[Vacuolar inclusions with multivesicular structure in leukemic multiple myeloma].

A case of leukemic multiple myeloma with IgG-lambda type, which plasma cells in the peripheral blood and the bone marrow had large vacuolar inclusions is reported. A 67-year-old male was admitted because of bone pain. A diagnosis of leukemic multiple myeloma of IgG-lambda type was established, based on Bence Jones proteinuria (1.5 g/day), marked plasmacytosis in peripheral blood (63%) and bone marrow (90%), serum M-component (IgG-lambda type, 6.0 g/dl) and multiple osteolytic lesions. Most plasma cells in the bone marrow as well as in the blood had vacuolar inclusions in the cytoplasm which were 1-8 microns across and were negative with PAS and myeloperoxidase staining. Acid phosphatase reaction was distributed densely around vacuolar inclusions and sparsely within them in the form of fine granules. Ultrastructurally, most of the vacuolar inclusions were electron-lucent cytoplasmic spaces, encircled in a distinct limiting membrane, in which inner microvesicles were distributed diffusely. A few vacuoles showed fibrillary structures. These findings suggested that the lysosomal system might play a major role in the vacuolation of these plasma cells.