Immunoglobulin D Multiple Myeloma: A Rare Variant

Immunoglobulin D multiple myeloma (IgD MM) is a rare isotype of multiple myeloma (MM), comprising less than 2% of all cases. It is often associated with advanced disease at the time of diagnosis, an aggressive clinical course, and shorter overall survival (OS) than other subtypes of MM. There is an increased frequency of undetectable or small monoclonal (M-) protein levels on electrophoresis, hypercalcemia, anemia, lytic bony lesions, and renal failure. However, given the rarity of the disease, there are few cases of IgD MM described in the literature. Given the very small amount of IgD immunoglobulins, they may form very small or undetectable M spike on electrophoresis, making the diagnostic error in diagnosing this specific subgroup very easy. Treatment for MM has seen significant advancement, especially over the last decade, with the advent of medications such as proteasome inhibitors, immunomodulatory agents, and monoclonal antibodies. It is important to understand how IgD MM responds to these newer agents and why this disease continues to be associated with poor outcomes despite advancements in treatment. Small clinical studies on patients with IgD MM show better outcomes following a combination of high-dose chemotherapy (HDCT) and autologous stem cell transplant (ASCT) compared to standard chemotherapy. Given the rarity of the disease, there are no large studies done to see the effectiveness of these treatments, and most of the data are derived from small case series. We report a case of IgD kappa MM that was incidentally discovered following a traumatic bicycle accident. The patient started treatment with bortezomib and dexamethasone (Vd) as an inpatient while he was in the rehabilitation unit and was later switched to bortezomib, dexamethasone, and lenalidomide (VRd) as an outpatient. He has now completed seven cycles and successfully underwent autologous hematopoietic stem cell transplantation.