Fig. 1

Morphologic features of mu heavy chain disease. The bone marrow was markedly hypercellular due to a diffuse proliferation of small lymphocytes and plasma cells with prominent cytoplasmic vacuolization (A: bone marrow aspirate, Wright-Giemsa stain, 1000 × and B: bone marrow core biopsy, hematoxylin and eosin stain, 1000 ×). The immunohistochemical studies performed on the bone marrow biopsy demonstrated that the B-cells and plasma cells were strongly positive for IgM (C: 1000 ×) and the plasmacytic component strongly expressed kappa light chains (D: 1000 ×). Scale bars indicate 20 µm