Insulinoma in a marathon runner illustrating the effects of exercise on insulin sensitivity and glucose homeostasis

Insulinoma is an uncommon but important cause of hypoglycemia. Most patients with insulinoma present with symptoms of hypoglycemia while fasting. Endurance exercise improves insulin sensitivity by increasing the expression of glucose transporters in skeletal muscles. On the other hand, acute exercise decreases insulin secretion and sensitivity. We present a case report of insulinoma in a marathon runner who presented with hypoglycemia at rest and minimally elevated insulin levels at the time of hypoglycemia who was able to continue long-distance running without experiencing symptoms. We also describe the effects of exercise on insulin secretion and sensitivity in endurance athletes that lead to symptomatic hypoglycemia only at rest despite a minimally elevated serum insulin level.