Phenytoin-induced Pure Red Cell Aplasia: a Rare and Challenging Diagnosis

Pure Red Cell Aplasia (PRCA) is a rare hematologic disorder characterized by normochromic, normocytic anemia with reticulocytopenia, while the white blood cell and platelet counts remain generally normal. Bone marrow biopsy typically shows a lack of erythroblasts but normal granulopoiesis and megakaryopoiesis. We report a case of a 72-year-old male who developed severe anemia following phenytoin administration for post-traumatic seizure prophylaxis. The patient's hemoglobin dropped from 11.1 g/dL to 6.6 g/dL within 32 days of phenytoin initiation. Bone marrow examination revealed markedly decreased erythroid precursors (4%) with preserved other cell lineages, confirming the diagnosis of PRCA. Following discontinuation of phenytoin and supportive transfusions, the patient showed complete hematologic recovery. This case represents the oldest reported patient with phenytoin-induced PRCA to date and demonstrates that elderly patients may develop this complication more rapidly than younger individuals. This emphasizes the importance of monitoring for rare but serious hematologic complications among patients receiving phenytoin therapy, particularly during the initial months of treatment.