A case of vasoactive intestinal polypeptide-secreting tumor presenting without diarrhea in the setting of multiple endocrine neoplasia type I syndrome

Multiple endocrine neoplasia type I syndrome (MEN I) results in parathyroid, anterior pituitary, and pancreatic islet tumors. An uncommon tumor in MEN I is the vasoactive intestinal polypeptide-producing tumor (VIPoma), which usually presents with diarrhea and hypokalemia. We describe a case of MEN I and VIPoma presenting with hypercalcemia and hypokalemia but no diarrhea. This 19-year-old woman with a family history of MEN I presented with metabolic acidosis, hypokalemia, hypercalcemia, and intact parathyroid hormone (iPTH) of 11 pg/mL (normal, 8-48 pg/mL). A computed tomography scan revealed a pancreatic mass. VIP concentration was 249 pg/mL (normal, <50). The pancreatic mass was resected, stained positive for VIP, and her VIP level normalized. VIPomas usually present with diarrhea, resulting in metabolic acidosis and hypokalemia. This patient demonstrated hypokalemia and hypercalcemia without diarrhea or elevated parathormone. Thus, VIPomas can have biologic actions, such as hypokalemia and hypercalcemia without inducing diarrhea and should be considered in the differential diagnosis of hypercalcemia in MEN I.