A case report on reversible Pelger-Huët anomaly depending on serum free fraction of valproic acid.

Pelger-Huët anomalies, which are characterized by an abnormal nuclear shape and chromatin organization in blood granulocytes, and are frequently confused with myelodysplastic syndrome. We herein report a case of Lenox syndrome in a patient treated with VPA for more than 25 years who developed significant Pelger-Huët anomalies. Despite the lack of any changes in the total VPA level throughout the patient's clinical course, the free fraction of VPA potently increased, likely due to a reduction in serum albumin. Following the administration of a smaller dose of VPA that reduced the serum free fraction of VPA to the normal range, the Pelger-Huët anomalies completely disappeared. It is necessary to monitor the free fraction of VPA in order to detect an overdose, which may induce adverse effects under conditions of hypoalbuminemia. The present case showed, for the first time, that VPA-induced Pelger-Huët anomalies occur in a dose-dependent and reversible manner.