Nonsecretory multiple myeloma. Immunohistologic and ultrastructural observations on two patients.

Two well documented examples of nonsecretory multiple myeloma were studied by electron microscopic and immunohistologic methods. In one case, repeat studies revealed no intracytoplasmic immunoglobulins, and the cells displayed a "plasmacytoid" appearance with poor development of rough endoplasmic reticulum and Golgi regions. In the other case, most cells contained intracytoplasmic immmunoglobulins of a monoclonal type and the ultrastructural appearance was that of cells actively engaged in protein synthesis. These findings and others in the literature suggest that myelomas without an M component can be separated into nonproducers and true nonsecretors of immunoglobulins. In one case, immunofluorescence of bone marrow smears with double labels demonstrated three different plasma cell populations: those producing either monoclonal immunoglobulins M (IgM) or A (IgA) and those synthesizing simultaneously IgM and IgM. Dual immunoglobulin production, although known to occur in myelomas with paraproteinemia, has not been previously documented in the nonsecretory variety.