Hypouricemia in chronic schizophrenic patients with polydipsia and hyponatremia

Polydipsia is a common disorder among chronic psychiatric patients. Impaired water excretion due to enhanced action and secretion of antidiuretic hormone has been reported in hyponatremic patients with polydipsia. Hypouricemia coexisting with hyponatremia is a hallmark of the syndrome of inappropriate secretion of antidiuretic hormone (SIADH). The transitory coexistence of hyponatremia and hypouricemia in patients with polydipsia-hyponatremia syndrome is presented.

We examined the course of hypouricemia and hyponatremia in three schizophrenic patients with a long-standing history of polydipsia resulting in the presence of these conditions. In addition, we investigated the renal clearance of uric acid in five polydipsic patients without a previous history of water intoxication or hyponatremia (simple polydipsia).

Both hyponatremia and hypouricemia were demonstrated in the presence of SIADH in one patient, during an episode of acute water intoxication in another, and in association with chronic hyponatremia in a patient who was following the target weight procedure. Elevated fractional excretion of uric acid percentage (FEUA%) was detected in two patients. These states appeared to be episodic or transitory. In the five patients with simple polydipsia, serum uric acid concentrations and FEUA% were maintained within the normal range.

Altered uric acid regulation that resembles SIADH is present in patients with polydipsia-hyponatremia syndrome. Monitoring the uric acid concentration and FEUA% in polydipsic patients may be useful in identifying those patients with transiently impaired water excretion.