Ectopic insulin and Occam's razor: reappraisal of the riddle of tumour hypoglycaemia

Persistent Hypoglycemia in Patient with Hodgkin's Disease

Hypoglycemia is a rare complication of Hodgkin's disease. Several explanations have been postulated but the exact pathophysiology is not well understood. We are presenting a case of newly diagnosed Stage IV Hodgkin's disease that developed persistent and recurrent hypoglycemia despite giving glucagon, repeated 50% dextrose, and D5 and D10 continuous infusion. Hypoglycemia workup showed the C-peptide level to be low. Patient was suspected of having hypoglycemia related to lymphoma and was given a trial of prednisone which resolved the hypoglycemic episodes and made the patient euglycemic for the rest of his hospital stay. The presence of a substance that mimicked the effects of insulin was highly suspected. Several case reports strengthen the hypothesis of an insulin-like growth factor or antibodies secreted by the cancer cells causing hypoglycemia in Hodgkin's disease but none of them have been confirmed. Further investigation is warranted to more clearly define the pathophysiology of persistent hypoglycemia in patients with Hodgkin's disease.

Hypoglycemia Attributable to Insulin-Like Growth Factor-II Prohormone-Producing Metastatic Leiomyosarcoma

OBJECTIVE

To review the causes of nonpancreatic tumor-associated hypoglycemia and report the first case of hypoglycemia attributable to a leiomyosarcoma, which did not cause hypoglycemia in its primary site but only after metastasizing.

METHODS

A case report is presented of a 62-year-old man with a gastric leiomyosarcoma diagnosed and surgically treated 8 years previously, who was found to have 14 large, rounded masses in his liver and a blood glucose level of 19 mg/dL. Biopsy of the largest mass revealed a leiomyosarcoma.

RESULTS

Evaluation of the cause of the hypoglycemia revealed that circulating insulin, connecting peptide, proinsulin, insulin-like growth factor-I (somatomedin C), and insulin-like growth factor-II levels were below normal, whereas the insulin-like growth factor-II prohormone concentration was increased twofold. Basal and corticotropin-stimulated serum cortisol values were normal.

CONCLUSION

This is the first case report of hypoglycemia occurring only after metastasis of a leiomyosarcoma. A possible causal relationship between the hypoglycemia and the increased circulating insulin-like growth factor-II prohormone is suggested, and alternative explanations and treatment are discussed.

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.

Metabolic effects of an insulin-like factor causing hypoglycaemia in a patient with a haemangiopericytoma

We have studied a patient with fasting hypoglycaemia and skin lesions (sign of Leser-Trélat) related to a retroperitoneal haemangiopericytoma in whom removal of the tumour resulted in immediate cure of hypoglycaemia. Before removal of the tumour, severe fasting hypoglycaemia was associated with undetectable insulin and C-peptide levels. She required 16.9 mumol/kg/min (10.4 g/h) of glucose intravenously to prevent hypoglycaemia and endogenous glucose production (measured using tritiated glucose) was suppressed to 1.3 mumol/kg/min while the whole-body glucose utilization rate was elevated at 18.2 mumol/kg/min. After removal of the tumour both endogenous glucose production rate and utilization rate returned to normal (11.5 mumol/kg/min). Resting energy expenditure, measured by indirect calorimetry, was markedly elevated at 2109 kcal/day (161% of predicted) and fell to 1205 (97% of predicted) after the tumour was removed. Glucose oxidation was also enhanced at 8.5 mumol/kg/min and fell to 3.3 mumol/kg/min after removal of the tumour. Other metabolites and hormones measured, and their response to oral glucose, were all consistent with the presence of a circulating substance with similar properties to insulin. We conclude that her hypoglycaemia resulted primarily from suppression of endogenous glucose production but also from enhanced glucose utilization. These effects were the result of a circulating growth factor sharing many metabolic effects with insulin, but with a much greater effect on resting energy expenditure and glucose oxidation.

Hypoglycemia: a pathophysiologic approach

An exploration of the factors that sustain glucose levels in the normal fasting subject reveals that the single major component is conservation of glucose rather than gluconeogenesis. Conservation is achieved by recycling of glucose carbon as lactate, pyruvate and alanine, and a profound decrease in the oxidation of glucose by the brain brought about by the provision and use of ketones. What glucose continues to be oxidized is for the most part formed from glycerol. Gluconeogenesis from protein plays little part in the process. Fasting hypoglycemia results from disorders affecting either one of the two critical sustaining factors--the recycling process or the availability and use of ketones. Individual hypoglycemic entities are examined against this background.

