Paraneoplastic syndromes, such as syndrome of inappropriate secretion of anti-diuretic hormone and watery diarrhea-hypokalemia-achlorhydria syndrome, have been reported in previous reports. Esophageal NECs are related to a poor prognosis. A 38-year-old male with the histologic diagnosis of esophageal NEC, which initially manifested as hypertrophic osteoarthropathy (HOA), later developed brain metastases. Here, AVP is linked to Hypokalemia.