Plasmacytoma of the Thyroid

Plasmacytomas arise from plasma cells and are part of a family of plasma cell neoplasms. Extramedullary plasmacytomas are usually located in the upper respiratory tract and oral cavity. Thyroid involvement is rare and can be solitary or secondary to systemic multiple myeloma and constitutes less than 5% of all plasma cell neoplasms and 1.4% of extramedullary plasmacytomas. Fine needle aspiration biopsy may falsely predict medullary thyroid cancer or follicular neoplasm of Hurthle cells. Since plasma cells in thyroid are rare, such a finding in frozen section should raise a suspicion of plasma cell neoplasm. Here we report a case presenting with a 4 cm firm nodule in the thyroid. Fine needle aspiration biopsy was not diagnostic. Pathologic examination of the surgical specimen revealed an extramedullary plasmacytoma located in the thyroid. The association of solitary EMP of the thyroid gland with lymphocytic thyroiditis is known and 82% of patients show lymphocytic thyroiditis as was the case with our patient. Clinical outcome of patients with localized disease is favorable. 10-year overall survival rate is 70%. The disease may progress to multiple myeloma in 11-30% of patients. Surgery and/or radiotherapy are the treatment of choice for these patients. Follow-up is required for disease progression and development of multiple myeloma.