Polyclonal Proliferation of Plasma Cells Associated with Marked Hypergammaglobulinemia in an Elderly Patient

We describe an 89-year-old woman who presented with prominent plasmacytosis mimicking plasma cell leukemia. The apparent serum M-protein level of >7 g/dL of γ mobility was revealed to be a polyclonal increase of immunoglobulins. The plasma cells in the peripheral blood expressed polyclonal surface/cytoplasmic immunoglobulins as well as CD19, CD30, CD38, and CD138 antigens but lacked CD10, CD20, CD25, and CD56. The bone marrow plasma cells showed the CD45+, CD19+, CD56-, MPC-1-/+, and CD49e- immunophenotype, which was in clear contrast with the immunophenotypes of the neoplastic myeloma cells. Abdominal lymphadenopathy, splenomegaly, and a high level of soluble interleukin 2 receptor may have been reflections of an underlying lymphoproliferative disorder, potentially leading to the polyclonal proliferation of plasma cells.