Polydipsia and chronic hyponatremia in schizophrenic inpatients.

The occasional presence of polydipsia in psychiatric patients, at times progressing to hyponatremia with severe medical complications, has been previously noted. The clinical history and laboratory data from eight chronically hyponatremic psychiatric inpatients were examined. Common characteristics were a diagnosis of chronic undifferentiated schizophrenia, an early age of onset of their illness, extended hospitalizations with minimal response to neuroleptic medications, heavy tobacco use, and a relatively high frequency of tardive dyskinesia and brain scan abnormalities. Water loading in three patients showed responses consistent with inappropriate secretion of antidiuretic hormone. Potential pathophysiologic mechanisms and treatment considerations are discussed.