Eosinophilic pleural effusion related to taking valproic acid

Eosinophilic pleural effusions have multiple aetiologies. We report on the case of a 40-year-old man who experienced an eosinophilic pleural effusion with blood hypereosinophilia that occurred nine weeks after a treatment with valproic acid was introduced. Usual aetiologies of eosinophilic pleural effusion were excluded. Once valproic acid was discontinued, both pleural effusion and blood eosinophilia decreased rapidly. The persistence of a residual pleural effusion required the introduction of oral corticosteroids, which resulted in the effusion disappearing completely and rapidly. Valproic acid is a rare cause of eosinophilic pleural effusion. The effusion usually regresses when treatment is discontinued but short-term oral corticotherapy may be necessary in order to heal the patient.