Clinical features and differential diagnoses of solitary extramedullary plasmacytoma of the thyroid: a case report.

A 40-year-old woman presented with a rapidly enlarging palpable thyroid mass. The patient underwent a total thyroidectomy. The tumor fulfilled the criteria of primary solitary extramedullary plasmacytoma (SEP), including cellular expression of the CD138 and lambda light chain antibodies. Solitary extramedullary plasmacytoma of the thyroid occurs most commonly in patients with Hashimoto thyroiditis and must be distinguished from involvement of thyroid in multiple myeloma, inflammatory pseudotumor plasma cell variant, mucosa-associated lymphoid tissue lymphoma, and medullary carcinoma. The distinction is determined on the basis of histologic findings, immunohistochemical analysis, and other laboratory tests. Currently, no standard treatment exists for this entity. In this report, we discuss the differential diagnosis of SEP of the thyroid and the clinical features observed in this case.