Inappropriate Secretion of Antidiuretic Hormone after Pancreatoduodenectomy for Pancreatic Head Cancer: A Case Report and Literature Review

Syndrome of inappropriate secretion of antidiuretic hormone (SIADH) is a disease that leads to dilute hyponatremia through excessive secretion of antidiuretic hormone. SIADH has various causes, including ectopic ADH-producing tumors, drug properties, and can be idiopathic. But there have been very few reports of cases in which SIADH has developed after surgery for malignant tumors. In addition, few cases have been reported where this disease has developed after surgery for pancreatic cancer, because the symptoms of hyponatremia are non-specific. These symptoms are particularly gastrointestinal symptoms; therefore, it is difficult to differentiate them, even if SIADH has developed after gastrointestinal surgery. The patient in our case was an 80-year-old woman. She had persistent epigastralgia and left back pain. Imaging studies revealed a tumor in the head of the pancreas, which was diagnosed as pancreatic head cancer. We performed subtotal stomach-preserving pancreatoduodenectomy. After the operation, she complained of appetite loss and general fatigue. Her serum sodium levels decreased to 109 mEq/L on postoperative day 11. She was diagnosed with SIADH using the SIADH diagnostic criteria listed by the Japanese Ministry of Health, Labor and Welfare. We treated the patient with sodium supplementation for hyponatremia, and her symptoms ameliorated. After the event, she did not relapse with hyponatremia. This case is significant in that we performed differential diagnosis after major gastrointestinal surgery for pancreatic cancer and diagnosed SIADH at an early stage.