Alleviation of non-islet cell tumour hypoglycaemia by growth hormone therapy is associated with changes in IGF binding protein-3

Endocrine and cellular physiology and pathology of the insulin-like growth factor acid-labile subunit

The acid-labile subunit (ALS) of the insulin-like growth factor (IGF) binding protein (IGFBP) complex, encoded in humans by IGFALS, has a vital role in regulating the endocrine transport and bioavailability of IGF-1 and IGF-2. Accordingly, ALS has a considerable influence on postnatal growth and metabolism. ALS is a leucine-rich glycoprotein that forms high-affinity ternary complexes with IGFBP-3 or IGFBP-5 when they are occupied by either IGF-1 or IGF-2. These complexes constitute a stable reservoir of circulating IGFs, blocking the potentially hypoglycaemic activity of unbound IGFs. ALS is primarily synthesized by hepatocytes and its expression is lower in non-hepatic tissues. ALS synthesis is strongly induced by growth hormone and suppressed by IL-1β, thus potentially serving as a marker of growth hormone secretion and/or activity and of inflammation. IGFALS mutations in humans and Igfals deletion in mice cause modest growth retardation and pubertal delay, accompanied by decreased osteogenesis and enhanced adipogenesis. In hepatocellular carcinoma, IGFALS is described as a tumour suppressor; however, its contribution to other cancers is not well delineated. This Review addresses the endocrine physiology and pathology of ALS, discusses the latest cell and proteomic studies that suggest emerging cellular roles for ALS and outlines its involvement in other disease states.

A Rare Diagnosis After the Fall of a 96-Year-Old Woman: Doege-Potter Syndrome

INTRODUCTION

Doege-Potter Syndrome (DPS) is a rare but life-threatening paraneoplastic syndrome, characterized by Non-Islet Cell Tumor-Induced Hypoglycemia (NICTH) secondary to a Solitary Fibrous Tumor (SFT), which secretes an incompletely processed form of Insulin-like Growth Factor 2 (IGF-2).

RESULTS

A 96-year-old woman was admitted with head trauma due to an accidental fall. During her hospital stay she experienced frequent hypoglycemic episodes. Multiple injections of 33% dextrose and continuous infusion with 10% dextrose were required to maintain normal blood glucose levels. Biochemical analyses revealed hypoinsulinemic hypoglycemia, low C-peptide levels, suppressed insulin-like growth factor-1, normal insulin-like growth factor-2, and an elevated IGF-2:IGF-1 ratio, all consistent with IGF-2 secretion by a non-islet cell tumor. A contrast-enhanced chest and abdominal CT scans showed a single large pleural mass in the left lower hemithorax measuring 15x14 cm without secondary lesions. Histological analysis of biopsied specimens suggested a solitary fibrous pleural tumor; accordingly, a diagnosis of Doege-Potter syndrome was considered. Due to extensive tumor burden and the advanced age of the patient, supportive and non-invasive management was chosen. Dexamethasone therapy was started, and while receiving this therapy she was able to discontinue glucose infusion and successfully maintain euglycemia.

DISCUSSION

In the elderly, a sudden and unexplained fall can be the expression of severe hypoglycemia, usually as a complication of insulin therapy or of oral hypoglycemic agents administered to patients with diabetes. However, in patients without diabetes, other causes should be investigated, and the hypothesis of neoplastic diseases should be considered.

CONCLUSION

In this case report we describe an uncommon cause of paraneoplastic hypoglycemia occurring in the oldest patient with a non-islet cell tumor reported thus far.

