Syndrome of inappropriate secretion of antidiuretic hormone in association with pulmonary carcinosarcoma.

A smoking patient presented with altered mental status, left sided weakness, and an opacity on the chest roentgenogram. During hospitalization he developed hyponatremia, which was corrected with hypertonic saline solution, fluid restriction, and demethylchlortetracycline. The clinical presentation and the laboratory findings supported the diagnosis of the syndrome of inappropriate secretion of antidiuretic hormone. This was believed to be associated with the pulmonary carcinosarcoma documented at necropsy.