Small cell gall bladder carcinoma complicated by syndrome of inappropriate secretion of antidiuretic hormone (SIADH) treated with mozavaptan.

Small cell gall bladder carcinoma (Scc-GB) is a very rare entity. Although some cases present with endocrine manifestations, paraneoplastic hyponatraemia has been reported in only one previous case. Recently, the antidiuretic hormone (ADH) receptor antagonist mozavaptan has become available. Herein we report a case with Scc-GB complicated with syndrome of inappropriate secretion of antidiuretic hormone (SIADH) treated with mozavaptan. A 47-year-old woman was referred to our hospital for hyponatraemia. Physical examination revealed elevated serum ADH, a gall bladder mass. She was clinically diagnosed with Scc-GB with SIADH as a paraneoplastic syndrome. Mozavaptan was used for SIADH. Serum sodium was quickly normalised after mozavaptan treatment. Two months later, metastasis to the subcutis of the abdominal wall was observed. The metastatic nodule was resected, and small cell carcinoma (Scc) was identified pathologically. Mozavaptan was effective for improvement of hyponatraemia in this patient with Scc-GB complicated with SIADH.