Background: Hyponatremia associated with neuroleptic malignant syndrome has thus far been described as a syndrome of inappropriate secretion of antidiuretic hormone.

Objective: To ascertain and describe the role of cerebral salt-wasting syndrome as the cause of hyponatremia in a patient with neuroleptic malignant syndrome.

Methods: A psychotic patient being treated with olanzapine presenting with sopor, muscle rigidity, polyuria, tachycardia, pyrexia, and severe hyponatremia. Methods: Serial serological examinations of plasma tonicity (sodium level and osmolality), brain natriuretic peptide, and antidiuretic hormone were performed, and sodium excretion and urine osmolality were determined from 24-hour urine collection. In addition, markers for rhabdomyolysis were monitored.

Results: The patient shows clear symptoms of cerebral salt-wasting syndrome in association with neuroleptic malignant syndrome, characterized by severe hyponatremia, volume depletion, and elevated brain natriuretic peptide but normal antidiuretic hormone levels. Cerebral salt-wasting syndrome improved under dantrolene sodium treatment and concomitant fluid and sodium replacement.

Conclusions: Hyponatremia in patients with neuroleptic malignant syndrome might more likely reflect cerebral salt-wasting syndrome than a syndrome of inappropriate secretion of antidiuretic hormone as an additional aspect of autonomic dysregulation caused by antidopaminergic drugs.