Multiple endocrine neoplasia I (MEN I) is a genetic disorder that consists of neoplasia of neuroendocrine type in the parathyroid glands, in the islets of Langerhans in the pancreas, and in the anterior pituitary gland. Primary hyperparathyroidism is the most common feature and occurs in approximately 95% of MEN I patients. Pancreatic islet cell tumors occur in 40% of MEN I patients.Most of these tumors produce excessive amounts of hormones, such as gastrin, insulin, glucagon and vasoactive intestinal polypeptide (VIP). VIP-producing pancreatic tumors (VIPoma) associated with MEN I are rare and so far only one has been reported in Korea.Recently, we came across a case of MEN I, associated VIPoma presented persistent hypercalcemia after a parathyroidectomy. A 70 year old man had suffered from large amount of watery diarrhea, severe general weakness and paralysis of lower limbs for 3 months which suggests symptoms of hypercalcemia. Before the patient visited our hospital, he underwent subtotal parathyroidectomy due to hyperparathyroidism. Even though he was operation, there was no subsidization of the symptoms and abnormal findings of blood chemistry such as hypercalcemia, hypocalemia were remained unchanged. However, the parathyroid hormone level was still within normal limits. Abdominal computerized tomography scan demonstrated a mass of 2.5 cm diameter in tail of the pancreas. As serum level of VIP hormone was also elevated, distal pancreatectomy was carried out to performed.

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