Multiple myeloma with a sarcoidosis-like reaction.

An unusual case of multiple myeloma with extramedullary dissemination and co-existing systemic non-necrotic granulomas is described. Immunoperoxidase staining revealed that both lymph node and bone marrow infiltrating plasma cells contained the same IgG-lambda type paraprotein, and that the granuloma epithelioid histiocytes contained intracytoplasmic lysozyme. As there was no evidence of either systemic infection or sarcoidosis, the non-necrotic granulomas may represent the host's response to the myeloma, not unlike the reaction observed in Hodgkin's disease or solid tumours. A causal association cannot, however, be entirely excluded.