A plasma cell dyscrasia resembling leukemia with cells of lymphocytic, plasmacytic, or intermediate morphology, which secrete an IMMUNOGLOBULIN M monoclonal component. There is diffuse infiltration of bone marrow and also, in many cases, of the spleen, liver, or lymph nodes. The circulating macroglobulin produces symptoms of hyperviscosity syndrome: weakness, fatigue, bleeding disorders, and visual disturbances. Peak incidence is in the sixth and seventh decades. (Dorland, 28th ed).