IMMUNOHISTOCHEMICAL, ELECTRON-MICROSCOPIC, AND IMMUNOELECTRON MICROSCOPIC FEATURES OF PLASMACYTOMA OF THE THYROID WITH AMYLOID DEPOSITION

A rare case of primary plasmacytoma of the thyroid with amyloid deposi tion is reported. The tumor consisted of diffuse proliferation of atyp ical plasma cells showing IgG lambda-type monoclonal growth. Amyloid d eposition with focal giant cell reaction was also observed. Bone marro w aspiration and systemic skeletal radiographic surveys revealed no ev idence of multiple myeloma and myelomatosis. Radial arrangement of amy loid bundles was observed ultrastructurally. By immunoelectron microsc opic examination, lambda chain was detected in the amyloid fibrils and rough endoplasmic reticulum of the tumor cells. Our findings suggest the following: amyloid fibrils originate from monoclonal light chains produced by tumor cells, and histiocytes contribute to amyloid deposit ion as well as to giant cell reaction in extramedullary plasmacytoma.