Atypical Morphological Presentation of Neoplastic Plasma Cells: A Series of Five Cases

The diagnosis of Multiple Myeloma (MM) is made by demonstration clonal plasma cells in Bone Marrow (BM) aspiration/biopsy, in addition to assessing serum biochemical parameters, conducting radiological examinations, and considering the clinical presentation. In most cases, predominantly mature plasma cells are observed, along with scattered immature forms in the BM. Several morphological variants of plasma cells have been reported, including Auer rod-like inclusions, small lymphocyte-like cells, hairy cell-like cells, anaplastic variants, promonocyte-like cells, crystal-storing histiocytes, Burkitt-like cells, and blastoid cells. In this series of five cases, most showed a typical clinical presentation and laboratory findings suggestive of plasma cell dyscrasia. However, the morphology of each case exhibited unusual morphological variants, posing diagnostic challenges. These variants included Auer rod-like inclusions, small lymphocytes/lymph-plasmacytoid cells, hairy-like cells, multilobulated nuclei, and anaplastic variants mimicking dysplastic megakaryocytes, leading to various differential diagnoses. The age range of these cases was 57-76 years. Most of the cases presented with generalised dull aching body pain. Imaging studies revealed lytic lesions involving various parts of the bone, including the skull, ribs, vertebrae, and femur. Biochemical assays suggested the possibility of plasma cell dyscrasia. Two of the cases had primary Plasma Cell Leukaemia (PCL), which is a rare and highly aggressive plasma cell neoplasm. The anaplastic variant is associated with a poor prognosis, aiding in predicting treatment responses. However, due to the unusual morphological presentation, the diagnosis of MM or PCL was made after conducting ancillary studies such as Serum Protein Electrophoresis (SPEP), serum free light chain assay, Immunofixation Electrophoresis (IFE), and immunophenotyping through Immunohistochemistry (IHC) or flow cytometry.