Hypoglycemia induced by excessive rebound secretion of insulin after removal of pheochromocytoma.

During an 8-year-period from 1981, a total of 6 of 45 patients with pheochromocytoma developed severe hypoglycemia (plasma glucose, 12-50 mg/dl) 2-4 1/2 hours after removal of the tumor. In order to elucidate the pathogenesis of the hypoglycemic attack, the levels of plasma immunoreactive insulin (IRI) and glucose were sequentially measured at surgery in 10 patients with pheochromocytoma, from the beginning of the operation until usually 5 hours after tumor resection. The same examinations were carried out in 4 patients with primary aldosteronism and 1 patient with Cushing's syndrome as controls. The highest plasma IRI levels observed in the 2 patients with postexcisional hypoglycemia were 174 and 2,081 microU/ml and those in the 8 patients without hypoglycemia were 13-222 microU/ml (mean, 77), but they were only 14-33 microU/ml (mean, 22) in the 5 control patients. The mean of the highest plasma IRI/glucose ratios in the immediate postoperative phase was 1.37 +/- 0.87 in the 10 patients with pheochromocytoma but only 0.16 +/- 0.04 in the 5 control patients (p less than 0.01). Review of the clinical data in our series disclosed that patients with higher levels of preoperative urinary epinephrine excretion and those with either diabetes mellitus or impaired glucose tolerance tended to develop postoperative hypoglycemia. These observations suggest that endogenous insulin secretion is suppressed by increase plasma catecholamines, and that excessive rebound secretion of insulin after removal of a pheochromocytoma is a rather common phenomenon. Intravenous infusion of glucose is necessary and plasma glucose levels should be monitored after resection of a pheochromocytoma.