applied instead of local cutoffs. The results from healthy controls illustrate the high false-positive rate resulting from application of guideline-derived cutoffs, which was significantly above the generally accepted 2.5% for the combined tests (P = .02). *, P < .005 compared with patients. B, Prevalence of insufficient test responses in the subgroups of patients (black columns, n = 169) and controls (white columns, n = 117) undergoing dual testing, as defined by either local cutoff values or guideline-derived cutoff values. Confirmed insufficiency was defined as a concordant positive result to both the ITT and a combined test. Whiskers indicate the 95% CI. [Reproduced with permission]. From: Klose et al. (28)

Main Conclusions

 

True GH deficiency is an important clinical entity that should be tested, treated, and managed properly. On the other hand, it is important to avoid false diagnosis, which might lead to unnecessary life-long therapy with GH replacement.

 

The diagnosis of GH deficiency is rather simple in patients with a typical structural pathology in the hypothalamo-pituitary region, especially in cases of multiple pituitary hormone deficiencies and low IGF-I concentrations, where the likelihood of GH deficiency exceeds 97% (Fig 11), and a stimulation test is rarely indicated (Fig 8). In all other cases a stimulation test is needed for the diagnosis and in some patients 2 tests should be performed in order to avoid the risk of overtreatment on a false basis. The knowledge of one’s own laboratory performance as well as own reference population data with BMI cut offs for control persons is crucial in interpretation of results. The same holds true for the testing of the other hormone axes, some of which have similar challenges in diagnosing correctly in hypothalamo-pituitary disease states.

 

New indications for GH deficiency testing should not be accepted without prior stringent evaluation of test reliability for the particular condition in question by several tests, and preferably in different laboratories, given that the classical GH deficiency phenotype such as obesity, fatigue and QoL often has other causes than GH deficiency.

 

Table 3. Strategy for Diagnosing Adult GH Deficiency for the Purpose of Replacement Therapy

  • Assess basis for hypopituitary diagnosis
  • Check if the patient is eligible for GH replacement
  • Measure IGF-I age related reference SDS – if below 0 SDS continue testing
  • Assess number of other pituitary hormone deficiencies
  • Make sure other pituitary hormone deficiencies are properly replaced
  • Choose GH stimulation test(s)
  • Perform stimulation test according to:
    • Guidelines
    • Proper local test validation
    • Own reference cut off based on local assay and normal reference population
    • BMI
    • Other confounders
  • MR/CT scan of pituitary in patients with abnormalities
  • QoL assessment (e.g., QoL-AGHDA)(requirement in UK)
  • Severe GH deficiency as defined by the respective GH stimulation tests (fig. 8)

 

GH: Growth Hormone; SDS: Standard Deviation Score; IGF-I: Insulin like Growth factor-I; BMI: Body mass index; MR: Magnetic Resonance; CT: Computer Tomography; QoL: Quality of Life; AGHDA: Adult growth hormone deficiency assessment.

 

RESPONSE TO GH REPLACEMENT IN ADULT GROWTH HORMONE DEFICIENCY

 

Quality of Life and Psychological Well-Being              

 

Potentially, the greatest immediate indication for growth hormone supplementation is in patients who are assessed as having impaired QoL, and this is in some countries, such as the UK, a prerequisite for reimbursement (table 4) (103). This recommendation from NICE is unchanged and has not been updated.

 

Table 4. NICE Recommendations for Treatment with Growth Hormone

NICE has recommended that recombinant human growth hormone should be used only for adults with severe growth hormone deficiency that is severely affecting their quality of life. To be a part of this group, NICE says a person should:

● have a peak growth hormone response of less than 9 mU/L (<3 µg/L) in the ‘insulin tolerance test’ for growth hormone deficiency or a similar low result in another reliable test, and

● have an impaired quality of life because of their growth hormone deficiency (judged using a specific questionnaire called the 'Quality of life assessment of growth hormone deficiency in adults’ designed to assess the quality of life in people with growth hormone deficiency; a person should score at least 11 in this questionnaire), and

● already be receiving replacement hormone treatment for any other deficiencies of pituitary hormones if he or she has one or more other deficiencies.

From: NICE guidelines (103)

 

The early high dose placebo controlled trials suggested that around 50% of these patients demonstrated a significant improvement and a desire to continue with replacement longer term (8). The greatest benefit was shown in patients who had severe GH deficiency and greater distress, in terms of energy and vitality, prior to commencing GH. More recent experience using lower doses with fewer side effects, also indicated clear improvement with wish to continue in >90% of patients selected on the basis of a perceived QoL deficit (53, 158). A six-month course of optimally titrated GH replacement is usually needed before the benefits can be assessed clearly, although many patients show a substantial improvement in QoL within three months. For reasons that are unclear, a small proportion of patients (<20%) may not demonstrate significant subjective benefit in QoL until 9 to 12 months after commencing treatment (159). It is important to recognize that the time taken to achieve a maintenance dose of GH may extend to 12 weeks in some patients and is longer on average in women than in men; this should be recognized in therapeutic trials of GH replacement with a finite time frame. It is clear that the time taken to derive subjective benefit from GH replacement in many patients provides strong evidence against a pure placebo effect in this respect. Furthermore, the duration of benefit in QoL, which has been observed for periods of up to 10 years, is similarly indicative of a therapeutic rather than a placebo phenomenon (106, 111, 160). Patients QoL improves most rapidly in the first 12 months of treatment, but even after this there is continued improvement towards the country specific population mean, with particular improvement in problems socializing, tenseness, and self-confidence, which normalize to the background population (161). The improvement is seen in patients with all etiologies of GH deficiency including previous acromegaly (162-164), isolated GH deficiency (56) and previous Cushing’s disease (99, 100). However, not all aspects of QoL normalize and this is particularly true in patients under 60 yrs of age.

 

The reasons for the differences in QoL outcome between the early studies and current clinical practice has been the subject of much debate and at least three factors are likely to be particularly relevant. Firstly, the initial randomized control trials utilized GH doses based on body weight or surface area and did not take account of the substantial variation in individual responsiveness to GH occurring as a result of gender and other factors. This strategy resulted in excessive GH doses in men and obese subjects and relative undertreatment of women. The adverse symptoms associated with excess GH doses included arthralgia and myalgia, due to GH-induced anti-natriuresis, and it is probable that these factors may have obscured potential subjective benefit. In addition, it is probable that the strict entry criteria inherent in any placebo-controlled study designed to prove concept may have inadvertently eliminated patients who were most likely to demonstrate a benefit in QoL (Table 3) (164). Finally, the current strategy of GH replacement is not to await the full-blown phenotype to develop, but rather to start replacement as soon as the diagnosis is made, as with any other hormone replacement.

 

These latter phenomena are readily evident when baseline indices of QoL in patients enrolled into randomized control trials are compared with those of patients commencing GH replacement selectively in the clinical practice setting (53, 158, 165), and even more so with the changed selection of patients eligible for GH replacement over the years (16).

 

The mechanism for the beneficial effect of GH on well-being and QoL remains speculative (164). GH has been shown to cross the blood brain barrier (166, 167) and to exert physiological effects in the central nervous system as evidenced by the generation of neurotransmitters (166), an effect reduced by progressive aging (168, 169). However, the effects of GH in restoring normal hydration and increasing exercise capacity are additional potential contributors to the positive effects on well-being (170).

 

Table 5. Effects of Growth Hormone Replacement Therapy on Quality of Life in Adults in Published Trials

Reference

GHD onset

(etiology)

N

Dosage per day or titration

Duration

Design (Controls)

Tests

Change in QoL in the GHD adults

Baum et al

(1998)

AO

40

2-6 μg/kg

18 m

PCDB

NHP

PGWB

GHQ

MMPI-2

Cognition tests

= cognition, QoL

Burman et al

(1995)

Mostly

AO

36

2-4 U

21 m

PCDB

NHP

PGWB

HSCL

Spousal report

↑ QoL placebo + GH

groups (HSCL)

↑QoL GH group

(NHP, spousal report)

McGauley et al (1989)

Mostly

AO

24

0.07 U/kg

6 m

PCDB

NHP

PGWB

GHQ

↑ subjective well-being

↑ QoL (NHP)

↑ QoL (PGWB)

Soares et al

(1999)

Not stated

9

0.035 U/kg

6 m

PCDB

HDS

BDI

Cognitive tests

↑ QoL, cognition

Attanasio et al(1997)

AO+ CO

173

12.5 μg/kg

18 m

6m PCDB

12 m open

NHP

=mobility, energy (6 m)

↑mobility, energy (12m)

Beshyah et al

(1995)

AO+ CO

40

0.04 U/kg

18 m

6m PCDB

12 m open

CPRS

GHQ

↑QoL 12m (CPRS)

↑QoL 6m placebo (GHQ)

Caroll et al

(1997)

Not stated

42

0.024 (6m)

0.012 (6m)

μg/kg

12 m

6m PCDB

6m open

NHP

PGWB

↑ QoL on both scales

↑ NHP score in placebo

Mahajan et al

(2004)

AO+CO

25

0.04 (1m)

0.08 (1m)

mg/kg/week, Normal IGF-I

4 m

PCDB

Cross over

NHP

HDRS

MADRS

=mobility, pain

↑energy and emotional reactions

↓social isolation, sleep disturbance

↓depression

Mardh et al

(1994)

AO

124

Not stated

12-18 m

6m PCDB

6-12m open

NHP

PGWB

↑ QoL (NHP)

↑ Well-being

Urushihara et al (2007)

AO+CO

64

0.021-0.042-0.083

mg/kg/week, Normal IGF-I

16 m

24 weeks DBPC

48 weeks Open

SF-36

↑ physical functioning and general health (AO)

↓social functioning and mental health (CO)

Wallymahmed et al (1997)

Mostly

AO

32

0.018 (1m)

0.035 (5m)

U/kg

12 m

6m PCDB

6m open

GHD-LFS

GHD-IS

NHP

HADS

SES

MFS

↑ Self esteem

↑ Energy and emotional

reaction (transient)

Bengtsson et al (1993)

AO

10

13-26 μg/kg

6 m

PCDB

Cross-over

CPRS

SCL-90

↑ QoL (CPRS)

= QoL (SCL-90)

Degerblad et al (1990)

AO

6

0.07-0.09 U/kg

3 m

PCDB

Cross-over

Mood questionnaires

Psychometric

Testing

= mood, cognition

↑ vitality, mental

alertness

Whitehead et al (1992)

AO+ CO

14

0.07 U/kg

6 m

PCDB

Cross-over

PGWB

= QoL, but no ↑ IGF-I

Cuneo et al

(1998)

Mostly

AO

166

0.018 (1 m)

0.036 (11m)

U/kg

12 m

6m PC

6m open

NHP

GHDQ

Social history

↑ QoL 12m (NHP)

= QoL (GHDQ)

Deijen et al

(1998)

CO (men)

48

1-3 U/m2

24 m

PC

Psychological

Testing

= well-being

↑ memory

Florkowski et al

(1998)

AO+ CO

20

0.035 U/kg

3m

Randomized

PC

Cross-over

DSQ

SCL-90

SAS

↑ QoL placebo + GH

groups

Giusti et al

(1998)

AO

25

0.5-1 U

6 m

Randomized

PC

HDS

KSQ

↑ QoL (HDS)

= KSQ

Miller et al

(2010)

AO (Acromegaly)

30

Normal IGF-I

6 m

Randomized PC

AGHDA

SF-36

SQ

↑ QoL (AGHDA)

↑ vitality, mental health, soc functioning, general health

↓ role limitation

Verhelst et al

(1997)

Mostly

AO

148

0.035 U/kg

24 m

6m PC

18m open

NHP

Social history

↑ QoL placebo + GH

↓ sick leave

 hospitalization

Ahmad et al

(2001)

AO

46

Normal IGF-I

3 m

Open

AGHDA

↑ QoL after 1 and 3 m

Abs et al

(2005)

AO+CO (IGHD)

1775

Not stated

12 m

Open (MPHD)

AGHDA

↑ QoL IGHD+MPHD

IGHD=MPHD

Drake et al

(1998)

AO

50

Normal IGF-I

6 m

Open

AGHDA

↑ QoL after 3 and 6 m

Follin et al.

(2010)

CO (ALL)

13

0.2-0.8 mg/d

60 m

Open

(No GH)

Symptom checklist-90

ISSI

= QoL

Gibney et al

(1999)

AO+ CO

11

0.025 U/kg

120 m

Open

(No GH)

NHP

↑ QoL (NHP), energy,

emotional reaction

Gilchrist et al

(2002)

AO+ CO

61

Not stated

108 m

Open

(No GH)

NHP

PGWB

↑ energy (NHP)

↑ vitality (PGWB)

Hernberg-Stahl

et al (2001)

AO

304

0.125-0.25 U/kg

12 m

Open

AGHDA

↑ QoL after 1 m,

higher after 3 m

Höybye et al

(2010)

AO (CD)

1070

Normal IGF-I

36 m

Open

(NFPA)

AGHDA

↑ QoL CD+NFPA

CD > NFPA

Kelestimur et al (2005)

AO (SS)

143

Normal IGF-I

24 m

Open

(NFPA)

AGHDA

↑ QoL SS+NFPA

SS=NFPA

Klose et al.

(2009)

AO (IGHD)

1152

Normal IGF-I

24 m

Open

(MPHD)

AGHDA

↑ QoL IGHD+MPHD

IGHD=MPHD

Koltowska-H et al (2006)

AO

1117

Normal IGF-I

1 – 8 yrs

Open

AGHDA

↑ QoL

Kreitschmann-Andermahr et al. (2008)

AO+CO (TBI)

41

Normal IGF-I

12 m

Open

(NFPA)

 

AGHDA

↑ QoL TBI+NFPA

GHD TBI = GHD NFPA

Link et al.

(2006)

CO (ALL)

14

Normal IGF-I

12 m

Open

Neuropsycho-

logical testing

=

Maiter et al

(2006)

AO+CO (irradiated)

1077

Normal IGF-I

12 m

24 m

Open

(non-irradiated)

AGHDA

↑ QoL irradiated+non-irradiated

irradiated=non-irradiated

Moock et al.

(2009)

Mostly AO

651

Normal IGF-I

12 m

Open

AGHDA

↑ QoL

Mukherjee et al (2005)

AO+CO

(cancer survivors)

97

Normal IGF-I

3-13 m

24-77 m

Open

(pituitary pathology)

PGWB

AGHDA

↑ QoL cancer+pit. GHD cancer survivors = pituitary pathology

Mukherjee et al (2005)

AO+CO

30

Normal IGF-I

3 m

6 m

Open

PGWB

AGHDA

↑ QoL

Murray et al

(1999)

AO + CO

65

Normal IGF-I

8 m

Open

PGWB

AGHDA

↑ QoL

Murray et al

(2001)

CO (cancer)

27

Normal IGF-I

18 m

Open

PGWB

AGHDA

↑ QoL (large, 3 m)

Rosilio et al

(2004)

AO + CO

576

Normal IGF-I

12 m

48 m

Open

QLS-H

↑ QoL

Van der Klaauw et al. (2009)

AO

(Acromegaly)

16

Normal IGF-I

12 m

Open

HADS

MFI-20

NHP

AGHDA

= QoL

Verhelst et al.

(2005)

AO (CP)

721

Normal IGF-I

24 m

Open

(NFPA)

AGHDA

↑ QoL CP+NFPA

CP = NFPA

Wiren et al

(1998)

AO + CO

71

6-12 μg/kg

20-50 m

Open

NHP

PGWB

↑ QoL

QoL, quality of life; GHD, growth hormone deficiency; AO, adult onset; CO, childhood onset; ALL, acute lymphoblastic leukemia CP, craniopharyngioma; CS, Cushing’s Disease; NFPA, non-functional pituitary adenoma; SS, Sheehan’s syndrome; TBI, traumatic brain injury; n, number of subjects; PC, placebo-controlled; PCDB, placebo-controlled, double-blind; open, open label; Tests used to quantify QoL  ↑, =, ↓, change in QoL parameter in GH-treated patients and when available compared to controls (Modified and updated from Hull and Harvey(171) with permission from the authors). From: Klose et al (164)

 

Body Composition: Fat Mass, Fat Distribution, and Lean Body Mass

 

GH replacement produces a significant redistribution of body mass, decreasing body fat, and particularly central fat, and increasing lean body mass (6-9, 172). Body fluid balance is also restored. The beneficial effects of GH on total body fat and its distribution have been examined by means of dual energy X-ray absorptiometry (DEXA), computerized tomography (CT), bioelectrical impedance, and ratio of waist to hip circumference (55, 173) (fig 13) and qualitatively similar results have been obtained with excellent concordance between virtually all reported studies. The restoration of normal total body water may result in an artefactual increment in determinations of lean body mass particularly when the latter is measured by bioelectrical impedance. The abnormal fat distribution in GH deficiency is characterized by an increase in the ratio of waist to hip circumference and during long term follow up, serial measurement of waist circumference provides a simple, rapid and reproducible means of monitoring improvement in body fat distribution.

Fig. 13. Median waist/hip ratio at 0, 6 and 12 months after commencement of GH replacement, men versus women. From: Data from Drake et al (173)

Reductions in body fat are attributed to the lipolytic effect of GH but additional indirect hormonal effects may be important. The conversion of thyroxine to triiodothyronine was shown to be enhanced by GH in early studies of GH replacement (123, 174) although this is a dose related phenomenon and is less evident with the lower doses in current use. However, levothyroxine replacement has very likely not been optimal (121, 122), and increased dosages have improved the lipids over time (121, 122). Also, the enzyme 11ßHSD1 that reduces cortisone to the active hormone cortisol shows increased activity in the GH deficient state and is normalized by low dose GH replacement(81); the consequent increase in cortisol metabolism may result in reduced tissue specific exposure to glucocorticoid in adipocytes and hepatocytes (81). The latter effect provides an additional explanation for decreased total and central fat mass during GH replacement.

 

Serum Lipoprotein Profiles

 

The effect of GH replacement on lipoprotein profiles has been examined in numerous studies using differing dose regimens. Regardless of whether the GH dose has been based on body weight or titrated against serum IGF-I the universal finding has been a reduction of serum total cholesterol, accounted for virtually entirely by a reduction in LDL-cholesterol (48, 69, 160, 175-182). The extent of this reduction is greatest in those patients with higher baseline serum cholesterol (fig 14), and independent on obesity variables (182). The median change in an unselected hypopituitary population is between 0.3 and 0.4 mmol/L (48, 175). Importantly, the improvement in LDL-cholesterol is additive to the effects of HMG CoA reductase inhibitors if the patient is receiving concurrent therapy and possibly even synergistic (173), as well as synergistic with optimization of levothyroxine therapy (120-123). The degree of reduction of serum LDL-cholesterol during GH replacement would predict an overall reduction in cardiovascular events in the range of 20%. In addition, some studies have documented an increase in serum HDL-cholesterol, but serum triglyceride levels remain unchanged. Serum lipoprotein(a) has been shown to increase in some studies in patients who demonstrated favorable changes in LDL-cholesterol (45, 183, 184) but the data remain somewhat contradictory by virtue of lipoprotein(a) assay differences; the overall significance in terms of cardiovascular risk is unclear (185).

Fig 14. Relationship between the lowering of cholesterol (∆Cholesterol) and the pretreatment serum Cholesterol concentration. Derived from data from Florakis et al (175)

Carbohydrate Metabolism and Insulin Sensitivity

 

Untreated GH deficiency of adult onset is associated with reduced insulin sensitivity, which is, at least in part, related to increased central adiposity (45, 77). The latter improves within the first 3 months of GH replacement but this does not result in an immediate improvement in insulin sensitivity (45). In fact, because of the antagonistic effects of GH on the actions of insulin mediated by hepatic effects, and the increase in circulating free fatty acids, there is on average a further decline in insulin sensitivity, which subsequently returns to baseline over the first year of GH replacement therapy (77). The decline in insulin sensitivity during GH therapy is associated with a slight elevation of fasting plasma glucose and a parallel increase in glycated hemoglobin, both within the normal reference range. Importantly, the increment in glycated hemoglobin is not evident in patients with prior abnormalities of glucose tolerance but is significantly correlated with baseline body mass index, the latter emphasizing the importance of additional dietary and lifestyle advice in these patients.

 

Reference to the KIMS database indicates that there is an increased baseline prevalence of impaired glucose tolerance and diabetes mellitus prior to commencing GH replacement but subsequently the incidence of new cases of diabetes is not increased provided the body mass index is accounted for. Thus, a recent study of data from the NordiNet® surveillance database concluded that 4 years' GH-replacement therapy did not adversely affect glucose homeostasis in the majority of adults with GH deficiency (186). Yet, the long-term effects of GH replacement on insulin sensitivity can still not be considered quite clear although they are likely to vary depending on age, duration of pituitary disease, and increase in weight/BMI/waist circumference.

 

Cardiac Function

 

The GH/IGF-I axis is a recognized modulator of cardiac function and a positive inotropic effect of GH/IGF-I occurs early in the natural history of acromegaly. In contrast, GH deficiency is associated with a reduction in left ventricular wall mass and cardiac output, which is most evident in childhood-onset disease. The variable discordance between childhood-onset and adult-onset GH deficiency in this regard is likely to be due to additional factors impacting on cardiac morphology in adult-onset, including an increased prevalence of hypertension. GH replacement results in increased left ventricular wall mass, fractional shortening, stroke volume and favorable changes in the echocardiographically determined e/a ratio reflecting improved diastolic function (8, 65-75). In some studies, in adult-onset patients, left ventricular hypertrophy has been documented during GH replacement, confirming further the heterogeneity in response to GH replacement. Importantly, GH replacement does not increase blood pressure; in fact, a modest reduction may be seen in patients with pre-existing hypertension reflecting increased generation of nitric oxide as a result of activation of nitric oxide synthase.

 

Exercise Capacity and Performance

 

Increased exercise capacity, as measured by maximal oxygen uptake, power output, and isometric muscle strength, has been observed during GH replacement in GH deficient adults (63, 64, 187, 188). A meta-analysis concluded that evidence from short-term controlled studies failed to support a benefit on muscle strength of GH replacement in GH deficient patients, which is likely to occur over a longer time-course, as seen in open-label studies (188) (Fig 15).

 

The impact of these changes for individual patients is variable and dependent on age and previous exercise requirements. It is intuitively probable that the improvements depend at least in part on improvements in lean body mass. However, restoration of normal circulating volume may also play a positive role (170). In addition, improvement in psychological well-being might be expected to enhance physical activity whilst the latter may have a reciprocal beneficial effect on well-being.

Fig 15. Per cent change from baseline in lean body mass (Panel A), fat mass (Panel B), anaerobic power (Panel C) and VO2max (Panel D) following 1 month of placebo and 1 month of GH (randomized controlled study) and 6 months of GH (open-label study) in 18 patients with GH deficiency. From: Chikani et al (170).

Indices of Bone Remodeling and Bone Mineral Density

 

GH deficiency is associated with reduced activity of bone formation and resorption. GH replacement reverses this situation rapidly resulting in increases in markers of bone formation (e.g., osteocalcin and bone specific alkaline phosphatase) and bone resorption (e.g., urine deoxypyridinoline) (Fig 16) (189).

Fig 16. Markers of bone turnover during 18 months of GH (▲) treatment in a randomized, placebo- controlled (O), double blinded study. Values are given as means (^S.E.). The P values for differences of change from baseline between GH- and placebo-treated patients are *P, 0:05; **P, 0:01; ***P, 0:001; ****P, 0:0001: Creat, creatinine. From: Sneppen et al (189).

This increase in bone metabolism eventually results in an increase in bone mineral density (BMD) but this is not evident for approximately 18 months of treatment and is preceded by a reduction attributable to an increase in the bone remodeling space (53, 93, 189-197). The fact that BMD increases under the influence of GH replacement at physiological doses provides important surrogate evidence for an etiological role for GH deficiency in mediating the reduced BMD observed in hypopituitarism. The improvement is quantitatively more obvious in men than women despite the achievement of similar serum IGF-I SD scores and therefore constitutes a genuine difference in gender susceptibility (fig 17).

Fig 17. Bone mineral density of the lumbar spine during long-term GH replacement therapy. From Drake et al (173).

Although the improvement in BMD would predict a reduction in fracture rates confirmation of this necessitates long term follow up. Evidence is now emerging supporting a lower fracture risk with GH replacement (92, 198). A prospective cohort study has shown that GH deficient patients treated with GH before the onset of osteoporosis have a lower fracture risk than those untreated, over a mean follow up of 4.6 years (SD 3.8)(199). Increased fracture risk in child onset GH deficiency women can most likely be explained by interaction between oral estrogen and the GH-IGF-I axis. The adequate substitution rate of testosterone (90%) and GH (94%) may have resulted in significantly lower fracture risk in adult-onset GH deficiency men (198). Finally, although in vitro studies have shown that GH has a direct effect on bone remodeling, present physiological concepts and the results of clinical trials from 1996 to 2008 suggest that the anabolic changes in muscle mass and strength may also contribute to changes in BMD/BMC in GH-treated adult GH deficiency patients (200).

 

GH REPLACEMENT IN ELDERLY HYPOPITUITARY PATIENTS

 

Published work indicates that the baseline characteristics and response to GH replacement in hypopituitary patients aged over 65 years are qualitatively similar to those in younger patients (52, 201-203). Importantly, GH deficiency in the elderly is distinguishable on dynamic tests from the well-recognized physiological reduction in spontaneous GH secretion with advancing age (142). It is therefore appropriate to consider older hypopituitary patients for GH replacement and to apply similar criteria to those outlined above. Elderly people with GH deficiency, in particular women, require less GH than at their earlier age, since they will be either spontaneously postmenopausal or taken off estrogen replacement.

 

TRANSITION BETWEEN PEDIATRIC AND ADULT CARE FOR CHILDHOOD ONSET GH DEFICIENCY

 

The transition from childhood into adulthood is generally a very vulnerable period in any young person’s life. It is therefore pertinent to make the transition as smooth as possible. The best way to do this is to have common transition clinics with both a pediatrician and adult endocrinologist having joint consultations to prepare the adolescent for what is going to happen. The timing can be somewhat individual but aiming at a time around final height and completion of puberty seems appropriate. The pediatrician should prepare the child for this/these consultation(s), and the adult endocrinologist taking over future follow up needs to be aware of the fact that obtaining final height and a post pubertal state does not mean that the adolescent is fully matured in a physiological as well as psychological sense.   

 

It is important to confirm persistence of GH deficiency at the time of completion of linear growth, particularly in children with isolated GH deficiency (18). In the presence of a structural lesion in childhood and multiple hormone deficiencies or some genetic causes, a low IGF-I (in the absence of poorly controlled diabetes, liver disease, or oral estrogen) is sufficient to confirm GH deficiency, without a stimulation test (19). Subsequently, decisions must be taken regarding recommencement of GH or longitudinal clinical observation off treatment. Arguments supporting continuation of GH therapy include the observation of increased accumulation of fat mass off treatment (204, 205) and continued acquisition of bone mass in young adults continuing GH in contrast to static bone mass in those discontinuing treatment at the time of completion of linear growth (206). There is no detriment seen in QoL in those patients who withdraw from GH at the completion of linear growth. There is an apparent improvement in insulin sensitivity but, as is the case during normal puberty, this may not be beneficial in the context of continuing somatic development. Given that the major indication for adult GH replacement is the impairment of QOL, then there is no clear consensus as to which patients should continue therapy seamlessly, virtually without interruption, and in which patients it may be reasonable to undertake a period of careful clinical assessment. A recent observational study has raised concern about discontinuation of GH replacement therapy in pediatrics in severely persistent GH deficiency patients, as well as about the often insufficient dose of GH in the treatment of adult patients (207). Follow-up showed improvement in lipid profile and bone mineral density in severely persistent GH deficiency patients under GH therapy. In multivariate analysis, the associated pituitary deficits seemed stronger determinant factors of metabolic and bone status than GH deficiency per se. A consensus meeting convened by The European Society for Pediatric Endocrinology suggested offering continuation of therapy (after retesting) and monitoring those who decline continuation of treatment. If therapy is continued the optimum dosing strategy has not been clearly defined although a titration approach as outlined above would seem empirically appropriate (208). The Endocrine Society Clinical practice guidelines recommend GH therapy to be continued after adult height to allow full skeletal and muscle maturation, which is often delayed in this population (18, 19).

 

INTERACTIONS WITH OTHER PITUITARY AND ADRENAL HORMONES

 

GH is known to inhibit 11ßHSD-1, therefore favoring metabolism to inactive cortisone over active cortisol (72). Hence patients who are partially ACTH deficient or on suboptimal replacement should be carefully monitored at initiation of GH replacement, which might otherwise lead to partial cortisol deficiency, and risk of Addisonian crisis by even simple infections (118, 209).

 

GH also interacts with the TSH axis (120, 123). Patients without defined TSH deficiency demonstrate a reduction in serum thyroxine (T4) after initiation of GH replacement, although maintain stable serum liothyronine (T3) (10, 210, 211), and patients on thyroxine replacement frequently require an increase in their dose (120, 121, 212).The mechanism remains unclear, but it has been postulated that GH may enhance peripheral conversion of T4 to T3 but also have a central inhibitory effect on TSH release at least in children. Clinicians should therefore be aware that the hypothalamo-pituitary-thyroid axis can very easily be both underdiagnosed and under replaced in GH deficiency, and upon commencement of GH preplacement (120, 121, 213).

 

Women require a higher GH dose than men to achieve a similar increment in IGF-I. GH sensitivity is blunted in females on oral estrogen (214-216). Transdermal estrogen reduces IGF-I generation to a lesser extent than oral estrogen. The effect of estrogen is thought to be mainly due to first pass metabolism inhibiting hepatic synthesis of IGF-I (217, 218). Testosterone stimulates GH secretion centrally, and also amplifies GH stimulation of IGF-I (216, 217). In addition to gonadal steroids, DHEA replacement has been shown to have an impact on IGF-I generation and psychological well-being (219, 220). DHEA improves psychological well-being independently of an effect on IGF-I (229). DHEA has been shown to potentiate IGF-I generation (219, 220) such that females on DHEA replacement require a lower GH dose to achieve the same IGF-I (219, 221). The mechanism is unknown, but DHEA is metabolized to testosterone and it is postulated that increased serum testosterone may be responsible, hence explaining the lack of a DHEA effect in men who are either eugonadal or are on testosterone replacement.

 

GROWTH HORMONE REPLACEMENT

 

Selecting Patients for Growth Hormone Replacement

 

The diagnosis of GH deficiency in adults is usually straightforward and consensus guidelines have been established with generalized acceptance (Fig 8). Nonetheless there is continuing debate regarding the selection of patients for GH replacement. Practice varies between countries and is undoubtedly influenced by availability of funding for treatment. In clinical practice, patients are selected for treatment on the basis of perceived need according to one or more of a number of specific criteria as outlined in Tables 3 and 4, including severe GH deficiency defined by the insulin tolerance test (ITT), glucagon test or alternative tests such as arginine plus growth hormone releasing hormone (GHRH) or the Macimorellin test.

 

Establishing the Maintenance GH Dose 

 

When the indication for GH-replacement has been ascertained, the patient is usually on a low initial dose (0.2 mg daily), but dependent on age, since adolescents during transition may benefit from higher initial doses, as will also women on estrogen therapy (replacement or oral contraceptives) a higher dose may be employed (214, 222-224). The dose titration is monitored by IGF-I concentrations (12, 154, 158), and a number of end organ end responses, which may act as ‘biomarkers’ of the treatment effects (table 6).

 

The doses used in published studies vary widely and much of the published data in this area is derived from dosing schedules established on body weight or surface area criteria which were in effect an extrapolation of earlier pediatric practice. Ongoing assessment in the routine clinical setting has indicated that patients can now be managed on much lower doses (158). Using a widely accepted clinical strategy, patients are commenced on 0.2 mg somatotrophin subcutaneously once a day initially. The dose is reviewed every two to four weeks according to clinical response, serum IGF-I levels, and any side effects and the dose is increased, if necessary, at 4 weekly intervals until the maintenance level is achieved (225). This results in a median dose requirement of 0.4 mg daily with a greater sensitivity to a given dose in male patients so that median dose requirement is lower in men. Several sustained release long-acting GH preparations are currently undergoing clinical trials (226-230) and may become an alternative, with some now being marketed in Asia, US and Europe. However, long-term surveillance of safety and efficacy of long-acting GH analogs are not available to address potential pitfalls of the sustained release preparations (231).Serum IGF-I levels may be in the lower part of the age-related reference range in approximately 40% of patients with adult-onset hypopituitarism before any GH treatment across the total age range and this becomes more likely with advancing age. An empirical strategy is to use the minimum dose of GH, which places the serum IGF-1 level between the median value and the upper limit of the age matched normal range for the individual patient. This approach minimizes the risk of overtreatment and the potential sequelae, which may ensue. Serum IGF binding protein-3 and acid-labile subunit lack sensitivity for the titration of GH replacement and are not recommended for this purpose. IGF-I, however, is regulated by several other factors than GH and changes in body composition can be seen with the addition of GH even without any alteration in the IGF-I level. For this reason other biomarkers of GH action are being sought (232).

 

Table 6. What variables and organ functions should be followed in diagnosed GH deficient adult patients treated with GH replacement?

