Plasmacytoma of the thyroid gland.

Primary plasmacytoma of the thyroid gland is a rare disease, and clinicopathologic features of this disease are not fully understood. Six cases of primary plasmacytoma of the thyroid, in which immunoperoxidase procedures confirmed a monoclonal nature of proliferating plasma cells are presented. All patients had antithyroid antibodies in their serum together with histologic evidence of chronic lymphocytic thyroiditis, suggesting an intimate relationship of these diseases. Review of the literature revealed that 18 cases, 14 cases from Western countries and 4 cases from Japan, described primary thyroid plasmacytoma. The authors summarized the clinicopathologic features in the current and previously reported cases.