Idiopathic Pure Red Cell Aplasia Presenting With Chronic Macrocytosis and Early Relapse: A Case Report and Literature Review.

Idiopathic pure red cell aplasia (IPRCA) is a rare immune-mediated bone marrow failure syndrome characterized by isolated anemia and reticulocytopenia. Relapse after remission is incompletely described, and macrocytosis is an uncommon presenting feature that may delay recognition. We report the case of a 69-year-old man with longstanding macrocytic anemia who presented with severe isolated anemia and reticulocytopenia. Extensive evaluation excluded secondary causes, and bone marrow biopsy demonstrated near-complete absence of erythroid precursors, confirming IPRCA. Treatment with concurrent cyclosporine and prednisone resulted in remission within three months. One month after therapy discontinuation, the patient experienced biochemical relapse and achieved re-remission with re-treatment using the same regimen. Immunosuppressive therapy was subsequently discontinued, and the patient remains under active surveillance. To contextualize this case, we performed a Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA)-guided review of published IPRCA case reports. Cyclosporine-based regimens were associated with the highest remission rates, while relapse and macrocytosis were infrequently reported. This case highlights macrocytosis as a potential atypical presenting feature of IPRCA and underscores the importance of recognizing relapse and ensuring long-term follow-up.