Variables

·       IGF-I (therapy monitoring, titrate to concentration between 0 and + 2SDS)

·       Other pituitary hormone deficiencies

·       MR/CT scan of pituitary in if abnormalities present

·       Safety (adverse effect)

·       QoL assessment (AGHDA)

Metabolic variables

·       Glucose metabolism

·       Lipids

·       BMI

·       Body composition (waist-hip, fat mass, lean body mass)

·       Dexa scan of bones

·       Physical capacity

·       Cardiovascular

IGF-I: Insulin like Growth factor-I; MR: Magnetic Resonance; CT: Computer Tomography; QoL: Quality of Life; AGHDA: Adult growth hormone deficiency assessment: BMI: Body mass index                     

 

Adverse Effects

 

The main adverse effects directly attributable to GH replacement result from the correction of the sodium and water depletion present in GH deficiency patients. This manifests as arthralgia, myalgia, edema, and carpal tunnel syndrome and are usually rapidly reversible with GH dose reduction. They were predominantly a feature of the early experience when GH dose was determined by body weight rather than being based on a titration regimen commencing with a low starting dose as described above. Such adverse effects were predictably more frequent in male patients reflecting their greater sensitivity to GH. Benign intracranial hypertension is a recognized complication of GH replacement in pediatric practice but is much less likely in adult patients especially when low doses are used. However, persistent severe headache should prompt examination and investigation to exclude raised intracranial pressure. The potential mitogenic effects of IGF-I have raised concerns regarding a possible increased risk of either neoplasia or regrowth of residual pituitary and peripituitary tumors. Extensive surveillance studies based on large multinational databases, including several thousand patients on GH replacement followed longitudinally, have not demonstrated an increased incidence of de novo neoplasia and prospective magnetic resonance imaging studies have not indicated an increased risk of pituitary or parasellar tumor regrowth (233, 234). In the childhood cancer survivor study (235) there was no increased risk of recurrence over 5 years follow-up in those who received GH and on 15-year follow-up of patients with previous cranial irradiation who receive GH replacement there was no increased risk of malignancy (236). In addition, there has been no correlation between the serum IGF-I level within the normal reference range and risk of further malignancy (237).

 

Mortality

 

Definition of the precise relationship between GH deficiency and mortality must await long term observations of mortality rate in patients on GH replacement set against background mortality rates in the general population adjusted for national variations but a recent Dutch study provides some evidence that mortality is not increased by replacement and may play a role in normalizing it (particularly in men) (238).

Fig 18. Mortality in hypopituitary patients with-/without GH replacement. From: Gaillard et al (26)

The potential impact of GH replacement on the increased mortality rates described in hypopituitary patients can only be determined by long-term surveillance of treated patients in comparison with normal population data. The multinational databases designed to monitor safety of long-term GH replacement may provide useful information in this regard. Reassuringly, the mortality rates in the KIMS database were similar to the background populations (fig 18), and a later large study in a much larger population with longer follow-up did not observe any increased mortality in GH treated GH deficient patients in the KIMS database (26). Danish nationwide studies have indicated that mortality was not increased in GH treated patients with childhood onset GH deficiency (239, 240), but was highly dependent on the primary cause of GH deficiency (241), since the primary causes of childhood onset GH deficiencyand concomitant diseases severely impaired socioeconomic conditions and impacted mortality; and only the subgroup of patients with idiopathic GH deficiency conditions was similar to the background population. In two Swedish publications there was evidence that hypocortisolism during acute stress, and de novo malignant brain tumors contributed to increased mortality (242), and GH deficient men receiving GH treatment had a mortality rate no different from the background population. In women, after exclusion of high-risk patients, mortality was not different from the background population except for CVD. Mortality due to malignancies was not elevated in adults receiving GH treatment. Next to gender, the heterogeneous etiology influences mortality in GH deficient adults with GH treatment (243). In the French SAGhE study mortality rates were increased in their population of adults treated as children with recombinant GH, particularly in those who had received the highest doses. Specific effects were detected in terms of death due to bone tumors or cerebral hemorrhage but not for all cancers. These results highlight the need for additional studies of long-term mortality and morbidity after GH treatment in childhood (244). Thus, the more recent studies have been reassuring concerning GH replacement and mortality, since those groups with higher mortality seem to have been limited to patient groups with a prior higher risk due to concomitant confounding mortality risks.

 

COSTS VERSUS BENEFITS OF GH REPLACEMENT THERAPY

 

Population studies in Sweden have documented a significantly greater medical and social burden for patients with established hypopituitarism. This continuing cost occurs irrespective of the initial cost of treating the pituitary pathology and derives from issues including unemployment, early retirement, depressive illness, and requirement for disability pension. A social circumstances analysis of the KIMS database has shown that approximately 11% of males and 31% of females require assistance with activities of daily living (245) (fig 19). Additional treatment cost factors, which might be inferred from risk factor profiles in adult GH deficiency populations, include increased prevalence of ischemic heart disease and increased fracture rates. So, whilst the cost of GH replacement to the hypopituitary population is easily determined, matching this with data for economic benefit requires a quantification of long-term complications arising from surrogate markers for long-term morbidity observed in GH deficient patients. Assessments of the effectiveness of GH replacement over time is influenced by the changing characteristics of the patients, with lower doses of GH replacement being used and a shorter period of time from diagnosis of GH deficiency to treatment (181). This means that accurate assessments of cost benefit using long-term data is not yet possible, and probably never will be. A recent study based on patients enrolled into the KIMS database has demonstrated significant reductions in the numbers of patients requiring assistance with the activities of daily living, a decrease in medical consultations and a decrease in hospital in-patient stays over a period of 24 months of GH replacement (fig 20).

Fig 19. Activity of daily living in adult patient with GH deficiency before and after GH replacement therapy. From: Hernberg-Stahl et al (245)

Fig 20. Sick leave and length of hospital stays in adult patients with GH deficiency before and after GH replacement therapy. From: Hernberg-Stahl et al (245).

ADHERENCE TO MANAGEMENT OF ADULT GROWTH HORMONE DEFICIENCY IN CLINICAL PRACTICE

 

Despite 30 years of evidence, guidelines, and clinical experience with adult GH deficiency and its management, a very recently published survey within the auspices of European Society of Endocrinology (246) has indicated that despite many guidelines on safety and efficacy of GH replacement in deficient patients as well as the above health economic considerations, GH replacement is still not available or reimbursed in all European countries. It also seems that both health care professionals and health administrators need improved knowledge to optimize the care of adults with GH deficiency. The publication results were further commented upon (247) indicating that in some health care communities reimbursement has been a major issue, because the discussion of GH replacement in truly GH deficient adults has been mixed with the discussion of utilizing GH therapy for sporting enhancement or for anti-ageing purposes, both of which are strongly discouraged. Also continuous presentations of unclear indications for GH diagnosis and replacement in small cohorts of mixed etiologies also pollute the field of health care discussions of proper clear cut cases of GH deficiency according to the official guidelines (248).

 

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Hyperglycemic Hyperosmolar State

CLINICAL RECOGNITION

 

The hyperglycemic hyperosmolar state (HHS) is a life-threatening metabolic decompensation of diabetes which presents with severe hyperglycemia and profound dehydration, typically accompanied by alteration in consciousness ranging from lethargy to coma. In contrast to diabetic ketoacidosis (DKA) in which acidemia and ketonemia are key features, these are limited in HHS. Mortality in HHS ranges from 5-20% and is higher at the extremes of age and in the presence of coma. HHS is more prevalent in type 2 diabetics and in about 7-17% of cases is the initial presentation classically seen in institutionalized elderly patients with diminished thirst perception or inability to ambulate to get free water as needed. HSS is extremely rare as first presentation in patients with type 1 diabetes. Infections are the leading precipitant of HHS, but it can also be precipitated by poor medication compliance, cerebrovascular accident, myocardial infarction, pancreatitis, trauma, alcohol abuse and drugs such as corticosteroids and atypical antipsychotics.

 

PATHOPHYSIOLOGY

 

HHS and DKA represent the two ends of the spectrum of markedly decompensated diabetes, differing mainly in severity of acidosis, ketosis and dehydration. HHS usually occurs with a lesser degree of insulinopenia compared with DKA, but the pathophysiology is otherwise thought to be similar. In both entities, there is a decrease in net effective insulin action with concomitant elevation of counterregulatory hormones. In the setting of relative insulin deficiency, glucagon, catecholamines and cortisol stimulate hepatic glucose production though glycogenolysis and gluconeogenesis. High catecholamines and low insulin reduce peripheral glucose uptake. Unlike DKA, there is adequate insulin available in HHS to restrain lipolysis and ketogenesis, as well as to restrain marked elevation of counterregulatory hormones, such cortisol, glucagon and growth hormone. However, there is significant hyperglycemia with resultant glycosuria leading to loss of water and electrolytes, dehydration, decreased renal perfusion, decreased glucose clearance, and exacerbation of hyperglycemia, ultimately causing impaired level of consciousness. In HHS, the initial increase in proinflammatory cytokines, reactive oxygen species, and plasminogen activator inhibitor-1 can contribute to increased prothrombotic risk.

 

DIAGNOSIS AND DIFFERENTIAL

 

HHS usually has a slower onset than DKA, with symptoms developing over several days or weeks. Patients present with polyuria, polydipsia, weakness, and blurred vision. Altered sensorium is classic in HHS, but mental status can range from fully alert to confused, lethargic, or comatose. Seizure can occur in up to 20% of the patients. Exam reveals physical signs of dehydration, including dry mucous membranes, poor skin turgor, cool extremities, hypotension, and tachycardia. Fever may or may not be present, suggesting underlying infection, although normothermia or even hypothermia may be present due to concomitant vasodilatation.

 

The diagnostic criteria for HHS include severe hyperglycemia and hyperosmolality with preservation of near normal pH and bicarbonate, and minimal or absent serum and/or urine ketones. ADA guidelines note glucose level at presentation should be > 600 mg/dl, with pH > 7.3 and bicarbonate level > 20 mEq/L. These are common diagnostic criteria that differentiate HHS from DKA (Table 1). However, it is clear that a subpopulation of patients with type 2 diabetes can present with overlapping features of HHS and DKA. Patients with ketosis prone type 2 diabetes present with ketosis and milder acidosis than the one expects in DKA and in some cases with near normal pH and bicarbonate. More rarely, HHS can present in the setting of diabetes insipidus where patients are treated with intravenous dextrose for the severe dehydration leading to hyperglycemia and glycosuria.

 

Table 1. Diagnosis of HHS Versus DKA

 

HHS

DKA

Diagnostic criteria

pH

>7.30

≤7.30

Plasma Glucose

>600 mg/dl

>250 mg/dl

Serum bicarbonate

>15 mEq/L

<18 mEq/L

Plasma and urine ketones

None or trace

Positive

Anion gap

 

<12

>12

Serum Osmolality

>320 mOsm/kg

Variable

Glycosuria

 

++

++

Typical Deficit

Water (ml/kg)

100-200 (9L)

100 (6L)

Na+ (mEq/kg)

5-13

7-10

Cl- (mEq/kg)

5-15

3-5

K+(mEq/Kg)

4-6

3-5

P04 (mmol/kg)

3-7

5-7

Mg++& Ca++(mEq/kg)

1-2

1-2

Adapted from Kitabchi A, et al. Diabetes Care, 2006, 29: 2739-2747

 

DIAGNOSTIC TESTS NEEDED

 

Initial laboratory tests should include electrolytes with calculated anion gap, plasma glucose, blood urea nitrogen (BUN), creatinine, serum and urine ketones, osmolality, and arterial blood gas.  Evidence of infection should be sought by checking complete blood count with differential and urinalysis, with consideration of additional evaluation including chest X-ray, and culture of blood, sputum and urine. Electrocardiogram and head CT should be done if clinically indicated.  HHS produces significant loss of several electrolytes as well as a prerenal azotemia and increased hematocrit, the latter due to hemoconcentration. An increase of serum sodium in the presence of hyperglycemia indicates severe dehydration. Altered mentation appears to correlate with the degree of hyperosmolality; hence significantly diminished mentation in the setting of an osmolality of <320 mOsm/kg should prompt a search for other causes. It is notable that despite significant potassium losses, serum potassium is usually normal or even elevated on presentation because of extracellular shift in the setting of hyperosmolality and insulin deficiency. HgbA1c may be useful to discriminate chronic uncontrolled hyperglycemia from acute metabolic decompensation.   

 

THERAPY

 

There is a lack on randomized controlled trials for the treatment of HHS and the American Diabetes Association (ADA) has developed guidelines that combine the treatment of HHS and DKA. The treatment of HHS includes a four-pronged approach:

  • reestablishment of volume status with vigorous intravenous hydration;
  • electrolyte replacement;
  • correction of hyperglycemia with volume expansion and administration of intravenous insulin;
  • diagnosis and management of potential precipitants.

 

The initial emergent treatment has been summarized in table 2.

 

Fluid Replacement

 

Aggressive fluid replacement is critical in order to prevent cardiovascular collapse, with repletion of intravascular and extravascular volume and restoration of renal perfusion. The total fluid deficit should be estimated (usually 100-200 ml/kg), with the goal of replacement over 24 hours. In the absence of heart failure, 1-1.5 liters of isotonic saline should be given over the first hour. Subsequent fluid replacement depends on the hydration and electrolyte status. In patients with hypotension, aggressive isotonic saline infusion should continue until the patient is stabilized. Increased plasma sodium concentration in the setting of hyperglycemia suggests a significant water deficit; clinical practice guidelines recommend adding a correction factor of 1.6 mg/dl to the plasma sodium concentration for each 100 mg/dl of glucose above 100 mg/dl. In the normotensive patient with a corrected serum sodium level that is normal or high, fluid replacement can be continued with half normal saline given at 250-500 cc/hour, whereas if the corrected serum sodium level is low, isotonic saline should be administered at similar rate. When serum glucose reaches 200-300 mg/dl, fluid should be changed to 5% dextrose solution in half normal saline.

 

Electrolyte Replacement

 

Electrolyte replacement is the second crucial step in HHS management. Serum potassium can be normal or elevated on presentation despite total body potassium depletion. Osmotic-induced intracellular dehydration results in potassium efflux from the cells. Since insulin causes a shift of potassium into the cell, it is mandatory to correct the potassium level to >3.3 mEq/L before starting insulin therapy. If potassium is between 3.3 and 5.3 mEq/L, 20-30 mEq of potassium should be given in each liter of intravenous fluid to keep serum potassium between 4 to 5 mEq/L. The potassium should be monitored if >5.3 meq/L and potassium replacement initiated when potassium < 5.3 meq/L. Magnesium should be checked and repleted as necessary; this is important to prevent renal wasting of potassium with exacerbation of hypokalemia. Routine administration of phosphate is not recommended (17); however, careful phosphate replacement can be considered in patients with very low levels (<1 meq/L), cardiac dysfunction, or respiratory distress.

 

Insulin Therapy

 

The treatment of choice for correction of hyperglycemia is regular insulin by continuous infusion after adequate fluid and potassium replacement. While randomized controlled studies in patients with DKA have shown that insulin therapy is effective regardless of the route of administration, there is limited data supporting the use of subcutaneous or intramuscular insulin in HHS and continuous intravenous insulin administration remains the treatment of choice in patient with significant dehydration, reduced level of consciousness, and critical illness. Insulin should be given as initial bolus of 0.1 unit per kilogram body weight, followed by a drip of 0.1 unit per kilogram per hour; alternatively, 0.14 units per kilogram per hour can be given as an infusion without a bolus. If the glucose level does not decrease by 50-70 mg/dl in the first hour, the insulin dose may be doubled.  When the plasma glucose level reaches 300 mg/dl, insulin infusion may be reduced to 0.05-0.1 unit/kg/hour and dextrose can be added to the fluids to keep the glucose level between 250-300 mg/dl until hyperosmolality has resolved and the patient is alert.

 

Evaluation of Precipitant Factors

 

Evaluation for and treatment of potential precipitant factors is important. Patients with HHS have a mortality rate of about 5-20%, 10-fold higher than patients with DKA and several studies have shown that the increased mortality is likely because of the precipitating factors. For this reason, appropriate work up and treatment should be given as indicated.

 

Table 2. Initial Emergent Treatment for HHS

1--IV Fluids

a-Cardiogenic shock

b-Severe hypovolemia

c-Mild dehydration

Hemodynamic Monitoring/ Pressors/ 0.9% NaCl

0.9% NaCl (1L/hr.)

Na* low:

0.9% NaCl (250-500 ml/hr.) † 
Na* normal or high:

0.45% NaCl (250-500 ml/hr.) † 

 

When serum glucose ≤300 mg/dl, 5% dextrose/0.45% NaCl (150-250 ml/hr.)

2-IV Potassium (with adequate renal function)

 

a--K+ <3.3 mEq/L

b--K+ 3.3-5.3 mEq/L

c--K+ >5.3 mEq/L

Hold insulin, K 20-30 mEq/ hr. until K+ >3.3 mEq/L

K 20-30 mEq in each liter of IV fluid to keep K+ 4-5 mEq/L

Do not give K; monitor

3-IV Insulin

 

Bolus 0.1 unit/Kg, then 0.1 unit/Kg/hr. infusion (or 0.14 unit/kg/hr. infusion w/o bolus)

Double infusion if glucose does not decrease by 50-70 mg/dl in the first hour

When serum glucose 300 mg/dl, ↓ insulin infusion to 0.05-0.1 units/Kg/hr.

Adapted from Kitabchi A, et al. Diabetes Care, 2006, 29: 2739-2747

*Corrected serum sodium; † depending on the hydration status

 

FOLLOW-UP

 

Meticulous clinical and laboratory follow up is critical in patients with HHS. Capillary blood glucose levels should be monitored every hour to allow adjustment of the insulin infusion. Electrolytes, BUN, creatinine and plasma glucose should be checked every 2-4 hours until the patient is stable. When plasma osmolality is <315 mOsm/L, and the patient is alert and able to eat, a multidose insulin regime consisting of long-acting insulin and short/rapid acting insulin before meals may be initiated. Intravenous insulin infusion should be continued for 1-2 h after the subcutaneous insulin is given to ensure adequate plasma insulin levels are maintained.

 

It is also important to monitor for possible treatment-related complications, the most common of which are hypoglycemia and hypokalemia.  These are both usually due to overzealous treatment with insulin and can be minimized with frequent monitoring. Cerebral edema is extremely rare in patients with HHS, and usually occurs in younger adults. To reduce the risk of cerebral edema in high-risk patients, sodium, glucose, and water deficit may be more gradually corrected to avoid the rapid decline in plasma osmolality. Recurrence of HHS can be prevented by improved patient as well as caregiver education and enhanced access to medical care. For elderly nursing home residents, nursing home staff should be educated in recognition of signs and symptoms of HHS and on the importance of adequate fluid intake.

 

REFERENCES

 

            Gosmanov AR, Gosmanova EO, Kitabchi AE. Hyperglycemic Crises: Diabetic Ketoacidosis and Hyperglycemic Hyperosmolar State. 2021 May 9. In: Feingold KR, Anawalt B, Boyce A, Chrousos G, de Herder WW, Dhatariya K, Dungan K, Hershman JM, Hofland J, Kalra S, Kaltsas G, Koch C, Kopp P, Korbonits M, Kovacs CS, Kuohung W, Laferrère B, Levy M, McGee EA, McLachlan R, Morley JE, New M, Purnell J, Sahay R, Singer F, Sperling MA, Stratakis CA, Trence DL, Wilson DP, editors. Endotext [Internet]. South Dartmouth (MA): MDText.com, Inc.; 2000–. PMID: 25905280

 

Pasquel, F.J., and Umpierrez, G.E. 2014. Hyperosmolar hyperglycemic state: a historic review of the clinical presentation, diagnosis, and treatment. Diabetes Care 37:3124-3131.

 

 

Umpierrez, G., and Korytkowski, M. 2016. Diabetic emergencies - ketoacidosis, hyperglycaemic hyperosmolar state and hypoglycaemia. Nat Rev Endocrinol 12:222-232.

 

Kitabchi, A.E., Umpierrez, G.E., Miles, J.M., and Fisher, J.N. 2009. Hyperglycemic crises in adult patients with diabetes. Diabetes Care 32:1335-1343.

 

Palmer, B.F., and Clegg, D.J. 2015. Electrolyte and Acid-Base Disturbances in Diabetes Mellitus. N Engl J Med 373:2482-2483.

 

Dhatariya, K.K., and Vellanki, P. 2017. Treatment of Diabetic Ketoacidosis (DKA)/Hyperglycemic Hyperosmolar State (HHS): Novel Advances in the Management of Hyperglycemic Crises (UK Versus USA). Curr Diab Rep 17:33.

 

 

 

 

 

 

 

 

 

Initial Management of Severe Hyperglycemia in Type 2 Diabetes

CLINICAL RECOGNITION

 

Type 2 diabetes mellitus (DM) is a common disease affecting 26 million people, 8.3% of the US population.  Of these, an estimated 7 million people are undiagnosed.

 

Type 2 DM typically has two pathophysiologic defects:  an insulin secretory defect and insulin resistance.  Symptoms of uncontrolled hyperglycemia include polyuria, polydipsia, blurry vision, and possibly dehydration and weight loss. Patients may complain of thirst, sweet cravings, generalized fatigue, abdominal discomfort, and muscle cramps. They may have a history of poor wound healing and/or frequent infections. Basic metabolic laboratory tests may reveal a random blood glucose level over 200 mg/dL [11.1 mmol/L], hyper- or hyponatremia, hypokalemia, metabolic acid-base derangements, and acute renal or prerenal insufficiency. Historical clues for the diagnosis of type 2 DM might include pre-existing history of pre-diabetes, a family history of type 2 diabetes, an ethnicity at higher risk for DM (African-American, Hispanic, Native American, Pacific Islander), a history of gestational diabetes, obesity, and sedentary lifestyle. 

 

PATHOPHYSIOLOGY  

 

Table 1. Clinical Features of the Acute Presentation of Type 2 Diabetes and Pathophysiology

Hyperglycemia

Insulin resistance, insulin deficiency (pancreatic beta cell failure), increased gluconeogenesis, glycogenolysis

Dehydration, polyuria, polydipsia

Osmotic diuresis, compensatory thirst

Weight loss, sweet cravings

Glycosuric calorie loss and inadequate glucose utilization

Muscle pain and abdominal discomfort

Lactic acid accumulation, hypokalemia, electrolyte /acid-base derangements

Metabolic alkalosis and/or acidosis, electrolyte disturbances

Dehydration and ketogenesis

Ketogenesis

Insulin deficiency resulting in lipolysis yielding free fatty acids, substrate for formation of ketone bodies

 

DIAGNOSIS AND DIFFERENTIAL

 

Diabetes can be diagnosed in several ways: 1) Presence of symptoms of hyperglycemia with a random blood glucose of 200 mg/dL [11.1 mmol/L]; 2) fasting blood glucose > 126 mg/dL [7.0 mmol/L; 3) the 75-gram oral glucose tolerance test with a blood glucose > 200 mg/dL [11.1 mmol/L] at 2 hours; 4) hemoglobin A1C value > 6.5%.  If asymptomatic, the diagnosis of diabetes is confirmed with two consecutive day abnormal results from the same test or a different test or with two different tests on the same day. If using the hemoglobin A1C for diagnosis, one should be aware of several conditions (some common) making this measure un-interpretable

 

Adult patients with type 1 and type 2 DM can sometimes present similarly.  If a patient presents with hyperglycemia, ketonemia, and metabolic acidosis, distinguishing between types of diabetes is not necessary in this acute setting because initially, both type 1 and type 2 DM are treated with insulin.  Later the two diseases may be distinguished with antibody testing although this is neither completely sensitive nor specific. Type 2 DM can also present acutely with a hyperglycemic hyperosmolar state (HHS) with dehydration, altered level of consciousness, and a lesser degree of clinical ketosis than seen in diabetic ketoacidosis (DKA). Consideration for genetic syndromes and concomitant rare conditions of endocrine hormone excess (cortisol, growth hormone, epinephrine, glucagon) leading to hyperglycemia should be in the non-urgent setting for patients with new diagnoses of diabetes.

 

DIAGNOSTIC TESTS NEEDED AND SUGGESTED

 

For an acute presentation of diabetes with hyperglycemic symptoms, the patient should have a basic metabolic panel of laboratory tests including glucose, electrolytes, blood urea nitrogen, creatinine, blood and or urinary ketones, liver function tests, and urinalysis. Other testing should be guided by a patient’s history and physical exam and might include evaluation for infection or cardiac dysfunction.  A hemoglobin A1C reflects the average blood glucose over the last 90 days and is a helpful test.  Distinguishing type 1 from type 2 DM can on occasions be difficult but can be assisted with autoantibody testing [tyrosine phosphatase antibody (IA-2) or glutamic acid decarboxylase (GAD) 65 antibody]. The presence of antibody suggests an autoimmune lesion as seen in type 1 DM. In type 1 DM insulin and C-peptide levels are characteristically low, whereas they may be normal or elevated at the onset of type 2 DM.

 

TREATMENT

 

Insulin therapy is the initial management choice for patients presenting with hyperglycemia and catabolic symptoms including weight loss. If laboratory abnormalities suggest concurrent DKA or HHS, these must be treated emergently with aggressive saline rehydration, intravenous insulin, potassium and other electrolyte replacement.

 

For a severely hyperglycemic patient, with a catabolic presentation that usually includes moderate to severe volume depletion, the first therapeutic step is rehydration, usually with intravenous saline.  After adequate hydration, therapy with physiologic doses of insulin (0.3-0.4 units per kilogram body weight daily) is recommended. The ideal treatment regimen would be a combination of a long-acting basal insulin plus multiple premeal prandial “bolus” injections to manage meal-related insulin requirements and correction of pre-meal hyperglycemia, referred to as basal-bolus insulin therapy. A good starting place is to prescribe half the total daily insulin dose as basal and the other half as bolus. The combination of long-acting insulin and a rapid acting analogue are good options for basal-bolus therapy. The basal dose is given as a separate injection from the bolus injection.

 

The premeal “bolus” dose is calculated by summing the dose required to cover the carbohydrate load plus the dose to correct premeal hyperglycemia and is given as one injection 10-15 minutes before the meal. Particularly with premeal hyperglycemia but even with mealtime glucose levels within target, today’s rapid-acting analogues require time for absorption to avoid more severe postprandial hyperglycemia (this is typically called the “lag time”).  In an acute setting, and in a less sophisticated patient, it might be more appropriate to begin therapy with a twice-daily pre-mixed insulin. Even though this regimen is not ideal for many for the long-term because it does not allow for sufficient dose titration, this regimen allows approximate physiologic basal-bolus insulin coverage with fewer injections. Nevertheless, if starting with basal-bolus or premixed insulin, it is best to teach the patient to use the strategy of correcting pre-meal hyperglycemia with an additional dose of rapid acting insulin analogue, given 10-15 minutes before the meal. This adds tremendous flexibility to an otherwise rigid regimen.

 

Until more education is possible, the need to limit high glycemic-load carbohydrate intake (such as with sweetened beverages and juice) should be strongly reinforced with counseling. Certainly, arrangements for general and dietary diabetes education should be made for a newly diagnosed diabetic patient or for a patient new to insulin therapy.

 

FOLLOW-UP

 

The patient will use a glucose meter to check his/her fasting and premeal blood glucose levels.  For the patient on basal-bolus insulin therapy, he/she will increase bedtime basal insulin doses by 1-2 units every 3 days until fasting blood glucose falls into target range of 90 -130 mg/d [5 – 7.2 mmol/L]. Ideally, bedtime and fasting glucose levels are about the same at the end of the basal insulin titration. If there is a consistent reduction in bedtime to fasting glucose by more than 50 mg/dL [2.8 mmol/L], basal insulin dose is too high.

 

Adjustments for pre-meal insulin doses are most easily made with an algorithm written clearly for the patient to reference. The importance of injecting the mealtime insulin 10 -15 minutes before eating needs to be emphasized. In contrast to type 1 diabetes where carbohydrate counting is standard, most type 2 patients do well by taking the same mealtime dose or altering up or down based on the size of the meal. For example, one might take 8 units for a smaller meal and 12 units for a large one. If patients feel hypoglycemic symptoms (sweating, shaking, mental fogginess, hunger) despite concurrent blood glucoses levels in the normal range, one could use smaller insulin dose increments to lower blood glucose into the target range more gradually.  Generally, increases of insulin dose by10% are well tolerated by patients.  Late night snacks without insulin coverage may lead to morning hyperglycemia and interfere with the assessment of the adequacy of the bedtime insulin doses.  Correction doses are “trial and error” but most patients with type 2 diabetes require an “insulin sensitivity factor” of 30 (i.e., 30 mg/dL glucose reduction expected from one unit of insulin injected). For example, if additional insulin is provided for premeal glucose levels above 150 mg/dL, 1 extra unit would be given for 150-180 mg/dL, 2 units for 181-210 mg/dL, etc.  When starting insulin, it may be appropriate to use a more conservative insulin sensitivity factor such as 40 or 50.

 

Table 2.  Premeal Bolus Dose Calculation Using Rapid-Acting Insulin Analogue

Total premeal insulin dose is sum of:

Suggested Units

Meal coverage

5-8 units for smaller meal, 9-12 units for larger meal

Pre meal hyperglycemia correction

1 unit per 30-50 mg/dL above150 mg/dL

 

Initial diabetes therapy includes counseling for lifestyle and diabetic nutritional interventions.  Starting therapy with metformin could also be considered as an adjunctive therapy with insulin to reduce insulin requirements and minimize weight gain. Overtime with lifestyle changes, a decrease in glucose toxicity, and the addition of other hypoglycemic agents some patients who present with very high glucose levels may be able discontinue insulin therapy.

 

GUIDELINES

 

2019 Update to: Management of Hyperglycemia in Type 2 Diabetes, 2018. A Consensus Report by the American Diabetes Association (ADA) and the European Association for the Study of Diabetes (EASD). Buse JB, Wexler DJ, Tsapas A, Rossing P, Mingrone G, Mathieu C, D'Alessio DA, Davies MJ. Diabetes Care. 2020 Feb;43(2):487-493

 

REFERENCES

 

Donner T, Sarkar S. Insulin – Pharmacology, Therapeutic Regimens, and Principles of Intensive Insulin Therapy. 2019 Feb 23. In: Feingold KR, Anawalt B, Boyce A, Chrousos G, de Herder WW, Dhatariya K, Dungan K, Hershman JM, Hofland J, Kalra S, Kaltsas G, Koch C, Kopp P, Korbonits M, Kovacs CS, Kuohung W, Laferrère B, Levy M, McGee EA, McLachlan R, Morley JE, New M, Purnell J, Sahay R, Singer F, Sperling MA, Stratakis CA, Trence DL, Wilson DP, editors. Endotext [Internet]. South Dartmouth (MA): MDText.com, Inc.; 2000–. PMID: 25905175

 

Feingold KR. Oral and Injectable (Non-Insulin) Pharmacological Agents for the Treatment of Type 2 Diabetes. 2021 Aug 28. In: Feingold KR, Anawalt B, Boyce A, Chrousos G, de Herder WW, Dhatariya K, Dungan K, Hershman JM, Hofland J, Kalra S, Kaltsas G, Koch C, Kopp P, Korbonits M, Kovacs CS, Kuohung W, Laferrère B, Levy M, McGee EA, McLachlan R, Morley JE, New M, Purnell J, Sahay R, Singer F, Sperling MA, Stratakis CA, Trence DL, Wilson DP, editors. Endotext [Internet]. South Dartmouth (MA): MDText.com, Inc.; 2000–. PMID: 25905364

 

Gosmanov AR, Gosmanova EO, Kitabchi AE. Hyperglycemic Crises: Diabetic Ketoacidosis and Hyperglycemic Hyperosmolar State. 2021 May 9. In: Feingold KR, Anawalt B, Boyce A, Chrousos G, de Herder WW, Dhatariya K, Dungan K, Hershman JM, Hofland J, Kalra S, Kaltsas G, Koch C, Kopp P, Korbonits M, Kovacs CS, Kuohung W, Laferrère B, Levy M, McGee EA, McLachlan R, Morley JE, New M, Purnell J, Sahay R, Singer F, Sperling MA, Stratakis CA, Trence DL, Wilson DP, editors. Endotext [Internet]. South Dartmouth (MA): MDText.com, Inc.; 2000–. PMID: 25905280

 

 

Diabetic Ketoacidosis

CLINICAL RECOGNITION

 

Omission of insulin and infection are the two most common precipitants of diabetic ketoacidosis (DKA). Noncompliance may account for up to 44% of DKA presentations; while infection is less frequently observed.

 

Acute medical illnesses involving the cardiovascular system (myocardial infarction, stroke, acute thrombosis), gastrointestinal tract (bleeding, pancreatitis), endocrine axis (acromegaly, Cushing`s syndrome, hyperthyroidism) and recent surgical procedures can contribute to the development of DKA by causing dehydration, increase in insulin counterregulatory hormones, and worsening of peripheral insulin resistance.

 

Medications such as diuretics, beta-blockers, corticosteroids, second-generation anti-psychotics, anti-convulsants, sodium-glucose cotransporter-2 (SGLT-2) inhibitors, and/or immune checkpoint inhibitors may affect carbohydrate metabolism and volume status and, therefore, could precipitate DKA. SGLT-2 inhibitors have been associated with euglycemic DKA (glucose level < 250mg/dL)

 

Other factors leading to DKA include psychological problems, eating disorders, insulin pump malfunction, and drug abuse. It is well recognized that new onset T2DM can sometimes manifest with DKA. These patients are obese, mostly African Americans or Hispanics and have undiagnosed hyperglycemia, impaired insulin secretion, and impaired insulin action. A recent report suggests that cocaine abuse is an independent risk factor associated with DKA recurrence.

