[Valproate related syndrome of inappropriate secretion of antidiuretic hormone (SIADH)--a case report]

We report an 82-year-old retired man who developed syndrome of inappropriate secretion of ADH (SIADH) caused by sodium valproate (VPA). He had been taking VPA for treatment of symptomatic epilepsy due to cardioembolic stroke. Although he was clinically asymptomatic, he was found to have decreased level of serum sodium concentration (128 mEq/l). Association of hyponatremia, normal urinary sodium concentration, high urine osmolality and increased concentration of serum ADH strongly suggested the presence of SIADH. There were no underlying disorders which can cause SIADH, such as malignant neoplasm with autonomous ADH release, non-malignant pulmonary diseases and active disorders of the central nervous system. Eight days after discontinuation of VPA administration serum sodium level increased (142 mEq/l) to the normal level. Then, we started the administration of VPA again to confirm that VPA was responsible for developing hyponatremia. As a result, he developed SIADH with hyponatremia (128 mEq/l) again, which improved after discontinuation of the administration. Therefore, we concluded that the SIADH might have been caused by administration of VPA. This is the first report on adverse effect of VPA causing SIADH.