Concomitant lymphoplasmacytic lymphoma and plasma cell myeloma, a diagnostic challenge

Background: Lymphoplasmacytic lymphoma and plasma cell myeloma are two B cell lymphoproliferative neoplasms derived from mature B-lymphocytes in different differentiation stages. The coexistence of these two tumors in the same patient is exceedingly rare and can be difficult to diagnose. Case presentation: A 76-year-old male presented with a pathologic fracture after a fall. Radiography showed a lytic lesion in the pelvis. Serum immunofixation showed distinct IgM kappa and IgA kappa monoclonal protein bands. Bone marrow examination revealed aggregates of small, mature lymphoid cells with admixed plasma cells. Immunohistochemical studies and flow cytometric analysis showed the lymphoid cells were CD10-/CD5- kappa restricted monoclonal B cells. The plasma cells were monoclonal with kappa light chain restriction. The majority of plasma cells were positive for IgA and cyclin D1 with a few plasma cells positive for IgM. Additional studies showed the presence of both a positive MYD88 L265P mutation and a CCND1/IGH fusion. A diagnosis of concomitant lymphoplasmacytic lymphoma and plasma cell myeloma was rendered. Conclusion: Concomitant lymphoplasmacytic lymphoma and plasma cell myeloma can be rarely encountered and is diagnostic challenging. It is commonly associated with biclonal monoclonal proteins. This case demonstrates the importance of a comprehensive work-up in the diagnosis of this disease combination and highlights the diagnostic role of MYD88 mutation study