 

PATHOPHYSIOLOGY

 

Insulin deficiency, increased insulin counter-regulatory hormones (cortisol, glucagon, growth hormone, and catecholamines), and peripheral insulin resistance lead to hyperglycemia, dehydration, ketosis, and electrolyte imbalance which underlie the pathophysiology of DKA.

 

Hyperglycemia of DKA evolves through accelerated gluconeogenesis, glycogenolysis, and decreased glucose utilization – all due to absolute insulin deficiency. Of note, diabetes patients who developed DKA while treated with SGLT-2 inhibitors can present without hyperglycemia, i.e., with euglycemic DKA.

 

Due to increased lipolysis and decreased lipogenesis, abundant free fatty acids are converted to ketone bodies: β-hydroxybutyrate (β-OHB), acetoacetate, and acetone. Hyperglycemia-induced osmotic diuresis, if not accompanied by sufficient oral fluid intake, leads to dehydration, hyperosmolarity, electrolyte loss, and subsequent decrease in glomerular filtration. With decline in renal function, glycosuria diminishes and hyperglycemia/hyperosmolality worsens. With impaired insulin action and hyperosmolality, utilization of potassium by skeletal muscle is markedly diminished leading to intracellular potassium depletion. Also, potassium is lost via osmotic diuresis causing profound total body potassium deficiency. Therefore, DKA patients can present with broad range of serum potassium concentrations. Nevertheless, a “normal” plasma potassium concentration may indicate that potassium stores in the body are severely diminished and the institution of insulin therapy and correction of hyperglycemia will lead to hypokalemia.

 

DIAGNOSIS AND DIFFERENTIAL DIAGNOSIS

 

Diagnostic criteria for DKA are presented in Table 1.

 

Table 1. Criteria and Classification of DKA

DKA

Mild

Moderate

Severe

Plasma glucose (mg/dl)

>250 mg/dl

>250mg/dl

>250mg/dl

Arterial pH

7.25-7.30

7.00-7.24

<7.00

Serum bicarbonate (mEq/L)

15-18

10- 15

<10

Urine ketone*

+

+

+

Serum ketone*

+

+

+

Effective Serum Osmolality**

Variable

Variable

Variable

Anion Gap***

>10

>12

>12

Mental Status

Alert

Alert/drowsy

Stupor/coma

*Nitroprusside reaction method

** Serum osmolality: 2[measured Na+ (mEq/L)] + glucose (mg/dl)/18 = mOsm/kg

*** Anion Gap: [ (Na+)– (Cl- + HCO3- (mEq/L)]

 

CLINICAL PRESENTATION

 

Polyuria, polydipsia, weight loss, vomiting, and abdominal pain usually are present in patients with DKA. Abdominal pain can be closely associated with acidosis and resolves with treatment. Physical examination findings such as hypotension, tachycardia, poor skin turgor, and weakness support the clinical diagnosis of dehydration in DKA. Mental status changes may occur in DKA and are likely related to degree of acidosis and/or hyperosmolarity. A search for symptoms of precipitating causes such as infection, vascular events, or existing drug abuse should be initiated in the emergency room. Patients with hyperglycemic crises can be hypothermic because of peripheral vasodilation and decreased utilization of metabolic substrates.

 

DIFFERENTIAL DIAGNOSIS

 

Hyperglycemic hyperosmolar state is not associated with ketosis. Starvation and alcoholic ketoacidosis are not characterized by hyperglycemia >200 mg/dl and bicarbonate level <18 meq/L. With hypotension, decreased renal function, and history of metformin use, lactic acidosis (lactic acid level >7 mmol/L) should be suspected. Ingestion of methanol, isopropyl alcohol, and paraldehyde can also alter anion gap and/or osmolality and need to be investigated.

 

Table 2. Laboratory Evaluation of Causes of Acidosis

Factor Studied

DKA

HHS

Starvation

Uremic acidosis

pH

normal

normal

Mild↓

Plasma glucose

>500 mg/dl

normal

normal

Glycosuria

+ +

+ +

0

0

Total plasma ketones*

↑↑

0 or ↑

Mild↑

0

Anion gap

Normal

Mild↑

Mild↑

Osmolality

>330 mOsm/kg

normal

Normal/↑

Other

     

BUN>200 mg/dl

HHS- hyperglycemic hyperosmolar state

BUN –blood urea nitrogen

*Acetest and Ketostix (Bayer; Leverkusen, Germany) measure acetoacetic acid only; thus, misleadingly low values may be obtained because the majority of “ketone bodies” are β-hydroxybutyrate.

 

DIAGNOSTIC TESTS NEEDED

 

Initial Necessary Tests

 

Basic metabolic panel, osmolality, ketones, β-hydroxybutyrate (β-OH), complete blood count with differential, urinalysis and urine ketones by dipstick, and arterial blood gases.

 

Additional Tests

 

Electrocardiogram, chest X-ray, and various tissue cultures, if indicated, and HbA1c.

 

Caveats to Diagnostic Tests

 

Anion gap acidosis is calculated by subtracting the sum of Cl and HCO3 from measured (not corrected) Na concentration and should be corrected for hypoalbuminemia. Usually, a HCO3 level of 18-20 meq/L rules out metabolic acidosis. Arterial blood gases with pH<7.30 support the diagnosis. β-OHB is early and abundant ketoacid and indicative of ketosis. Acetoacetate but not acetone, is a product of ketone body formation and is measured by a nitroprusside reaction that is widely used but may be negative in the blood in early DKA. Effective serum osmolality can be measured directly or derived from following formula: 2 x [measured Na+(meq/L)] + glucose/18. High measured Na indicates a significant degree of dehydration. A white blood cell count >25,000 should warrant a comprehensive search for infection. Serum creatinine can be falsely elevated because of acetoacetate interference with the colorimetric creatinine assay. When patients with DKA present with mixed acid-base disorder, measurement of serum β-OHB will be required to confirm that acidosis is due to ketoacidosis.

 

THERAPY 

 

The therapeutic goals of management include optimization of:

  • volume status,
  • hyperglycemia and ketosis/acidosis,
  • electrolyte abnormalities,
  • potential precipitating factors.

 

Steps to follow in early stages of DKA management (Figures 1, 2, 3):

  • Start IV fluids after blood sample for biochemistry was sent to laboratory (Fig. 1);
  • Potassium level should be >3.3 meq/L before initiation of insulin therapy (supplement potassium intravenously if needed) (Fig. 3);
  • Initiate insulin therapy only when steps 1-2 are executed (Fig. 2).

 

Resolution of DKA:

  • Plasma glucose <200-250 mg/dl,
  • Serum bicarbonate concentration >18 meq/L,
  • Venous blood pH >7.3, and
  • Anion gap <10

 

Fluid therapy: Replace fluid deficit in DKA (~6 L) within 24-36 hours with the goal of 50% volume replacement within first 12 hours.

 

Insulin Therapy: Transition to subcutaneous insulin by giving long-acting insulin 2 hours before the discontinuation of IV insulin.

 

Bicarbonate therapy: If pH is < 7.0 or bicarbonate level is < 5 meq/L, administer 100 mmol (2 ampules) of bicarbonate in 200 ml of water with 20 meq of potassium chloride over two hours.

Figure 1. Fluid management in adult patients with DKA

 

Figure 2. Insulin management in adult patients with DKA

Figure 3. Potassium management in adult patients with DKA

 

FOLLOW UP: COMPLICATIONS AND DISCHARGE

 

Hypoglycemia and hypokalemia are the most frequent complications and can be prevented by timely adjustment of insulin dose and frequent monitoring of potassium levels.

 

Non-anion gap hyperchloremic acidosis occurs due to urinary loss of ketoanions which are needed for bicarbonate regeneration and preferential re-absorption of chloride in proximal renal tubule secondary to intensive administration of chloride-containing fluids and low plasma bicarbonate. The acidosis usually resolves and should not affect treatment course.

 

Cerebral edema is reported in young adult patients. This condition is manifested by appearance of headache, lethargy, papillary changes, or seizures. Mortality is up to 70%. Mannitol infusion and mechanical ventilation should be used to treat this condition.

 

Rhabdomyolysis is another possible complication due to hyperosmolality and hypoperfusion.

 

Pulmonary edema can develop from excessive fluid replacement in patients with CKD or CHF.

 

Discharge planning should include diabetes education, selection of appropriate insulin regimen that is understood and afforded by the patient, and preparation of set of supplies for the initial insulin administration at home.

 

REFERENCES

 

Kitabchi AE, Umpierrez GE, Fisher JN, Murphy MB, and Stentz FB. Thirty years of personal experience in hyperglycemic crises: diabetic ketoacidosis and hyperglycemic hyperosmolar state. The Journal of clinical endocrinology and metabolism 93: 1541-1552, 2008.http://www.ncbi.nlm.nih.gov/pubmed/18270259

 

Kitabchi AE, Umpierrez GE, Miles JM, and Fisher JN. Hyperglycemic crises in adult patients with diabetes. Diabetes care 32: 1335-1343, 2009.

 

Karslioglu French E, Donihi AC, Korytkowski MT. Diabetic ketoacidosis and hyperosmolar hyperglycemic syndrome: review of acute decompensated diabetes in adult patients.

BMJ. 2019 May 29;365:l1114.

 

Gosmanov AR, Gosmanova EO, Kitabchi AE. Hyperglycemic Crises: Diabetic Ketoacidosis and Hyperglycemic Hyperosmolar State. 2021 May 9. In: Feingold KR, Anawalt B, Boyce A, Chrousos G, de Herder WW, Dhatariya K, Dungan K, Hershman JM, Hofland J, Kalra S, Kaltsas G, Koch C, Kopp P, Korbonits M, Kovacs CS, Kuohung W, Laferrère B, Levy M, McGee EA, McLachlan R, Morley JE, New M, Purnell J, Sahay R, Singer F, Sperling MA, Stratakis CA, Trence DL, Wilson DP, editors. Endotext [Internet]. South Dartmouth (MA): MDText.com, Inc.; 2000–. PMID: 25905280

Thyroid Nodules and Thyroid Cancer Prior to, During, and Following Pregnancy

ABSTRACT

 

Thyroid cancer is the second most common malignancy to co-occur in pregnancy. Further, the rising prevalence of treated thyroid cancer in women of child-bearing age means that survivors of thyroid cancer are frequently presenting for obstetric care, occasionally in the setting of persisting structural disease. To ensure that optimal health outcomes are achieved for mother and child, it is essential that pre-pregnancy issues are comprehensively addressed, and that management decisions during pregnancy remain both patient and child focused, best achieved through a woman-centered multidisciplinary team. As new data emerge regarding the impact of radioactive iodine on fertility, careful balancing of risk and benefits of this treatment is required. 

 

INTRODUCTION

 

Thyroid nodules are common in women of childbearing age. Thyroid nodules may be detected due to symptoms of local compression (either due to larger size, or pressure on the trachea or esophagus), but are more commonly detected incidentally on imaging performed for other reasons. As well as determining if compressive symptoms are present, all thyroid nodules must be risk-stratified for the presence of malignancy. A third factor is to determine whether the nodule is functional (i.e., autonomously producing thyroid hormone), however this cannot be reliably assessed during pregnancy as it is dependent on radionucleotide imaging which is contra-indicated during pregnancy. 

 

In general, the investigation or treatment of any new or co-existent medical conditions in pregnancy should be weighed against the separate risks and benefits to both the mother and fetus. Although most thyroid nodules will not grow during pregnancy, and therefore permit management decisions to be deferred to after birth (thus prioritizing fetal wellbeing), a small proportion of cases will require emergent management within pregnancy to prioritize maternal wellbeing (1).

 

Thyroid carcinomas generally develop from follicular epithelial cells (termed differentiated thyroid cancer, DTC) and present morphologically as papillary (PTC) or follicular (FTC) subtypes. Anaplastic thyroid cancer (ATC) is a rare, highly aggressive de-differentiated variant of DTC. Rarely, parafollicular, neuro-endocrine derived C-cells can give rise to medullary thyroid cancers (MTC). Thyroid lymphoma and metastases from other solid organ cancers are rare. In general, DTC has an greater than 98% 10 year survival in women of child-bearing age (2).

 

EPIDEMIOLOGY OF THYROID NODULES AND THYROID CANCER 

 

Thyroid Nodules

 

There is a clear female preponderance for the development of thyroid nodules that is demonstrated in studies from varied ethic groups, and in populations that are iodine-replete and iodine deficient (3-5). Thyroid nodules are also more prevalent with increasing age (6){Reiners, 2004 #1161}.  This may partly be explained by exposure to female reproductive hormones, as studies have demonstrated associations with increasing thyroid nodularity and multiparity, older age at menopause, and the presence of uterine fibroids (6-9). In a single study, use of oral contraceptive hormones was associated with reduced thyroid volume, but not a change in thyroid nodularity (10).

 

Carcinoma of the Thyroid Gland

 

The increased prevalence of thyroid nodules in females is matched by an increased prevalence of thyroid cancer amongst women.  SEER data from the United States cancer registry reports thyroid cancer incidence at 21 cases per 100,000 females, compared to 7.1 per 100,000 males (11).  When stratified by age, it is evident that this gender-based divergence is seen as early as puberty (Figure 1). The peak incidence of thyroid cancer amongst females occurs in midlife (age 35-59), and occurs earlier than the peak incidence in males (age 65-75), which corresponds with exposure to female reproductive hormones. ATC and MTC have equal incidence between genders.

Figure 1. Incidence of thyroid cancer by age- and gender- in the United States. Data source: SEER 18 (2010-2014). https://seer.cancer.gov/faststats

Although epidemiological data would suggest a strong link between exposure to female reproductive hormones and development of thyroid cancer, firm evidence linking reproductive factors to thyroid cancer risk is less clear. Some studies have shown a small (or transient) increase risk of DTC following pregnancy compared to nulliparous women (12).  Age of menarche, menopause, and menstrual cycle patterns present conflicting data (12), however in general, longer exposure to reproductive hormones appears associated with increased thyroid cancer risk (13-15). Conversely, extended periods of breastfeeding (resulting in prolonged reductions in cirulating estradiol), have been associated with with decreased incidence of thyroid cancer (14, 16, 17).

 

Incidence of Thyroid Carcinoma in Pregnancy

 

Multiple studies confirm that carcinoma of the thyroid gland is the second most frequent pregnancy-associated cancer, behind carcinoma of the breast. Registry studies suggest that thyroid cancer is present in between 14-27 per 100,000 mothers giving birth (18, 19). In most cases, this represents newly diagnosed thyroid cancer during pregnancy, which is usually organ-confined. However, a combination of increasing diagnosis of thyroid cancer amongst young women and excellent prognosis has resulted in an increasing cohort of survivors of thyroid cancer requiring obstetric care (20). This is demonstrated by data from Taiwan, showing thyroid cancer prevalence amongst women (175 cases per 100,000 women) is 9-fold higher than the incidence (18 cases per 100,000 women) (21). Occasionally, pregnancy occurs in a woman with known or suspected metastatic disease. A recent study from the USA reports that a historical diagnosis of thyroid cancer was the most common cancer present in women presenting for obstetric care (22).

 

IMPACT OF A PREGNANCY ON NUMBER AND SIZE OF THYROID NODULES

 

Impact of Pregnancy Hormones on Thyroid Follicular Epithelium

 

Pregnancy represents a stimulatory environment for thyroid follicular cells. The pregnancy hormone human chorionic gonadotrophin (HCG) is a heterodimeric glycoprotein. Although the beta subunit is unique, the alpha subunit is common to follicle stimulating hormone, luteinizing hormone, and thyroid stimulating hormone (TSH). As a result, this structural homology causes cross-stimulation of the TSH receptor by HCG, leading to physiological TSH-independent stimulation of the TSH-receptor, predominantly in the first trimester when HCG levels are highest. As well as contributing to gestational hyperthyroidism, in this way HCG mediated TSH-receptor signaling acts to stimulate growth of the thyroid follicular epithelium (23). Sustained activation of the signaling cascade mediated by the TSH-receptor has been associated with an increased risk of thyroid cancer in large observational studies. However, it is not known whether more limited periods of increased TSH-receptor signaling, such as would occur during pregnancy, materially contributes to thyroid cancer risk (24).

 

Iodine (not a pregnancy hormone) is a trace element required for normal maternal thyroid function and fetal thyroid development and function. Pregnancy increases maternal demands for iodine and a daily intake of approximately 250-300mcg is recommended (25).  Iodine excess and iodine deficiency states are both associated with an increased prevalence of thyroid nodules (3, 26).  

 

Changes in Number and Size of Thyroid Nodules During Pregnancy

 

As previously outlined, the hormonal environment of pregnancy is associated with the development of new thyroid nodules, and with potential growth of existing thyroid nodules.  Using ultrasound screening, thyroid nodules are demonstrated in 3-21% of pregnant women (26-28), although most nodules are small (<1cm) and not detectable clinically (26).  Prospective studies of pregnant women show an increase in thyroid nodule number and size during pregnancy. In a study of 221 women in China using repeated sonographic evaluation, an increase in nodule volume during pregnancy was shown in 15% of women in whom nodules were already present at baseline evaluation. New thyroid nodules were detected in 13% of the cohort. Post-partum, the number of women with thyroid nodules had increased from 15% to 24% (26). All nodules had a benign sonographic appearance. Similarly, a study of 726 pregnant women in Belgium identified a 3% incidence of thyroid nodules at baseline (determined by two-step screening with palpation followed by ultrasound). Of those with nodules, 60% showed an increase in size of at least 50%. Further, 20% (4/20) of women with regular sonographic surveillance developed new nodules during pregnancy (27).

 

PRESENTATION OF A NEW THYROID NODULE IN THE PREGNANT PATIENT       

 

A thyroid nodule usually comes to attention in pregnancy following the identification of a palpable abnormality. Screening for thyroid nodules in asymptomatic individuals without risk factors, both in the pregnant and non-pregnant population, is not recommended (29).

Thyroid nodules should be assessed using a triple assessment, including clinical assessment, sonographic risk stratification, and biopsy (in selected cases). Scintigraphy, which is part of the standard workup for functional nodules in the non-pregnant population, is contra-indicated in pregnancy due to the risk of ionizing radiation to the fetus.   

 

Important historical factors that increase the chance of a nodule being malignant include the presence of:

 

  • A familial cancer syndrome, including multiple endocrine neoplasia 2 (MEN2), familial PTC, Cowden’s syndrome, familial adenomatosis polyposis, and Carney Complex.
  • Neck irradiation in childhood, e.g., treatment for cancers of the head and neck
  • Exposure to ionizing radiation in early life (age <18 years)

 

On clinical examination, a palpable lump should be characterized. The presence of a large, very firm or rapidly growing nodule should raise concern for malignancy. Neck lymph nodes should be evaluated. Symptoms and signs of compression of local adjacent structures should be sought. 

 

Many thyroid nodules are functional, however the determination of the functional status of a thyroid nodule in pregnancy is limited. Firstly, although TSH should be checked, a low TSH may reflect gestational hyperthyroidism and should be interpreted with reference to the current gestational age. Most functional nodules progress slowly, therefore a pre-pregnancy TSH level which is at, or below, the lower limit of the reference range may provide a helpful clue. Secondly, radioactive isotopes used for thyroid scintigraphy readily cross the placenta, and the radiation exposure to the fetus does not justify the use of this modality in pregnancy.  Therefore, conclusive determination of whether a thyroid nodule is functional (and thus of very low malignant potential), or non-functional, during pregnancy is usually not possible. 

 

Serum biomarkers for thyroid cancer are not currently in routine use.  Although serum calcitonin is highly sensitive for the diagnosis of MTC (30), it is not validated for use in pregnancy, especially as calcitonin levels rise over the course of a normal pregnancy.  Further, its use in assessment of thyroid nodules in non-pregnant women is not universally established. Carcino-embryonic antigen, also a marker of MTC, can rise during pregnancy, and should be interpreted with caution (31).

 

Neck ultrasound is the definitive tool for assessment of thyroid nodules, and is safe in pregnancy. A high-frequency linear transducer is optimal to provide detailed characterization of the sonographic features, including size, echogenicity, shape, margins, the presence of calcification, and the presence of abnormal lymph nodes in the central and lateral neck.  All nodules should be risk stratified according to a validated scoring system, such as from the American Thyroid Association (32) or the American College of Radiology (33).  If fine-needle aspiration biopsy (FNAB) is required, this can be safely performed in all trimesters of pregnancy, with indications identical to that of the non-pregnant population (32). 

 

Nodules with higher risk features, such as larger size, growth in pregnancy, suspicion of extra-thyroidal extension, presence of large-volume nodal metastases, or suspicion for MTC or ATC should be considered for biopsy and surgery during pregnancy.  However, for smaller nodules without any high-risk features, consideration should be given to deferring biopsy (and any planned intervention) until the post-partum period, as several studies have confirmed that there is no survival benefit for surgery during pregnancy for low risk DTC (34).

 

IMPACT OF PREGNANCY ON A NEW DIAGNOSIS OF THYROID CANCER   

 

Impact of Pregnancy on Outcome of Thyroid Cancer

 

A diagnosis of thyroid cancer during pregnancy has the same excellent long term survival outcomes as seen in other settings. Large retrospective studies in the US population between 1962-1999 (35-37) show similar mortality data irrespective of the diagnosis setting (inside or outside pregnancy) or the timing of surgery (during pregnancy or post-partum).  Although these studies have the benefit of long follow up periods, they are inherently retrospective. Further, the ability of these studies to assess impact of pregnancy on thyroid cancer recurrence is limited, not only due to their retrospective nature, but also due to lack of availability of highly sensitive thyroglobulin assays and high resolution neck ultrasound in historic series (34).

 

In contrast, recent studies suggest that thyroid cancer diagnosed in pregnancy may have a higher risk of recurrence. A retrospective study from Italy showed higher rates of persistent or recurrent thyroid cancer in women diagnosed either during pregnancy or within 12 months after birth (60% persistent or recurrent disease), compared to women diagnosed with thyroid cancer more than 12 months after a pregnancy (4% persistent or recurrent disease) or women who were never pregnant (13% persistent or recurrent disease) (38). However, it is important to note that most of the pregnant women with thyroid cancer underwent surgery in the second trimester (73%), and it is possible that a more limited surgical approach in this setting may have confounded these results. 

 

Similarly, a second retrospective Italian study found a higher rate of persistent or recurrent disease in women with thyroid cancer diagnosed within two years of a pregnancy (11%), compared to women diagnosed more than two years after a pregnancy (1%) or those who were never pregnant (5%) (39). 

 

A pathology study from Australia found that DTC diagnosed within 12 months of pregnancy were more likely to be larger, and have nodal metastases than matched controls (40).

 

Overall, these data should reassure clinicians and patients that the impact of pregnancy on a newly diagnosed thyroid cancer is low, with excellent overall survival outcomes. Epidemiological and clinical data would suggest that the stimulatory milieu of pregnancy may contribute to a slightly higher overall risk of recurrence, which should be taken into consideration when planning follow up strategies.  

 

Timing of Thyroidectomy

 

Expert consensus affirms that thyroidectomy can safely be performed in the second trimester, but is often more appropriately deferred to the post-partum period (34). Clinical markers of aggressive pathology, such as large primary size, rapid growth, or bulky lateral neck nodal disease, would support a strategy of earlier surgery. At present, these clinical markers of aggressiveness are detected by specialized thyroid and neck ultrasound, which should occur at first assessment, and subsequently around 20 weeks (to allow for planning of thyroidectomy in the second trimester, if indicated). Suspicion of non-DTC pathology, such as MTC and ATC, should warrant strong consideration of early surgery. 

 

The optimal timing of surgery in the peri-partum period is uncertain.  Whist many women undergo safe surgery and anesthesia in the second trimester, small risks for mother and fetus remain. However, deferring surgery to the post-partum period potentially disrupts dyadic attachment between mother and child, and may interrupt breast-feeding. As evidence is lacking, patient-centered decision making, with inputs from a multi-disciplinary team, is appropriate. 

 

Small case series support a strategy of deferred surgery for low-risk lesions. For example, 19 women with PTC diagnosed around the time of conception were followed sonographically in pregnancy (41). Nearly 70% were microcarcinomas, and 3 cases had sonographic N1 disease. During pregnancy, 3 tumors had a detectable increase in maximal diameter, while 5 increased in volume. In 2 out of 3 with N1 disease, lymph nodes increased in size although no new nodal disease was detected, and the extent of surgery was not changed. Post-partum, 16 cases proceeded to surgery around 12 months following diagnosis.

 

Maternal Supportive Management During Pregnancy

 

Thyroid stimulating hormone (TSH) is a trophic factor for follicular thyroid cells and is associated with progression of thyroid cancer (23). However, there is no evidence to support the practice of pharmacological suppression of TSH to minimize growth of a primary tumor in pregnancy, and exogenous maternal hyperthyroidism is associated with fetal risk.  Maintaining maternal serum TSH within the lower half of the pregnancy-specific reference range is a reasonable therapeutic goal, and levothyroxine should be initiated, if required, to achieve this target.

 

Dietary iodine should not be restricted, as it is essential for fetal thyroid development.  Maternal physiological demands for iodine increase in pregnancy, and maternal iodine deficiency is associated with development of goiter in the mother. 

 

A recent cohort study found that pregnancies complicated by a diagnosis of thyroid cancer prior to or during pregnancy had a higher incidence of venous thromboembolism (odds radio 2.4) and blood transfusions (odds ratio 2.1), however there was no impact on neonatal outcomes (42). Similarly, the rate of post-partum hemorrhage in women with a history of thyroid cancer was higher than controls (odds ratio 1.23) in a large retrospective observational study, however no other adverse maternal, neonatal, or child outcomes (followed to 80 months post-partum) were found (43).

 

Measurement of Serum Thyroglobulin

 

During pregnancy, maternal serum thyroglobulin levels are higher than pre-pregnancy. This may be an effect of stimulation of maternal thyrocytes by estrogen and HCG. Therefore, maternal thyroglobulin levels during pregnancy must be interpreted with caution. Maternal serum thyroglobulin levels return to baseline values within 1-6 months of pregnancy (44-46).  In general, thyroglobulin status should be assessed no earlier than 6 weeks post-partum. 

 

Considerations in the Planning of Radioiodine Therapy

 

Radioactive iodine therapy following total thyroidectomy, either for remnant ablation, or as adjuvant therapy, is recommended for a subset of DTC with higher risk of recurrence (32).  The administration of radioiodine following pregnancy poses unique challenges, both medically and socially. Firstly, radiation safety precautions necessitate that close contact between the mother and her infant (as well as other young children) must be avoided for around 7 days following a radioactive iodine dose (precise recommendations are determined at the time of therapy) (47). Radioactive iodine is contra-indicated in pregnancy, and if administered, the risks to the fetus must be carefully assessed, based on administered dose and gestational age (48). Secondly, breast tissue expresses the sodium-iodide symporter, which is upregulated during lactation to concentrate iodine in breast milk (48, 49).  Consequently, to minimize exposure of breast tissue to ionizing radiation, lactation should cease a minimum of 8 weeks before radioactive iodine and should not be recommenced so as to avoid potential breast-milk associated radioactive iodine exposure. 

 

In light of this, the timing of radioactive iodine (if required) should be considered, balancing the potential risk of DTC progression without treatment, the benefits of a period of breastfeeding, and family unit dynamics. The literature is conflicting as to whether radioiodine administered early (within 3 months) or late (within 12 months), has any impact on prognosis. For example, a large retrospective database study including more than 9,000 patients diagnosed with high-risk PTC (primary tumor >4cm, N1 disease, positive surgical margins) found that timing of radioactive iodine within the first 12 months did not impact mortality (the median survival in this cohort was 75 months), after adjustment for confounders (50). In contrast, a small retrospective study of patients with lower risk DTC (235 cases classified as either ATA Low- or ATA-Intermediate- risk) found that deferring radioactive iodine longer than 3 months post-operatively was associated with higher rates of biochemical incomplete or structural incomplete responses compared to earlier radioactive iodine ablation(19% vs 4%) (51).

 

PRE-CONCEPTION CARE OF WOMEN WITH A HISTORY OF THYROID CANCER             

 

Pregnancy following diagnosis and treatment for thyroid cancer is common, and presents specialized management issues. Nonetheless, excellent obstetric outcomes are expected (52).  Pre-conception counselling is recommended for all women with a past history of thyroid cancer.

 

Checklist: Management issues prior to pregnancy in survivors of thyroid cancer.

 

  1. Assessment of thyroid cancer status:
    • Remission? Assessment of disease status: structural and biochemical
    • Potential impact of pregnancy on disease progression
  2. Impact of prior radioiodine therapy on timing of conception and future fertility
    • Ensure > 6 months between radioactive iodine and conception
  3. Thyroid hormone replacement
    • Pre-pregnancy optimization of levothyroxine replacement
    • Pre-emptive adjustment to levothyroxine dosing following conception
    • Potential for unmasking thyroid hormone insufficiency in women with sufficient pre-pregnancy thyroid hormones from a residual hemithyroid
    • Use of pregnancy supplements that may interfere with levothyroxine absorption

 

Establishment of Thyroid Cancer Status

 

To provide a framework for discussing the potential impact of thyroid cancer on pregnancy, an assessment of disease status is valuable, such as recommended by the ATA in its 2015 guidance (Table 1) (32). Evidently, counselling and management discussions will differ depending on what treatment has previously been received (total thyroidectomy vs hemithyroidectomy), the presence of any functional thyroid hormone production (if prior hemithyroidectomy only), the timing of any radioactive iodine administration, and the presence of any residual cancer. MicroPTC under active surveillance is a distinct management issue which is discussed separately.

 

Table 1. 2015 American Thyroid Association Risk Stratification for DTC

2015 ATA Response-to-Therapy classification

Description

Excellent response

No clinical, biochemical or structural evidence of persistent or recurrent thyroid cancer.

Biochemical-incomplete response

Elevated serum thyroglobulin, or rising anti-thyroglobulin antibodies, in the absence of structural disease identifiable on imaging.

Structural-incomplete response

Persistent or recurrent thyroid cancer visible on imaging, either in neck or distant metastases

Indeterminate response

Non-specific biochemical or structural findings that are not able to be classified as benign or malignant (includes stable/declining anti-thyroglobulin antibody levels without evidence of structural disease)

2015 American Thyroid Association Risk Stratification for DTC, tabulated from Haugen et al. (2016).  Refer to ATA Guideline (32) for full discussion of each class and qualifying criteria (Table 13).

 

In women with a history of MTC, the tumor markers calcitonin and CEA are sensitive to detect residual or recurrent disease, and allow for post-operative risk stratification (53).  There are no studies examining whether pregnancy impacts the prognosis of MTC. 

 

Discussing Impact of Pregnancy on Risk of Recurrence

 

There is a growing body of evidence reporting the long-term oncological outcomes in the setting of pregnancy following treatment for thyroid cancer. Key studies are reviewed below.

 

Leboeuf et al. (46) reported outcomes of 36 women between 1997 and 2006, with pregnancy a median 4 years following treatment for DTC. Three women had structural disease present prior to pregnancy, and of these, one showed growth in a cervical lymph node. A further two women developed recurrence following pregnancy that was not present on pre-operative physical examination. Of the full cohort, 22% had a sustained >20% rise in serum thyroglobulin post-partum. 

 

Rosario et al. (54) describe the outcome of 64 pregnancies, occurring a median of 2.4 years after treatment for DTC. In this cohort, no patient had evidence of structural disease either prior to or following pregnancy. Of the subset 49 women with undetectable thyroglobulin prior to pregnancy, this remained undetectable in the post-partum period. Of the 8 patients with low level thyroglobulin prior to pregnancy, no significant post-partum change was observed. 

 

Hirsch et al. (55) studied the outcome of 63 women, where pregnancy occurred a median of 5 years after treatment for PTC.  Of the subset of 6 women with known structural disease prior to conception, 80% were found to have progressed within 12 months of birth (2 with biochemical progression, 3 with structural progression). Of the subset of 5 women with detectable pre-pregnancy thyroglobulin, no significant change was observed post-partum.  Of the remaining 39 women with undetectable pre-pregnancy thyroglobulin, no progression was observed. 

 

Finally, Rakhlin et al. reported the outcome of pregnancy in 235 women following treatment for DTC (56), retrospectively grouped into ATA Response to Therapy criteria (Table 1).  In the 197 women without structural disease prior to pregnancy, no new structural disease was detected following post-partum evaluation.  However, 8% had a significant rise in thyroglobulin.

 

Overall, these data are reassuring that women with an ATA Excellent response to therapy have a very low risk of DTC progression occurring during pregnancy, and a low risk of DTC progression following pregnancy. As such, additional monitoring of thyroid cancer status during pregnancy for these women is not required (34). 

 

However, women with biochemical or structural evidence of disease may have a progression of their thyroid cancer status as a result of pregnancy.  Based on the above studies, the degree of disease progression appears minor, only affects a subset of women, and does not appear to have an impact on the outcome of the pregnancy. 

 

Reducing the Impacts of Prior Thyroid Cancer Treatment on Pregnancy.

 

LEVOTHYROXINE REPLACEMENT  

 

It is essential that all women who are planning pregnancy receive written instructions for the management of thyroid hormone replacement prior to, and immediately following conception.  Requirements for thyroid hormone rise early in gestation, in part as a result of an increase in thyroid-binding globulin. Adequate levels of thyroid hormones are required for healthy fetal development and pregnancy progression.

