Syndrome of Inappropriate Antidiuresis Associated with Pancreatic Neuroendocrine Tumor: Case Report

Abstract BackgroundFunctional pancreatic neuroendocrine tumors (pNETs) rarely produce vasopressin. To the best of our knowledge, only one case of an ADH-producing pNET has been reported thus far. Here, we report a case of pNET producing vasopressin in a 78-year-old man with hyponatremia.Case presentationThe patient presented with anorexia 4 years ago, and the lowest serum sodium level was 121 mmol/L. Upon admission, serum osmolarity was 277 mOsm/kg·H2O, urine osmolarity was 465 mOsm/kg·H2O, urine sodium level was 82.5 mmol/L, and 24-hour urine sodium level was 140.25 mmol. There was no evidence of adrenal insufficiency or hypothyroidism. Syndrome of inappropriate antidiuresis (SIAD) was diagnosed on the basis of laboratory and clinical findings. The serum sodium level was maintained within the normal range after the oral administration of tolvaptan 7.5 mg. 68Ga-tetraazacyclododecanetetraacetic acid–DPhe1-Tyr3-octreotate positron emission tomography-computed tomography (68Ga-DOTATATE PET-CT) showed a high uptake lesion measuring approximately 1 cm in diameter in the pancreatic body, and the possibility of the pNET was considered. The patient underwent surgery, and the immunohistochemical study showed that the tumor cells were positive for somatostatin receptors 2 (SSTR2) and vasopressin. The patient was weaned from tolvaptan post-surgery, and low-dose corticosteroids were started due to signs of relative adrenal insufficiency, which was probably related to heart failure and surgery. Serum sodium level was maintained within the normal range.ConclusionsThis case illustrates the potential ectopic production of vasopressin resulting in SIAD in pNETs, highlighting the adoption of 68Ga-DOTATATE PET-CT and vasopressin immunohistochemical staining in the evaluation of the etiology of SIAD.