MANAGEMENT OF ENDOCRINE DISEASE: Pathogenesis and management of hypoglycemia

Glucose is the main substrate utilized by the brain and as such multiple regulatory mechanisms exist to maintain glucose concentrations. When these mechanisms fail or are defective, hypoglycemia ensues. Due to these robust mechanisms, hypoglycemia is uncommon and usually occurs in the setting of the treatment of diabetes using glucose-lowering agents such as sulfonylureas or insulin. The symptoms of hypoglycemia are non-specific and as such it is important to confirm hypoglycemia by establishing the presence of Whipple's triad before embarking on an evaluation for hypoglycemia. When possible, evaluation of hypoglycemia should be carried out at the time of spontaneous occurrence of symptoms. If this is not possible then one would want to create the circumstances under which symptoms occur. In cases where symptoms occur in the post absorptive state, a 72-h fast should be performed. Likewise, if symptoms occur after a meal then a mixed meal study may be the test of choice. The causes of endogenous hyperinsulinemic hypoglycemia include insulinoma, post-bariatric hypoglycemia and noninsulinoma pancreatogenous hypoglycemia syndrome. Autoimmune hypoglycemia syndrome is clinically and biochemically similar to insulinoma but associated with high levels of insulin antibodies and plasma insulin. Other important causes of hypoglycemia include medications, non-islet cell tumors, hormonal deficiencies, critical illness and factitious hypoglycemia. We provide an overview of the pathogenesis and management of hypoglycemia in these situations.

Doege-Potter syndrome: A review of the literature including a new case report

RATIONALE

We reviewed 76 published cases of Doege-Potter syndrome, and non-islet cell tumor hypoglycemia (NICTH) secondary to a solitary fibrous tumor (SFT) between 1989 and 2016, to study disease pathogenesis, diagnosis, and treatment of this rare paraneoplastic disease. Further, we report 1 new case of a patient presenting with Doege-Potter syndrome.

PATIENTS CONCERNS

The tumors originated from the pleural cavity, lung, pelvis, liver, retroperitoneum, kidney, mediastinal, the sella, uterus, bladder, intestine, mandibular, and the thigh. The most common location was the pleural cavity (left 12 cases and right 28 cases). Moreover, 28/71 (39.4%) were benign and 43/71 (60.6%) were malignant. SFTs with NICTH were more likely to be malignant and present at a higher rate than previously published (5%-10.4%). The malignancy rate of extrathoracic SFTs was higher than that of thoracic SFTs, 20 (66.7%) as compared with 23 (56.1%). Age of onset varied from 24 to 85 years (mean 59 years), with 47 males and 28 females, and gender unavailable for 1 case. When comparing clinical characteristics of patients with benign as compared malignant tumors, no significant differences in the age of onset, gender, or size of tumor were seen. Among 15/19 cases, the insulin-like growth factor II (IGF-II)/IGF-I ration was >10.0. Complete tumor resection remained the only definitive treatment.

OUTCOMES AND LESSENS

Glucocorticoids dose-dependently reduce the frequency and severity of hypoglycemic episodes. Low doses of prednisone were ineffective at relieving hypoglycemia. The effect of neoadjuvant treatment, consisting of chemoradiation, and consecutive selective embolization of vessels feeding the tumor were not identified.

Management of non-islet-cell tumor hypoglycemia: a clinical review

CONTEXT

Non-islet cell tumor hypoglycemia (NICTH) is a rare but serious paraneoplastic syndrome in which a tumor secretes high molecular weight IGF-II, causing hypoglycemia. Complete tumor resection is curative but is often delayed or unfeasible. There is no clear "standard of care" for managing these patients.

EVIDENCE ACQUISITION

PubMed searches were conducted for: "non-islet-cell tumor hypoglycemia," "NICTH," "Doege-Potter," "Doege-Potter syndrome," "high molecular weight IGF-II," and "big IGF-II." Relevant articles were reviewed in detail. We limited our review to English-language articles, focusing on 1988-2013 (corresponding with the elucidation of the pathophysiology of NICTH).

EVIDENCE SYNTHESIS

The available literature exists as case reports or small case series, with a void of higher-order treatment studies. Thus, an evidence-based approach to data synthesis was difficult. Nevertheless, the available literature is presented objectively with an attempt to describe clinically useful trends and findings in the management of NICTH.

