Plasma cell myeloma with cleaved, multilobated, and monocytoid nuclei.

The neoplastic cells in most cases of multiple myeloma closely resemble normal plasma cells. The authors report six cases of myeloma in which most of the neoplastic cells had cleaved, multilobated, or monocytoid nuclei and presented some diagnostic difficulty. All cases were clinically aggressive (five patients with stage III disease and one patient with stage II disease). Three patients died during their initial hospitalization, and three patients are alive with progressive disease from 5 to 14 months after combination chemotherapy. Immunohistochemical studies on paraffin-embedded tissue demonstrated monotypic immunoglobulin in each case (three lambda and three kappa). Recognition of these morphologic variants of neoplastic plasma cells is important to the pathologist to avoid erroneous diagnoses and to alert the clinician to an aggressive form of myeloma associated with a poor prognosis. Immunohistochemical studies on paraffin-embedded tissue sections are useful in the diagnosis of this tumor.