Glucose-responsive and octreotide-sensitive insulinoma

Insulinoma is the most common cause of fasting hypoglycemia resulting from autonomous insulin hypersecretion. We describe herein a unique case with paradoxical hypoglycemic episodes induced by hyperglycemia. A 55-year-old female had repeated hypoglycemic episodes after meal or during increased physical activity. Although fasting (10 hr) failed to provoke hypoglycemia, oral glucose tolerance test (GTT) caused an exaggerated insulin response (885 microU/ml) at 30 min, followed by hypoglycemia (36 mg/dl) after 90 min. Moreover, intravenous GTT also induced an exaggerated insulin response (>2900 microU/ml) at 10 min, followed by hypoglycemia (34 mg/dl) after 40 min. Although MRI and CT scan of the abdomen failed to detect any mass lesions in the pancreas, Octreoscan revealed increased radioactive uptake around the pancreatic head region. Treatment with a daily injection of octreotide (100 microg) alleviated her hypoglycemic episodes. At surgery, two islet cell adenomas were identified in the pancreas and resected. Postoperatively, she was free from hypoglycemic episodes after meal. Postoperative oral and intravenous GTT did not induce hypoglycemia. Thus, this is a very rare case of glucose-responsive and octreotide-sensitive insulinoma in whom GTT and octreotide proved to be a useful provocation and treatment for hypoglycemic episodes.