CONCLUSIONS

Appropriate identification of NICTH and prompt and complete tumor resection represents ideal management. However, when prompt resection is not feasible, iv glucose or dextrose often does not suffice to prevent hypoglycemia. In such cases, we suggest consideration of local antitumor therapies for disease control and trial of glucocorticoids alone or in combination with GH. Continuous glucagon infusion can be successful if the patient has a positive response to a glucagon stimulation test, and parenteral nutrition may allow higher glucose delivery, but both are limited by the need for continuous iv infusion. Diazoxide and octreotide have no role in NICTH.

Hypoglycemia due to paraneoplastic secretion of insulin-like growth factor-I in a patient with metastasizing large-cell carcinoma of the lung

CONTEXT

Nonpancreatic tumors may cause recurrent hypoglycemia known as nonislet cell tumor hypoglycemia. It is due to overproduction and secretion by the tumor of incompletely processed IGF-II, termed big IGF-II. We recently identified a patient with recurrent hypoglycemia and low insulin, but without elevated big IGF-II. Multiple small lung nodules were detected by computed tomography scan. An undifferentiated large-cell carcinoma was diagnosed from an axillary lymph node metastasis.

OBJECTIVE

The objective was to investigate whether the patient's hypoglycemia was due to excessive IGF-I production by the tumor.

METHODS

Serum IGF- I and IGF-II, insulin, and GH were measured by RIA; the distribution of IGFs between IGF binding protein complexes in serum was analyzed after neutral gel filtration. Tissue IGF-I was identified by immunohistochemistry and in situ hybridization, and by RT-PCR after RNA extraction.

RESULTS

Total and free serum IGF-I, but not total, free, and big IGF-II, was increased, and the IGF-I content of the two IGF binding protein complexes was elevated. Immunohistochemistry demonstrated IGF-I peptide in situ hybridization IGF-I mRNA in the lymph node metastasis. Combined GH/glucocorticoid treatment prevented hypoglycemia, but did not lower IGF-I. After chemotherapy with carboplatinum/etoposide, the lung nodules largely regressed, and serum IGF-I and the IGF-I content of the two binding protein complexes became normal. Hypoglycemia did not recur despite discontinuation of GH/glucocorticoid treatment.

CONCLUSION

Our findings are compatible with a new form of tumor hypoglycemia caused by circulating tumor-derived IGF-I.

Mechanisms and management of non-islet cell tumour hypoglycaemia in gastrointestinal stromal tumour: case report and a review of published studies

Tumour-related hypoglycaemia is a rare paraneoplastic phenomenon most frequently occurring with insulinomas, but also associated with non-islet cell tumours. It has been observed in a range of tumour types, but recently a small number of cases have been described in association with gastrointestinal stromal tumours. We describe a further case of a patient with gastrointestinal stromal tumour that was complicated by non-islet cell tumour hypoglycaemia, and discuss the mechanisms and management of non-islet cell tumour hypoglycaemia in the context of gastrointestinal stromal tumour.

Non islet cell tumor hypoglycaemia in a metastatic Leydig cell tumor

Non islet cell tumour hypoglycaemia (NICTH) is a rare cause of hypoglycaemia associated with malignancy and can be considered as a paraneoplastic syndrome. The hormonal factor associated with this condition is big IGF II, which exerts negative feedback effect and decreases the production of growth hormone and insulin. Due to low growth hormone levels, hepatic production of IGFBP 3 (the main binding protein of IGF II) is impaired. Excess free big IGF II is thus available for binding with insulin receptors to cause hypoglycaemia. Treatment options are either surgical removal of the tumour, administration of growth hormone, glucocorticoids or combination of treatments. A case of metastatic Leydig cell tumour causing NICTH has been discussed and the mechanism of NICTH hypoglycaemia and the treatment is outlined.