Hyperinsulinism associated with primary renal cell carcinoma

A case is reported of a patient with symptomatic hyperinsulinism associated initially with a renal cell carcinoma and then later, with secondary deposits from the same tumor. Evidence points to a strong possibility of renal tumor involvement in the production of insulin hypersecretion.

Synthesis and secretion of insulin-like growth factor II by a leiomyosarcoma with associated hypoglycemia

We describe a case of recurrent hypoglycemia apparently caused by secretion of insulin-like growth factor II (IGF-II) by a leiomyosarcoma. A 67-year-old woman presented with recurrent severe hypoglycemia and a large mass in the thorax. During hypoglycemia, plasma cortisol was elevated, but insulin and growth hormone levels were low. After resection of a large leiomyosarcoma, the hypoglycemia resolved. After an eight-year remission, both the tumor and symptomatic hypoglycemia recurred. During a second operation a second large tumor was removed, with relief of the patient's hypoglycemia. The tumor contained high concentrations of IGF-II mRNA and 2100 ng of IGF-II immunoreactive peptide per gram. Filtration through a BioGel P-60 gel column established that 77 percent of the IGF-II was present as a larger molecule, demonstrating incomplete processing of the pro-IGF-II peptides. A similar fraction of high-molecular-weight IGF-II was present in the serum, indicating that the tumor was the chief source of IGF-II. The high-molecular-weight IGF-II found in both the tumor and serum was fully reactive with the IGF-II receptor. Radioimmunoassay showed that the concentrations of insulin-like growth factor I (IGF-I) in tumor and serum were low, suggesting feedback inhibition of growth hormone secretion by IGF-II. Eight months after reoperation, plasma concentrations of IGF-I and IGF-II were normal, and high-molecular-weight IGF-II was virtually undetectable. We conclude that the most likely cause of this patient's recurrent hypoglycemia was IGF-II produced by the leiomyosarcoma.

Ectopic insulin production by a primary ovarian carcinoid

An insulin-containing ovarian carcinoid was found at the autopsy of a 63-year-old woman with a 12-year history of episodic hyperinsulinemic hypoglycemia. In terms of histology, the carcinoid displayed both insular and trabecular patterns and contained a small focus of mucinous cystadenoma. Beta secretory granules were demonstrated by electron microscopy, and immunoreactivity for insulin was demonstrated in tumor cell cytoplasm by immunohistochemistry. Additional autopsy findings included a solitary parathyroid adenoma and a microscopic focus of pituitary hyperplasia. This is the first recorded case of insulin production by a primary ovarian neoplasm. The patient's constellation of endocrine findings may represent a variant of the syndrome of type I multiple endocrine neoplasia.

Hypoglycemia associated with carcinoid tumors. A case report and review of the literature

The authors report a 73-year-old man with a jejunal carcinoid tumor and spontaneous hypoglycemia. Plasma insulin was suppressed (insulin/glucose ratio, 0.2), and nonsuppressible insulin-like proteins (NSILP) were elevated. Seven other patients with carcinoid or related tumors associated with hypoglycemia were found in the literature. Nonsuppressible insulin-like proteins were not measured in these patients.

Surgical cure of hypoglycemia associated with cystosarcoma phyllodes and elevated nonsuppressible insulin-like protein

A woman with a large, benign cystosarcoma phyllodes of the breast was found to have recurrent, profound hypoglycemia. Plasma levels of nonsuppressible insulin-like protein were increased (15.18 micrograms/ml; normal = 1 to 4 micrograms/ml), whereas levels of insulin and nonsuppressible insulin activity soluble in acid ethanol were normal. Surgical excision of the tumor resulted in immediate and lasting correction of the metabolic abnormalities, although nonsuppressible insulin-like protein levels did not completely return to normal. Surprisingly, preoperative nonsuppressible insulin-like protein levels were highest in blood distant from the tumor site.

The riddle of tumour hypoglycaemia revisited

In summary, hypoglycaemia due to non-pancreatic tumour is relatively common among the causes of fasting hypoglycaemia in the adult. Most of the neoplasms are large, and present as masses in the mediastinum or retroperitoneal space. Although therapy is difficult, successful palliation by surgery or radiotherapy has been achieved in a number of cases. Although many theories have been advanced to explain the hypoglycaemia, the best documented mechanism is production of an insulin-like substance by the tumour. Both low molecular weight (NSILA-s) and high molecular weight (SNILP) peptides have been reported to be elevated in some cases of tumour hypoglycaemia. Further study of this class of peptides will no doubt lead to assays that may facilitate diagnosis of tumour hypoglycaemia, as well as offer new approaches to the therapy of this disease.