The introduction of vasopressin-receptor antagonists (vaptans), along with new information regarding morbidity and mortality, has stimulated a reconsideration of the importance of chronic hypo-natremia in psychotic patients.1 Hyponatremia (serum sodium concentration < 136 mEq/L) is the most common electrolyte disorder seen in psychotic patients, with prevalence rates ranging from 7%-10% among inpatients.2-3 The presence of hyponatremia seldom evokes much concern among mental health professionals unless an acute drop in serum sodium level leads to frank neurologic symptoms.1'4'5 Acute hyponatremia can cause cerebral edema resulting in confusion, stupor, coma, and seizures.6 Left untreated, acute hyponatremia can lead to irreversible neurologic damage, respiratory arrest, and even death. The symptoms often progress with little warning and constitute a medical emergency. Complicating the situation is the risk of correcting acute hyponatremia too quickly, which can cause severe damage to the myelin sheath of neurons in deep brain structures,7'8 a condition known as osmotic demyelination syndrome (ODS). Fortunately, acute hyponatremia is relatively rare among psychotic individuals.
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