Hyponatremia in psychogenic polydipsia

Twenty psychotic patients with psychogenic polydipsia had hyponatremia (98 to 124 mEq/L) lasting up to 28 months, with headache, hypertension, dementia, seizures, lethargy, and coma. Two deaths also may be attributed to this syndrome. Patients drank 7 to 43 L of water daily. Urine was dilute during this water load (37 to 95 mOsm/kg), and free water clearance ranged from 12 to 36 L/day, while plasma osmolality was 236 to 244 mOsm/kg. During fluid deprivation in seven such patients, urinary osmolality exceeded plasma osmolality when plasma concentration had risen to between 242 and 272 mOsm/kg, thus suggesting a "reset osmostat" or antidiuretic hormone response to nonosmotic stimuli. This tended to sustain hyponatremia. Polydipsia should be recognized as a cause of hyponatremia, perhaps with reset osmostat. This ultimately may cause dementia or death, possibly secondary to recurrent cerebral edema. This sequence of events is potentially preventable or correctable.