Multiple myelomas (MM) of the immunoglobulin D (IgD) subtype is rare amongst plasma cell malignancies. It can present a diagnostic challenge because of the low amount of immunoglobulin in the serum. The amount of monoclonal (M)-protein is often undetectable on electrophoresis. Historically, survival in these patients was typically shorter compared to the immunoglobulin A (IgA) and immunoglobulin G (IgG) subtypes due to advanced disease upon presentation. With the advent of better diagnostic techniques, the prognosis of this disease is changing. We describe a case of an extramedullary testicular plasmacytoma (EMP) of the IgD subtype as the primary feature of MM, which responded well to novel therapy. A 72-year-old White male presented to the emergency room with a right testicular mass for three months. He subsequently underwent right radical orchiectomy. Pathology of the specimen revealed plasmacytoid cells positive for cluster of differentiation (CD79a), lambda free light chain, IgD, and BCL-1 (Cyclin D1) on immunochemical stains. Urine and serum immunofixation were positive for monoclonal IgD with lambda light chain specificity and Bence Jones proteinuria. Bone marrow biopsy showed large sheets of plasma cells with greater than 90% cellularity. Flow cytometry displayed atypical plasma cells expressing cluster of differentiation (CD38, CD20, and CD56) with cytoplasm and lambda light chain, approximately 20%, consistent with a plasma cell dyscrasia. Stage 3 IgD lambda multiple myeloma was diagnosed. He received novel treatment with Bortezomib and dexamethasone for three months, followed by Lenalidomide. His performance status and lab data improved significantly. He had progression-free survival (PFS) of approximately three years and remained in complete remission low-dose dose of Lenalidomide daily. IgD myeloma was considered a diagnostic challenge due to undetectable M-protein levels on serum protein electrophoresis (SPEP). With the advent of serum free light chain assay and serum and cytologic examinations, diagnostic accuracy has significantly improved. The IgD subtype is commonly associated with poor clinical outcomes. However, the use of novel agents and autologous transplant has changed the prognosis of this disease.
Keywords: igd; immunoglobulin d; multiple myeloma; plasmacytoma; testicular plasmacytoma.