Immunoglobulin D (IgD) multiple myeloma (MM) is a very rare form of myeloma affecting less than 2% of all myeloma patients. It has a multiorgan involvement with renal failure being the key feature. We present here a case of IgD MM in a 62-year-old white male, smoker with past medical history of hypertension, who presented to emergency department with complaints of lower abdominal pain, constipation and decreased urination. Physical exam was unremarkable. Laboratory investigation showed S.Cr 5.99 mg/dL, hemoglobin 8.7 g/dL and corrected S.Ca 10.6 mg/dL. Urine dipstick showed 100 protein and TP/Cr ratio was 23. Serology was positive for serum free lambda chain level of 8,947.6 mg/L as well with free κ/λ ratio < 0.01. The results of serum and urine electrophoresis and immunofixation were also supportive of diagnosis of IgD MM. IgD level was remarkably elevated (27,300 mg/L) too. CT scan of abdomen/pelvis was negative for obstructive uropathy. Skeletal survey showed a solitary lytic lesion in the iliac crest. His kidney function deteriorated next day requiring hemodialysis. The bone marrow biopsy was positive for plasma cell hypercellularity (70-80%) and flow cytometry showed 8% monoclonal IgD lambda plasma cells. The patient was started on bortezomib and dexamethasone and he underwent bone marrow transplant 6 months later. He is doing well hematologically now but he remains dialysis-dependent. IgD MM is a very rare disease affecting younger population with poor prognosis; patients often end up on hemodialysis despite better control of the hematological component.
Keywords: Bortezomib; Immunoglobulin D; Light chain nephropathy; Multiple myeloma.