Hyponatremia in internal medicine ward patients: causes, treatment and prognosis.

A prospective study among unselected patients hospitalized in an internal medicine ward showed that 46 patients, 6.9% of total admissions, had serum concentrations of sodium less than 132 mEq/l. In 28.3% of hyponatremic patients (n = 13), the cause was the syndrome of inappropriate antidiuretic hormone secretion; 21.7% of the cases (n = 10) developed hyponatremia during hospitalization, mainly because of hypotonic solution administration. The mortality rate among the hyponatremic patients was high (30.4%) and was not influenced by treatment of hyponatremia. In our opinion, the high mortality reflects the severity of the underlying diseases, although 82.5% of the patients were asymptomatic or had mild neurological signs. There was no significant correlation between the degree of hyponatremia and neurological signs, or mortality.