Congenital nephrogenic diabetes insipidus with marked hyponatremia

A 42-year-old man previously diagnosed with congenital diabetes insipidus (DI) developed polydipsia and polyuria (water intake and urine excretion, above 201 per day). On admission, a serum sodium level of 124mEq/1, a serum chloride level of 87mEq/1, and plasma osmolality of 254mOsm/kg H2O were found, although urine osmolality was always less than 100mOsm/kg H2O, with daily urine excretion of more than 151. Creatinine clearance was 1531/day. Initially, he had free access to water and his daily water intake was 20-271. Restriction of water intake (101/day) normalized his serum sodium levels and alleviated his general fatigue. Hyponatremia is a rare fluid electrolyte disturbance in DI. We found no reports of hyponatremia associated with congenital nephrogenic DI, presumably because the osmosensing mechanism is intact in such patients. The use of thiazides for the treatment of polyuria, in combination with potassium-sparing diuretics and salt restriction, may accelerate the genesis of hyponatremia caused by psychogenic polydipsia in nephrogenic DI.