UNUSUAL CLUSTERS OF VALPROATE-ASSOCIATED THROMBOCYTOPENIA

In the spring of 1989, I observed a clustering of patients with valproate- (VPA) associated thrombocytopenia. I retrospectively studied all patients taking VPA and followed them through October 1, 1989. Another unexplained cluster of VPA-associated thrombocytopenia occurred in 1991 during a varicella outbreak; all clinically diagnosed varicella cases were then studied retrospectively. Although the 1989 results show that VPA-associated thrombocytopenia was significantly correlated with VPA dose, VPA level, and VPA monotherapy, none of these factors could explain the clustering of cases. The 1991 results suggest that varicella infection precipitated thrombocytopenia in patients taking VPA. I conclude that viral infections may cause clinically significant episodic thrombocytopenia in patients treated with VPA.