Metastatic Insulinoma Presenting With Post-Prandial Hypoglycemia

Background: Patients with an insulinoma, a type of pancreatic neuroendocrine tumor, typically present with fasting hypoglycemia (1). Occurrence of exclusively postprandial hypoglycemia as a result of a predominantly proinsulin-secreting metastatic neuroendocrine tumor is rare (2). Clinical Case: A 69-year-old man presented with episodes of postprandial blurry vision, sweating and confusion for the last two years that were becoming more frequent over the last several weeks. Self-monitoring of blood glucose at home revealed postprandial hypoglycemia (45-70mg/dl) and symptoms were consistent with Whipple’s triad. Continuous glucose monitoring over 14-days via Dexcom G6 showed no nocturnal or fasting hypoglycemia and revealed only postprandial hypoglycemia within one-two hours after meals. Laboratory measurements were performed at 8am in fasting state which revealed a blood glucose of 97mg/dl, insulin level 7.8 µIU/ml (2-21 µIU/ml), c-peptide 1.67 ng/ml (1.1-4.4 ng/ml) and elevated proinsulin level of 39 pmol/l (