 

Women previously treated with hemithyroidectomy may unmask relative thyroid hormone deficiency following conception, and may require early initiation of levothyroxine therapy in the first trimester.

 

Women who have been treated with total thyroidectomy will always require an increase in thyroid hormone replacement at conception, of a magnitude between 15-40% of the total weekly dose. A common practice is to advise women to “double the dose” of levothyroxine that they take on two days of the week as soon as pregnancy is confirmed, with further adjustment based on regular thyroid function tests throughout pregnancy (34, 57). Women who adhered to this advice were more likely to have TSH at the pregnancy target than those that deferred thyroxine adjustment until the first specialist consultation (58). 

 

Importantly, pregnancy multivitamins, iron supplements, or calcium supplements may interfere with the absorption of thyroxine, and women should be specifically instructed to take such supplements at a different time of day to minimize interference (59). 

 

Women should be reassured that levothyroxine is both safe and essential for a healthy pregnancy, as inadvertent discontinuation in early pregnancy has been reported (60). In most cases, the TSH target prior to pregnancy (usually targeting the lower half of the normal range) will remain appropriate in pregnancy. Pharmacological suppression of TSH with supra-physiological doses of levothyroxine could be continued in the setting of persistent structural disease, however care should be taken to avoid overt hyperthyroidism, which increases pregnancy risk. In settings where a TSH-suppression strategy has been pursued outside of pregnancy, but in the absence of known structural disease, a careful balancing of risk and benefit should be considered, as although mild hyperthyroidism in pregnancy has not been shown to lead to maternal or fetal complications, greater degrees of hyperthyroidism are associated with adverse pregnancy outcomes (34, 61, 62).

 

IMPLICATIONS OF PREVIOUS RADIOIODINE  

 

Women should defer conception for at least 6 months after radioactive iodine administration.  This period includes the expected time for radioactive iodine to fully decay (approximately 10 weeks), thus avoiding exposing the fetus to gamma-particle emission). A recent large population-based cohort study found that pregnancy occurring within 5 months of radioactive iodine had a higher rate of congenital malformations (odds ratio 1.74, 95%CI, 1.01-2.97; P = .04), which was not seen if conception occurred after 6 months (63). Deferring pregnancy for at least 6 months has the additional benefit of permitting assessment of the response to radioactive iodine therapy, and to determine that no additional treatment with radioactive iodine would be recommended in the following 15 months (conception, pregnancy and the post-partum period) (64). Stabilization of levothyroxine replacement can also take a period of months.

 

In the 12 months following radioactive iodine, 8-16% of women experience amenorrhea, and 12-31% have menstrual irregularities (65). Several studies (including a meta-analysis) have confirmed a small but significant fall in AMH levels following radioactive iodine, and a slightly earlier age of menopause than women who did not receive radioactive iodine (49.5 vs 51 years) (65, 66). 

 

Most studies have not shown that radioactive iodine has an impact on future fertility (65, 67, 68). However, in a retrospective database study comparing survivors of thyroid cancer, women in the age 35-39 subgroup who received radioactive iodine had a lower birth rate (11 vs 16 births per 1000 woman-years) than women who did not receive radioactive iodine.  However, as the time from diagnosis of thyroid cancer to first live birth was also prolonged in this study, it is not clear whether this finding is due to physician recommendation to delay pregnancy, or the biological effects of radioactive iodine (68). In addition, a recent population case-control study found a higher rate of infertility diagnosis amongst survivors of thyroid cancer (69), however this analysis did not take into account any disease-specific factors such as type of treatment received. 

 

In women with a history of thyroid cancer requiring assisted reproductive techniques, pregnancy outcomes were not different compared to controls, although the number of retrieved oocytes was lower (70). A history of radioactive iodine treatment was not associated with differing rates of clinical pregnancy or live birth rates in this group (71).

 

A large longitudinal study followed 2,673 pregnancies and did not show an increase in maternal or fetal adverse events in women previously administered radioactive iodine (72).  A population-based cohort study of women with thyroid cancer in Korea, comparing 59,483 women who underwent thyroidectomy alone, with 51,976 women who had thyroidectomy followed by radioactive iodine found no difference in pregnancy or obstetric outcomes in the 9.7% of the cohort where pregnancy occurred (63). A further systematic review (67), and meta-analysis (73), pooling additional studies reported similar findings, providing sufficient time had elapsed following radioactive iodine administration. 

 

In men, radioactive iodine may transiently impact testicular function, with a short-term rise in FSH, and decrease in normal sperm morphology seen in prospective studies (74). It is suggested that men avoid fathering children for 4 months following radioactive iodine (75, 76). In men who desire fertility, and who are expected to require high cumulative activities of radioactive iodine, sperm banking should be considered. 

 

Surveillance and Monitoring During Pregnancy

 

Based on available data, women with no structural or biochemical evidence of thyroid cancer do not require DTC-specific monitoring during pregnancy. At present, there is no evidence to guide whether additional post-partum surveillance should be instituted beyond that woman’s current surveillance strategy, however consideration of neck ultrasound and serum thyroglobulin at least 6 months post-partum is reasonable. 

 

For women with ‘ATA Biochemical Incomplete’ or ‘ATA Indeterminate’ classification, surveillance during pregnancy could include periodic neck ultrasound, and determination of thyroglobulin and Tg-Ab levels. Clear evidence of progression of thyroid cancer could prompt an increase in the level of TSH suppression, or rarely prompt expedited delivery. Management in the context of a multidisciplinary team is advised. 

 

CONTINUED ACTIVE SURVELLANCE OF PAPILLARY THRYOID MICROCARCINOMA DURING PREGNANCY

 

Non-operative management of microPTC (<10mm in maximal dimension) is increasing, with emerging data on implications for active surveillance during pregnancy. Shindo et al report 9 women with microPTC followed during pregnancy, finding demonstrable growth in 44% (compared to microPTC growth of 11% in non-pregnant controls) (77). Ito et al reported outcomes of 50 pregnancies with microPTC, finding growth of >1mm in 8%, reduced size in 2%. The remaining 90% of cases showed no growth in pregnancy, and there were no nodal metastases detected (78). Oh et al described 13 microPTC in pregnancy, with a single lesion demonstrating growth (41). The available evidence supports the continuation of active surveillance during pregnancy, monitored with periodic neck ultrasound. However, women contemplating pregnancy who are under active surveillance should be advised that a small number of microPTC will grow during pregnancy, and this may result in anxiety for the patient and clinicians. Further studies are awaited in this population (32).      

 

Germline RET Mutations

 

Women with clinically diagnosed MEN2, or who carry a germline mutation in the REarranged during Transfection (RET) proto-oncogene, should be under the care of a specialized clinical team, and should be offered detailed pre-natal genetic counselling.  Individual RET mutations can be characterized for their risk of early-onset MTC, allowing personalized management decisions. The highest risk mutations should prompt consideration of total thyroidectomy in early childhood (53). The presence of hyperparathyroidism and pheochromocytoma should be biochemically excluded prior to pregnancy in any woman with MEN2.

 

MANAGEMENT OF KNOWN RESIDUAL STRUCTURAL DISEASE IN PREGNANCY

 

Case series of pregnancy in women with co-existent thyroid cancer metastases have been reported. The largest study retrospectively studied a cohort of 124 women from China, aged 16-35 years, with lung metastases from thyroid cancer, stratified by whether pregnancy occurred (n=35) and followed for a median 68-82 months after completing treatment with radioactive iodine (79). This study found that pregnancy after thyroid cancer had no measurable difference in 5 year or 10-year progression free survival or overall survival. 10-year overall survival in the pregnancy group was 86%, compared to 82% in the non-pregnant group. Although the groups appeared to have similar characteristics, it remains possible that women who chose pregnancy had a lower severity of disease than those who avoided pregnancy. 

 

Another study retrospectively described outcomes for 38 women at a large cancer center in the USA (56). Included in the cohort were 10 women with pulmonary metastases at the time of diagnosis (and of whom 7 had persistent structural disease prior to pregnancy). During pregnancy, 29% of women had progression of structural disease (11/38, with 5/38 increasing size of known abnormal nodes, 3/38 with newly abnormal lymph nodes, and 1/38 with progression of distant metastases). In total, 3/38 (~8%) were considered “clinically significant” by the study team (required further treatment within 12 months of birth).

 

These data are reassuring that the clinical impact of pregnancy in the setting of persistent structural disease appears low, despite in vitro studies and smaller case series confirming that pregnancy represents a potentially stimulatory setting for thyroid cancer cells. 

 

In general, TSH suppression should be maintained where benefit is felt to outweigh risk to the pregnancy. Serial neck ultrasound during pregnancy will monitor the status of neck disease, however imaging the chest is usually avoided to minimize ionizing radiation to the chest. Where progression of lung metastases is to be monitored, serial lung function testing may be informative.  

 

Currently approved small molecule tyrosine kinase inhibitors have been shown to have embryotoxicity, fetotoxicity, and teratogenicity in rats and rabbits (80, 81), and pregnancy should be avoided in women on this treatment.  A case report of a pregnancy in a women treated with vandetanib up until 6 weeks gestation described no fetal adverse outcomes (82).

 

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Pathophysiology and Treatment of Pancreatic Neuroendocrine Neoplasms (PNENS): New Developments

ABSTRACT  

 

Pancreatic neuroendocrine neoplasms (PNENs) are a heterogenous group of relatively rare pancreatic malignancies with a unique biology and pathophysiology. Over the last few years, there have been significant improvements in imaging and treatment strategies, which have led to advances in patient’s management and quality of life (QOL). Yet, in practice, there are still a number of unanswered questions. For example, it remains a challenge to choose the optimal treatment sequence from the plethora of options and to properly monitor PNEN patients. Therefore, in this chapter, recent advances in the pathophysiology, diagnosis, monitoring, and management of these neoplasms will be summarized and placed in a historical context.

 

INTRODUCTION  

 

Pancreatic neuroendocrine neoplasms (PNENs) are an uncommon subset of neuroendocrine neoplasms (NENs) originating from endocrine cells (1-3). PNENs represent 1-2% of all pancreatic neoplasms and according to the Surveillance, Epidemiology and End Results (SEER) program, the annual age-adjusted incidence has risen from 0.32/100,000 persons in 2004 to 0.48/100,000 persons in 2021 (2, 4-7). Improvements in and a wider availability of high-quality imaging techniques and a well-established classification system are believed to be major factors in the increasing incidence of PNENs (5, 8, 9).

 

PNENs can be divided into both functional (10-40%) and non-functional (60-90%) neoplasms (2, 6, 7, 10, 11). Functional PNENs (F-PNENs) are characterized by a specific clinical course and symptoms due to excessive hormone production (e.g., insulin, gastrin) (10-12). The most frequent, recognized F-PNENs are listed in Table 1 (1). Less common F-PNENs include somatostatinomas, ACTHomas and PNENs that cause carcinoid syndrome, acromegaly, or hypercalcemia (2). Patients with non-functional PNENs (NF-PNENs) lack symptoms related to clinical hormonal syndromes and are therefore usually diagnosed at a more advanced stage with characteristically large primary tumors (70% >5 cm) and liver metastasis in more than 60% of the cases (2, 9, 12, 13). NF-PNENs are hence frequently discovered by chance on imaging studies performed due to nonspecific abdominal pain, often caused by tumor bulk (2, 9, 12, 14). Although NF-PNENs do not secrete peptides causing clinical syndromes, they characteristically secrete a number of other peptides including chromogranin A (CgA) and pancreatic polypeptide (PP). However, elevated levels of PP or CgA are not specific for NF-PNENs as they are also observed in patients with renal failure and inflammatory conditions (2, 9, 12-14).

 

Table 1. Overview of Recognized Functional PNENs and Their Characteristics

Tumor

[syndrome]

Hormone

Clinical symptoms

Biochemical diagnosis

Insulinoma

[Whipple’s triad]

Insulin

Hypoglycemia

At hypoglycemia:

Insulin > 6 µU/L

Glucose 40 mg/dL

C-peptide 0.6 ng/mL

Proinsulin ³ 20 pmol/L

Gastrinoma

[Zollinger-Ellison]

Gastrin

Abdominal pain, Gastroesophageal reflux, Diarrhea, Duodenal ulcers

Serum fasting gastrin level ³ 10 times normal range

VIPoma

[Verner-Morrison]

Vasoactive intestinal peptide (VIP)

Severe watery diarrhea, Hypokalemia

Fasting serum VIP > 60 pmol/L

Glucagonoma

Glucagon

Rash, Glucose intolerance (diabetes), Necrolytic migratory erythema, Weight loss

Fasting glucagon > 500 pg/mL

Note: This table was assembled based on information from Gastroenterology, Metz D. and Jensen R., Gastrointestinal neuroendocrine tumors: Pancreatic Endocrine tumors, 1469-1492 © 2008 (2) and World Journal of Gastroenterology, Ma Z., Gong Y., Zhuang H. et al., Pancreatic neuroendocrine tumors: A review of serum biomarkers, staging and management, 2305-2322 © 2020 (7) and Current Opinion in Gastroenterology, Perri G., Prakash L. and Katz M., Pancreatic neuroendocrine tumors, 468-477 © 2019 (3).  

 

CLASSIFICATION AND STAGING  

 

The World Health Organization (WHO) classification from 2019 (Table 2) takes into account both differentiation status and proliferation rate of the tumor. The former is determined through a histological examination of tumor morphology in which well-differentiated neuroendocrine tumors (NETs) can be distinguished from poorly differentiated neuroendocrine carcinomas (NECs). A grade is then assigned based on the proliferation rate assessed via Ki-67 index and mitotic count. Well-differentiated NETs can be divided into low grade (G1), intermediate grade (G2), and high grade (G3) tumors that have respective Ki-67 values of <3%, 3-20%, and >20% or mitotic counts of <2, 2-20, and >20 per 2mm³ (10 high power fields (HPF)). In the poorly-differentiated NEC group (small and large cell types), only high grade G3 tumors with a Ki-67 value >20 are found. In addition, neoplasms exist that consist of neuroendocrine cells as well as non-neuroendocrine adenocarcinoma or squamous carcinoma cells (i.e., mixed non-neuroendocrine-neuroendocrine neoplasms (MiNEN)) (3, 6-8, 15, 16). Depending on tumor grade and primary site, the 5-year survival varies between 15-95% and median overall survival (OS) from approximately 12 years for patients with G1 to 10 months in patients with G3 PNENs (3, 17). PNENs most often occur sporadically, but can also occur in patients with various inherited disorders (2, 18). For example, PNENs develop in 80-100% of patients with Multiple Endocrine Neoplasia type 1 (MEN1), in 10-17% of patients with von Hippel-Lindau syndrome (VHL), and occasionally in patients with tuberous sclerosis and neurofibromatosis (3, 18). 

 

Table 2. WHO Classification (2019) of PNENs

Type

Differentiation status

Grade

Proliferation rate

Ki-67 (%)

Mitotic count (2mm²)

NEN

Well-differentiated NETs

G1

< 3

< 2

G2

3 – 20

2 – 20

G3

> 20

> 20

Poorly-differentiated NECs

Small cell (SCNECs)

Large cell (LCNECs)

G3

> 20

> 20

MiNEN

NET or NEC + ADC or SCC

G1-G3

See above

See above

Note: This table was adapted from Histopathology, Nagtegaal I., Odze R., Klimstra D. et al., The 2019 WHO classification of tumours of the digestive system, 182-188. © 2019 (16). NEC- neuroendocrine carcinomas; NET- neuroendocrine tumors; ADC- adenocarcinoma cells; SCC- squamous carcinoma cells

 

PNENs are also classified based on the tumor-node-metastasis (TNM) classification which estimates the prognosis of the tumors based on the anatomy of the tumor (3). Previously there was no generally accepted staging system, so in Europe usually the European Neuroendocrine Tumor Society (ENETS) staging system was applied, while in America the America Joint Committee on Cancer (AJCC)/Union for International Cancer Control (UICC) system was being used (19-21). In the 7th edition of the AJCC/UICC, the same ordering system was employed for PNENs as for pancreatic adenocarcinoma (PAAD), but due to biological differences between both tumor types, this staging system proved to have some limitations (19, 20). Consequently, in the revised 8th edition of the AJCC/UICC, the classification system of ENETS was implemented (21). Two research groups demonstrated that the system employed in this 8thedition was superior to that of the 7th edition as well as the ENETS staging system and should be considered as golden standard (20, 22).

 

INDUCTION OF PNENs

 

PNENs are also often referred to as islet cell tumors since it is presumed that they arise from the islets of Langerhans (3, 23, 24). These islets contain A-, B-, D-, D1-, and D2-cells that respectively secrete glucagon, insulin, somatostatin, pancreatic polypeptide, and vasoactive intestinal polypeptide (VIP) (25). Logically, the F-PNENs most definitely arise from these cells, but the cell of origin in NF-PNENs is still a matter of debate (26, 27). Chan et al. revealed that NF-PNENs with ATRX, DAXX, and MEN1 mutations (A-D-M mutant) had a worse clinical outcome than A-D-M wild-type (WT) tumors. In addition, they were able to demonstrate, through RNA sequencing and DNA methylation analysis, that the A-D-M mutant PNENs had high ARX and low PDX1 expression which is consistent with the expression profile found in a-cells (28). Cejas et al. found that NF-PNENs could be divided into two subgroups with epigenomes and transcriptomes very similar to those of a- and b-cells, respectively (29). These findings were confirmed by Di Domenico and colleagues who were able to demonstrate that the genome-wide DNA methylation profiles of NF-PNENs were very consistent with the methylation profiles of a- and b-cells (24). Based on these findings, it was hypothesized that NF-PNENs evolve primarily but not exclusively from the a-cell lineage and b-cell lineage (27).

Figure 1. Visualization of the pancreatic duct glandular structures (PDGs) (arrowheads) in (A) large and (B) small ducts using scanning electron microscopy (SEM). PDGs can occur as single outpouches or form a complex of sac-like dilatations as illustrated in (C). This figure has been adapted from Gastroenterology, Strobel O., Rosow D. E., Rakhlin E. Y., et al., Pancreatic duct glands are distinct ductal compartments that react to chronic injury and mediate Shh-induced metaplasia, 138 (3): 1166-77 © 2010 (30).

Others in turn suggest that PNENs develop from multipotent pancreatic progenitor (MPP) cells in the ductal and islet regions of the pancreas that would be able to generate new pancreatic islet cells (31, 32). However, it remains unclear whether these cells originate in the islets or whether they migrate from the pancreatic ducts to subsequently transform into endocrine cells (33). This hypothesis is strengthened by the fact that early endocrine progenitors in fact appear to originate from a bipotent ductal endocrine progenitor, which in turn originates from MPP cells (34). However, not a lot is known about where these MPP cells are present. One hypothesis states these could be present in the pancreatic duct glandular structures (PDGs) that can be found as specialized compartments with a gland-like outpouching look (Figure 1) in the ductal epithelium (30, 35). The actual origin and location of the MPP that can evolve into islet cells is not known to date and thus needs to be further investigated for a better understanding of the potential origin of PNENs.

 

MOLECULAR (EPI)GENETICS  

 

Genetic Syndromes

 

Although PNENs typically occur sporadically, approximately 10-20% of them develop in the context of hereditary syndromes. The syndrome most at risk for PNEN development is Multiple Endocrine Neoplasia (MEN1) (60%), an autosomal dominant disease caused by inactivating mutations in the MEN1 gene (10, 36-39). MEN1 is a tumor suppressor gene located on chromosome 11q13 that encodes for the nuclear protein menin which plays an important role in the PI3K/Akt/mTOR pathway, histone modifications, DNA repair mechanisms, and cell cycle control (10, 37, 38, 40, 41). In addition, 5 to 18% of the patients with von Hippel-Lindau (VHL) syndrome develop PNENs. These patients carry a germline mutation in the VHL gene located on the short arm of chromosome 3. The VHL protein can be found in different complexes that mediate ubiquitin-mediated degradation and stimulate angiogenesis (10, 42, 43). Other hereditary syndromes at risk include Tuberous Sclerosis (TS) and neurofibromatosis type 1, caused by mutations in TSC1, TSC2 and NF1, respectively (36-39).

 

Sporadic PNENS  

 

Through next-generation sequencing of PNENs, it became apparent that there are distinct genetic differences, strongly depending on differentiation and functionality of the tumor (36).

For example, genetic analyses of F-PNENs revealed that insulinomas are often characterized by a hotspot mutation (p. T372R) in the Yin Yang 1 (YY1) gene in 30% of the Asian and 8-33% of the Western/Caucasian population (10, 36, 44). This recurrent mutation is located in the DNA binding domain of YY1, hence strongly affecting the DNA binding capacity of this transcriptional activator/repressor (44). In NF-PNENs, on the other hand, somatic mutations were most commonly identified in MEN1 (44.1%) followed by DAXX (25%) and ATRX (17.6%) (41). Atrx interacts with DNA methyltransferases (DNMT) 3A and 3L to form the Atrx-DNMT3A-DNMT3L (ADD) complex. This interaction is crucial for maintenance of histone methylation patterns in newly replicated chromatin, hence indirectly ensures correct gene expression. Moreover, Atrx also interacts directly with Daxx. In doing so, Daxx functions as a kind of chaperone for the deposition of histone variant H3.3 at the level of CpG islands, telomeric and ribosomal repeats and the rest of the genome. Consequently, a loss of ATRX and DAXX results in changes in DNA methylation patterns throughout the genome (45). In addition, mutations in PTEN, TSC2, and PIK3CA have already been reported in respectively 7.8%, 8.8% and 1.4% of PNENs, and they all affect the PI3K/Akt/mTOR pathway (41). Later, Scarpa and colleagues identified mutations in DNA repair genes MUTYH, CHEK2, and BRCA2 as well (39).

 

Distinct genetic differences could also be observed between G3 pancreatic NETs (PNETs) and pancreatic NECs (PNECs). The latter do not carry mutations in the known genes for PNETs (MEN1, DAXX, and ATRX), but instead appear to have mutations in TP53, RB1, KRAS, and CDKN2A/p16 (10, 36, 38). Considering that these mutations tend to result in altered protein expression, IHC might facilitate in distinguishing PNETs from PNECs, which have similar Ki-67 values. Nevertheless, results should always be interpreted with caution (10, 36, 46). 

 

Besides point mutations, copy number alterations (CNAs) have also attracted attention. CNA patterns that were frequently identified included whole or partial loss of chromosomes 1, 2, 3, 6, 8, 10, 11, 15, 16, 21 and 22, while gains have been observed in chromosomes 5, 7, 12,14 and 17 (10). Moreover, PNENs appear to display very specific CNA patterns that allow to distinguish PNENs from the more common PAADs. Boons and colleagues therefore developed a classification model, based on tumor tissue, which demonstrated a sensitivity, specificity and area under the curve (AUC) of 100%, 95% and 100% in the validation cohort (47). Benign insulinomas tend to display lower rates of CNAs (36).        

 

Since genes such as MEN1, DAXX and ATRX are of importance in several epigenetic regulatory processes, it was extremely likely that also epigenetic alterations commonly occur in PNENs. In fact, both in hereditary and sporadic PNENs promotor hypermethylation is observed in tumor suppressor genes, which is associated with silencing of gene expression (10, 48). Chan and colleagues checked whether methylation profiles and expression were different in the A-D-M mutated group versus the A-D-M WT group. They observed that both groups clustered in two separate clusters and even revealed that gene expression of the A-D-M mutated group was respectively high and low in the ARX and PDX1 gene and the latter gene also displayed hypermethylation. This profile appeared to be quite similar to that of acells in the pancreas (28). These results were confirmed by Neiman et al., who observed high methylation levels in the PDX1 promotor region in a cells, while β cells tend to have low methylation in this region (49). Based on this PDX1 gene methylation, Boons and colleagues performed unsupervised hierarchical clustering and could subsequently observe two subpopulations, A and B, which respectively contained the a and β cells. Of note, the majority of the mutated PNENs was found in group A confirming the findings of Chan et al. (28, 50). These results suggest that methylation profiling of the PDX1 gene could potentially help to divide PNENs into distinct clinically relevant groups that have different prognosis and risk of relapse (50). Recently, three subgroups (T1, T2 and T3) of PNENs have been identified, based on their methylation profile. Here, the T1 group consisted of the A-D-M WT tumors, while the T2 subgroup encompassed the A-D-M mutated tumors with recurrent chromosomal losses and methylation in the gene body of the MGMT gene. The last group, T3, displayed mutations in MEN1 and recurrent loss of chromosome 11. Tumors found in the latter group tend to have a better prognosis (51).   

 

DIAGNOSIS AND MONITORING           

 

The gold standard for diagnosing PNENs remains an immunohistochemical examination of the tumor tissue, but imaging and serum markers are also extremely important in the diagnostic process. The clinical presentation often determines the sequence of examinations. For example, patients with F-PNENs will usually undergo a biochemical blood analysis first based on their hormonal symptoms, whereas NF-PNENs are often detected by chance on imaging (25, 52, 53).  

 

Immunohistochemistry

 

To correctly classify PNENs, tumor morphology and proliferation rates (Ki-67 and mitotic index) should be evaluated in tissue biopsies. These are usually obtained from surgical specimens, percutaneous core biopsies, or preoperative biopsies (52, 54, 55). The latter were mainly derived from endoscopic ultrasound (EUS) guided fine-needle aspirations (FNA) which, in recent years, have been increasingly replaced by fine-needle biopsies (FNB) as these enable histological tissue samples to be obtained, hence immunohistochemistry (IHC) to be performed (56, 57). This immunohistochemical examination is most often initiated by confirming the neuroendocrine differentiation by checking CgA and synaptophysin (SYP) expression (52, 54). Other markers such as neuron-specific enolase (NSE) and CD56 are less specific, hence less useful (58). Next, tumor morphology is assessed to determine whether the PNEN is well- or poorly-differentiated (Figure 2). In general, well-differentiated PNENs are characterized by uniform cells with a finely granular cytoplasm and round to oval nucleus which are arranged in a trabecular, glandular, or tubuloacinar pattern (54, 59). Moreover, typically all cells have a heterogeneous expression of CgA in their cytoplasm, whereas SYP stains more diffusely. Poorly-differentiated PNECs, on the other hand, consist of atypical neoplastic cells that often lack CgA and even SYP (59, 60). Ultimately, tumors are graded by proliferation rate that is influenced by two parameters, Ki-67 and mitotic count. The latter is usually reported as the number of mitoses per mm² which in practice is often complicated by a limited tissue area. The mitotically active regions are then measured again via IHC to determine the Ki-67 index (Figure 3). It is therefore logical that the Ki-67 index is usually higher than the mitotic count since it considers the entire mitotic process and not just the number of mitoses. If both values assign a different grade to the same tumor, the highest grade, associated with the worst prognosis, is assumed (17, 23, 52, 54).

Figure 2. Hematoxylin-eosin IHC staining of (A) well-differentiated PNET and (B) poorly-differentiated PNEC. This figure has been adapted from Archives of Pathology & Laboratory Medicine, Fang J. M. and Shi J., A clinicopathologic and molecular update of pancreatic neuroendocrine neoplasms with a focus on the new world health organization classification, 143 (11): 1317-1326. © 2019 (59).

Figure 3. (A) PNEN G1 with Ki-67 index of less than 3%. (B) PNEN G2 with Ki-67 index of 3% to 20%. (C) PNEN G3 with Ki-67 index higher than 20%. This figure has been adapted from Archives of Pathology & Laboratory Medicine, Fang J. M. and Shi J., A clinicopathologic and molecular update of pancreatic neuroendocrine neoplasms with a focus on the new world health organization classification, 143 (11): 1317-1326. © 2019 (59).

Imaging

 

Regardless of whether a PNEN is functional or non-functional, imaging is critical to assess the extent of the disease by localizing the primary tumor and identifying the size of metastatic disease. Localization is required preoperatively to increase the accuracy of intraoperative techniques and to reduce the need for repeated surgery. Besides, imaging is involved in patient’s management as it allows to monitor tumor growth and evaluate response to treatment (2, 25, 53, 55, 61). A multimodal approach is applied to diagnose and stage PNENs which comprises both anatomical and functional imaging modalities (2, 61-66).

 

ANATOMIC IMAGING   

 

Anatomical imaging modalities such as Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) are capable of depicting normal and diseased tissue at high spatial resolution (67). Contrast enhanced CT is the most commonly used and preferred modality as it is widely available, renders clear anatomical images of the pancreas, lymph nodes, and liver metastasis and allows to assess vascular invasion and resectability (25, 52, 62, 64, 68, 69). The more recent, multiphase multidetector CT scan exhibits even more advantages including reduced artifacts due to rapid scan time, improved arterial phase images due to accurate contrast medium tracking and improved resolution by generating thinner slices that can be studied in different anatomical planes (61, 65). In addition, the frequent hypervascular nature of PNENs results in typical high contrast uptake in the arterial phase on CT which can aid in differentiating from pancreatic adenocarcinoma. The average sensitivity of contrast-enhanced CT varies from 63% to 83% and detection rates range from 69% to 94.3% (52, 67, 70). It appears that imaging of PNENs is often influenced by their biological heterogeneity. For example, gastrinoma become more apparent on postcontrast images and large NF-PNENs often have a necrotic or cystic appearance which tend to complicate diagnosis with imaging alone. In the latter case, MRI can be useful as cystic neoplasms can be better visualized due to the higher resolution, rendering MRI complementary to CT. MRI displays a similar sensitivity to CT (79%), but has some advantages over CT as it displays a good sensitivity even without administration of contrast agents, employs non-ionizing radiation, and is hence safer for patient follow-up (52, 53, 67). Limitations on the other hand include a higher frequency of motion-related artifacts as well as a longer acquisition time compared to CT (71).

 

Still, both conventional imaging modalities depend to a large extent on the tumor size (2, 25, 61, 72, 73). More than 70% of PNENs larger than 3 cm are detected, but only 50% of PNENs smaller than 1 cm are identified. As a result, small primary PNENs, especially insulinoma and duodenal gastrinoma, are frequently missed as well as small liver metastases (2, 25, 61, 62, 72-74). For small PNENs, which cannot be detected using CT and MRI, EUS is considered the predominant imaging technique (68). Because of the high spatial resolution of this modality, it is possible to localize even very small lesions (2-3 mm) (3, 74). Additionally, it is feasible to obtain high yield tissue samples by means of an FNA/B that can be used for Ki-67 measurements. Such EUS-FNA/B have a diagnostic accuracy of 80% for pancreatic adenocarcinoma and 46% for PNENs. In patients with proven insulinoma, EUS displays a sensitivity of 94% as a first-line modality. This renders EUS extremely valuable for localizing primary insulinoma (2, 68, 74, 75). However, EUS is not generally available, can be technically challenging, and results are operator dependent. In the hands of an expert, sensitivities of 79 to 100% can be achieved (61).  

 

FUNCTIONAL IMAGING  

 

Prior to the development of the current functional imaging modalities, selective angiography and sampling for hormone gradients were employed. However, due to the highly invasive nature of these techniques, minimally invasive modalities were developed which had a great impact on patient management (2, 53, 64).

 

Although PNENs exhibit highly heterogeneous biological behavior, 80-100% of PNENs, with the exception of insulinomas (50-70%), overexpress the G-linked protein somatostatin receptors (SSTRs), mainly subtypes SSTR-2 and -5. These receptors interact with somatostatin, a peptide hormone that affects neurotransmission and cell proliferation, but also the secretion of various compounds in the digestive system (2, 52, 62-64, 67, 76). Interestingly, these SSTRs also bind synthetic, radiolabeled somatostatin analogs (SSAs) with high affinity, which constitutes the basis of the primary functional imaging tool for PNENs, namely Somatostatin Receptor Imaging (SRI). SRI will not only allow to stage PNENs, but will also predictively identify patients eligible for SSA therapy (2, 52, 53, 64, 67, 68). One of the first SSAs used to target the SSTRs was octreotide labeled with 111Indium via chelator, diethylene-triamine-pentaaceticacid (DTPA). This 111In-DTPA-octreotide emits gamma rays that are detected 24 hours after intravenous injection using Single Photon Emission CT (SPECT) or SPECT/CT, the so-called Octreoscan® (53, 62, 64, 70, 77). The Octreoscan® is often combined with CT to improve the anatomic localization making it highly sensitive (77%), detecting 50-70% of primary PNENs, but less of the insulinomas and duodenal gastrinomas (2, 62-64, 68, 78-81). Major drawbacks include the availability and price of 111In-DTPA octreotide, the staggering acquisition time as well as the intrinsic shortcomings of SPECT, such as low spatial resolution (8-12 mm) (67, 82).

 

Positron Emission Tomography (PET) could provide better spatial resolution and greater precision (71). One of the most widely employed PET radiotracers currently used to image tumors is 18Fluor-labeled deoxy-glucose (18FDG). For high-grade NETs, especially NECs, 18FDG-PET/CT is a better choice as nuclear medicine modality as SSTR expression decreases when proliferation rates increase. 18FDG-PET can even be positive in G2 and G3 NETs. To this date, no cut-off value has been determined. However, it seems like neoplasms with Ki-67 values > 15% are more likely to exhibit a positive 18FDG-PET/CT, which is also a predictor of a more aggressive course (53, 81, 83, 84). However, 18FDG-PET/CT appears to be less useful in the majority of PNENs as these often show limited glucose uptake due to a rather slow growth rate (52, 64).

