Severe Pancytopenia with Marked Bone Marrow Plasmacytosis in a Young Adult: A Diagnostic Dilemma in Differentiating Reactive Plasmacytosis from Plasma Cell Dyscrasia

Abstract

Bone marrow plasmacytosis is most commonly associated with plasma cell dyscrasias such as multiple myeloma; however, it may also arise as a reactive phenomenon in various clinical contexts. Distinguishing between these entities is particularly challenging in young adults, in whom plasma cell malignancies are uncommon, yet misdiagnosis may lead to unnecessary and potentially harmful therapy. We report the case of a 30-year-old male presenting with hemorrhagic manifestations including gingival bleeding, diffuse purpura, and macroscopic hematuria. Laboratory evaluation revealed severe pancytopenia, and fundoscopic examination showed bilateral retinal hemorrhages. Bone marrow analysis demonstrated marked plasmacytosis (23–30%) without morphologic atypia. Immunohistochemistry confirmed polyclonal plasma cells. Extensive workup, including serum protein electrophoresis, immunofixation, serum free light chain assay, autoimmune panel, and infectious screening, showed no evidence of monoclonality or underlying systemic disease. The patient was managed conservatively with supportive care only. Progressive and complete recovery of hematologic parameters occurred within six weeks, supporting a reactive etiology. This case highlights the diagnostic challenge of differentiating reactive plasmacytosis from plasma cell dyscrasias and underscores the importance of integrating clinical, biological, and histopathological findings to avoid overtreatment.