An Unusual Case of Lymphoplasmacytic Variant of Multiple Myeloma

Abstract Introduction/Objective Multiple myeloma is characterized by unregulated growth of monoclonal plasma cells with overt production of nonfunctional intact immunoglobulins or immunoglobulin chains. Immunohistochemically, the plasma cells are positive for CD138 and CD38, and are rarely positive for CD20 or cyclin D1. CD20 positivity and plasmacytoid morphology in our case pointed towards a lymphoplasmacytic variant of multiple myeloma. The translocation t(11;14) has been detected in this variant, which can explain the positive cyclin D1 immunostaining. The differential diagnosis of this myeloma variant includes lymphoplasmacytic lymphoma. Methods/Case Report We present a case of a 75-year-old female with no significant past medical history who suffered a fall and hesitated to get evaluated until her pain persisted. Initial ER evaluation revealed she had a compression fracture of the T10 and T11 vertebrae with no other abnormality identified. Subsequently, she underwent kyphoplasty, and bone biopsies were performed. The biopsies showed prominent monotonous lymphocytes and some plasmacytoid cell proliferation. Immunostains showed the tumor cells were positive for CD20, Pax-5, Bcl-2, cyclin D1, CD138, and kappa light chain, weakly positive for CD23; and negative for CD5, CD3, CD10, Sox11, and lambda light chain. Based on the morphology and immunoprofile, current findings were considered suggestive of a low-grade B cell lymphoplasmacytic proliferation with cyclin D1 expression. The differential diagnosis includes a lymphoplasmacytic lymphoma or lymphoplasmacytic variant of multiple myeloma. This case was forwarded to a higher-level care facility for consultation and the diagnosis of plasmacytoma, kappa light chain restricted, was rendered. Results (if a Case Study enter NA) NA Conclusion Misdiagnosis of lymphoma can be made in lesions showing classic plasma cells, numerous lymphoplasmacytic cells, and cyclin-D1 positivity on immunohistochemistry if additional testing is not performed. We recommended further testing, including but not limited to bone marrow biopsy, molecular testing, FISH, and genetic testing for a definitive diagnosis.