Treatment of hypoglycemia using combined glucocorticoid and recombinant human growth hormone in a patient with a metastatic non-islet cell tumor hypoglycemia

BACKGROUND

Non-islet cell tumor hypoglycemia(NICTH) is a rare cause of recurrent hypoglycemia. It has been associated with the tumoral overproduction of high-molecular-weight insulin-like growth factor (IGF)-2 ("big IGF-2"). Big IGF-2 suppresses growth hormone (GH) biosynthesis and impairs the storage of IGFs by suppressing the formation of the GH-dependent ternary complexes containing IGF, IGF binding protein 3 (IGFBP-3), and acid-labile subunit (ALS). Thus, big IGF-2 exerts hypoglycemic activity. The only effective treatment of NICTH is surgery. However, in inoperable patients with NICTH, treatment of hypoglycemia may require high doses of glucocorticoid (30-60 mg/d [0.5-1.0 mg/kg x d]) or recombinant human GH (rhGH) (2.6-12.0 mg/d [0.043-0.20 mg/kg x d]).

OBJECTIVE

We hypothesized that the association of low doses of glucocorticoid and rhGH could be an effective therapy for hypoglycemia in inoperable patients with NICTH.

METHODS

A 3-phase treatment regimen was conducted in an inoperable 67-year-old woman with NICTH. Decreasing dosages of prednisone (from 30 to 10 mg/d [from 0.50 to 0.15 mg/kg x d]), followed by decreasing doses of rhGH (from 2.6 to 1.3 mg/d [from 0.043 to 0.016 mg/kg x d]), and then a combination of the lowest doses of each, were tested. Glucose, insulin, and IGF monitoring were performed at each of the 3 treatment phases.

RESULTS

Fasting plasma glucose (FPG) level was normalized and the IGF-1 concentration was increased with high-dose prednisone monotherapy (30 mg/d [0.50 mg/kg x d]) or rhGH (2.6 mg/d [0.043 mg/kg x d]). Prednisone monotherapy partially suppressed big IGF-2 secretion, and rhGH monotherapy acted on IGFBP-3 and ALS concentrations. FPG level was normalized with combined low-dose prednisone and rhGH, and this combination was more effective than high-dose monotherapy with either drug in reestablishing the IGF system. No adverse effects (AEs) were found.

CONCLUSIONS

In this patient with inoperable NICTH, the combination of low doses of prednisone and rhGH was a successful long-term therapy for hypoglycemia, with no AEs. This therapy could be proposed for use in patients with inoperable NICTH.

The role of the growth hormone-insulin-like growth factor axis in glucose homeostasis

Homeostatic mechanisms normally maintain the plasma glucose concentration within narrow limits despite major fluctuations in supply and demand. There is increasing evidence that the growth hormone (GH)-insulin-like growth factor (IGF) axis may play an important role in glucose metabolism. GH has potent effects on intermediary metabolism, some of which antagonize the actions of insulin. In contrast, IGF-I has insulin-like actions, which are, in the case of glucose metabolism, opposite to those of GH. There is often deranged glucose metabolism in situations where GH is deficient or in excess. The clinical administration of GH or IGF-I results in altered glucose metabolism and changes in insulin resistance. Despite these observations, the precise role of GH and IGF-I and their interactions with insulin in controlling normal glucose homeostasis are unknown. In diabetes, GH secretion is abnormally increased as a result of reduced portal insulin resulting in impaired hepatic IGF-I generation. Evidence suggests that this may contribute to the development of diabetic microvascular complications. IGF-I 'replacement' in diabetes is under investigation and new methods of delivering IGF-I as a complex with IGFBP-3 offer exciting new prospects.

Treatment of haemangiopericytoma-associated hypoglycaemia with embolisation

A 48-year-old woman with a known history of metastatic haemangiopericytoma presented with intractable hypoglycaemia. Hypoglycaemia was accompanied by undetectable serum insulin levels with high levels of proforms of insulin-like growth factor-II ('big' IGF-II). Reduction of tumour load with embolisation resulted in a normal pattern of serum glucose levels throughout the day.