 

The development of new PET/CT radiotracers has been a major breakthrough in PNEN imaging. 11Carbon-5-hydroxytryptophan-labeled or 68Gallium-labeled SSAs including DOTA-tyrosine-3-octreotide (DOTA-TOC), DOTA-octreotate (DOTA-TATE), and DOTA-1-NaI-octreotide (DOTA-NOC) showed better sensitivity and diagnostic accuracy than the conventional imaging studies (Figure 4) and the Octreoscan® (Figure 5) (2, 52, 64, 71, 85-87). A meta-analysis revealed that 68Ga-DOTA-SSA PET for the diagnosis of NETs has a pooled sensitivity and specificity of 93% and 91%, respectively (88). Admittedly, the majority of the studies involved heterogenous populations, but most included a sizable minority of 20-30% PNENs. Hence, the overall data, although far from perfect, support use of 68Ga-DOTA-SSA PET over the Octreoscan® (89). Moreover, it is highly sensitive for the detection of bony metastases and it might obviate the need for additional radiologic studies. In addition to a higher sensitivity, other advantages of 68Ga-DOTA-SSA PET include patient convenience (imaging sessions take 70-90 minutes instead of 24 hours), lower radiation exposure, utility in finding unknown primary PNENs and it can lead to changes in treatment plans in about 33-41% of the patients (67, 89-93). 68Ga-DOTA-SSA PET might also be better at quantifying SSTR expression which facilitates targeted therapy such as PRRT (89). Consequently, 68Ga-DOTA-SSA PET quickly became the imaging modality of choice (67, 68, 71). However, similar to other imaging studies, false positives may occur due to pancreatic uncinate process activity, inflammation, osteoblastic activity, and splenosis (94). No doubt other PET agents will follow since PNENs express a variety of receptors for which there are potential ligands. For example, insulinomas express SSTRs in 50% of the cases, so tracers targeting the glucagon-like peptide-1 (GLP-1) receptor might be more useful in those patients (80, 95, 96).

Figure 4. Overview of (A) 68Ga-PET/CT, multiphase (B) atrial and (C) portal vein CT scan images from patient with partially cystic PNEN. The arrow indicates a liver metastasis which is only visible on the 68Ga-PET/CT scan. This figure has been adapted from Current treatment options in oncology, Morse B., Al-Toubah T. and Montilla-Soler J., Anatomic and functional imaging of neuroendocrine tumors, 21 (9): 75 © 2020 (67).

Figure 5. Comparison of (A) planar Octreoscan®, (B) Octreoscan®/SPECT/CT fusion, (C) planar 68Ga-DOTATOC-PET and (D) 68Ga-DOTATOC-PET/CT in the same patient. Images C and D clearly display a more precise delineation of the lesions. This figure has been adapted from International journal of endocrine oncology, Maxwell J. E. and Howe J. R., Imaging in neuroendocrine tumors: and update for the clinician, 2 (2): 159-68 © 2015 (82).

All benefits taken into account, the FDA approved 68Ga-DOTATOC PET in 2016 in the US, after being available in Europe for a number of years. Furthermore, with the development of an FDA approved 68Ga generator, an on-site cyclotron is no longer required, making this technology more widely available. A multi-society workgroup has recommended that 68Ga-DOTA-SSA PET replace use of Octreoscan®, unless it is not accessible, in combination with at least one anatomic imaging technique (66, 70).

 

Assessment Through Circulating Biomarkers

 

As stated earlier, the current gold standard for diagnosing and molecularly profiling PNENs remains the analysis of surgical or biopsy tissue samples. However, these samples have a highly invasive character, rendering repetitive sampling unfeasible. Further limitations are the individual patients’ risk and procedural costs. Besides, they represent merely a snapshot of tumor heterogeneity, which strongly influences accuracy. Hence, liquid biopsies aroused strong interest since they form a cost-effective and minimally invasive way to analyze the tumor’s behavior. The most frequently used source is blood as it allows to examine the so-called tumor circulome that consists of a set of circulating components that originate from the tumor (97-101). These blood-based biomarkers play a pivotal role in diagnosing and staging PNENs, monitoring response to therapy, and detecting tumor progression. In case of F-PNENs, specific circulating biomarkers such as insulin, gastrin, and glucagon are employed in hormonal assays to correctly diagnose F-PNENs. Moreover, both F- and NF-PNENs frequently secrete non-specific markers including CgA, neuron-specific enolase (NSE), pancreastatin, etc., which can be detected in patients’ blood as well (2, 9, 13, 52, 53, 55, 102). Besides circulating proteins, PNENs also shed circulating tumor cells (CTCs), circulating tumor RNA (ctRNA) and DNA (ctDNA) which could serve as potential biomarkers (98-100, 103, 104).

 

SPECIFIC BIOMARKERS AND HORMONAL ASSAYS  

 

Depending on the type of F-PNENs (outlined in Table 1), specific biochemical tests are performed. When insulinoma is suspected, serum levels of insulin and C-peptide are measured at a confirmed hypoglycemia during prolonged period of fasting (approximately 72 hours) as patients present with increased levels (> 6 µU/L and 0.6 ng/mL, respectively) even when glucose levels are low (7, 31, 52, 53, 104). In case of gastrinomas, the serum gastrin levels will be 10 times higher than the upper limit and gastric pH will be lower or equal to 2 (3, 7, 52, 53, 105). In patients with suspected VIPoma and glucagonoma, diagnosis is confirmed by determining the fasting levels of VIP and glucagon (7, 53).  

 

Chromogranin A (CgA)

 

CgA, a glycoprotein stored in and secreted by the secretory granules of the neuroendocrine cells, plays an important role not only in immunohistochemistry, but also as a circulating marker (7, 17, 52, 53, 102). CgA is useful as a marker for both functional and non-functional PNENs, as elevated levels are noted in 50-100% of the patients with PNENs (2, 106-108), depending upon the histological subtype (104, 109, 110). For example in gastrinoma, CgA levels are consistently high due to gastrin-induced enterochromaffin-like cell hyperplasia (111), while insulinoma show significantly lower levels of circulating CgA (112). Besides, blood levels depend upon malignant nature of the tumor, tumor burden, and progression, hence small tumors may be associated with normal CgA levels (113, 114).

 

The ENETS still recommends the use of circulating serum CgA as marker during diagnosis and follow-up in NF-PNENs (7, 115). However, the actual diagnostic value of this marker is still questionable (115). Sensitivity, specificity and overall accuracy of this clinical biomarker equal 66%, 95% and 71%, respectively (7), but these values tend to vary according to the specific assays and diagnostic threshold (52). Common conditions that can falsely elevate CgA levels, thus impair specificity, include decreased renal function, treatment with proton pump inhibitors (116), and even essential hypertension (117). In addition, 30-50% of NENs do not show elevated CgA levels, limiting sensitivity (47, 115, 118). This group mostly involves small, localized, non-functional NETs where CgA levels are normal in approximately 70% of the cases (119). As a result, these patients are in a higher need for accurate biochemical markers as diagnosis is harder both clinically and by use of imaging techniques. Moreover, SSA treatment cause a decrease in CgA secretion, which is why results should always be interpret with caution (104). In terms of follow-up, prospective studies demonstrated that elevated CgA levels do not correlate with imaging and tumor progression, hence questioning the potential of CgA as follow-up biomarker (115). Compared to CgA, CgB is not impacted by for example proton pump inhibitor treatment (112, 116). However, only in 25% of the cases with elevated CgA levels, CgB was elevated as well, thus routine estimation of CgB in all patients seemed not informatic in clinical practice (120).

 

Neuron-Specific Enolase (NSE)

 

NSE is a glycolytic enzyme expressed in the neuroendocrine cells of which levels can be elevated in PNEN patients, particularly those with a poorly-differentiated tumor (58, 110). However, its clinical use is limited as a blood-based biomarkers for NETs because sensitivity and specificity are only 39-43% and 65-73% to distinguish NETs from non-NETs. Consequently, NSE is therefore inferior to CgA in clinical practice (17, 110, 121). When combined with CgA measurement, sensitivity improves and reliability of NET diagnoses increases. Moreover, elevated CgA/NSE levels appear to provide prognostic information on progression-free survival (PFS) and OS (7, 102, 122).  

 

Pancreastatin

 

Pancreastatin, a post-translational processing product of CgA, is suggested to be a useful prognostic marker of NETs as pre-treatment levels > 500 pmol/L are an independent indicator of poor prognosis. Moreover, this marker is reported to correlate with the number of liver metastases and an increase in pancreastatin levels after treatment with SSAs is associated with poorer survival (52, 123). For diagnosis of NETs, pancreastatin is less sensitive than CgA, but also less susceptible to non-specific elevation (52, 121).

 

Pancreatic Polypeptide (PP)

 

PP is a hormone predominantly produced in pancreatic polypeptide cells, located in the head of the pancreas (7, 17, 109, 124). When used alone, a sensitivity of 63% is achieved in PNENs, but when combined with CgA sensitivity increases to 94%, better than either marker alone (109). However, less than 50% of PNEN patients display elevated serum levels and increases do not correlate with tumor burden and/or aggressiveness (102, 124). Moreover, there are several clinical conditions that can induce falsely elevated levels such as physical exercise, hypoglycemia, and food intake, whereas diarrhea, laxative abuse, high age, inflammatory processes and chronic renal disease could lead to a decrease (7, 102).   

 

Other Protein-Based Markers

 

Besides the above-mentioned markers, ProGRP and Neurokinin A can be used to further improve diagnostic and especially prognostic information. ProGRP in fact stimulates cell proliferation which is why increased levels are often associated with a more aggressive tumor and therefore worse prognosis (7, 12). In addition, several markers were reported to be useful for the detection of bone metastases that can be either osteolytic or osteoblastic. Bone alkaline phosphatase (BAP) indicates osteoblast function, while urinary N-telopeptide reflects osteoclast activity or bone resorption. An increased osteoclast activity predicts a poor outcome (12, 125, 126).    

 

Circulating Tumor Cells (CTCs)

 

CTCs have been investigated in a wide range of tumor types, and have gained increased interest in PNENs due to the limitations of the current circulating markers (98-100, 104, 121, 127, 128). The recently developed platform, CellSearch®, allows to detect and isolate CTCs based on expression of the epithelial cell adhesion molecule (EpCAM) on the cell membrane. EpCAM is a transmembrane epithelial glycoprotein that is overexpressed in adenocarcinoma, but recent studies (127-129) revealed EpCAM positivity in ileal, pancreatic, unknown primary, and gastric NETs as well. However, only 21-24% of the metastatic PNEN patients had detectable CTCs in the blood stream, which could potentially be explained by a slow shedding of CTCs or loss of EpCAM expression. Presence of CTCs was associated with increasing tumor burden and grade, while CgA failed to reveal this relationship. Changes in CTC levels were associated with treatment response and OS, revealing its potential as marker during treatment follow-up (127, 129). Furthermore, presence of CTCs could distinguish between patients suffering from PNENs with and without bone metastases with an area under the curve (AUC) of 79% (130). A phase II PAZONET study, during which Pazopanib treatment was evaluated, even demonstrated that patients without baseline CTCs showed improved response and longer median PFS (131). Contrarily, the CALM-NET phase IV study reported no notable effect of the presence of CTCs at baseline on PFS in patients treated with Lanreotide (132). Lastly, CTCs provide the opportunity to detect (epi)genetic alterations in PNENs through DNA and RNA extraction, but they can also be used to determine the SSTR status via immunohistochemistry which could facilitate therapeutic management (133, 134).

 

Circulating Tumor DNA (ctDNA)

 

ctDNA is the fraction of cell-free DNA (cfDNA) that originates from the tumor and constitutes one of the most promising new markers. It provides a representation of the whole tumor and contains tumor-specific genetic and epigenetic alterations, which allow to distinguish healthy from tumoral DNA (98-100, 104, 135). However, ctDNA research regarding NENs is still in its infancy. Boons et al., published the first paper confirming the presence of ctDNA in the plasma of metastatic PNEN patients by looking for tumor-specific single nucleotide variants (SNVs) via custom digital droplet PCR (ddPCR). In patients with localized PNENs, ctDNA could not be detected (136). In the same study, they revealed a significant correlation between CNA profiles of PNEN tissue and ctDNA and demonstrated the feasibility to detect ctDNA using these profiles (136). These findings were exploited in a more recent study, where they performed a cfDNA CNA analysis in a cohort of 43 NEN patients. Using this analysis, ctDNA could be detected in 13 of the 21 PNEN patients. ctDNA positivity appeared to be significantly associated with higher WHO grade, location of the primary tumor and higher levels of CgA and NSE. Besides, a worse OS was observed in ctDNA-positive patients. In addition, they illustrated that CNA patterns in cfDNA could even assist in distinguishing PNENs from the more common PAADs. Moreover, the longitudinal tumor fraction (i.e., amount of ctDNA vs. total cfDNA) measurements were associated with PFS and could indicate tumor progression (47).  

 

MicroRNA (miRNAs)

 

miRNAs are short noncoding RNAs (< 30 nucleotides) designated to regulate many processes including cell proliferation, apoptosis, and development (134, 137), by inducing translational repression or degradation of certain mRNAs (138). In cancer, miRNA regulation is often altered as is the case in PNENs (138). Normal pancreatic islets and PNENs display a distinctly different miRNA profile as PNENs express miRNA-103 and-107, but lack miRNA-155. A set of 10 miRNAs was even able to perfectly distinguish 40 PNENs from 4 PAADs (137). miRNA-204 was overexpressed in insulinomas only, miRNA-196a had a prognostic function and overexpression of miRNA-21 was associated with higher Ki-67 rates and presence of liver metastasis (137). A more recent study, demonstrated that the combination of a set of miRNAs together with CgA measurements could improve diagnostic accuracy (139). However, data on circulating miRNA is still scarce as miRNA measurements in NETs are not properly standardized, requiring further research (140).

 

NETest

 

The NETest, a blood-based multi-analyte transcript assay, was developed in 2013 by Modlin and colleagues (141). The expression of 51 marker genes, encompassing genes associated with NENs, is examined using a quantitative PCR (qPCR) and analyzed using multivariate algorithms (142, 143). These algorithms enable the calculation of a disease-activity score, ranging from 0 to 100, with scores higher than 20 representing tumoral samples (140, 142, 143). The NETest captures accurate diagnosis and tumor biology of NETs with the most recent study demonstrating an accuracy of more than 91%. More specifically, the NETest has proven useful for diagnosing PNEN patients, as PNENs could be distinguished from other pancreatic malignancies with an accuracy of 94% (142, 143). The test also shows to be a real-time monitor of clinical status through the disease-activity score of NEN patients. Low biological activity corresponds to a score of less than 40, while intermediate and high biological activity, indicating tumor progression, have scores of 41-79 and 80-100, respectively (103, 140, 143). Stable and progressive disease could be differentiated with an accuracy of 84.5-85.6%, consistent with image-based categorizations (103). Moreover, changes in NETest disease-activity scores over time correlated with response to treatments including SSAs, PRRT, and surgery (144-147). For example, in a prospective analysis, performed by Modlin and colleagues, 35 pancreatic and small intestine NEN patients were included that all displayed elevated NETest levels prior to surgery, while only 14 of them had increased CgA levels. After tumor removal, the disease-activity scores reduced from 80 ± 5 to 29 ± 5 (p < 0.0001), whereas changes in CgA levels did not correlate with resection. Four of the 11 patients with complete tumor resection still presented increased NETest scores one month after surgery and showed positive evidence of recurrence 6 months post-surgery (144).

 

Since 2013, the NETest has proven to perform better than the single analyte tests (e.g., CgA) and these results appeared to be highly robust and reproducible (103, 140, 142). However, a large independent validation study conducted in the Netherlands has revealed that the test is more sensitive, but less specific than CgA suggesting its suitability as a marker for disease follow-up, but not as a screening tool (147). This test is not affected by food intake or specific medication, is easy to use and available which all increases clinical utility (140). The NETest possess advantages from an economic point of view too. Identifying patients with molecularly stable disease (SD) could potentially lead to fewer use of imaging modalities. Moreover, by enabling faster identification of the clinical status than with imaging, ineffective therapies can be ceased more quickly with another obvious cost-benefit effect (140, 142). Despite all advantages, NETest is currently not implemented in a clinical setting. Results of additional independent validation studies and other practical aspects such as costs and transparency will ultimately determine its integration in clinical practice.

 

MANAGEMENT OF PNENs

 

With a better understanding of the heterogeneity in PNENs, the number of treatment options has increased substantially over the years. Unfortunately, there is a lack of head-to-head comparison data. Therefore, treatment must be individualized considering the age and overall health of the patient, the specific toxicities of potential treatment(s), costs, and potential impact on quality of life (QOL). Consequently, decisions with regard to patient management must be made by an experienced, multidisciplinary team together with the primary care physician (52). Generally, the management of PNEN patients consists of a series of well-defined steps. These comprise of: 1) establishing a diagnosis, 2) determining localization and extent of tumor, 3) controlling hormone excess state in case of F-PNENs, 4) resecting tumor, if possible, 5) checking for presence of hereditary disease (MEN1), 6) treating advanced and metastatic PNENs, and 7) long-term monitoring for tumor progression (63, 148).

Figure 6. Possible treatment scheme for PNENs based on functionality and extent of the tumor. This figure has been adapted from Cancers, Akirov A., Larouche V., Alshehri S. et al., Treatment options for pancreatic neuroendocrine tumors, 11 (6) © 2019 (149).

It is crucial to consider grade/differentiation, stage/extent, and functional status of the tumor as different treatment schemes evolved based on these factors (Figure 6). For example, surgery is usually advocated for PNENs that are functional, larger than 2 cm, or intermediate-to-high grade (3, 8, 52). For patients with metastatic disease, the treatment options are extensive and encompass surgical debulking, systemic therapies including chemotherapy, or targeted therapy such as liver-directed therapy and peptide receptor radionucleotide therapy (PRRT) (149). It is not unusual for the management plan to change based on treatment response and disease progression. Failure to respond to treatment or unexpected changes in the tempo of disease due to tumor dedifferentiation and tumor heterogeneity are well-described in PNENs. Accordingly, most patients will receive multiple treatments during the course of their disease, but there is no data on the optimal treatment sequence (52, 105). The various treatment modalities are discussed below.

 

Surgical Management

 

Surgery continues to play a major role in the management of patients with PNENs as it remains the only potentially curative treatment for PNEN patients and it can alleviate clinical symptoms caused by excessive hormone production and tumor bulk (2, 3, 7, 149-151). Furthermore, several studies revealed that patients who underwent surgical resection had a reduced risk of metastases as well as showed an improved disease-free survival (DFS) (152, 153). Different approaches exist such as resection of the primary tumor and surrounding lymph node metastases through pancreaticoduodenectomy (Whipple procedure) and pancreatectomy (central or distal) as well as the more conservative methods including sparing enucleation and wait-and-see observations (7, 52).

 

Choosing the appropriate approach depends on the extent and location of the tumor, the functional status as well as the presence or absence of metastases (52, 150, 154-156). Generally, surgery is recommended in patients with localized NF-PNENs. Besides the primary tumor, peritumoral metastases should be eradicated as well since nodal metastases occur in at least 30% of NF-PNEN patients which affect tumor grade, but more importantly DFS (157, 158). Exceptions occur in patients with sporadic, low-grade (G1/G2) NF-PNENs smaller than 2 cm (3, 8, 52, 149, 150, 154-156). For those patients, optimal management is controversial as some recommend surgical interventions such as enucleation, whereas others including the ENETS advocate a wait-and-see attitude due to the indolent nature of these tumors (3, 8, 52, 148-150, 159, 160). A similar conservative approach is encouraged in MEN1 patients with NF-PNENs of 2 cm or smaller as these tend to have a low disease-specific mortality (161). Thakker and colleagues, on the other hand, suggest resection of NF-PNENs larger than 1 cm that demonstrate significant growth over 6 to 12 months (162).

Surgical excision of the tumor is also recommended for patients with F-PNENs as these display high cure rates (2, 13, 149, 163-165). The National Comprehensive Cancer Network (NCCN) guidelines describe that insulinomas and gastrinomas are preferably removed by enucleation with peritumoral node dissection if the tumor is located in the head of the pancreas. Deeper, more invasive tumors are more appropriately eradicated by pancreaticoduodenectomy. The former strategy should also be applied for small peripheral glucagonomas and VIPomas. PNENs in the distal part of the pancreas, in turn, are ideally removed through distal pancreatectomy (149). Surgery for MEN1 patients with NF-PNENs and gastrinoma remains controversial as they often present with multiple primary tumors which renders curative surgery almost impossible. Aggressive resection of all PNENs smaller than 2 cm in MEN1 patients seems contra-indicated as several studies revealed that these patients rarely develop advanced disease and have a good prognosis (2, 18, 75, 165-167).

 

The traditional surgical approach is open laparotomy as this allows thorough abdominal exploration including bimanual palpation and intraoperative ultrasound of the pancreas and liver (2, 168). However, several studies reported that certain lesions in particular those amenable to enucleation or to distal pancreatectomy may be approached with laparoscopic or robotic techniques (169). Venkat and colleagues even demonstrated that patients who underwent laparoscopic resection had less blood loss and a lower overall complication rate, and were consequently permitted to leave the hospital sooner than patients who had had open pancreatic resection (170). Gastrinomas form an exception since palpation plays an important role in the detection of these often small malignancies. Moreover, 60-90% of these patients will have lymph node metastases in addition to the primary tumor (169, 171). Adopting a purely laparoscopic approach to these tumors will depend upon improvements in haptic feedback technology. For tumors requiring a Whipple procedure both laparotomic and laparoscopic approaches are used in centers worldwide as the latter is still associated with technical difficulties. However, when performed by trained hepatobiliary or laparoscopic surgeons’ effectiveness and safety are similar and, in some cases, even superior to open surgery (168, 171).     

 

In patients with distant metastases, surgical intervention remains important, although it may no longer result in cure (52). The most common site of distant metastasis is the liver since 46-93% of NET patients develop liver metastases which can lead to liver failure, a common cause of death (52, 172-174). There are multiple options available for patients with hepatic metastases, including surgical resection which, in selected cases, appears to improve survival in uncontrolled series (157). The optimal approach depends on several factors including the extent of primary tumor and liver metastases, planned treatment as well as the age and overall health of the patient. Accordingly, the NCCN recommends complete resection (R0 resection) of primary tumor and liver metastases, if possible and otherwise consider tumor debulking (149). Aggressive resection of the primary tumor in the setting of liver metastases is associated with a survival benefit as both obstruction and further metastatic spread may be prevented. The 5-year survival rate after this surgery ranged from 65% to 73% which is significantly better than that of patients with nonresectable metastases (20%) although this difference might be at least partially explained by selection bias, where only very fit patients receive surgery (174-176). In case of the latter, numerous non-surgical options are available (see liver-directed therapy) and primary tumor, when found to be asymptomatic and stable, is not removed (52, 177). However, R0 resection can only be achieved in 10-20% of the cases as the majority of patients presents with multifocal and bilateral metastases and studies suggest that only one third of all liver metastasis are visible on imaging (52, 174, 175, 178, 179). Consequently, cytoreductive hepatic surgery is more frequently opted for, but this approach remains controversial as it is incomplete and the target population is not clearly described. It is therefore generally considered that patients with metastatic G1/G2 PNEN in which preferably less than 25% of the liver is affected are eligible for tumor debulking (2, 52). Several studies already showed that this procedure can alleviate clinical symptoms in F-PNENs, but also provide better long-term survival (2, 52, 149, 180-183). Moreover, debulking may also be associated with an improved response to concomitant therapy such as embolization (184). Radiofrequency ablation (RFA) is increasingly used in PNEN patients to address hepatic metastases and is often performed during surgery or laparoscopically (2). Patients with extensive liver involvement, who are consequently ineligible for R0 resection and tumor debulking, may be aided with a liver transplant to improve life expectancy (52, 176, 185). A non-randomized study in 88 patients who met strict criteria of transplant eligibility reported a difference in OS in the transplant (88.8%) and no transplant group (22.4%) after 10 years (185). Important concerns are the availability of the grafts as well as the lifelong immunosuppression required after transplantation. Also, the exact criteria for eligibility are very similar to those for tumor debulking which makes patient selection difficult (52).

 

Medical Therapy

 

Use of medical therapy is limited to those with locally advanced or metastatic disease. Some of the current and promising options for targeted systemic therapy are shown in Figure 7.

Figure 7. Overview of the current (blue) and promising (red) options for targeted medical therapy in (P)NETs. This figure has been retrieved from Drugs, Herrera-Martinez A. D., Hofland J., Hofland L. J., Targeted Systemic Treatment of Neuroendocrine Tumors: Current Options and Future Perspectives 79:21–42 © 2019 (186).

Figure 8. Visualization binding affinity of each of the three FDA-approved SSAs to the different SSTR subtypes. This figure was retrieved and adapted from Drugs, Herrera-Martinez A. D., Hofland J., Hofland L. J., et al., Targeted systemic treatment of neuroendocrine tumors: current options and future perspectives, 79:21-42. © 2019 (186).

SOMATOSTATIN ANALOGS  

 

As previously described in the functional imaging section, SSTRs are often highly overexpressed in PNENs. Several SSAs including Octreotide (Sandostatin®) and Lanreotide (Somatuline®), which have affinity for different SSTR subtypes (Figure 8), were therefore marketed. These inhibit hormone secretion and thus reduce clinical symptoms in patients with F-PNENs (149, 186). Additionally, several studies revealed that SSAs are also capable to control tumor growth with a positive impact on PFS. The antiproliferative effect of SSAs in PNETs was confirmed in the Controlled Study of Lanreotide Antiproliferative Response in Neuroendocrine Tumors (CLARINET) trial. A total of 204 patients with well-differentiated, progressive NETs were included who were then randomly assigned to either Lanreotide or placebo treatment for 96 weeks. After 24 weeks, PFS rates were 65.1% and 33.0% in the Lanreotide and placebo groups respectively (Figure 9). The study also demonstrated that there was no significant difference in QOL and OS in both groups (149, 186-189).

Figure 9. PFS among patients that received Lanreotide (red) or placebo (blue). This figure was retrieved and adapted from The New England journal of medicine, Caplin M. E., Pavel M., Cwikla J. B., et al., Lanreotide in metastatic enteropancreatic neuroendocrine tumors, 371 (3): 224-33 © 2014 (189).

As an extension to the core CLARINET study, the CLARINET open-label extension (OLE) reported long-term safety and additional efficacy data. For this purpose, 88 patients with SD were selected from the core study. Forty-one patients continued their Lanreotide treatment, while 47 patients shifted from placebo to Lanreotide. Safety and tolerability were favorable during a mean treatment period of 40 months. In addition, adverse effects, that were either attributable or not to Lanreotide, were found to improve as duration of treatment, hence exposure, increased. Median PFS in patients who had already received Lanreotide in the core study was estimated at 32.8 months (Figure 10). Of the 32 placebo-treated patients who exhibited progressive disease (PD) in the core study, 17 patients persisted in PD, while the remaining 15 patients had a median time to progression (TTP) of 14 months (187, 190). Based on the findings from the CLARINET trial, the use of SSAs as first-line treatment for symptom relief and tumor control is recommended in the NCCN and ENETS guidelines for advanced, well-differentiated, unresectable PNENs, particularly those with a high burden of liver metastases (149, 188, 191).

Figure 10. PFS of patients that received Lanreotide in the core and OLE CLARINET study. The OLE data is only visualized for patients that were originally assigned to and continued the Lanreotide treatment. This figure was retrieved and adapted from Endocrine-related cancer, Caplin M. E., Pavel M., Cwikla J. B., et al., Anti-tumor effects of lanreotide for pancreatic and intestinal neuroendocrine tumours: the CLARINET open-label extension study, 23 (3): 191-9 © 2016 (190).

MOLECULAR-TARGETES AGENTS  

 

Newly developed molecular-targeted treatments including Sunitinib and Everolimus (Figure 7) have shown to improve PFS in advanced, metastatic PNENs and represent the most common second line treatments that are currently available (52, 149). An overview of the most recent findings can be found in Table 3.    

 

The tyrosine kinase inhibitor (TKI), Sunitinib, has been approved for the treatment of patients with well-differentiated, unresectable, locally advanced or metastatic PNENs as it displays an antiangiogenic working mechanism. It actually inhibits vascular endothelial growth factor receptors (VEGFR) 1 and 3, stem cell factor (SCF) receptor as well as platelet-derived growth factor receptors (149, 186, 192). A two-cohort phase II study, examining 107 patients with advanced NETs (of which 66 PNENs), reported an overall objective response rate (ORR) of 16.7% and SD in 68% of PNEN patients. Median TTP was 7.7 months in PNENs and 10.2 months in carcinoid patients (193). A phase III multinational, randomized, double-blind, placebo-controlled trial (SUN 1111) confirmed the activity of Sunitinib in patients with advanced, well-differentiated PNENs (Figure 11A). A total of 171 patients were enrolled in this study. Median PFS was 11.4 months in the Sunitinib group compared to 5.5 months in the placebo group, with the latter group having a higher mortality rate (25% vs 10%) (194). A retrospective analysis of the previous phase III trial reported an increased PFS in both the Sunitinib and placebo group (12.6 vs. 5.8 months). Median OS after 5 years were 38.6 and 29.1 months of the Sunitinib and placebo groups, respectively. Important to note here is that 69% of the placebo-treated patients shifted to Sunitinib treatment (195). Sunitinib presented with an acceptable safety profile as the most frequent adverse effects in the sunitinib group included diarrhea, nausea, vomiting, asthenia, and fatigue which can be managed through dose interruption or modification (192, 194, 196).  

 

Everolimus (Afinitor®) is an oral, protein kinase inhibitor of the mammalian target of rapamycin (mTOR) pathway that displays proven antitumor activity in advanced PNENs, either alone or combined with Octreotide therapy. A multinational phase II study, the RADIANT 1 trial, has reported the efficacy of Everolimus alone and in combination with Octreotide in patients with metastatic PNENs that have progressed on chemotherapy (197). Monotherapy with Everolimus provided SD in 67.8% of patients and a partial response (PR) in 9.6%, while combination therapy resulted in 80% SD and 4.4% PR. Everolimus treatment also led to a decrease in CgA and NSE levels in 50.7% and 68.2% of the patients (Table 4). An early tumor marker response (i.e., > 50% decrease by 4 weeks) was associated with a significantly longer PFS (197). The RADIANT 3 trial, later on, investigated Everolimus as first line therapy in patients with advanced PNENs (Figure11B). Four hundred and ten patients with radiologic progression of disease were randomized to either Everolimus (10 mg once daily) or placebo. The median PFS was 11 months with Everolimus compared to 4.6 months with placebo representing a 65% reduction in estimated risk of progression or death. The proportion of patients alive and progression free at 18 months was 34% with Everolimus compared to 9% with placebo. Toxicities were mostly grade I or II (198). Similar PFS rates were reported regardless of whether patients were chemo-naïve or had received prior chemotherapy (199, 200). Addition of Pasireotide to Everolimus did not improve PFS compared to Everolimus alone (201).

 

Based on the recent, above-mentioned data, the European Society for Medical Oncology (EMSO) guidelines 2020 recommend the use of molecular-targeted agents such as Sunitinib and Everolimus in advanced, progressive PNENs (G1/G2) (191). Likewise, the North American Neuroendocrine Tumor Society (NANETS) guidelines 2020 recommend both treatments for well-differentiated, metastatic PNETs (G1/G2) (202). Both guidelines state there is no support to use Sunitinib nor Everolimus in treatment of PNET G3 or PNECs (191, 202). When comparing both molecular-targeted agents, response rates appear comparable (Figure 11). Since there has been no trial comparing the two agents directly, choice of agent may be based on the potential side-effects and patient’s overall health. For example, in patients with poorly-controlled hormonal symptoms, especially hyperinsulinism, congestive heart failure, hypertension, high risk of gastrointestinal bleeding or a history of myocardial infarction or stroke, Everolimus is thought to be the preferred choice (194, 202, 203). On the other hand, in patients with poorly controlled diabetes mellitus, pulmonary disease, or high risk of infection, sunitinib would be a more appropriate choice (192, 203). Moreover, up until now several biomarkers have been identified that correlated with the patient’s outcome. An overview of the currently known biomarkers can be found in Table 4 (204).

