Plasmacytosis in Acute Myeloid Leukemia: A Diagnostic Challenge

Introduction: Bone marrow plasmacytosis is an uncommon finding at the time of acute myeloid leukemia (AML) diagnosis and may mimic plasma cell dyscrasias, potentially leading to diagnostic confusion. Case Presentation: We report the case of a 43-year-old man who presented with pancytopenia and was found to have 35% myeloid blasts and 22% mature plasma cells on bone marrow aspirate. No monoclonal protein was identified, and flow cytometry revealed co-expression of plasma cell and myeloid markers. Cytogenetic analysis revealed t(8;21). A diagnosis of AML with marked reactive plasmacytosis was established. Discussion: Marked plasmacytosis at AML onset is rare. It may result from cytokine-mediated immune activation. Distinguishing reactive from clonal plasmacytosis is critical to avoid misdiagnosis with plasma cell neoplasms such as multiple myeloma. Conclusion: This case highlights the diagnostic complexity posed by AML with associated plasmacytosis and underscores the importance of a multimodal diagnostic approach incorporating morphology, immunophenotyping, cytogenetics, and protein studies.