[Hypoglycemia associated with pleural fibromas. Study of insulin-like growth factors (IGF) and pathogenic considerations]

PURPOSE

Pathogeny of hypoglycemia associated with non-islet-cell tumors is unclear. We discuss the mechanisms of this syndrome.

CURRENT KNOWLEDGE AND KEY POINTS

We report three cases of spontaneous hypoglycemia revealing pleural fibroma. Endocrine tests before surgery showed low serum growth hormone and insulin-like growth factor I (IGF-I), reduced serum IGF-II levels in two patient. Insulin-like growth factor binding protein-3 (IGFBP-3) was low and electrophoretic profile of IGF-II was the 'big IGF-II' type. We discuss the mechanisms of hypoglycemia associated with non-islet-cell tumor. Impaired formation of the ternary complexes and its consequences seem the main pathogenic factor.

FUTURE PROSPECTS AND PROJECTS

Analysis of IGF and IGFBP and in situ measurements of IGF mRNA could help in understanding this syndrome and allow therapeutic considerations in the management of hypoglycemia by corticosteroids and growth hormone.

Severe hypoglycaemia caused by raised insulin-like growth factor II in disseminated breast cancer

A 60 year old woman with disseminated ductal carcinoma of the breast developed non-islet cell tumour induced hypoglycaemia (NICTH). The concentrations of the two insulin-like growth factors, IGF-I and IGF-II, were < 2 nmol/l and 94.1 nmol/l, respectively. The IGF-II to IGF-I ratio was > 47 (normal < 10). Insulin (< 3 mu/l) and C peptide (< 100 pmol/l) were both undetectable.

Gene expression and serum levels of insulin-like growth factors (IGFs) and IGF-binding proteins in a case of non-islet cell tumour hypoglycaemia

We describe a case of non-islet cell tumour hypoglycaemia (NICTH) associated with a renal cell carcinoma. Serum insulin-like growth factors (IGFs) (including IGF-II E peptide), IGF-binding proteins (IGFBPs), insulin and C-peptide were measured before and after surgical removal of the tumour. IGFBPs were visualized by Western ligand blotting. Preoperatively 'big' IGF-II and IGFBP-2 levels were raised. IGF-I, IGFBP-1 and IGFBP-3 were low, while insulin, C-peptide and GH were undetectable. These changes were reversed by 2 days postoperatively. Protease assays showed little IGFBP-3 protease activity preoperatively. Preoperatively, neutral chromatography demonstrated most of the immunoassayable IGFBP-3 in a high molecular weight form with a small amount of IGF-II. Most of the IGF-II and big IGF-II eluted in lower molecular weight forms. Postoperative samples showed a shift in IGF-II which became increasingly associated with IGFBP-3 in both low and high molecular weight complexes. By Northern blotting, expression of all species of IGF-II mRNA in the tumour was 10-fold greater than in normal human liver. The tumour did not express IGFBP-1 or IGFBP-2. IGFBP-3 was expressed in small amounts, while the expression of IGFBP-4 was two-fold higher than in liver. In conclusion, we have confirmed high levels of big IGF-II and IGFBP-2 in NICTH, changes which are reversed postoperatively. The IGF-II is derived from the tumour which overexpresses these genes but IGFBP-2 probably arises from extratumour upregulation.

Glucocorticoid therapy suppresses abnormal secretion of big IGF-II by non-islet cell tumours inducing hypoglycaemia (NICTH)

OBJECTIVE

To assess the relative efficacy of hGH and glucocorticoids in the treatment of non-islet cell tumour hypoglycaemia (NICTH) by examination of their influence on the composition of the various molecular species involving tumour and mature forms of IGF-II in association with IGFBP-3.

DESIGN

Two groups each of 4 patients, all diagnosed as cases of NICTH, were treated with either hGH or glucocorticoids. Through the use of acidic size exclusion chromatography serum levels of tumour (big) and mature IGF-II were evaluated. Neutral size exclusion chromatography was used in the separation of molecular species before assay for immunoreactive IGF-II and IGFBP-3 content.