 

 Table 3. Results from Most Important Phase II and III Studies of Sunitinib and Everolimus in PNENs

Study

Patients

Active treatment

PD at entry

ORR

PFS/TTP (months)

Safety and other comments

Sunitinib

Phase II, open label (193)

N = 107 

 

- PNETs = 66

 

 

- Carcinoid = 41

 

50 mg daily

Schedule 4/2*

No

 

 

ORR = 16.7%

SD = 68%

 

ORR = 2.4%

SD = 83%

 

 

TTP = 7.7

 

 

TTP = 10.2

G3 fatigue: 24.3%

Phase III,

RCT,

SUN 1111 (194)

 

[Retrospect]

(195)

N = 171

 

- Sunitinib = 86

 

 

 

- Placebo = 85

 

 

37.5 mg daily

CDD**

Yes

 

 

ORR = 9.3%

SD = 63%

PD = 14%

 

ORR = 0%

SD = 60%

PD = 27%

 

 

PFS = 11.4

[PFS = 12.6]

 

 

PFS = 5.5

[PFS = 5.8]

Common AEs:

30%: diarrhea, nausea, asthenia, vomiting and fatigue 

 

10-12%: G3/4 neutropenia and hypertension

Everolimus

Phase II,

open label,

RADIANT 1 (197)

N = 160

 

- Stratum1 = 155

 

 

 

- Stratum2 = 45

 

 

10 mg daily

 

 

 

10 mg daily + 30 mg LAR Octreotide

Yes

 

 

PR = 9.6%

SD = 67.8%

PD = 13.9%

 

PR = 4.4%

SD = 80%

PD = 0%

 

 

PFS = 9.7

 

 

 

PFS = 16.7

 

Specific AEs:

 

5.2%: G3/4 asthenia

 

 

8.9%: G3/4 thrombocytopenia

 

Common AEs:

30%: stomatitis, rash, diarrhea, fatigue, nausea

Phase III,

RCT,

RADIANT 3 (198)

N = 410

 

- Everolimus = 207

 

 

- Placebo = 203

10 mg daily

Yes

 

 

PR = 5%

SD = 73%

 

PR = 2%

SD = 51%

 

 

PFS = 11

 

 

PFS = 4.6

 

Common AEs:

64%: stomatitis

49%: rash

34%: diarrhea

31%: fatigue

23%: infections

Abbreviations: ORR, objective response rate; PFS, progression-free survival; TTP, time to progression; SD, stable disease; PD, progressive disease; CDD, continuous daily dosing; AE, adverse event; LAR, long-acting release; PR, partial response; RCT, randomized clinical trial

* Concomitant use of SSA in 27% of PNET patients and 54% of patients with carcinoid tumors.

** Concomitant use of SSA in 26.7% of patients.  

 

Figure 11. This figure compares the PFS in patients with advanced metastatic PNENs, (A) treated with Sunitinib in the SUN 1111 trial (194) and (B) Everolimus in the RADIANT 3 trial (198). Figure A was retrieved and adapted from The New England journal of medicine, Raymond E., Dahan L., Raoul J. L., et al., Sunitinib malate for the treatment of pancreatic neuroendocrine tumors, 364 (6): 501-13 © 2011 (194). Figure B was retrieved and adapted from The New England journal of medicine, Yao J. C., Shah M. H., Ito T., et al., Everolimus for advanced pancreatic neuroendocrine tumors, 364 (6): 514-23 © 2012 (198).

 

Table 4. Current Soluble Biomarkers and Correlations with Outcomes with Targeted Therapies in PNENs

Study

Biomarker

Results

Sunitinib

(204, 205)

 

VEGF

Increased in 53% of patients after 4 weeks of treatment

Return to baseline after 2 weeks off treatment

When Sunitinib level > 50 ng/dL higher changes observed

No significant difference between PNET and carcinoids

sVEGFR

Decrease of ³ 30% in sVEGFR-2 and -3 levels

Return to baseline after 2 weeks off treatment

Reduction in sVEGFR-3 correlated with better OR and PFS

Lower baseline sVEGFR-2 with radiological SD for > 6 months

Elevated baseline sVEGFR-2 correlated with improved OS

IL-8

Increase (>2-fold) in 43% and (>3-fold) in 23% of patients after 4 weeks of treatment

Return to baseline after 2 weeks off treatment

Increase (1.8-fold) after 4 weeks on treatment

SDF-1a

Increase (20%) after 4 weeks on treatment

Elevated baseline correlated with significantly shorter TTP, PFS and OS

Everolimus

(197, 206)

 

CgA

Increase (> 2-fold) of CgA at baseline correlated with decreased PFS and OS

Reduction of > 30% in CgA levels after 4 weeks correlated with increased PFS and OS

NSE

Elevated NSE levels at baseline correlated with decreased PFS and OS

Reduction of > 30% in NSE levels after 4 weeks correlated with improved PFS

Abbreviations: VEGF, vascular endothelial growth factor; sVEGFR, soluble VEGFR; SDF-1a, stromal cell-derived factor 1 alpha.

Note: This table was adapted from Molecular Diagnosis and Therapy, Mateo, J., Heymach, J. V. and Zurita, A. J., Biomarkers of response to Sunitinib in gastroenteropancreatic neuroendocrine tumors: current data and clinical outlook, 151-161. © 2012 (204).

 

CYTOTOXIC CHEMOTHERAPY  

 

There is currently no unanimity on which cytotoxic chemotherapy would be optimal for the treatment of PNENs. Therefore, patient selection is key so factors such as primary tumor site and stage, differentiation, and proliferation index should be considered. Conventional cytotoxic chemotherapy is often used as first-line therapy for metastatic and progressive PNETs or PNECs (149, 207). ENETS guidelines describe the following indications: progression under SSA treatment, worsening clinical symptoms, and/or Ki-67 values > 10% (208). In a neoadjuvant setting, chemotherapy can play a potential role in tumor shrinkage prior to resection (7). Two major types of chemotherapeutic agents can be distinguished namely alkylating and platinum agents (7, 149, 207). In practice these are often combined with antimetabolites and anthracyclines (209). An overview of the most commonly used combinatory therapies and when to employ them is described in more detail below.

 

Alkylating agents such as Streptozocin, Dacarbazine, and Temozolomide are key in the treatment strategy of PNEN patients since they are often employed as second line treatment after progression under SSA (207). First of all, Streptozocin, a nitrosourea alkylating agent, is taken up by cells via a glucose protein 2 (GLUT2) after which cell damage is induced. Since the compound is associated with significant renal and hematological toxicity in high doses, it is often combined with 5-fluorouracil (5-FU) or Doxorubicin with dose reduction, hence reduced toxicity as a result (2, 149, 209). A comparative, phase III study conducted in 1992 reported that the combinatory therapy of Streptozocin + Doxorubicin provided more favorable results than Streptozocin + 5-FU in patients with advanced PNENs (210). However, the results described in this study have not been confirmed in any subsequent study (163, 209). Kouvaraki and colleagues retrospectively studied 84 PNEC patients treated with Streptozocin, 5-FU and Doxorubicin. Response rate was 39% with 2-year PFS and OS of 41% and 74%, respectively (211). Dacarbazine, a second alkylating agent, serves as a less toxic alternative. A phase II study tested Dacarbazine as a monotherapy in 50 PNEN patients and reported an ORR of 34% and median OS of 19.3 months (212). When combined with 5-FU, the overall response rate and PFS in advanced NENs were 38.2% and 13.9 months, respectively (213). A third alkylating agent that is primarily used as monotherapy for treatment of glioblastoma and melanoma is Temozolomide (163, 209). When combined with other compounds including Capecitabine (214), Bevacizumab (215), Bevacizumab and Octreotide (216), Thalidomide (217) and Everolimus (200) it shows significant activity in advanced PNENs (149, 209). A 2011 retrospective study reported that the combination treatment Capecitabine + Temozolomide (CAPTEM) in 30 chemonaive NEC patients resulted in an ORR of 70% with a PFS of 18 months (214). In 2018, a prospective, randomized phase II trial investigated Temozolomide therapy versus the CAPTEM combination therapy in PNEN patients. PFS was significantly better in the latter group (14.4 vs. 22.7 months) (218). However, a more recent retrospective analysis showed that CAPTEM was not able to improve PFS. Consequently, it was suggested by the authors that CAPTEM might be more useful for tumor shrinkage rather than improving PFS (219). 

 

In poorly-differentiated G3 NECs, platinum agent regimens are often used in patients with adequate performance status. The first-line chemotherapy for NEC patients encompasses Cisplatin or Carboplatin combined with Etoposide or Irinotecan, based on the reported results (52, 220-223). Moertel and colleagues investigated the effect of Cisplatin + Etoposide in 45 patients with metastatic NENs, of which 27 were well-differentiated. The ORR was 67% in the 18 poorly-differentiated NECs with complete response (CR) in 17% of the patients, while unfortunately, only 2 patients (17%) of the well-differentiated NEN patients showed a response. Moreover, they reported a median survival of 19 months which was significantly longer than those described in literature (6-7 months). However, toxicity was a major issue (220). These results were confirmed by Mitry and colleagues in 1999 (221). Lower toxicity levels were observed when patients were treated with Carboplatin, but efficacy was similar to that of Cisplatin, rendering Carboplatin a valuable alternative (222, 224). Moreover, Oxaliplatin-based therapy appeared to have a greater activity in advanced PNETs (207).

 

The role of second-line chemotherapy for NEC patients is currently unknown, but many combinatory options have been examined (223, 225). Capecitabine + Oxaliplatin (CAPOX) and 5-FU + Oxaliplatin (FOLFOX) have been evaluated in two retrospective trials in well-differentiated NENs. ORRs of 26% and 30% were reported, respectively (226, 227). In addition, FOLFIRI and FOLFIRINOX (5-FU-based chemotherapies) have recently proven some effect in NEC patients progressing on platinum-based regimens (225, 228).

 

Radiotherapy

 

PEPTIDE RECEPTOR RADIONUCLIDE THERAPY (PRRT)

 

Peptide receptor radionuclide therapy (PRRT) is a therapy whereby a radiolabeled SSA (117Lutetium or 90Yttrium) is used to treat SSTR-positive, locally advanced and/or metastatic GEP-NENs, including PNENs. Adverse effects include nausea, renal toxicity, transient bone marrow suppression and seldom myelodysplastic syndrome or acute myeloid leukemia in 1-2% of patients (7, 149, 229, 230).

 

In a study of 504 patients, treatment with the analog 177Lu-DOTATATE showed activity in GEP-NENS (230). Looking specifically at the PNEN subgroup there was a 6% CR and a 36% PR in NF-PNENs and no CR and 47% PRs in functioning PNENs (230). Striking improvements in QOL of responders was also noted (231). A more recent study of 68 patients with PNENs treated with PRRT showed PRs in 41 patients (60.3%), minor responses in 8 (11.8%), SD in 9 (13.2%) and PD in 10 (14.7%) (232). The authors concluded that the outstanding response rates and survival outcomes suggest that PRRT is highly effective in advanced G1/2 PNENs when compared to other treatment modalities. Independent predictors of survival were the tumor proliferation index, the patient’s performance status, tumor burden and baseline plasma NSE level. PRRT also provided improvements in PFS compared to Octreotide in midgut NENs (232). The NETTER-1 phase III trial confirmed the efficacy in PRRT in midgut NENs in 2017 (229, 233, 234). Therefore, the FDA approved use of 177Lu-DOTATATE based on the results obtained in the NETTER-1 trial in midgut NETs (229, 234). Thus, the number of centers where this treatment is available is expected to increase in the US, although it has been used in Europe since 1996. Joint society practice guidelines have been developed (235). There are a number of ongoing international clinical trials listed on Clinical Trials.gov. Third party payer reimbursement is an ongoing issue which hopefully will be resolved.

 

For PNENs, the effects of PRRT have only been investigated in several single-arm prospective and retrospective trials (229). These, however, identified several signals in favor of PRRT use in PNENs as disease control rates and PFS varied between 84-85% and 30-34 months, respectively (232, 236). Additionally, a meta-analysis compared the efficiency of PRRT to Everolimus in GEP-NENs that were not eligible to surgical resection. An ORR of 47% was reported in the PRRT treated subgroup versus only 12% of the Everolimus treated patients. Moreover, disease control rates (81% vs. 73%) as well as PFS (25.7 vs. 14.7 months) were also superior in the PRRT treated subgroup (237). A recent retrospective study evaluated the association of upfront PRRT vs. upfront chemotherapy or targeted therapy with PFS in enteropancreatic NET patients who progressed under SSA treatment. Patients with a Ki-67 value of £10% who received upfront PRRT, were reported to have a statically and clinically meaningful prolonged PFS (238). Based on these findings, it seems important to better define the role of PRRT in the treatment of PNENs within the future.

 

Liver-Directed Therapy

 

As mentioned earlier, the liver constitutes the most common site for distant metastases (52, 172-174). Since surgical resection and RFA are only feasible in a minority of patients, there are multiple liver-directed therapies available to treat the remaining patients. These methods include transarterial chemoembolization (TACE), transarterial embolization (TAE), or radioembolization, which will be discussed below. Given the lack of randomized data, it is difficult to determine with certainty which method is preferred. Moreover, NANETS guidelines recommend to consider systemic therapy rather than liver-directed therapy when >50-75% hepatic tumor burden is present (239).  

 

A study of chemoembolization combined with SSA treatment resulted in a relief of symptoms in 78% of the patients. Monitoring serum pancreastatin levels predicted a response to this therapy in which radiographic improvement or stability were seen in 45% of patients (77). In NEN patients that underwent TACE, plasma levels of pancreastatin above 5000 pg/ml pre-treatment were associated with increased peri-procedure mortality (240).

Radioembolization (also known as selective intrahepatic radiotherapy or SIRT) involves embolization of 90Yttrium embedded either in a resin microsphere (Sir-Sphere) or a glass microsphere (TheraSphere). Acute toxicities associated with 90Yttrium microsphere embolization appear to be lower than other embolization techniques, primarily due to the fact that the procedure does not induce ischemic hepatitis. Thus, the procedure can be performed on an outpatient basis. A rare, but potentially serious complication is radiation enteritis, which can occur if particles are accidentally infused into arteries supplying the gastrointestinal tract. Chronic radiation hepatitis is another potential toxicity. Response rates associated with radioembolization in metastatic NEN patients have been encouraging. In one retrospective multi-center study of 148 patients treated with Sir-Spheres, the objective radiographic response rate was 63% with a median survival of 70 months, with no radiation-induced liver failure (241). Another study of 42 patients treated with either Sir-Spheres or TheraSpheres reported a response rate of 51%. However, only 29 of the 42 enrolled patients were evaluable (242). Grozinsky-Glasberg and colleagues examined 57 patients which underwent either TACE, TAE or SIRT. They reported symptomatic control and a stabilization of tumor growth in 95% of the patients. Noteworthy, they observed improvements regardless of the extent of the liver metastasis (243).

 

Novel Targets for the Treatment of (P)NENs

 

While there has been a quantum leap in the ability to treat NENs successfully we have a long way to go to cure the disease. Fortunately, research into improved and novel therapeutic strategies is ongoing. So far, the results of immunotherapy as monotherapy in PNET patients remain disappointing. Examples include the inhibition of the programmed death-ligand 1 (PDL-1) and cytotoxic T-lymphocyte antigen-4 (CTLA4), by treating patients with Pembrolizumab to enhance the immune response towards tumor cells (186, 244, 245). The KEYNOTE-028 phase I study treated PDL-1 positive PNEN patients with Pembrolizumab and reported an ORR of 6.3%, but no CRs occurred. Responses were better in metastatic carcinoids (ORR: 12%) (246). These findings were confirmed by the KEYNOTE-158 phase II study, in which the ORR was 3.7% with 3 PRs in PNEN and 1 in rectal NEN patients (247). Currently, several other clinical trials that are investigating the antitumor effect of immune checkpoint inhibitors include NCT02939651 for Pembrolizumab and NCT02955069 for other PDL-1 receptor antibodies (247). Moreover, there is also much speculation that PRRT cytotoxic drugs induce genotoxicity, hence increase the neoantigen load and thereby could potentially enhance the efficacy of immunotherapy (149, 244, 245, 248). Bevacizumab, a monoclonal antibody against the VEGF, showed no real benefit in PFS in a phase III trial in which Bevacizumab + Octreotide was compared to Interferon + Octreotide (249). The BETTER phase II trial, on the other hand, demonstrated that Bevacizumab + 5-FU/Streptozocin in patients with metastatic, well-differentiated PNENs could reach a PFS of 23.7 months and they reported an OS at 24 months of 88% (250). The SANET-ep (251) and SANET-p (252) phase III studies examined the efficacy and safety of Surufatinib in extrapancreatic NENs and PNENs, respectively. Surufatinib, a small-molecule inhibitor that targets VEGFRs as well as the fibroblast growth factor (FGF) receptor 1 and macrophage colony-stimulating factor 1 (CSF1) receptor, effectively prolonged PFS in both studies and was therefore suggested a potential treatment option in both patient populations (251, 252).

 

QUALITY OF LIFE IN PATIENTS WITH PNENs

 

The measurement of health-related quality of life (HRQOL) has become essential for evaluating the impact of the disease process and the treatment on patient’s symptoms, social, emotional, physiological, and physical functioning. The European Organization for Research and Treatment of Cancer (EORTC) developed the QLQ-C30 tool for oncology patients (253) and the QLQ-GINET21 tool was specifically developed for a spectrum of NEN patients (28% PNENs) (254). The Norfolk QOLNET was specifically developed for midgut NETs (carcinoids) and may provide some additional advantages for that specific group of patients (231).

 

The most commonly used QOL tool in GEP-NENs (including PNENs) is the EORTC QLQ-C30 (255). SSAs and Sunitinib have shown to improve HRQOL in diverse groups of GEP-NEN patients (255). In the CLARINET study, QLC-C30 data were mapped to EQ-5D utilities and not surprisingly worse utility values were noted with PD compared to SD. Of note, tumor location (midgut vs. pancreas) did not affect utility (256). PNEN patients treated with everolimus showed stable HRQOL scores as opposed to worse scores in non-PNEN patients (Pavel). PRRT treatment of PNEN patients resulted in significantly improved global health status, social functioning and mitigation of physical complaints (257). Thus, data are emerging on HRQOL in PNEN patients. However, most studies are too heterogenous in terms of patient populations and treatment interventions to draw firm conclusions (258). Moving forward, it will be important for HRQOL to be measured as a key component of clinical trials.

 

EXPERT COMMENTARY  

 

After many years of frustration, our knowledge regarding the biology, pathophysiology and genetics of (P)NENs increased. This has led to marked improvements in (functional) imaging, with the development of 68Gallium-labeled SSAs, as well as targeted treatments such as the tyrosine-kinase inhibitor Sunitinib, and the mTOR inhibitor Everolimus. In addition, PRRT seems to be expanding its role in treatment from midgut to PNENs. In the future, both imaging and treatment options will continue to evolve as more specific imaging agents and therapeutic targets are being developed and evaluated in numerous studies. The relatively uncommon nature of PNENs has made designing and completing randomized studies of adequate power challenging for a single institution. Therefore, we encourage the recent trend of multi-institutional, multinational studies in more homogeneous patient populations. We also strongly agree with the recommendation of NANETS, ENETS and other groups that all of these patients should be entered into clinical trials whenever feasible. Determining study availability and patient eligibility has been greatly facilitated by Clinical trials.gov as well as institutional and organizational websites. Enrolling more patients in clinical trials by overcoming barriers to participation will be required to move patient care forward.

 

Unfortunately, to date, the optimal treatment(s) and treatment sequences have yet to be defined. The lack of treatment standardization, the plethora of treatments that most patients receive, and different treatment sequences make it extremely difficult to assess the effectiveness of a particular treatment relative to others. Moreover, head-to-head comparisons are lacking as well. Available consensus guidelines establish broad principles, but are generally not helpful in managing a specific patient. Management has become even more complex given the multiplicity of effective treatments for advanced disease, none of which has convincingly been shown to be superior to the other. Hence, an experienced multidisciplinary team is essential to guide management of these patients. Given relative parity of effectiveness, decisions regarding choice of treatment need to be based on multiple considerations, including patient’s overall health, disease burden, symptomatology, rate of progression, treatment toxicity, effect on QOL, and cost. These considerations will usually lead to one treatment being favored over another.

 

Because of the relatively indolent nature of many (or most) NENs, long-term follow-up to assess differences in treatment outcomes, is required. However, biomarkers that can predict response to a particular therapy are currently not available. We expect that in the future the so-called tumor circulome, especially ctDNA, could play an important role in this as recent studies revealed its potential to diagnose, prognosticate and monitor disease progression.

 

5 Year View

 

Knowledge of the biology and genetics will continue to accumulate, which could potentially lead to further refinements in classification, staging, and personalized treatment. Genetic profiling will become clinically useful as data will accumulate on treatment effectiveness in patient subgroups leading to more tailored therapies. Moreover, biomarkers will be developed that better predict response to a particular therapy. Results of the ongoing clinical trials on newer SSAs and targeted agents will add to the number of available treatments. The role of PRRT in the treatment of PNENs will be better defined. There will be increased knowledge as to optimal treatment sequences. Designing randomized clinical trials of adequate power will remain a challenge for many reasons including the scarcity and indolent growth of these tumors. Consensus guidelines will evolve, but patient management will continue to require an experienced multidisciplinary team.

 

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Control of Energy Expenditure in Humans

ABSTRACT

 

Resting and meal-related energy requirements can be assessed by measuring energy expenditure with indirect calorimetry. The indicated method to assess free-living energy expenditure is the doubly labelled water technique. Variation in energy expenditure is mainly a function of body size and composition (resting energy expenditure) and of physical activity (activity energy expenditure). Thus, energy expenditure can be calculated with a prediction equation for resting energy expenditure, based on height, age, weight and sex, in combination with the measurement of the physical activity level of a subject with a doubly labelled water validated accelerometer for movement registration. Energy balance in humans is maintained by adjusting energy intake to energy expenditure. Over- and underfeeding induces changes in activity-induced and maintenance energy expenditure as a function of changes in body weight and body composition. Additionally, underfeeding causes a metabolic adaptation as reflected in a reduction of maintenance energy expenditure below predicted values and defined as adaptive thermogenesis. When intake exceeds energy requirements, the excess is primarily stored as body fat. As a substrate for energy metabolism, fat is less likely to be oxidized for fuel than carbohydrate or protein. Consumed fat is mostly stored before oxidation, especially in heavier people, increasing the likelihood of creating a positive energy balance. An activity-induced increase in energy requirement is typically followed by an increase in energy intake, whereas a reduction in physical activity does not result in an equivalent reduction of energy intake. Thus, preventing weight gain is more effectively reached by eating less than by moving more.

 

MEASURING ENERGY EXPENDITURE

 

Living can be regarded as a combustion process. The metabolism of an organism requires energy production by the combustion of fuel in the form of carbohydrate, protein, fat, or alcohol. In this process oxygen is consumed and carbon dioxide produced. Measuring energy expenditure means measuring heat production or heat loss, and this is known as direct calorimetry. The measurement of heat production by measuring oxygen consumption and/or carbon dioxide production is called indirect calorimetry.

 

Early calorimeters for the measurement of energy expenditure were direct calorimeters. At the end of the 18th century Lavoisier constructed one of the first calorimeters, measuring energy expenditure in a guinea pig. The animal was placed in a wire cage, which occupied the center of an apparatus. The surrounding space was filled with chunks of ice (Figure 1). As the ice melted from the animal's body heat, the water was collected in a container, and weighed. The ice cavity was surrounded by a space filled with snow to maintain a constant temperature. Thus, no heat could dissipate from the surroundings to the inner ice jacket. Today, heat loss is measured in a calorimeter by removing the heat with a cooling stream of air or water or measuring the heat flow through the wall. In the first case, heat conduction through the wall of the calorimeter is prevented and the flow of heat is measured by the product of temperature difference between inflow and outflow and the rate of flow of the cooling medium. In the latter case instead of preventing heat flow through the wall, the rate of this flow is measured from differences in temperature over the wall. This method is known as gradient layer calorimetry.

Figure 1. Lavoisier’s calorimeter. Heat expended by the animal melts the ice in the inner jacket. Snow in the outer jacket prevents heat exchange with the surrounding environment (From reference (1)).

In indirect calorimetry, heat production is calculated from chemical processes. Knowing, for example, that the oxidation of 1 mol glucose requires 6 mol oxygen and produces 6 mol water, 6 mol carbon dioxide and 2.8 MJ heat, the heat production can be calculated from oxygen consumption or carbon dioxide production. Heat production and the energy equivalent of oxygen and carbon dioxide varies with the nutrient oxidized (Tables 1 and 2).

 

Table 1. Gaseous Exchange and Heat Production of Metabolized Nutrients

Nutrient

Consumption oxygen (l/g)

Production carbon dioxide (l/g)

Heat (kJ/g)

Carbohydrate

0.829

0.829

17.5

Protein

0.967

0.775

18.1

Fat

2.019

1.427

39.6

 

Brouwer (2) drew up simple formulae for calculating the heat production and the quantities of carbohydrate (C), protein (P) and fat (F) oxidized from oxygen consumption, carbon dioxide production and urine-nitrogen loss. The principle of the calculation consists of three equations with the mentioned three measured variables:

 

Oxygen consumption              = 0.829 C + 0.967 P + 2.019 F

Carbon dioxide production      = 0.829 C + 0.775 P + 1.427 F

Heat production                       = 21.1 C + 18.7 P + 19.6 F

 

Usually, only urine nitrogen is measured when information on the contribution of C, P, and F to energy production is needed. Protein oxidation (g) is calculated as 6.25 x urine-nitrogen (g), and subsequently oxygen consumption and carbon dioxide production can be corrected for protein oxidation to allow calculation of carbohydrate and fat oxidation. The general formula for the calculation of energy production (E) derived from these figures is: 

 

E = 16.20 * oxygen consumption + 5.00 * carbon dioxide production - 0.95 P.

 

In this formula the contribution of protein (P) to energy production (E), the so-called protein correction, is very small. In the case of a normal protein oxidation of 10-15 per cent of the daily energy production, the protein correction for the calculation of E is about one per cent. For this reason, in the calculation of energy production, the protein correction is often neglected.

 

Metabolizable energy is available for energy production in the form of heat and for external work. At present, the state of the art for assessing total energy expenditure is with indirect calorimetry. With indirect calorimetry, the energy expenditure is calculated from gaseous exchange of oxygen and carbon dioxide. The result is the total energy expenditure of the body for heat production and work output. With direct calorimetry, only heat loss is measured. At rest, total energy expenditure is converted to heat. During physical activity, there is work output as well. The proportion of energy expenditure for external work is the work efficiency. At rest, indirect calorimetry-assessed energy expenditure matches heat loss as measured with direct calorimetry. During physical activity, heat loss is systematically lower than indirect calorimetry-assessed energy expenditure and can be up to 25% lower than total energy expenditure during endurance exercise. The difference increases with exercise intensity. For example, during cycling, indirect calorimetry assessed energy expenditure matches the sum of heat loss and power output (3) and work efficiency during cycling, the power output divided by energy expenditure, is in the range of 15 to 25%.

 

Current techniques utilizing indirect calorimetry for the measurement of energy expenditure in humans include a facemask or ventilated hood, respiration chamber (whole room calorimeter), and the doubly labelled water method. A facemask is typically used to measure energy expenditure during standardized activities on a treadmill or a cycle ergometer. A ventilated hood is used to measure resting energy expenditure and energy expenditure during nutrient processing and absorption (diet-induced energy expenditure). A respiration chamber is an airtight room that is ventilated with fresh air, with the only difference between a usually, ventilated hood system and respiration chamber being size. In a respiration chamber the subject is fully enclosed instead of enclosing the head only, allowing physical activity depending on the size of the chamber. For measurements under a hood or in a respiration chamber, air is pumped through the system and blown into a mixing chamber where a sample is taken for analysis. Measurements taken are those of the airflow and of the oxygen and carbon dioxide concentrations of the air flowing in and out. The most common device to measure the airflow is a dry gas meter comparable to that used to measure natural gas consumption at home. The oxygen and carbon dioxide concentrations are commonly measured with a paramagnetic oxygen analyzer and an infrared carbon dioxide analyzer respectively. The airflow is adjusted to keep differences in oxygen and carbon dioxide concentrations between inlet and outlet within a range of 0.5 to 1.0%. For adults, this means airflow rates around 50 l/min at rest under a hood, 50-100 l/min when sedentary in a respiration chamber, while in exercising subjects the flow has to be increased to over 100 l/min. In the latter situation, one has to choose a compromise for the flow rate when measurements are to be continued over 24 hours that include active and inactive intervals. During exercise bouts, the 1% carbon dioxide level should not be surpassed for long. During times of rest, like an overnight sleep, the level should not fall too far below the optimal measuring range of 0.5-1.0%. Changing the flow rate during an observation interval reduces the accuracy of the measurements due to the response time of the system. Though the flow rate of a hood and a chamber system is comparable, the volume of a respiration chamber is more than 20 times the volume of a ventilated hood. Consequently, the minimum length of an observation period under a hood is about 0.5 hours and in a respiration chamber in the order of 5-10 hours.

 

The doubly labelled water method is an innovative variant on indirect calorimetry based on the discovery that oxygen in the respiratory carbon dioxide is in isotopic equilibrium with the oxygen in body water. This technique involves enriching the body water with an isotope of oxygen and an isotope of hydrogen and then determining the washout kinetics of both isotopes. Doubly labelled water provides an excellent method to measure total energy expenditure in unrestrained humans in their normal surroundings over a time period of one to four weeks. After enriching the body water with labelled oxygen and hydrogen by drinking doubly labelled water, most of the oxygen isotope is lost as water, but some is also lost as carbon dioxide because CO2 in body fluids is in isotopic equilibrium with body water due to exchange in the bicarbonate pools (4). The hydrogen isotope is lost as water only. Thus, the washout for the oxygen isotope is faster than for the hydrogen isotope, and the difference represents the CO2 production. The isotopes of choice are the stable, heavy, isotopes of oxygen and hydrogen, oxygen-18 (18O) and deuterium (2H), since these avoid the need to use radioactivity and can be used safely. Both isotopes naturally occur in drinking water and thus in body water. The CO2 production, calculated from the difference in elimination between the two isotopes, is a measure of metabolism. In practice, the observation duration is set by the biological half-life of the isotopes as a function of the level of the energy expenditure. The minimum observation duration is about three days in subjects with high energy turnover like premature infants or endurance athletes. The maximum duration is 30 days or about 4 weeks in elderly (sedentary) subjects. An observation period begins with collection of a baseline sample. Then, a weighed isotope dose is administered, usually a mixture of 10% 18O and 6% 2H in water. For a 70 kg adult, between 100-150 cc water would be used. Subsequently, the isotopes equilibrate with the body water and the initial sample is collected. The equilibration time is dependent on body size and metabolic rate. For an adult the equilibration would take between 4-8 hours. During equilibration, the subject usually does not consume any food or drink. After collecting the initial sample, the subject performs routines according to the instructions of the experimenter. Body water samples (blood, saliva or urine) are collected at regular intervals until the end of the observation period. The doubly labelled water method gives precise and accurate information on carbon dioxide production. Converting carbon dioxide production to energy expenditure needs information on the energy equivalent of CO2 (Table 2), which can be calculated with additional information on the substrate mixture being oxidized. One option is the calculation of the energy equivalent from the macronutrient composition of the diet. In energy balance, substrate intake and substrate utilization are assumed to be identical.

 

Table 2. Energy Equivalents of Oxygen and Carbon Dioxide

Nutrient

Oxygen (kJ/l)

Carbon dioxide (kJ/l)

Carbohydrate

21.1

21.1

Protein

18.7

23.4

Fat

19.6

27.8

 

ENERGY EXPENDITURE AND COMPONENTS

 

Daily energy expenditure consists of four components: 1) sleeping metabolic rate, 2) the energy cost of arousal, 3) the thermic effect of food (or diet-induced energy expenditure (DEE)), and 4) the energy cost of physical activity or activity-induced energy expenditure (AEE). Usually, sleeping metabolic rate and the energy cost of arousal are combined and referred to as resting energy expenditure (REE). Overnight when one sleeps quietly, food intake and physical activity are generally low or absent and energy expenditure gradually decreases to a daily minimum before increasing upon awakening (Figure 2). Then, increases in energy expenditure during arousal are primarily the result of activity-induced energy expenditure as well as diet-induced energy expenditure. Thus, energy expenditure varies throughout a day as a function of body size and body composition (the major components determining REE), physical activity as determinant of AEE, and food intake as determinant of DEE.

Figure 2. Average energy expenditure (upper line) and physical activity (lower line) as measured over a 24-h interval in a respiration chamber. Arrows denote meal times. Data are the average of 37 subjects, 17 women and 20 men, age 20-35 y and body mass index 20-30 kg/m2 (5).

Resting energy expenditure is defined as the metabolic rate required to maintain vital physiological functions of an individual that is in rest, awake, in a fasted state, and in a thermoneutral environment. To perform an accurate measurement of REE, a subject is instructed not to exercise the day before, to fast overnight, transported to a laboratory after waking up in the morning and habituated for 15-30 min to the testing procedure under a ventilated hood, before the actual measurement of 20-30 min, at a comfortable room temperature of 22-24 0C (6).

 

Standardizing to fat-free mass as an estimate of metabolic body size is most commonly used in the literature to compare REE between individuals. However, although fat-free body mass is a strong predictor of REE, energy expenditure should not be solely divided by the absolute fat-free mass value as the relationship between energy expenditure and fat-free mass has an Y-intercept (the value for energy expenditure when fat-free mass is theoretically absent) that is not zero (Figure 3). For example, fat-free adjusted REE is significantly different between women and men (Figure 3, 0.143±0.012 and 0.128±0.080 MJ/kg for women and men, respectively, P < 0.0001). The smaller the fat-free mass, the higher the REE/ fat-free mass ratio and thus the REE per kg fat-free mass is on average higher in women than men. Instead, a more accurate approach for comparing REE data is by regression analysis that includes both fat-free mass and fat mass as covariates.

 

REE (MJ/d) = 1.39 + 0.93 fat-free mass (kg) + 0.039 fat mass (kg), r2 = 0.93.

 

Using this equation, gender no longer comes out as a significant contributor to the explained variation in the group of women and men (Figure 3).

