A Case with Insulinoma Experiencing Syndrome of Inappropriate Secretion of ADH - Case Report

Abstract
We report a case of thirty-five years old woman with insulinoma, syndrome of inappropriate secretion of antidiuretic hormone (SIADH). She had a previous history of epidural hematoma operation. She was given oxcarbazepine 300 mg/day because of epilepsy. At the third month of the treatment the patient referred to our clinic with tonic-clonic convulsion, hypoglycemia (serum glucose level of 34 mg/dl) and hyponatremia (118 mEq/l) were detected. The biochemical diagnosis of hypoglycemia was established in the third hour of prolonged fasting test when blood glucose level was 32 mg/dl, serum insulin level was 26.5 mIU/ml, C-peptid was 6.8 ng/ml, the insulin/glucose ratio was 0.82. Endoscopic ultrasonography detected 18x19 mm lesion in pancreas. Hyponatremia  was diagnosed as SIADH after excluding other possible etiologies of hyponatremia. Because of hyponatremic effect of oxcarbazepine, it was changed with valproate sodium. Water restriction therapy was applied. After enucleation of insulinoma, hyperglycemia persisted for a week, but there was no need for insulin and plasma glucose levels never exceeded 250 mg/dl. Then sustained improvement in hypoglycemic attacks and hyponatremia has been observed. Thus the patient was cured and remained euglycemic. Although oxcarbazepine was started again, hyponatremia did not reoccur. Hypoglycemia stimulates the secretion of neurotransmitter and neuropeptides including arginine-vasopressin (AVP), but hypoglycemia related hyponatremia has not been reported up to now. This is the first case with insulinoma presenting with persisting hyponatremia and improving after insulinoma resection.