Acute confusional state and hyponatraemia due to inappropriate antidiuretic hormone secretion in polyarteritis nodosa.

An acute confusional state, which developed in a patient with polyarteritis nodosa (PAN), proved to be secondary to inappropriate secretion of antidiuretic hormone and consequent hyponatraemia. This is a very unusual complication of PAN and may well reflect a direct stimulation of the supraoptic nuclei owing to cerebral vasculitis.