 

Figure 3. Resting energy expenditure (REE) plotted as a function of fat-free mass for the subjects from reference 5 as described in Figure (2) (17 women: closed symbols; 20 men: open symbols) with the calculated linear regression line (REE (MJ/d) = 2.27 + 0.091 fat-free mass (kg), r2 = 0.78).

Diet-induced energy expenditure is defined as the energy-required for intestinal absorption of nutrients, the initial steps of their metabolism and the storage of the absorbed but not immediately oxidized nutrients during the post-prandial period. As such, the amount of food ingested quantified as the energy content of the food is a determinant of DEE. The most common way to express DEE is derived from the difference between energy expenditure after food consumption and REE, divided by the rate of nutrient energy administration. Theoretically, based on the amount of ATP required for the initial steps of metabolism and storage, the DEE is different for each nutrient. Reported DEE values for separate nutrients are 0 to 3% for fat, 5 to 10% for carbohydrate, and 20 to 30% for protein (7). In healthy subjects in energy balance with a mixed diet, DEE represents about 10% of the total amount of energy ingested over 24 hours.

 

A typical mean pattern of DEE throughout the day is presented in Figure 4. Data are from a study where DEE was calculated by plotting the residual of the individual relationship between energy expenditure and physical activity in time, as measured over 30-min intervals from a 24-h observation in a respiration chamber. The level of REE after waking up in the morning, and directly before the first meal, was defined as basal metabolic rate. Resting metabolic rate had still not returned to basal metabolic rate before lunch four hours after breakfast, or before dinner at five hours after lunch. Instead, basal metabolic rate was restored overnight, approximately eight hours after dinner consumption.

Figure 4. The mean pattern of resting energy expenditure throughout the day, where arrows denote meal times (adapted from reference (8)).

Activity-induced energy expenditure, the most variable component of daily energy expenditure, is derived from total energy expenditure (TEE) minus resting energy expenditure and diet-induced energy expenditure.

 

AEE = TEE – REE – DEE.

 

Total energy expenditure is measured with doubly labelled water as described above. When diet induced energy expenditure is assumed to be 10% of TEE in subjects consuming the average mixed diet and being in energy balance, AEE can be calculated as: AEE = 0.9 TEE – REE.

 

A frequently used method to quantify the physical activity level (PAL) of a subject is to express TEE as a multiple of REE:

 

PAL = TEE/REE.

 

This assumes that the variation in total energy expenditure is due to body size and physical activity. The effect of body size is corrected for by expressing TEE as a multiple of REE. Data on daily energy expenditure, as measured with doubly labelled water, permit the evaluation of limits to the physical activity level. In our site, data were compiled for more than 500 subjects, where energy expenditure was measured over an interval of two weeks with the same protocol. The sample excludes individuals aged less than 18 years, involved in interventions of restricted or forced excess energy intake, whose physical activity including athletic performance, who were pregnant or lactating, and with an acute or chronic illness. The sample includes similar numbers of women and men, with a wide range for age, height, weight, and body mass index. Despite the wide variation in subject characteristics, a narrow range of the physical activity level (between 1.1 and 2.75) amongst the subjects was found (Figure 5) with no sex differences (9).

 

The physical activity level of a subject can be classified in three categories as defined by the last Food and Agriculture Organization/World Health (FAO/WHO/UNU) expert consultation on human energy requirements (10). The physical activity for sedentary and light activity lifestyles ranges between 1.40 and 1.69, for moderately active or active lifestyles between 1.70 and 1.99, and for vigorously active lifestyles between 2.00 and 2.40. An active lifestyle improves heath parameters like insulin sensitivity (11). Higher PAL values, while difficult to maintain over a long period, generally result in weight loss.

 

An alternative for the measurement of energy expenditure with indirect calorimetry is a prediction equation for resting energy expenditure, in combination with an estimation of activity energy expenditure from measurement of body movement with an accelerometer. Typically, prediction equations for resting energy expenditure can explain 70-80% of the variation from race, height, age, weight and gender of a subject (12). Doubly labelled water studies show the best accelerometers for movement registration so far can explain 50-70% of variation in activity energy expenditure (13).

Figure 5. Frequency distribution of the value of the physical activity level (PAL) calculated as the total energy expenditure / resting energy expenditure, in a group of 556 healthy adults, women closed bars and men open bars (data from reference (9)).

DETERMINANTS OF ENERGY EXPENDITURE

 

The main determinants of energy expenditure are body size and body composition, food intake, and physical activity. Additional determinants are ambient temperature and health. As most people are able to live in a thermoneutral environment or prevent heat loss with appropriate clothing, energy expenditure is not affected by ambient temperature for longer time intervals.

Body size and body composition determine REE, the largest component of daily energy expenditure (Figure 6). Energy expenditure is generally higher in men than in women because men generally have a larger metabolic body size. They are on average heavier than women and for the same weight men have relatively more fat-free mass. For similar reasons, gaining weight implicates gaining fat mass and fat-free mass, and daily energy expenditure is generally higher in people who are overweight and have obesity compared with people who are lean matched for age, height and gender. This higher energy expenditure in people with obesity is mainly a consequence of higher resting energy expenditure than people who are lean (Figure 6).

Figure 6. The three components of energy expenditure: resting energy expenditure (closed bar), diet-induced energy expenditure (stippled bar), and activity-induced energy expenditure (open bar) as observed in subjects who are lean and who have obesity. In the lean group, women and men weighed 61 kg and 74 kg with 29% and 17% body fat, respectively. In the group with obesity, subjects were, on average, 40 kg heavier, where 70% of the additional weight was fat mass and 30% fat-free mass. The figure illustrates the higher energy expenditure (primarily in resting energy expenditure) in men than women and in those with obesity compared to those who are lean. (After reference (14)).

Food intake affects all three components of daily (total) energy expenditure: REE, DEE and AEE. The most obvious effect is on DEE, which represents about 10% of the amount of daily energy ingested. Thus, changing energy intake changes total energy expenditure accordingly. Overeating induces an additional increase for storage of excess energy, estimated at about 10 % of the energy surplus (15). When overfeeding is lower than twice the maintenance requirements, there does not seem to be an effect of this overfeeding on physical activity (16). Undereating induces a decrease in REE, DEE and AEE. Undereating induces weight loss accompanied by adaptive thermogenesis, a disproportional or greater than expected reduction of REE. The reduction in REE is sustained even while weight loss is maintained (17). Weight loss due to a negative energy balance is accompanied by a decrease in AEE as well. Here, the decrease is due to less body movement and a lower cost to move a smaller body mass. The reduction in body movement recovers to baseline values or higher when weight loss in maintained (18). A classic example of the effect of undereating on energy expenditure is the Minnesota Experiment from the 1950’s (19). Energy intake of normal-weight men was reduced for 24 weeks from 14.6 MJ/d to 6.6 MJ/d. The subjects reached a new energy balance by saving 8 MJ/d (Table 3). Of the total saving of 8 MJ/d the main part stemmed from reduced AEE, which was mainly due to moving less.

 

Table 3. Energy Saved by 24 Weeks Underfeeding in the Minnesota Experiment (19)

 

MJ/d

% of saving

Explanation

Resting energy expenditure

2.6

32

65% for a decreased bodyweight

35% for a lowered tissue metabolism

Diet-induced expenditure

0.8

10

 

Activity-induced expenditure

4.7

58

40% for a decreased bodyweight

60% for less body movement

Total

8.0

   

 

Activity induced energy expenditure is the most variable component of daily expenditure and can be increased through exercise. Variation in energy expenditure between subjects is a function of body size and physical activity, where AEE is an important contributor. Most of the variation in AEE is accounted for by genetic factors. Genes determine for a large part whether a person is prone to engage in activities and how much energy is expended for these activities (20). Exercise training can increase AEE. However, under some conditions the added exercise expenditure is compensated for by a reduction of non-training activity. Examples are non-ad libitum food intake and older age (Figure 7).

 

Figure 7. The physical activity level, total energy expenditure as a multiple of resting energy expenditure, before (open bar) and at the end of a training program (closed bar), for eight studies displayed in a sequence of age of the participants as displayed on the horizontal axis (After reference (21)).

Activity-induced energy expenditure does not increase linearly with increasing physical activity. For example, novice runners training to run a half marathon could increase the training amount without a change in AEE (22). In the selected group of sedentary subjects, the initial training-induced increase in AEE was twice as high as predicted from the training load. However, subsequent training allowed a doubling of the training load for the same AEE, probably through an improvement of exercise economy. Similarly, exercise training has been shown to decrease the energetic cost of walking in older adults (23).

 

Physical activity level reaches a maximum value of 2.0-2.4 (Figure 7). Higher values can be reached over shorter time intervals. For example, runners in a 140-day transcontinental race across the USA showed an initial increase in PAL from a pre-race value of 1.76 to 3.76 over the first five days of running (24). In the final week (week 20) of running, PAL had decreased to a mean value of 2.81. This subsequent decrease in PAL during sustained physical activity was hypothesized to have resulted from a limit in alimentary energy supply.

 

During negative energy balance, additional exercise is compensated by a reduction of non-training activity. In elderly subjects, exercise training has a similar compensatory effect on spontaneous physical activity, even under ad-libitum food conditions. Despite the absence of an effect of exercise training on total energy expenditure in elderly people, there are many beneficial effects of exercise training like aerobic capacity, endurance, flexibility, and range of motion.

 

ENERGY BALANCE

 

Adult humans maintain weight stability through a balance between energy intake and energy expenditure. When weight is stable, the energy store of the body does not fluctuate much, as evident by constancy in body weight and body composition. This weight constancy can be achieved through the balanced control of energy intake and expenditure. This balance does not, however, take place on an immediate basis. For example, on days with high energy expenditure, energy intake is usually normal or even below normal. The 'matching' increase in energy intake comes several days afterwards (25). Energy intake can change by at least a factor of three when adapting to changes in energy expenditure. Under sedentary living conditions the energy balance is maintained at about 1.5 times basal metabolic rate (BMR), while during sustained exercise levels of 4.5 times BMR are reached (26).

 

Humans are discontinuous eaters and continuous metabolizers. An animal that takes its food in meals, such as a human, periodically consumes more than their physiological needs even when in (daily) energy balance. During meal-related hyperphagia, metabolites are initially stored then mobilized during inter-meal intervals of energy deficiency. This pattern of intermittent feeding and fasting has consequences for energy expenditure (Figure 4). During and after a meal, expended energy increases to process the ingested food, while energy deficiency before a new meal is started can lead to a reduction of energy expenditure. The latter probably does not occur during short-term energy deficiency. However, people tend to be less energetic during prolonged inter-meal intervals or extended fasts.

 

Disturbances of energy balance result in energy mobilization from, or energy storage in, body reserves. Energy intake occurs via macronutrients consumed in meals in the form of carbohydrate, protein, fat and alcohol. During positive energy balance, excess energy is stored as carbohydrate in glycogen, primarily in the liver, and as fat in adipose depots. The storage capacity for carbohydrate is small, typically covering energy needs during the overnight fast that accompanies sleep. Longer-term shortages are mainly covered by mobilization of the larger energy stores in fat. On days with a positive energy balance, protein and carbohydrate intake match protein and carbohydrate oxidation and the difference between energy intake and energy expenditure shows up in a positive fat balance (27). In the early morning, at arousal, carbohydrate oxidation goes up and continues to increase at the first food intake of the day (28). After awakening, initial energy (‘fast’) requirements are met by glycogen reserves. Subsequently, carbohydrate requirement is higher at breakfast, and one eats relatively more fat at the evening dinner (29,30).

 

Energy balance does not equate to substrate balance, and when in substrate balance one does not produce energy just from the foods consumed. Fat, as a substrate for energy metabolism is at the bottom of the oxidation hierarchy that determines fuel selection and studies show a direct link between macronutrient balance for fat and energy balance. Changes in alcohol, protein, and carbohydrate intake elicit auto regulatory adjustments in oxidation whereas a change in fat intake fails to elicit such a response, or only in the long term (31).

 

One explanation for this macronutrient oxidation disparity is the routing of dietary fat. Fat metabolism can be traced with isotope-labelled fatty acids. Oxidation and adipose tissue uptake of dietary fat can be measured by adding fatty acid labelled with heavy hydrogen (2H) to meals. Upon oxidation, these deuterated fatty acids enrich the body water with deuterium, which is subsequently detectable in urine. Therefore, the urine enrichment for deuterium is a measure of dietary fat oxidation. The first label appears in the urine in about two hours and the peak concentration is reached after 12-24h (Figure 8). After 24 hours, 5-30% of the fat from a meal is oxidized and the remaining part partitioned to the reserves. The percentage of dietary fat oxidation is independent of the composition of the meal with respect to protein, carbohydrate and fat. However, there is a clear relation of dietary fat oxidation with the body fat content. The larger the fat mass, the lower the fractional oxidation of the fat consumed on the same day (32). The observed reduction in dietary fat oxidation in subjects with greater body fat may therefore play a role in expression and maintenance of human obesity. This low dietary fat oxidation makes subjects prone to weight gain.

Figure 8. Cumulative oxidation (mean ± standard deviation) of dietary fat as a percentage of intake, over time after ingestion, as calculated from tracer recovery in urine produced at two-hour intervals (From reference (32)).

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An Overview of Glucocorticoid-Induced Osteoporosis

ABSTRACT

 

Glucocorticoid (GC)-induced osteoporosis (GCOP) is the most common cause of iatrogenic osteoporosis (OP). Fractures may occur in 30-50% of patients on chronic GC therapy. Most of the epidemiological data associating fracture risk with GC therapy are from the use of oral GCs. The process of bone remodeling is complex, regulated by an intricate network of local and systemic factors. With prolonged GC administration, cortical bone becomes increasingly affected and long bones show increased fragility. As some patients on a low GC dose show bone loss at a much higher rate than others on a higher GC dose, genetics may play a role in determining this difference. Any patient that is treated with long-term GCs should be suspected as suffering from GCOP. Laboratory evaluation for GCOP should include total blood cell count, markers of renal and liver function, serum electrophoresis, serum and 24-hr urine calcium, serum levels of 25-hydroxyvitamin D, alkaline phosphatase, thyroid-stimulating hormone and parathyroid hormone, estradiol in women and total and free testosterone in men. Changes in BMD early on during GC therapy can be detected by dual-energy X-ray absorptiometry (DXA). In patients under GC treatment fractures tend to occur at BMD values that are lower than the conventional threshold T-score of -2.5. Recently simple adjustments for the calculated fracture risk have been presented that take into account glucocorticoid dosage for the Fracture Risk Assessment tool (FRAX). Guidelines for the prevention and treatment of GCOP have been put forth from various authorities. Prevention of GCOP should start as soon as GCs are administered; bone loss is more rapid in the first months of therapy. Patients on GCs should receive supplementation with calcium and vitamin D. There are several antiresorptive agents available for the prevention and treatment of GCOP - bisphosphonates are the most widely used. Teriparatide and denosumab can also be therapies of choice for patients on GC treatment with or without GCOP.

 

INTRODUCTION

 

Glucocorticoid (GC)-induced osteoporosis (GCOP) is often the result of secondary osteoporosis (OP) (1). It is the most common cause of iatrogenic OP; adults aged 20 to 45 years are mainly affected (1-3). Important bone loss may occur with or without other manifestations and its severity is dependent on both the dose and duration of GC treatment (4). From a retrospective study conducted in the United Kingdom the prevalence of chronic use of oral GCs in the general population was shown to be 0.5%; the prevalence was higher in women over 55 years (1.7%) and as high as 2.5% in subjects older than 70 years (5, 6); more recently experts argued that approximately 2% of the population receives long-term GC treatment (7). It is of practical interest to note that only 4%-14% of patients taking oral steroids were receiving treatment for prevention of osteoporosis (mainly by rheumatologists), indicating that GCOP is often underestimated and left untreated (5, 8).

 

EPIDEMIOLOGY

 

The association between glucocorticoid (GC) excess and osteoporosis was first described nearly 80 years ago, but its importance in clinical practice has only recently been recognized (9). Although it shares some similarities with postmenopausal osteoporosis, glucocorticoid-induced osteoporosis (GCOP) has distinct characteristics, including the rapidity of bone loss early after initiation of therapy, the accompanying increase in fracture risk during this time, and the combination of suppressed bone formation and increased bone resorption during the early phase of therapy (10).

 

Although awareness of GCOP amongst health-care professionals has increased over recent years, several studies indicate that its management remains suboptimal (11, 12). Although increased rates of diagnosis and treatment have been reported, possibly as a result of national guidelines, but overall these rates remain low (12, 13).

 

There is clear epidemiological association between GC therapy and fracture risk (14-16). Oral GC therapy is prescribed in up to 2.5% of the elderly population (aged 70-79 years) for a wide range of medical disorders (17). Fractures may occur in 30-50% of patients on chronic GC therapy (18). The vertebrae and femoral neck of the hip are specifically involved (19), whereas risk at the forearm (predominantly consisting of cortical bone), is not increased, confirming that GCs affect predominantly cancellous bone (15). Vertebral fractures associated with GC therapy may be asymptomatic (20). When assessed by X-ray-based morphometric measurements of vertebral bodies, more than 1/3 of postmenopausal women on chronic (> 6 months) oral GC treatment have sustained at least one vertebral fracture (20).

 

Along with the demonstration that fractures can occur early in the course of GC therapy, fracture incidence is also related to the dose and duration of GC exposure (16).

 

Doses as low as 2.5 mg of prednisone equivalents per day can be a risk factor for fracture, but the risk is clearly greater with higher doses. Chronic use is also associated with greater fracture risk (1, 16). When daily amounts of prednisone - or its equivalent - exceed 10 mg on a continuous basis and duration of therapy is greater than 90 days, the risk of fractures at the hip and vertebral sites is increased by 7- and 17-fold respectively (16). The risk of fractures declines after discontinuation of GCs although the recovery of the lost bone is gradual and often incomplete (1, 16).

 

Most of the epidemiological data associating fracture risk with GC therapy, come from the use of oral GCs. There is less data about risk associated with inhaled GCs (21-25); from the data available it can be extrapolated that a small but persistent and clinically significant growth retardation may be expected in children receiving inhaled GCs (26). It is also important to bear in mind that the underlying disorder for which inhaled or systemic GCs is used may also be a cause of bone loss (27). The systemic release of local bone-resorbing cytokines in some of these disorders could stimulate bone loss (28, 29). In addition, there are also local factors to consider. In inflammatory bowel disease, bone loss may be due, in part, to malabsorption of vitamin D, calcium, and other nutrients (28). In chronic lung disease, hypoxia, acidosis, reduced physical activity, and smoking may all contribute to bone loss, independently of the use of inhaled GCs (14, 25, 30, 31).

 

SECONDARY CAUSES/RISK FACTORS OF BONE LOSS

 

Factors, such as advancing age, race, sex, menopausal status, family history of OP and fractures, and secondary causes of OP, such as hyperthyroidism, hyperparathyroidism, Cushing’s syndrome, hypogonadism, diabetes (particularly type 1), renal failure, inflammatory bowel disease, and rheumatoid arthritis can add to the effects of GCOP (14, 32-36). Some of the risk factors for GCOP are common to other forms of OP and can be modified; these include: low calcium and high sodium intake (37), high caffeine intake (when calcium intake is low) (38), tobacco and alcohol use, decreased physical activity, immobilization, and a number of medications (32, 39, 40). Medications/treatments that are administered concomitantly with GCs (such as methotrexate, cyclosporine, heparin, medroxyprogesterone acetate, gonadotropin releasing hormone (GnRH) analogs, levothyroxine, anticonvulsants, or radiotherapy) may add to the disease burden of GCOP.

 

The emerging use of aromatase inhibitors (41), androgen-deprivation therapy in men with prostate cancer (42), and the growing field of bariatric surgery (43) have emerged as novel and important etiologies of secondary osteoporosis.

 

Patients with classical congenital adrenal hyperplasia (CAH)  can be over-treated with GC and show loss of bone mineral density (BMD) (44). The iatrogenic suppression of adrenal androgens production in women with CAH is associated with increased risk for bone loss (45). Young adult men on GCs apparently show more rapid bone loss compared to older men or postmenopausal or premenopausal women. Of note, men are more susceptible to depression-associated bone loss, which may be in part, GC-mediated (46). Postmenopausal women receiving GCs show higher fracture risk compared to premenopausal women that is attributed to lower bone mass when starting GC therapy) (47, 48). Patients with sarcoidosis and those taking steroids to prevent rejection of grafts after heart or kidney transplant, are also more likely to experience rapid bone loss (49-51).

 

CELLULAR AND MOLECULAR MECHANISMS OF GCOP

 

The process of bone remodeling is complex, regulated by an intricate network of local and systemic factors. Although normal bone needs endogenous GCs for its development (for osteoblast differentiation in particular, via inhibition of mesenchymal stem-cell differentiation to adipocytes) (52-54), GCs, at least in mice models, exert negative effects on bone maintenance in old age (by lowering survival of osteoblasts and osteocytes and limiting angiogenesis) (52). Quiescent bone is covered by osteoblasts and osteoclasts. In response to bone-resorbing stimuli, osteoclastic migration and bone resorption are activated. Osteoclasts remove both the organic matrix and the mineral component of the bone, producing a pit. This bone remodeling cycle takes place under a canopy of osteoprogenitor cells (55). In the formation phase, osteoblasts deposit osteoid in the pit, which is then mineralized. In normal bone there is – apparently – no appreciable effect of GCs on osteoclasts (52). Quiescence is restored at completion of the cycle (56). GCs can influence bone remodeling in a number of ways and at any stage of the remodeling cycle (Figure 1). We have to note that regarding animal studies of GCOP experts point to the heterogeneity of used models and the need for their standardization (57).

 

Figure 1. Overview of the mechanisms of glucocorticoid-induced osteoporosis (GCOP). Osteoporosis results from an imbalance between osteoblast and osteoclast activity. BMP-2: bone morphogenic protein-2; Cbfa1: core binding factor a1; Bcl-2: B-cell leukemia/lymphoma-2 apoptosis regulator; Bax: BCL-2-associated X protein; IGF-I: insulin-like growth factor-I; IGFBP: IGF binding protein; IGFBP-rPs: IGFBP-related proteins; HGF: hepatocyte growth factor; RANKL: receptor activator of the nuclear factor-κB ligand; CSF-1: colony-stimulating factor-1; OPG: osteoprotegerin; PGE2: Prostaglandin E 2; PGHS-2 prostaglandin synthase-2

Bone Histomorphometry Under GCs

 

Trabecular bones and the cortical rim of vertebral bodies are more susceptible to the effects GCs compared to the cortical component of long bones (radius, humerus) (58-62). Under GC treatment, lumbar bone shows significantly greater bone loss compared to distal radius. Bone loss is also observed in the proximal femur (particularly at Ward’s triangle, an area rich in trabecular bone) (63, 64). Although bone remodeling is initially turned on with higher bone resorption, over time, resorption parameters fall and bone becomes quiescent (65, 66). Thus, with prolonged GC administration, cortical bone becomes increasingly affected and long bones show increased fragility.

 

Bone biopsies of patients on GC therapy for longer than 12 months show increased bone resorption, a decline in all aspects of bone formation, and decreased trabecular volume. Histomorphometric studies on subjects with GCOP show increased osteoclasts and bone-resorbing sites; bone loss is higher in the metaphyses compared to the diaphyses (67-69). A specific feature of GCOP is the decrease in canopy coverage of bone remodeling sites (52, 55). GCOP differs from post-menopausal OP in terms of microanatomical appearance; in GCOP the number of trabeculae and their surface area are relatively preserved, and individual plates are very thin (trabecular attenuation), although still connected, whereas in post-menopausal OP, trabecular width is relatively preserved but the lamellae are perforated by resorption, with a loss of trabecular surface and continuity (70). Such changes may lead to lower mechanical strength of bone. The particular histology of GCOP may have important implications for pharmacologic intervention: the preservation of thinned trabeculae in GCOP may provide the foundation for new bone apposition. With excess GCs, osteoclasts, over time, preferentially deepen their resorption pits than migrate to new resorption sites (52).

 

Glucocorticoid Receptors (GRs) and Bone

 

There is still no consensus on whether genomic or non-genomic actions of GCs are the major players in GCOP (71). Genomic actions result from the binding of GCs steroids to specific cytoplasmic receptors that belong to the nuclear receptor superfamily. The GC-GR complex can either activate or repress the expression of target genes. While activation requires binding of a dimerized receptor to GC-responsive elements (GREs) in the promoter region of target genes, repression is mainly mediated by interaction between receptor monomers and transcription factors (72). GC-induced osteoblast apoptosis does not require GR dimerization (52). Translation of GR mRNAs produces two GR isoforms; GRα, which is transcriptionally active and GRβ, which can heterodimerize with GRα inhibiting its transcriptional activity (73). In humans, normal osteoblasts, and specific osteoblastic cell lines show GRα expression, whereas mature osteoclasts show no GRα expression. Osteoclasts, in contrast, predominantly show GRβ expression. Osteoblasts and osteoclasts also express mineralocorticoid receptors (MRs) that bind to cortisol and form heterodimers with both GRα and GRβ (74). IL-6, in human osteoblasts, acts as an autocrine positive modulator that upregulates the number of GRs (75, 76). Cortisol, even at physiologic concentrations, modulates negatively the secretion of IL-11, a cytokine that decreases GR expression (77). Consequently, this interplay of cytokines through autocrine/paracrine loops may modulate bone sensitivity to GCs (78).

 

GCs and Osteoblast Activity

 

In response to pharmacologic doses of GCs, osteocytes trigger the protective process of autophagy; with excessive doses of GCs autophagy leads to apoptosis (79). GCs increase the apoptosis of osteoblasts and mature osteocytes via activation of caspase 3 (1, 80-83). Osteoblast/osteocyte apoptosis may involve decreased expression of the pro-survival factor BclXL and increased expression of the proapoptotic factors Bim and Bak (through induction of the leucine zipper E4bp4) (52, 84). Apoptosis is also assisted by GC-induced excess reactive oxygen species (ROS) production and inhibition of Akt, leading to suppression of the Wnt/β-catenin pathway, which is necessary for osteoblastogenesis as well as for cell survival (52, 85). Studies on the proaptototic effect of GCs on osteoblasts/osteocytes, indicate that it may be mediated by the process of endoplasmic reticulum stress (86). Furthermore, GCs reduce osteoblast proliferation and differentiation (62), possibly as a result of GC-induced repression of bone morphogenic protein-2 (BMP-2) and expression of core binding factor a1 (Cbfa1) (84). GCs also modify the expression of osteoblast specific genes, such as osteocalcin. Osteocalcin expression during the development of bone is tightly regulated by GCs, and multiple GREs have been identified on the human and rat osteocalcin promoter region (87, 88). The osteocalcin gene also contains several activator protein-1 (AP-1) sites that apparently contribute to the basal activity of the promoter. Therefore, repression of osteocalcin promoter activity by GCs may also involve interaction between GR and components of the AP-1 complex, independently of DNA binding, as it has been postulated for the collagenase promoter (89, 90).

 

The Wnt signaling pathway is important for osteoblast differentiation and function, bone development and level of peak bone mass (91). Mechanical loading results in increased bone mass in animals that carry activating mutations of Lrp5 (coding for a Wnt coreceptor)(91). Wnt signaling may be implicated in the osseous response to mechanical loading (91) and the observed inhibition of skeletal growth by GCs may be mediated by effects on Wnt signaling (92)by enhancing Dickkopf 1 (Dkk1) expression (which is a Wnt antagonist) and Sost (sclerostin, which is a disruptor of the Wnt-induced Fz-Lrp5/6 complex leading to β-catenin ubiquitination) (52, 62, 93). Interestingly, both short- and long-term GC administration decreases Dkk1 expression in humans whereas only long-term GC administration decreases Sost expression; Wnt signaling involvement in GCOP appears to be time-dependent (52). The inhibition of Wnt signaling is also involved in GC-induced adipocyte differentiation (52).

 

GCs are required for the differentiation of mesenchymal stem cells to bone cells; they can also promote an osteoblastic phenotype (by inhibiting collagenases (MMPs) and reducing collagen type 1 breakdown) (94-96). Impaired osteoblastogenesis by excess GCs involves the reduction in expression of microRNAs (endogenous RNAs of 18-25 nucleotides each that interact with mRNA to alter protein expression) (97), such as miR-29a/miR-34a-5p and reductions in the mRNA expression of Dkk1/receptor activator of the nuclear factor-κB ligand (RANKL) (98).

           

GCs and Osteoclast Activity

 

Compared to effects of GCs on osteoblasts, the effects of GCs on osteoclasts are less known as osteoclast isolation from bone is technically difficult and bone marrow cultures, hematopoietic cell lines and cells derived from giant-cell tumors (used as model systems to study osteoclast differentiation and activity) have produced varying results. GCs stimulate bone resorption (99-101). It has been shown that GCs stimulate osteoclastogenesis through their capacity to bind to the bone surface by altering the expression of N-acetylglucosamine and N-acetylgalactosamine (85, 102). Osteocyte apoptosis, induced by GCs, reduces osteoprotegerin (OPG, the decoy RANKL ligand) (52). GCs may decrease apoptosis and prolong the lifespan of mature osteoclasts (52, 62) but cannot affect directly their bone-resorbing activity, since these cells apparently lack functional GRs (103). GCs suppress calpain 6 (Capn 6) which is enmeshed in β-integrin (a mediator of osteocyte interaction with the osseous matrix) and expression of microtubules’ acetylation/stability within the bone cells cytoskeleton (52). Higher expression of the GR gene in subjects with lower BMD may lead to higher sensitivity of their monocytes/macrophages to GCs to differentiate into osteoclasts (104). Cytokines are also implicated in these actions (see next section on regulation of local bone factors by GCs) (105).

 

GCs and Local Bone Factors (Cytokines, Growth Factors, Prostanoids and Kinases)

 

CYTOKINES

 

Interleukin-1 (IL-1) and -6 (IL-6) induce bone resorption and inhibit bone formation. GCs partially inhibit the production of IL-1 and IL-6 and inhibit the bone resorbing activity of these cytokines (GC therapy could paradoxically protect osseous tissue from IL-induced bone resorption) (106-109). Transforming growth factor beta 1 (TGF-b, which inhibits IL-1-induced bone resorption and stimulates osteoblast activity) is decreased by GCs. (110). Lower levels of TGF-bmay increase the susceptibility of bone to the resorbing effects of IL-1. IL-1 suppression also inhibits the generation of nitric oxide, which modulates osteoclast activity (111). Excess GCs inhibit the expression of IL-11 on osteoblasts (and hinder this cytokine’s effect on their differentiation) independently of GR dimerization (52). GCs interfere with the RANKL-OPG axis. RANKL (which is expressed at high levels in pre-osteoblast/stromal cells) induces osteoclast differentiation in the presence of colony-stimulating factor-1 (CSF-1) by binding to the receptor activator of the nuclear factor-κB (RANK; a member of the TNF family on the surface of octeoclasts(108). OPG is also produced by osteoblasts and is found on their surface. OPG acts as a decoy receptor of RANKL: it binds RANKL and prevents it from binding its osteoclast receptor, therefore inhibiting osteoclast differentiation. GCs enhance RANKL and CSF-1 expression (78), and lower OPG expression in human osteoblasts cells in vitro (112). Serum OPG concentrations are significantly reduced in patients undergoing systemic GC therapy (113). This decrease in OPG is more marked than the GC-induced increase in RANKL (via suppression of miR-17/20a, which targets Rankl) (52), leading to an increased RANKL/OPG ratio that may mediate GC-induced bone resorption (114).

 

GROWTH FACTORS

 

Insulin-like growth factors (IGFs) have an anabolic effect on bone cells that affect IGF-I and IGF-II receptors. IGF-I and IGF-II are weak mitogens (they increase the replication of osteoblasts), they increase type I collagen synthesis and matrix apposition rates and decrease collagenase-3 (metalloproteinase-13) expression by osteoblasts (115, 116). Synthesis of IGF-I in osteoblasts is decreased by GCs via increased expression of the CAAT/enhancer binding protein (C/EBP) β and δ (transcription factors that bind to the IGF-I promoter and halt its transcription) (117). GCs inhibit IGF-II receptor expression in osteoblasts (while they have no effect on IGF-I receptor expression)(118, 119). Since the IGF-II receptor functions as an IGF-binding protein (IGFBP) its inhibition by GCs may result in higher levels of available growth factors although it may also lead to faster degradation of IGF-II. The activity of IGF-I and -II is regulated by at least six IGFBPs that are expressed by osteoblasts (120, 121). IGFBPs in skeletal cells are considered to be local reservoirs and modulators of IGFs. GCs decrease the expression of IGFBP-3, -4, and -5 in osteoblasts (122, 123). IGFBP-5 stimulates bone cell growth (and enhances the effects of IGF-I); its reduction in the bone microenvironment may be relevant to the inhibitory actions of GCs on bone formation and the process of GCOP (124). GCs also increase the synthesis of IGFBP-related proteins (IGFBP-rPs; a family of peptides related to IGFBPs that bind IGFs and are involved in cell growth) (125). Chondrocytes are involved in fracture healing and in OP this process is delayed. Among others, GCs inhibit the activation of GH and IGF-I receptors in chondrocytes and reduce IGF-I and GH receptor expression in these cells (126).

