Melatonin improves postprandial hypoglycemia: an unusual presentation of insulinoma

Insulinoma is the most prevalent neuroendocrine tumor of the pancreas, presenting with a spectrum of neuroglycopenic symptoms. This case report describes a 64-year-old woman with primarily postprandial hypoglycemia, resulting in altered consciousness and confusion occurring several hours after meals. Continuous glucose monitoring (CGM) was used to establish the postprandial pattern of the patient's hypoglycemia, and this facilitated the confirmatory biochemical evaluation by a single blood draw done at the time of symptoms, without performing a 72-hour fast. Imaging demonstrated an 11-mm tumor in the pancreas, which was removed and confirmed to be a well-differentiated neuroendocrine tumor on histopathology. While awaiting pancreatic surgery, the patient began taking melatonin for sleep and reported an improvement in the frequency and severity of hypoglycemia symptoms, which was supported by CGM data and a robust expression of melatonin receptors on the excised tumor. This case raises interest in the role of melatonin receptor signaling in counteracting hyperinsulinemia and corresponding hypoglycemia in patients with insulinoma.