IgD-kappa multiple myeloma. Case report and brief review of the literature

Immunoglobulin D multiple myeloma is considered a rare subtype of myeloma, accounting for less than 2% of all myelomas. It is associated with an increased frequency of undetectable or small monoclonal protein levels in electrophoresis. It also accompanied with an aggressive course, resistance to chemotherapy and poor outcome. We report a 71-year-old man with a background history of chronic kidney disease. He presented with history of low back pain for two months and noted during follow-up worsening of his renal function and decreasing trend of haemoglobin levels. Subsequent workup for multiple myeloma showed presence of a small monoclonal protein band between the beta and gamma region in serum protein electrophoresis. Urine protein electrophoresis showed presence of Bence- Jones proteinuria. However, the routine immunofixation electrophoresis of the serum and urine samples showed kappa light chains but was negative for anti IgG, A and M. Further immunofixation with IgD and IgE antisera identified IgD-kappa paraproteinaemia and kappa light chain in the urine. Bone marrow examination showed infiltration by plasma cells, which was further confirmed by immunohistochemistry staining and in situ hybridization. Furthermore, fluorescence in situ hybridization analysis showed deletion of 13q14.3. He was given various chemotherapy regimes, which he was refractory to. This case is reported to highlight the necessity of performing immunofixation for IgD routinely for all patients with suspected multiple myeloma as many cases are misdiagnosed as light chain disease.