Rapid development of hyponatraemic seizures in a psychotic patient.

A 60-year-old woman with a history of recurrent psychotic illness developed severe hyponatraemia after a short period of compulsive water drinking. The case provides a rare illustration of the rapidity of development of dangerously low levels of serum sodium. On discovery of mild hyponatraemia it is essential to repeat measurement of the serum sodium level should the patient's clinical condition change, in order to detect any further deterioration of serum osmolality which may result in severe and possibly fatal cerebral symptoms.