[Water intoxication in psychiatric patients. 13 cases of severe hyponatremia]

Water intoxication mostly occurs in psychiatric patients. We observed 13 episodes of severe hyponatremia (less than 120 mmol/l) following a period of increased water consumption in 10 psychiatric patients (5 men, 5 women, mean age 48.8 years) treated with neuroleptics and/or benzodiazepines. Other causes of hyponatremia were excluded. The initial clinical signs were associated with severe gastrointestinal and neurological disorders requiring intensive care. In every case a gradual return to normal of natremia was obtained by creating a negative water balance while compensating for the sodium loss. From a study of urine and plasma osmolality ratio (U/P osm) on admission, several physiopathological mechanisms could be envisaged. A U/P osm ratio lower than 1 (6 cases) suggested a water intake exceeding the maximum dilution capacity of the kidneys (20-25 1), or a lesser water intake with little or no osmolal intake, or again an intrarenal disorder of urine dilution. When the U/P osm ratio was higher than 1 (7 cases), reflecting inappropriate secretion of the antidiuretic hormone, the hyponatremia could be explained by the psychosis itself, the treatment taken by the patients, a disorder of thirst regulation and/or a non-osmotic stimulation of vasopressin. This population, therefore, was heterogeneous: the mechanisms which contribute to this pathology are not fully elucidated, and they probably involve several factors.