HYPOGLYCAEMIA IN NEOPLASIA

Diagnostic interpretation of the intravenous tolbutamide test for insulinoma

The plasma glucose and insulin responses to intravenous administration of tolbutamide in patients with insulinoma and healthy control subjects were compared to determine the sensitivity and specificity of the intravenous tolbutamide test for the diagnosis of insulinoma. The records of 406 healthy persons without concurrent disease known to affect glucose homeostasis or insulin concentrations and 41 patients with histologically confirmed insulinoma who underwent standard intravenous tolbutamide testing during the period from 1976 to 1986 were reviewed. The 5th percentile of the mean of plasma glucose levels at the 120-, 150-, and 180-minute points (G120-180) after injection of tolbutamide was 55 mg/dl for lean and 62 mg/dl for obese control subjects. With 95% specificity, the sensitivity of these criteria was 95% for lean and 100% for obese patients with insulinoma. Minimal differences were observed between men and women. At 95% specificity, the sensitivities were less for the ratio of the 180-minute plasma glucose to fasting plasma glucose level (64% in lean and 75% in obese patients), for mean of plasma insulin at the 120-, 150-, and 180-minute points (IRI120-180) (53% in lean and 36% in obese patients), for maximal insulin concentration (27% in lean and 31% in obese patients), for increase in insulin concentration above basal (18% in lean and 23% in obese patients), and for the combined criteria of the 5th percentile of G120-180 and the 95th percentile of IRI120-180 (47% in lean and 73% in obese patients).(ABSTRACT TRUNCATED AT 250 WORDS)

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

The concept of ectopic insulin production is challenged on the basis of a review of 120 cases from the literature on extrapancreatic tumours associated with hypoglycaemia in which insulin or insulin-like activity were measured. No case met two or more of five criteria of ectopic hormone production. The evidence indicates that hypoglycaemia of extrapancreatic tumours cannot be attributed to insulin. In those rare cases in which plasma insulin was reported as high, pancreatic beta-cells could not be excluded as the source of insulin. Interestingly, many of these dubious cases had carcinoid histology. The review also points out a close association between some spindle-cell tumours and carcinoid tumours which may be relevant to discussion on the disputed origin of some "mesothelial" tumours. Nonsuppressible insulin-like activity (NSILA) consists of a number of factors mimicking insulin activity which compete with insulin or proinsulin for membrane receptors and may crossreact in bioassays, immunoassays, and receptor assays. The question of whether one or several of these substances may be responsible for extrapancreatic hypoglycaemia remains to be elucidated.

Ultrastructure of hemangiopericytoma associated with paraneoplastic hypoglycemia

A recurred and metastasized hemangiopericytoma of menigeal origin caused a terminal hypoglycemia syndrome in a 40 year old man. The disease had been observed over a period of 10 years. The total weight of the tumour metastases was 1800 g. Electron microscopical examination of the tumour cells revealed, in particular, a markedly developed ergastoplasm, prominent Golgi complexes surrounded by many microvesicles, round to ovoid electron dense bodies and fine fibrillar structures. Furthermore, large deposits of basement membrane-resembling material were found in the pericapillary and intercellular spaces. On the basis of the structural characteristics which indicate distinct synthesizing capacity of the cells, an excessive glucose consumption by the tumour is suggested to be an important factor in the pathogenesis of tumour hypoglycemia. The question whether the ultrastructure of the tumour also exhibits secretory processes, which may be related to the release of a presumed inhibitor of hepatic gluconeogenesis and/or glycogenolysis, remains open. Typical granules as in polypeptide hormon secreting cells were not observed. The possibility that the demonstrated electron dense membrane limited bodies represent atypical secretory granules is discussed.

Insulin and proinsulin release during calcium infusion in a patient with islet-cell tumor

The infusion of calcium results in the release of gastrin, calcitonin, and serotonin from certain nonbeta islet cell tumors of the pancreas, medullary carcinomas of the thyroid, and carcinoid tumors, respectively. In this study, intravenous infusion of either calcium chloride or calcium aluconate in a patient with an islet-cell carcinoma resulted in a simultaneous rise in plasma immunoreactive insulin and proinsulin, and concurrent hypoglycemia. After resection of the tumor, calcium infusion caused no change in these parameters. Similarly, calcium infusion caused no change in plasma insulin or glucose in normal volunteers. The response of this tumor suggests that calcium infusion may be a useful provocative test to detect insulin-secreting neoplasia. A derangement of the stimulus-secretion coupling mechanism for insulin in the tumor cells may be responsible for their abnormal sensitivity to calcium ion.

Pleural mesothelioma and hypoglycaemia

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