RESULTS

High-dose hGH treatment produced increases in serum levels of big and mature IGF-II and IGFBP-3 but without generation of high molecular weight complexes. Glucocorticoid treatment suppressed big IGF-II permitting re-establishment of normal IGF/IGFBP association patterns.

CONCLUSION

Glucocorticoid therapy has been demonstrated to consistently reverse the biochemical abnormalities caused by tumour-derived big IGF-II compared with the potentially adverse stimulatory effects of hGH treatment in causing increases in serum levels of big IGF-II.

Hepatoma with severe non-islet cell tumor hypoglycemia

We report a 22-yr-old male patient with chronic hepatitis B and a large, well differentiated hepatoma who developed episodes of symptomatic fasting hypoglycemia, which were caused by paraneoplastic secretion of unprocessed "big" insulin-like growth factor-II. Initially, the patient presented with normal liver function, which deteriorated during the clinical course. Therapeutic attempts to reduce tumor mass failed and the patient subsequently died because of metastases of the hepatoma. The pathophysiology of non-islet cell tumor hypoglycemia, differential diagnosis, and therapeutic options are discussed.

Recurrent hypoglycaemia

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Insulin-like growth factor binding proteins as glucoregulators

Circulating insulin-like growth factors (IGFs) represent an important pool of potential hypoglycemic activity, which is largely inhibited by their sequestration in a heterotrimeric complex comprising growth factor, IGF-binding protein-3 (IGFBP-3), and acid-labile subunit (ALS). Less than 1% of total IGFs circulate in the free form, yet even this amount might contribute significantly to circulating insulin-like activity. The ternary binding protein complex appears to inhibit insulin-like activity of bound IGFs by preventing their egress from the circulation. Although the integrity of this complex might be affected by limited proteolysis of IGFBP-3 in pregnancy and catabolic conditions, the evidence that this increases IGF bioavailability, and thus hypoglycemic potential, is as yet unclear. However, in patients with IGF-II-secreting tumors, hypoglycemia may result from a failure of the ternary complex to adequately sequester the IGFs. Improvement in complex formation, by treatment with corticosteroids or growth hormone, alleviates the hypoglycemia, even if (as seen with growth hormone treatment) IGF-II hypersecretion persists. In these patients, blood glucose levels are inversely correlated with IGFBP-2 levels, suggesting that this protein might play a part in transporting IGFs to their target tissues. Conversely, ALS levels correlate positively with blood glucose, emphasizing the importance of the ternary complex in preventing hypoglycemia. Unlike the other IGF-binding proteins, IGFBP-1 is acutely regulated in the circulation, in a manner consistent with its acting as a glucose counterregulator. It might act in this way by inhibiting the activity of free IGFs in the circulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Non-islet-cell tumor associated with hypoglycemia in a child: successful long-term therapy with growth hormone

Hypoglycemia occurred in a 2-year-old girl with neuroblastoma. Initially, growth hormone secretion was suppressed, and she had low levels of insulin-like growth factor (IGF)-I and IGF binding protein-3, but elevated levels of large molecular weight IGF-II. We postulated that the pathogenesis of her hypoglycemia involved production of IGF-II by her neuroblastoma, leading to GH suppression and an abnormally elevated ratio of IGF to IGF binding protein. She was successfully treated with growth hormone; treatment was associated with normalization of the growth hormone-dependent growth factor levels and with euglycemia.

