Masked phenytoin-induced megaloblastic anemia in beta-thalassemia minor.

We report the occurrence of megaloblastic hematopoiesis with peripheral microcytosis in a beta-thalassemic heterozygote who developed profound anemia secondary to folate deficiency. The folate deficiency was precipitated by prolonged therapy with diphenylhydantoin. In thalassemic heterozygotes who develop anemia, the possibility of a megaloblastic pathogenesis should be pursued even when the RBC indices maintain their microcytic-hypochromic expression.