A Case of Endogenous Hyperinsulinemic Hypoglycemia Difficult to Discriminate Between Insulinoma and NIPHS (Non-insulinoma Pancreatogenous Hypoglycemia Syndrome)

Abstract

A 75-year-old man presented due to symptoms of hypoglycemia induced by 22 h of fasting. His serum glucose levels were 40 mg/dL, and his serum immunoreactive insulin and C-peptide levels were 6.9 μU/mL and 1.91 ng/mL, respectively, indicating that hypoglycemia had been induced by the hyperactivity of insulin. We could not detect any tumors in his pancreas using computed tomography, magnetic resonance imaging, or ultrasonography. A selective arterial calcium injection test revealed that the serum insulin levels obtained from the hepatic vein were paradoxically and drastically increased after the injection of calcium into the pancreatic tail artery. Based on these findings, we diagnosed the patient with insulinoma in the pancreatic tail. Hemi-pancreatectomy was performed and resulted in temporary remission of hypoglycemia. However, a histological examination did not reveal any insulinomas in the resected specimen. In addition, no mutations were identified in the ABCC8, KCNJ11, or GCK genes. Six months after the operation, hypoglycemia again occurred in the patient. Therefore, we considered non-insulinoma pancreatogenous hypoglycemia syndrome in the differential diagnosis. A histological reexamination indicated hyperplasia of the islet cells. The oral administration of diazoxide was partially effective in preventing hypoglycemia. However, the monthly administration of a long-acting octreotide completely prevented the occurrence of hypoglycemia in this case.