Immunoglobulin D-lambda type multiple myeloma presenting with FDG-PET/CT negative bone marrow involvement.

We here report a rare case of a patient with IgD-lambda-positive multiple myeloma presenting with FDG-PET/CT negative bone marrow involvement. A 72-year-old man was admitted to our hospital for evaluation of a paravertebral tumor of the chest. Thoracotomy was performed and a histopathological evaluation of resected intrathoracic tumor demonstrated a plasmacytic neoplasma. Initially we thought that this case was a solitary plasmacytoma because there were no positive findings on postoperative FDG-PET/CT. However, bone marrow aspiration study demonstrated massive infiltration of myeloma cells (72%). It is necessary to recognize that IgD-lambda type myeloma cells may not be sufficiently metabolically active to form high uptake on FDG-PET/CT.