 

Bone cells express transforming growth factor-b (TGF-b) -1, -2, and -3 genes (127). TGF-b stimulates bone collagen synthesis and matrix apposition rates, modifies bone cell replication, stimulates growth and proliferation of osteoblasts but inhibits their differentiation and the expression of osteocalcin (128, 129). TGF-b1 expression in osteoblasts is not modified by GCs. GCs, instead, induce activation of the latent form of TGF-b1 by increasing the levels of bone proteases (130, 131). Two signal-transducing TGF-b receptors are expressed in osteoblasts. GCs shift the binding of TGF-b from these receptors to betaglycan (by increasing the synthesis of this proteoglycan) and oppose the effects of TGF-b osteoblastic cell replication (130).                     

 Hepatocyte growth factor (HGF) is produced by both osteoblasts and osteoclasts. HGF is a potent stimulator of osteoblastic function and a potent suppressor of bone resorption in isolated rat osteoclasts (132). Osteoclast-produced HGF (in an autocrine fashion), may lead to changes in osteoclast shape and stimulate osteoclast migration and chemotaxis, while (in a paracrine fashion) may lead osteoblasts to enter the cell cycle, via DNA synthesis stimulation (132, 133). GCs inhibit the release of HGF in vitro, which suggests that the inhibitory effects on bone resorption of GCs may be in part mediated via regulation of osteoblast-produced HGF (134, 135).

 

Platelet-derived growth factor (PDGF) is a mitogen of bone cells (136). PDGF-A and PDGF–B are expressed in a limited fashion in osteoblasts, and neither the synthesis nor the binding of PDGF appear to be modified by GCs. Specific PDGF-A/B binding proteins are lacking, although SPARC (secreted protein acid rich in cysteine) and osteonectin (a protein abundant in bone matrix) bind and prevent the biologic actions of PDGF-B (137). Since GCs enhance osteonectin expression in osteoblastic cells they may also decrease the activity of PDGF-B in bone (138).

 

PROSTANOIDS

 

Prostaglandins (PGs) are produced by bone cells and affect both bone formation and resorption. PGs (and PGE2 in particular) stimulate bone collagen and non-collagen protein synthesis (139-141). PGs inhibit directly the activity of isolated osteoclasts and increase bone resorption in organ cultures, (probably by promoting osteoclastogenesis) (142). GC-induced inhibition of collagen synthesis in bone, down-regulation of c-fos oncogene expression and reduced osteoblast proliferation are all reversed by exogenous PGE2in vitro, suggesting an important pathogenic role for this PG in GCOP (143-147). GCs interfere with the production of PGs in bone (especially of PGE2) via the decreased expression of cyclooxygenases (the enzymes that convert arachidonic acid into PGs) (148, 149). Osteoblasts express two cyclooxygenases: constitutive prostaglandin synthase-1 (PGHS-1) and inducible prostaglandin synthase-2 (PGHS-2). Apparently, GC-inhibited PG-production in bone is mediated through a decrease in agonist-induced PGHS-2 expression.

 

KINASES

 

GCs modulate intracellular kinases (ERKs, MAPK/JNK and Pyk2) with a proapoptotic effect on the osteoblastic lineage  (150)

 

EXTRASKELETAL MECHANISMS OF GCOP

 

Effects of GCs on Calcium Absorption and Excretion

 

Although there is no consensus regarding the effect of GCs on calcium absorption, they mainly impair intestinal calcium absorption (151-158). GCs have no effect on the intestinal brush border membrane vesicles (159), but decrease synthesis of calcium binding protein and deplete mitochondrial ATP (160). Patients treated with GCs show increased renal calcium loss occasionally leading to the development of secondary hyperparathyroidism (161). In normal subjects receiving GCs the elevation of fasting urinary calcium proceeds the rise in immunoreactive parathyroid hormone (iPTH) (162). In patients on long-term GC therapy, hypercalciuria is most likely due to increased skeletal mobilization of calcium and decreased renal tubular reabsorption that occurs in spite of elevated PTH levels. The GC-induced decrease in bone formation lowers calcium uptake by newly formed bone and elevates the filtered load of calcium. High dietary sodium intake increases renal loss of calcium whereas sodium restriction and thiazide diuretics lower its renal loss (163).

 

Effects of GCs on the Excretion of Phosphorus

 

GCs, acting directly on the kidney and indirectly, via induction of secondary hyperparathyroidism, lower tubular reabsorption of phosphate, leading to phosphaturia (164, 165). Furthermore, GCs increase the amiloride-sensitive Na+/H+ exchange activity in the renal proximal tubule brush border vesicles and decrease the Na+ gradient-dependent phosphate uptake, resulting in  increased acid secretion and phosphaturia (166).

 

GC Effects on Parathyroid Hormone (PTH)

 

A direct stimulatory effect of GCs on PTH secretion may also exist (164, 167, 168). GCs induce a negative calcium balance that leads to secondary hyperparathyroidism; in patients receiving GCs iPTH is increased, that can be suppressed with exogenous calcium and vitamin D (168, 169). Chronic GC administration is accompanied by altered secretory dynamics of PTH; more particularly, it reduces its tonic secretion and increases its pulses (170). However, elevated iPTH levels can also be suppressed following calcium infusion, suggesting that its  elevation is more likely to be secondary to a negative calcium balance caused by GCs, rather than to direct stimulation of PTH secretion (171).

 

Effects of GCs on Vitamin D Metabolism

 

Low, normal, or increased circulating levels of 1,25-dihydroxyvitamin D (1,25-(OH)2D) have been reported in subjects taking GCs (171-174). These differences may originate from variations in the dietary intake and absorption of vitamin D and in exposure to sunlight. The rate of synthesis and clearance of 1,25-(OH)2D is normal in subjects receiving GCs (175). Although the administration in humans of 1,25-(OH)2D improves calcium transport, it does not normalize it (176).

 

GC Effects on Sex Hormones

 

GCs inhibit the secretion of gonadotropins and also show direct effects on the gonads and the target tissues of gonadal steroids. In rats, GCs reduce the action of follicle-stimulating hormone (FSH) on granulosa cells and inhibit the response of luteinizing hormone (LH) to gonadotropin-releasing hormone (GnRH) (177-179).In rats and primates, GCs also decrease GnRH secretion; furthermore, in rats, overexposure to GCs renders their pituitary insensitive to exogenously administered GnRH (180-182).In men and women given GCs the plasma concentrations of estradiol, estrone, dehydroepiandrosterone (DHEAS), androstenedione, and progesterone are decreased (183-185). High-dose GC therapy in women may lead to amenorrhea. Although the exact targets of GC inhibition of steroidogenesis in Leydig or granulosa-theca cells are not fully defined, recent studies have found a GC-responsive upstream promoter region of the cholesterol side-chain cleavage gene (186).  In postmenopausal women an additive effect of GC treatment with estrogen deficiency on bone loss is observed (187, 188).

 

GC Effects on Growth Hormone (GH)

 

GH is an important regulator of both bone formation and bone resorption. in vitro studies have shown that the GH-induced increase in bone formation is twofold: by direct interaction with GH receptors on osteoblasts, and through induction of an endocrine and autocrine/paracrine IGF-I effect (189). In contrast, in animals high endogenous GCs or exogenous exposure can inhibit linear growth and GH secretion in animals. In patients with GCOP a lower GH response to growth hormone–releasing hormone (GHRH) and a positive correlation between GH increment and osteocalcin are observed. This inhibitory effect of GCs on the secretion of GH may be dependent on an increase in somatostatin synthesis and secretion, which inhibits pituitary GH secretion. Arginine, which decreases hypothalamic somatostatin tone, normalizes the GH response to GHRH (190, 191). Bone sensitivity to GH may also reduce by GCs: an up-regulatory effect on GH receptor expression may be implicated (192).

 

GC Effects on Connective Tissue

 

Excess GCs hinder wound healing via suppression of DNA and protein synthesis in fibroblasts and impaired local macrophage recruitment (193, 194).

 

GC Effects on Muscle

 

Common side effects of GC excess include muscle weakness and loss of muscle mass. Alterations of muscle biopsies of GC-treated patients include selective atrophy of type IIa muscle fibers, relative increase in the number of type IIb fibers and decrease in the number of type I fibers (195-197). The main mechanisms implicated in GC-induced myopathy are increased protein catabolism, inhibition of glycogen synthesis, and interference with fatty acid β-oxidation (83). In fact, GCs stimulate ubiquitin-proteasome-dependent protein breakdown in skeletal muscle and regulate calcium-dependent proteolysis (198, 199).Moreover, levels of glycogen synthase, beta-hydroxyacyl-CoA dehydrogenase and citric acid synthase, are lower in muscle from GC-treated patients compared to muscle from disease-matched controls (200). A strong association between steroid myopathy and OP has been described (201).

 

INDIVIDUAL SUSCEPTIBILITY TO GCOP

 

Some patients on a low GC dose show bone loss at a much higher rate than others on a higher GC dose (202). Genetics may play a role in determining this difference. Little is known about the mechanisms of cellular sensitivity to GCs. Individual factors are also important in determining the risk of fractures when GCs are used. Polymorphisms in the GR gene have been linked to the varied degrees of susceptibility to GCs; these could explain the different rates of GC-associated fractures (97). Individuals that are heterozygous for a polymorphism at nucleotide 1,220 (resulting in an Asparagine-to-Serine change at codon 360), had increased BMI, increased blood pressure and lower spine BMD compared to control subjects (203, 204).

 

Another explanation for inter-individual variability among those exposed to GCs is related to differential activity of 11b-hydroxysteroid dehydrogenase (11b-HSD) (205). This enzyme system plays a critical role in the regulation of GCs activity (206). Two distinct 11β-HSD enzymes have been described; 11b-HSD1 (converting cortisone [E] to cortisol [F] and 11b-HSD2 (converting F to E) modulate GC and mineralocorticoid hormone action in target organs (205, 207, 208). 11β-HSD1 is widely expressed in GCs target tissues, including bone (206). The reductase activity does not show a large inter-individual variability, whereas the oxidase activity of 11b-HSD2 has a large inter-individual variability. Subjects with higher oxidase activity at bone level may be at greater risk of developing GCOP (209). Men with OP were shown to have increased endogenous GC availability, via apparent 11b-HSD1 activation (210). The activity of 11β-HSD1 and the potential to generate F from E in human osteoblasts is increased by pro-inflammatory cytokines (TNFa, IL-1b and IL-6) and by GCs themselves (211, 212). During inflammation pro-inflammatory cytokines may potentiate GC actions in bone through an “intracrine” mechanism (209, 213). An increase of 11β-SD1 activity occurs with aging, possibly providing an explanation for the enhanced GC effects in the skeleton of elderly subjects (214).

 

In the future, the characterization of factors accounting for the variability to GC-related bone loss among individuals may identify subjects at higher risk of developing GCOP and, possibly, customize treatment.

 

DIAGNOSIS OF GCOP

 

Medical History and Clinical Evaluation

 

Table 1 summarizes elements from medical history suggestive of GCOP and the modalities available for its diagnosis. Any patient that is treated with long-term (for over a month) GCs should be suspected as suffering from GCOP (215). The risk for GCOP is higher in postmenopausal women, transplant recipients, and patients with sarcoidosis (216-220). Bone loss depends on the dose, route, and duration of GC administration (218-220).

 

Table 1. Clues and Diagnostic Means for GCOP

Medical history

Sex and age

History of OP and/or trauma fractures

History of allergy, chronic inflammatory or autoimmune disease, hematologic, skin and renal disorders, transplantation

Calcium and alcohol intake, smoking, physical activity

Chronic use of anticonvulsants, heparin, immunosuppressants

Menstrual, menopausal or fertility status 

Clinical evaluation

Truncal obesity, edemas, striae, skin atrophy and ecchymoses

Myopathy (myalgias, weakness of the proximal muscles and pelvic girdle)

Assessment of temporal baldness, loss of body hair, gynecomastia, altered pubic hair pattern, decreased testicle and prostate size

Laboratory evaluation

Complete blood cell count, liver and renal function, serum electrophoresis

Serum calcium and phosphate, serum 25-OH-vitamin D, serum alkaline phosphatase, PTH

Osteocalcin, bone-specific alkaline phosphatase, procollagen type I extension propeptides)

Hydroxyproline, hydroxylysine glycosides, hydroxypyridinium cross-links, type I collagen telopeptides)

Thyroid hormone profile, total and free testosterone, estradiol, luteinizing hormone, prolactin, ferritin

Bone mineral density assessment

 

 

Lateral scan (vertebral bodies) and anteroposterior scans (spine, hip) with dual-energy X-ray absorptiometry (DXA) – Trabecular Bone Score (TBS) in lumbar spine (if available)

·                  Assessment of vertebral compression fractures with X-ray        

 

 

Cushingoid clinical features include truncal obesity, skin atrophy with increased fragility and ecchymoses, fluid retention, hyperglycemia, and symptoms of vertebral compression and myopathy. Muscle strength needs to be assessed by a trained physician or specialized physical therapist, with special attention to the testing of proximal muscle groups. A brief exposure to GCs may trigger myopathy that is not always dose-dependent, and is often difficult to differentiate from inflammatory myopathy. However, GC myopathy is characterized by creatinuria and normal muscle enzymes, including aspartate aminotransferase, creatine kinase, and aldolase (195, 201).

 

Men and women on chronic treatment with GCs often have symptoms of hypogonadism, such as decreased libido and sexual activity, and may show low rates of fertility or even infertility. In premenopausal women history taking should assess menstrual periods, since subtle changes, including less bleeding and shortened menstrual periods, may be indications of low estrogen levels. Menstrual irregularities are also common in women with endogenous GC excess.

 

Various respiratory, dermatologic, musculoskeletal, neurologic and gastrointestinal disorders are frequently treated with GCs. Signs and symptoms of such disorders need to be evaluated.

 

Laboratory Tests and Markers of Bone Turnover

 

Laboratory evaluation for GCOP should include total blood cell count, markers of renal and liver function, serum electrophoresis, serum and 24-hr urine calcium, serum levels of 25-hydroxyvitamin D, alkaline phosphatase, thyroid-stimulating hormone and parathyroid hormone, estradiol in women and total and free testosterone in men (218-221).

 

In patients receiving GCs a dose-dependent decrease in serum osteocalcin is found; this is a good indicator of the degree of inhibition of osteoblastic activity (222, 223). Other markers of bone formation, such as total and bone specific alkaline phosphatase and procollagen type I carboxy-propeptide are also lower in under GC therapy (162, 224). In subjects on GC therapy baseline levels of osteocalcin do not always correlate with subsequent bone loss (225-227). In some, but not all, studies of patients treated with GCs, markers of bone resorption (like urinary collagen N-telopeptides [NTX]) are elevated (165, 228-230). In view of such discrepancies, the measurement of serum markers of bone formation and resorption is considered to be of little clinical utility and it is not currently advocated for routine use (217).

 

Bone Mineral Density (BMD) Assessment

 

Changes in BMD early on during GC therapy can be detected by dual-energy X-ray absorptiometry (DXA) and quantitative computed tomography (QCT); classic X-ray studies are useful to detect vertebral compression fractures. Both QCT and DXA can measure cortical and trabecular bone density, however, the former is mostly used to evaluate trabecular bone density, whereas the latter is used to measure cortical and trabecular bone density (231, 232). DXA also helps estimate the risk for fractures, and provides an objective measurement to judge the efficacy of treatment (221, 233, 234). BMD measurement techniques that focus on the vertebral body and exclude the cortical bone of posterior processes, such as lateral DXA scanning, are more sensitive in detecting GCOP (61, 235). However, the selection of a BMD assessment method is influenced by the presence of vertebral deformities, osteophytes, or of calcifications in the aorta that may spuriously elevate spinal BMD values. If this is the case, lateral views of the vertebral bodies are considerably less precise than antero-posterior scans, and therefore less appropriate for following up changes in bone mass. When marked osteophytosis or scoliosis of the spine is seen, proximal femoral densitometry (in the femoral neck) should be chosen (63). The trabecular bone score (TBS), which is a DXA analytical tool that hones on lumber vertebral microarchitecture, may be useful in assessing GCOP (236, 237).

 

In patients under glucocorticoid treatment fractures tend to occur at BMD values that are lower than the conventional threshold T-score of -2.5 (238, 239). A T-score threshold value of – 1.5 SD is usually the cutoff for GCOP in Europe (5), whereas the American College of Rheumatology (ACR) has defined the T-score cut off to – 1.0 SD to separate “normal” from “not normal” BMD (220). Furthermore, the ACR recommends BMD baseline measurements at the lumbar spine and/or hip before starting any GC treatment longer than 6 months (220). At 6 month intervals from the baseline assessment, or at 12 month intervals, if the patient is receiving therapy to prevent bone loss, follow-up measurements should be done (240, 241). For the United States in particular, Medicare reimburses BMD evaluation for patients on chronic treatment with GC doses higher than 7.5 mg/day of prednisolone equivalent (242).

 

The Fracture Risk Assessment tool (FRAX) estimates the 10-year risk for osteoporotic fractures at the hip and other sites. FRAX is criticized since it uses hip BMD, whereas vertebral fractures may be more common than hip fractures in subjects receiving GCs (243). Recently simple adjustments for the calculated fracture risk have been presented that take into account glucocorticoid dosage (244) (Figure 2). Use of FRAX is currently advised to stratify GC-treated patients in low, moderate and high fracture risk categories (245, 246).

Figure 2. Fracture risk stratification and FRAX fracture risk corrections according to glucocorticoid usage (modified from (245); # fracture; T: T-score; postmenop: postmenopausal; corr: corrected; * x 1.15 if glucocorticoid dose > equivalent to 7.5 mg prednisone/day; **x 1.20 if glucocorticoid dose > equivalent to 7.5 mg prednisone/day; ***for > 6months; Z: Z-score; GC Rx: glucocorticoid therapy

PREVENTION AND TREATMENT OF GCOP

 

Guidelines for the prevention and treatment of GCOP have been put forth from the ACR in 2001, in 2010 (220, 247)and more recently in 2017 (245), the UK Consensus group in Management of GCOP (240) and the Belgian Bone Club (248), among others.

 

General Preventive Strategies

 

As soon as GCs are administered prevention of GCOP should start; bone loss is more rapid in the first months of therapy. The minimal effective GC dose should be used. Although alternate day therapy seems attractive it has not been proven to hasten bone loss in adults (202, 249); the persistent depression of adrenal androgen production may be the culprit (250).

 

The concept of “safe dose” for the treatment with oral GCs is controversial (66). More particularly, prednisone given at low doses (2.5-9 mg/d) may affect BMD whereas lower doses (1-4 mg/d) were reported to have very little or no skeletal effect (251, 252). Intravenous high-dose (up to 1 g) methylprednisolone administration is not onerous to bone (253) but even a single oral dose of 2.5 mg of prednisone has an almost immediate negative effect on osteocalcin secretion (254). Alternate-day GC administration may prevent growth retardation in children but not bone loss (202, 249). Thus, despite the ambiguity of the literature, an equivalent dose equal to or higher than 2.5 mg of prednisone per day for a month seems a sensible threshold to give protection against GCOP.

 

Inhaled GCs may be better than oral or systemic GCs vis-à-vis bone health, but still have their osseous tissue complications (22, 255). Newer inhaled GCs (such as budesonide), seem to have less adverse effects on the bone, as indicated by measurements in bone markers (256, 257). Dosing of the inhaled GC is important; beclomethasone dipropionate or budesonide given at low doses for more than one year did not affect spine BMD in asthmatic subjects (257). However, patients treated with high doses of inhaled budesonide or beclomethasone (1.5 mg/day, for at least 12 months) and without prior oral GC treatment for more than 1 month, had a significant decrease in BMD and bone formation markers, with no changes in bone resorption markers (258). In another study, inhaled GCs in adults with chronic lung disease were not associated with increased fracture risk (and more in detail no dose-response curve was verified) (259). Moreover, in children treated with beclomethasone for bronchial asthma, analysis after adjustment for the severity of the underlying disease did not show any association between inhaled GCs and fracture risk (260). Thus, in children, other factors, such as excess body weight, low muscle mass and limited exercise capacity may predispose to low BMD (261).

 

Another factor that should be noted is the change in lifestyle for the prevention of GCOP. Diet should be rich in calcium and protein (262). Alcohol and sodium intake should be reduced (to 1-2 units of alcohol/day (245)), smoking should be stopped and a regular exercise program should be followed (37). Subjects on GCs may benefit if they are protected from falls (217, 263).

 

An important, yet often neglected by most prescribing physicians (93), facet of GC-treatment is the need for proper patient information and acknowledgement regarding untoward effects. A signed relevant patient acknowledgement form should be included in medical charts/files to avoid malpractice litigation (243). 

 

Therapeutic Options

 

Therapy for GCOP aims to prevent and minimize bone loss, to increase BMD and, at least partially, to reverse the effects of GC excess. Some therapies should be continued for as long as GC treatment is pursued. The usual primary outcome in most reported – to date - trials of GCOP-specific treatments, is the change from baseline in vertebral BMD vis-à-vis placebo or other treatments; few trials have also assessed fracture rates (264, 265). 

 CALCIUM AND VITAMIN D SUPPLEMENTATION Patients on GCs should receive supplementation with calcium and vitamin D; this is better than no supplementation or calcium alone (262). A daily dose of 1,500 mg calcium and 800 IU vitamin D (1 μg/day of α-calcidiol or 0.5 of μg/day calcitriol) effectively oppose negative calcium balance (220). A two-year randomized clinical trial demonstrated the efficacy of combined calcium and vitamin D supplementation in preventing bone loss in patients with rheumatoid arthritis treated with low doses of GCs (266). However, these encouraging findings were not replicated in a three-year follow-up study, where the same combination did not show any benefit (267). From randomized clinical trials and meta-analyses it was shown that active metabolites of vitamin D (α-calcidiol and calcitriol) are more effective than vitamin D in maintaining bone density during medium-to-high dose GC treatment (268-271). Treatment with active forms of vitamin D entails a risk of hypercalciuria and hypercalcemia, consequently periodic assessment of serum calcium and creatinine levels at the beginning of the therapy, after 2-4 weeks, and thereafter every 2-3 months is advised (272, 273). Currently - according to the ACR (245) - optimal intake for calcium is set at 1000 mg/day and at 600-800 IU/day for vitamin D.

 

Thiazide diuretics lower urinary calcium excretion. Chronic treatment with thiazides decreased the incidence of hip fracture in elderly patients, and increased BMD in the general population (274-276). This evidence suggests that, together with sodium restriction, they may be useful in opposing calcium loss and secondary hyperparathyroidism caused by chronic GC therapy. However, there are currently no studies showing long-term effect of thiazide diuretics on BMD in patients treated with GCs.

 

ANTIRESORPTIVE THERAPY

 

There are several antiresorptive agents available for the prevention and treatment of GCOP.

 

Bisphosphonates decrease the resorptive activity of osteoclasts, increase osteoclast apoptosis and decrease osteoblast and osteocyte apoptosis (277). Their efficacy in preventing and treating GCOP has been clearly shown in large randomized controlled clinical trials (278-280). Treatment with alendronate for 18 months or two years increased total body BMD, and – according to some studies - significantly decreased risk of vertebral fractures in patients taking GC (281, 282). In a one-year study of patients on GCs having undergone cardiac transplantation subjects given alendronate had lower bone loss compared to subjects on calcitriol or no other treatment (-0.7%, -1.6% and -3.2% for the lumbar spine and -1.7%, -2.1% and -6.2% for the femoral neck BMD, respectively); vertebral fracture rates were not different in the three groups though (283).  In a meta-analysis of published randomized clinical trials of patients with GCOP who were given alendronate for 6-24 months, BMD in the lumbar spine as well as in the femoral neck increased but the fracture rate was not different compared to that of patients who were given only calcium, serving as a control group (284). Similarly, a one-year study with risedronate in patients taking prednisone (7.5 mg/day for at least 6 months) showed an increase in lumbar spine and femoral neck BMD and an impressive – though prone to bias due to limited sample size -  70% decrease in the relative risk of vertebral fractures (285). Zoledronic acid, a long-acting potent bisphosphonate given intravenously (4-10 mg once or twice a year) has excellent anti-OP results (286-291) and has been assessed in GCOP. The HORIZON study lasted for one year and tested the effectiveness of 5 mg intravenous zoledronic acid (n=416) vs. risedronate (n=417) in subjects with GCOP; the former led to greater increase in lumbar bone mineral density and greater decrease in bone turnover compared to the latter (292). The study did not show differences in fracture risk most probably because of its short duration. Pyrexia (particularly in the first three days post-infusion) and worsening of rheumatoid arthritis were noted more often in the zoledronic acid group (292).  

 

Oral bisphosphonates are a first choice for anti-resorptive therapy, followed by intravenous bisphosphonates (245), the latter are a first choice in pediatric GCOP (293). Currently, alendronate po (70 mg/week), risedronate po (35 mg/week or 75 mg on two consecutive days per month) and zolendronic acid iv (5 mg once a year) are recommended to treat men and women receiving GC treatment (247); therapy is advised for at least two years (294). Oral ibandronate (150 mg once a month) given for GCOP in men and women has positive results – particularly regarding spine BMD and vertebral fractures (295).

 

In patients with rheumatoid arthritis and connective tissue diseases who are treated with the RANKL inhibitor denosumab, lumbar spine (296-298) and femoral neck (297) BMD increase. Denosumab sc (60 mg every six months) is henceforth also proposed as treatment for GCOP (245, 299); it is considered to be superior in therapeutic effect on lumbar spine BMD, total hip/femoral neck BMD and vertebral fractures’ incidence compared to bisphosphonates (300, 301). The downside of Denosumab is that its discontinuation is followed by rapid bone loss (302); some experts consider that this makes it less attractive as a treatment for GCOP (303). Denosumab can also be a therapeutic option in patients with renal insufficiency who cannot receive bisphosphonates or teriparatide (243).

 

ANABOLIC THERAPY

 

Anabolic medications enhance bone formation, therefore antagonizing the suppressive effect of GCs on osteoblasts. However, some of the information on the use of these compounds to prevent or treat GCOP comes from small studies.

 

Recombinant PTH administration (400 IU of PTH 1-34; teriparatide) to postmenopausal women on prolonged estrogen replacement, who had developed OP after chronic GC therapy, resulted in increased lumbar spine bone mass, assessed by both DXA and QCT, which was maintained after discontinuation of teriparatide (304, 305). An 18-month long randomized double-blind trial compared teriparatide vs alendronate in subjects with GCOP; the increase in lumbar BMD was higher with teriparatide (+4.6 to +8.1% vs. +2.3 to +3.6%) than for alendronate at 18 months. Better results were noted for those taking low GC doses and fewer vertebral fractures occurred with teriparatide compared to alendronate (0.6% vs 6.1%) whereas the non-vertebral fracture rate did not differ between treatment groups (306). Analogous results were noted when the trial was extended to 3 years: lumbar spine BMD increased by +11.0% for teriparatide vs +5.3% for alendronate whereas the respective femoral neck BMD change was +6.3% vs +3.4% (307). Teriparatide can be a therapy of choice (20 microg/day sc) for patients on GC treatment and/or with GCOP, following intravenous bisphosphonates on a par with denosumab as proposed in the ACR guidelines (245, 247, 308, 309). The combination of teriparatide and bisphosphonates may not have an additive effect on bone (310); it is not advised for GCOP. Nevertheless, bisphosphonates given after stopping teriparatide therapy help maintain the bone formed by teriparatide (311).

 

Sodium fluoride, in combination with either calcium and vitamin D, or cyclic etidronate, improved lumbar spine BMD and trabecular bone volume in GC-treated patients. However, no reduction in the incidence of fractures was observed. Moreover, fluoride induced bone loss at the femoral neck (312, 313). Since most of the evidence indicates that sodium fluoride does not provide architecturally competent bone, its use is currently not recommended for GCOP (220).

 

Anabolic steroids have also been tested in GCOP. Cyclic nandrolone decanoate (50 mg i.m. every three weeks for six months) increased the forearm bone density in GC treated women, 10% of which developed virilizing side effects (314). The typical negative effects of steroids on bone are not present with nandrolone because it is metabolized to dihydrotestosterone (DHT). Similarly, cyclic medroxyprogesterone acetate (200 mg i.m. every 6 weeks for one year) augmented lumbar spine BMD in treated men (315). Currently, there is no recommendation for the use of anabolic steroids for GCOP.

 

GONADAL HORMONE THERAPY

 

Sex hormone treatment should be considered whenever a patient with GC excess develops hypogonadism (278). A retrospective study in postmenopausal women taking GCs found an increased BMD in those who were taking estrogens, compared to increasing bone loss in those who were not (316). Moreover, in a randomized controlled clinical trial of postmenopausal women taking GCs for rheumatoid arthritis, a significant increase in lumbar spine BMD was observed in those receiving hormone replacement therapy (HT) compared to those receiving placebo (317). This evidence suggests the potential benefit of HT in hypoestrogenic women treated with GCs. However, a large randomized clinical trial in postmenopausal women treated with a combination of estrogen and progestin planned to last 8.5 years was interrupted after 5 years, because the overall risks exceeded the benefits of the treatment (318). In the past the ACR recommended oral contraceptives (unless contraindicated) in premenopausal women on GCs who develop oligo-amenorrhea (220) but this option is no longer included in the more recent ACR guidelines. Similarly, adult men with GC excess who develop hypogonadism benefit from testosterone replacement. In GC-treated asthmatic men with testosterone deficiency, i.m. testosterone injections increased lumbar spine but not hip BMD (319). There are no data on the potential benefit of testosterone therapy in GC- treated eugonadal men (247). However, since most studies have shown an increase in prostate size and prostate-specific antigen levels in older men on testosterone supplementation/therapy (320-323), testosterone administration should be monitored with yearly digital examinations and prostate-specific antigen measurements.

 

OTHER THERAPIES

 

In addition to different combinations of the treatments so far discussed, selective estrogen receptor modulators (SERMs) alone or conjugated estrogens/SERMs belong to the pharmaceutic armamentarium against GCOP. SERMs, have positive effects on the bone. Tamoxifen reduces in vitro some of the deleterious effects of GC on the bone (324). Raloxifene, which is currently approved by the United States’ Food and Drug Administration (FDA) for the prevention and treatment of postmenopausal OP, might be a safer alternative to HT in the treatment of GCOP that develops in postmenopausal women (246, 325), given its favorable effects on serum lipids, together with the lack of growth stimulation on endometrial and breast tissues (326-328).

 

FUTURE THERAPEUTIC OPTIONS

 

Currently, denosumab is being evaluated for pediatric GCOP (293). Other newer agents that are tentatively evaluated for the treatment of osteoporosis either inhibit osteoclast resorption or stimulate osteoblast bone forming activity. These include antibodies against RANKL (RANKL inhibitors), recombinant osteoprotegrin, inhibitors of osteoclast enzymes, integrin antagonists and agonists to LRP5 (308).

 

At the time of writing, abaloparatide (PTHrp) and romosozumab (humanized monoclonal antibody that targets sclerostin) have been cleared by the FDA for the treatment of OP in women only (8, 329, 330). One would expect the former to be a good candidate for GCOP in analogy to teriparatide. However, this therapy is not yet approved for GCOP and to the best of our knowledge there are no relevant clinical studies to support its use in GCOP (331). Furthermore, we have to bear in mind that administration of GC > 15 mg/day may attenuate the osseous effects of teriparatide, and this has also been shown with abaloparatide in rodent GCOP models (331, 332). There is an ongoing trial of romosozumab in GCOP but at present this medication has no firm indication for GCOP (313); experimental studies in rodents were encouraging (333).

 

Other promising future therapeutic options target GC therapy per se. These include the use of disease-modifying antirheumatic drugs or tumor-necrosis factor agents, which could lead to the need for lower GC dosage for autoimmune disease. Furthermore, deflazocort (a prednisone derivative) and liposomal prednisone may be less onerous to bone (334). The search continues to find selective GR agonists (SGRMs) that possess the anti-inflammatory benefits of traditional GCs without the associated adverse effects (335). The SGRMs are selective ligands of the GR, which maintain the transrepressive properties of GCs (usually associated with their beneficial anti-inflammatory effect) while they do not have their transactivating properties (usually associated with metabolic negative effects, including perhaps those on the bone). Some of these molecules may represent an alternative to traditional GCs in the chronic treatment of inflammatory disorders (334, 336). Inhibitors to cathepsin K (which is involved in systemic bone resorption) (337) hold promise for treating GCOP (295, 338). There is interest in therapeutic inhibitors of 11b-HSD1 for patients with endogenous hypercortisolemia such as Cushing’s disease; these inhibitors – in theory – could also mitigate GCOP but no relevant research has been put forth (53). 

 

GLUCOCORTICOID DISCONTINUATION AND REVERSIBILITY OF GCOP

 

There is no consensus on the reversibility of GCOP. Bone mineral density increases after curative surgery for Cushing’s disease or interruption of exogenous GC treatment (339-341). A prospective study in patients with rheumatoid arthritis showed partial bone regain after discontinuation of low-dose GC therapy that was given for five months (67). If GCs are discontinued and treatment for GCOP is continued, a return to baseline BMD is to be expected within 9 to 15 months (303). In patients with sarcoidosis younger than 45 years, full recovery of bone mass was reported two years after cessation of therapy (342). However, it is unlikely that the large (10% or more) bone mass that is lost during high-dose GC therapy can be completely regained, with full recovery of the mechanical properties of the bone. The likelihood of bone regain may be negatively correlated with the duration of treatment as well as unknown host-related factors. Most complications of osteoporotic fractures, such as vertebral deformities and chronic back pain, are permanent. A sensible approach is to stop anti-osteoporotic treatment 6 to 12 months after discontinuation of GCs administration (303).

 

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