The estrogen connection: the etiological relationship between diabetes, cancer, rheumatoid arthritis and psychiatric disorders

For some considerable time, there has been a growing awareness that defective essential fatty acid metabolism plays a causal role in the pathogenesis of both schizophrenia and non-insulin-dependent diabetes mellitus (NIDDM) but the influence of defective essential fatty acid metabolism in the pathogenesis of rheumatoid arthritis and cancer is less well appreciated. An EFA deficiency, or defective EFA metabolism, negatively influences prostaglandin synthesis and glucose regulation and transport. Moreover, defective EFA metabolism negatively influences estrogen availability which contributes to the observed gender bias some of these illnesses manifest. While fluctuations of estrogen are known to contribute to the pathogenesis of these conditions, so also do fluctuations of IGF-II and there is some suggestion that IGF-II and insulin may well be inversely regulated. In addition, insulin-dependent diabetes mellitus (IDDM), rheumatoid arthritis, and schizophrenia are thought to be autoimmune disorders, while cancer is associated with immune system failure. Consequently, this paper aims to examine the pathophysiological similarities and differences between mental illness, diabetes, rheumatoid arthritis and cancer in respect of which the causal relationship that obtains between essential fatty acids, estrogen, IGF-II, glucose regulation and autoimmunity will be addressed.

Insulinlike growth factor binding proteins and tumor hypoglycemia

Hypoglycemia associated with nonislet cell tumors is a relatively rare metabolic disorder, which develops in the presence of low or unmeasurable serum insulin levels. Understanding of the pathogenetic mechanisms has been obscured by the lack of appropriate analytic methods. It now appears that this disorder can be classified as a paraneoplastic syndrome caused by the oversecretion of unprocessed (big) insulinlike growth factor (IGF) II propeptide by the tumor. In contrast to other paraneoplastic syndromes, however, this oversecretion does not lead to grossly elevated IGF II RIA values in the sera of the patients, but is masked by (a) a negative feedback that suppresses the production of mature (7.5-kD) IGF II, so that the total IGF II level remains more or less unchanged and (b) an altered distribution of the hormone between two specific IGF binding protein complexes in the circulation so that its bioavailability is essentially enhanced.

Hypoglycaemia in the adult

Hypoglycaemia is a relatively common cause for referral of patients to the accident and emergency departments of hospitals but most of it is iatrogenic. Occasionally, however, hypoglycaemia is due to any one of up to a hundred different disorders. In some, hypoglycaemia is the cause of intermittent neuroglycopenic symptoms that lead to their referral to medical outpatients for investigation. Only the most important are discussed here. Hyperinsulinism due to abnormal beta-cell function is an uncommon but important cause of spontaneous hypoglycaemia. The diagnosis is suspected from the history of episodes of altered consciousness confirmed by demonstrating raised plasma insulin, C-peptide and proinsulin levels in peripheral blood in the presence of hypoglycaemia. Differentiation of the various causes of endogenous hyperinsulinism before surgery is difficult if not impossible and the low predictive value of most of the localizing techniques that are available makes them an additional and unnecessary cost, producing little clinical benefit. Hypoglycaemia caused by non-islet cell tumours (NICTH) is seemingly rarer than hyperinsulinism from insulinoma and tends to occur in older patients. The clinical features are similar to those of hyperinsulinism but laboratory investigation reveals appropriately depressed plasma insulin, C-peptide and proinsulin levels in the presence of hypoglycaemia. The plasma IGF-II:IGF-I ratio is characteristically high and the concentration of the E-domain of proIGF-II is raised. Autoimmune hypoglycaemia is more common in some countries than others and is most often due to autoantibodies to insulin (AIS). It may also be caused by autoantibodies to the insulin receptor and possibly to autoantibodies that are stimulatory to pancreatic beta-cells. Contrary to popular belief, idiopathic reactive hypoglycaemia is rare and only one of the possible causes of the postprandial syndrome. It is characterized by a low blood glucose concentration in blood collected during a spontaneous symptomatic episode but not at other times. Its cause is unknown. Other causes of hypoglycaemia include endocrinopathies of various kinds; sepsis including malaria; congestive cardiac failure; hepatic and renal insufficiencies; diverse inborn errors of metabolism; and exogenous toxins, of which alcohol is probably the commonest.