IgD multiple myeloma preceding the development of extensive extramedullary disease without medullary involvement

We present a unique case of IgD multiple myeloma (MM) preceding the development of extensive extramedullary disease without medullary involvement. A 63-year-old man was diagnosed with IgD-lambda MM when he developed anemia. After 3 months of chemotherapy, he was in complete remission as evidenced by the disappearance of bone marrow (BM) plasmacytosis, monoclonal IgD protein in his serum, and Bence Jones proteinuria. Six months after diagnosis, his disease took an unusual course with the development of plasmacytomas in the skin, without medullary involvement. He then received chemotherapy, resulting in the complete disappearance of the subcutaneous plasmacytomas. Two years after the initial diagnosis, his disease took an aggressive clinical course with retroperitoneal relapse, leading to the patient's death within 1 month. The two separate episodes of extramedullary disease were associated with elevated serum lactic dehydrogenase levels and the absence of plasma cells in the BM. This case provides evidence of two separate transformations of the original malignant MM clone.