Extramedullary Plasmacytoma of the Thyroid Associated With a Serum Monoclonal Gammopathy

Extramedullary plasmacytoma is a malignant plasma cell dyscrasia that is most commonly found in the head and neck. Progression to disseminated disease in the form of multiple myeloma occurs in 17% to 32% of cases. Herein, we describe a patient with extramedullary plasmacytoma of the thyroid gland in whom a serum monoclonal gammopathy resolved with surgery and irradiation of the primary. Although rare, this diagnosis should be considered in patients presenting with obstructive thyromegaly and autoimmune thyroiditis.