Severe postoperative hypoglycemia in a patient with pheochromocytoma and preclinical Cushing's syndrome.

Background: Postoperative hypoglycemia is not a common complication following the removal of a pheochromocytoma. Although the mechanism of hypoglycemia is not fully understood, it seems that it is caused by excessive rebound secretion of insulin after surgical resection of pheochromocytoma.

Case Report: We report a 43-year-old woman with a very rare association of pheochromocytoma and preclinical Cushing's syndrome (PCS) in the same adrenal gland who developed severe postoperative hypoglycemia. Pheochromocytoma was diagnosed by high serum and urine metanephrine and normetanephrine levels. PCS was characterized by blunted cortisol diurnal rhythm, low ACTH level, and failure of cortisol suppression by dexamethasone without any clinical signs of cortisol excess. In the early postoperative period after surgical removal of right adrenal gland, the patient lapsed into a stuporous state. The blood glucose level was 0.7 mmol/l. During the next 48 hours, normoglycemia was maintained with a continuous infusion of 20% glucose. On the third postoperative day, infusion was discontinued, oral feeds were introduced, and the plasma glucose level normalized. The patient did not have further episodes of hypoglycemia. Pathology revealed medullary pheochromocytoma and a cortical tumor of right adrenal gland. During the fifth postoperative day, plasma metanephrine and normetanephrine were 0.13 nmol/l and 0.30 nmol/l, respectively. Urinary metanephrine decreased to 0.5 pmol/24 h and normetanephrine to 2.8 micromol/24 h.

Conclusions: This report indicates the importance of close monitoring of blood glucose level in a patient with pheochromocytoma after removal of an adrenal gland.