A Case of Insulinoma Associated With Glucagonoma, Whose Glucose Tolerance was Improved by Surgical Resection

Abstract

A 68-year-old woman was admitted for the examination of fasting hypoglycemia (42 mg/dL) and a tumorous lesion incidentally found by abdominal ultrasonography. A 75-g oral glucose tolerance test revealed that she had diabetes according to the Japan Diabetes Society criteria, with impaired first-phase insulin secretion. She also had postprandial hyperglycemia, as shown by a continuous glucose monitoring system. A dynamic computed tomography scan of the abdomen located a 4-cm-diameter mass lesion densely but inhomogeneously stained in the arterial phase in the pancreatic body. A prolonged 18-h fast reduced her plasma glucose without suppressing insulin secretion, while her serum glucagon (1030 pg/mL) and total ketone body (908 μmol/L) levels were not suppressed. After the prolonged fast, the administration of glucagon resulted in a 29-mg/dL increase in her plasma glucose levels, a finding compatible with insulinoma. Angiography and a selective arterial calcium injection test determined the localization of the insulinoma. Concomitant development of glucagonoma was also suggested in light of the elevated serum glucagon levels before surgery. The patient underwent distal pancreatectomy, and the pancreatic mass was histologically diagnosed as neuroendocrine tumor grade 2. Immunohistochemically, the tumor cells were positively stained for insulin, glucagon and somatostatin. After surgery, her glucose tolerance, the first-phase insulin secretion and postprandial hyperglycemia were totally improved. A case of comorbid insulinoma and glucagonoma, in which the patient's glucose tolerance was atypically modified by two hormone-secreting tumors, was reported.