Reactive bone marrow plasmacytosis: A common denominator with diverse etiology

Abstract

Background and Aims: Reactive plasmacytosis (RP) is characterised by the diffuse distribution of mature polyclonal plasma cells in the bone marrow (BM) and it is known to occur in various disorders. These need to be differentiated from the clonal plasma cell dyscrasias (PCD). We aim to study the morphological features of RP and to help differentiate them better from PCD. Materials and Methods: We analysed 1409 consecutive BM aspirates for the percentage of plasma cells along with the associated clinical findings. The study group included cases with BM RP and the polyclonality being supported by serum protein electrophoresis or by kappa/lambda immunohistochemistry on BM biopsy. The clinical records, haemogram and BM aspiration findings were retrieved and reviewed in all cases. Morphological features of RP cases were analysed in detail. Further, these cases were compared with 10 confirmed cases of PCD in an attempt to distinguish between the two on morphology. Results: A total of 210 BM aspirates showed increased plasma cells (>3.5%). Clonality could be proven in 135 cases, of which 98 cases were polyclonal and 37 were PCD. Majority of RP cases were >40 years with male predominance. The plasma cell concentration in RP ranged from 4% to 25%. The associated diseases included infections followed by autoimmune diseases. On the morphology, RP unveiled scattered, non-aggregated mature plasma cells while in PCDs, there was a mixture of both immature and mature forms including plasmablasts with frequent clustering. Conclusion: A number of diseases show increased percentage of plasma cells in BM raising suspicion of PCD. It may be difficult to distinguish reactive from neoplastic conditions as there is an overlap both in cell counts and morphology. Assessment of subtle morphological features along with associated clinical and laboratory findings are cardinal for making a correct diagnosis.