Non-secretory multiple myeloma with azurophilic granules and vacuoles: an immunological and ultrastructural study.

Cytoplasmic vacuolation was seen in patients with a variety of plasma cell dyscrasia. We report here a case of leukemic non-secretory multiple myeloma with many azurophilic granules. By electron microscopy, the myeloma cells were found to have a well-developed rough endoplasmic reticulum and a clear Golgi apparatus, and azurophilic granules were identified as phagocytic vacuoles. In addition to myeloma markers, the cells were positive for B cell-associated, myeloid and stem cell markers. The diagnosis is difficult because of its misleading morphology and unusual surface markers. We consider that electron microscopy is useful for the identification of cell lineage in this disorder.