Bone marrow plasmacytosis in idiopathic plasmacytic lymphadenopathy with polyclonal hyperimmunoglobulinemia: a report of four cases.

We report on bone marrow plasmacytosis in four cases of idiopathic plasmacytic lymphadenopathy with polyclonal hyperimmunoglobulinemia (IPL). Pathologically, the plasma cells increased in number and accounted for 20-40% of nucleated cells of bone marrow. These plasma cells diffusely infiltrated or formed numerous clusters with 50-200 cells on histological sections. Some binuclear plasma cells and Russell bodies were seen, but all plasma cells showed mature cytomorphology. One case contained two lymphoid follicles with normal germinal centers. Immunoperoxidase studies of light chain determinants for plasma cells and their precursors demonstrated a polyclonal pattern. The immunohistochemical study revealed that there were no human herpes virus-8-positive cells. Bone marrow plasmacytosis of striking proportions may occur in a number of inflammatory conditions, chronic infections, autoimmune diseases, and hypersensitivity states. These reactive plasmacytoses, although sometimes striking, are generally composed of scattered, non-aggregated plasma cells. The four cases described here contained numerous tumor-like aggregations on mature plasma cells. Our four cases should be differentiated from plasma cell myeloma composed of mature plasma cells. However, electrophoresis generally demonstrated a broad-based polyclonal hypergammmaglobulinemia. Moreover, the immunohistochemical study revealed a polytypic nature of the plasma cells. To avoid overdiagnosis and overtreatment, it is important to be aware of the bone marrow findings of IPL.