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.
(Arch Intern Med 140:1639-1642, 1980)