Extramedullary plasmacytoma of thyroid - a mimicker of medullary carcinoma at fine needle aspiration cytology: A case report.

A rare case of extra medullary plasmacytoma (EMP) of thyroid gland in a 60 year old male, occurring against a background of Hashimoto's thyroiditis is reported. The fine needle aspiration cytology (FNAC) initially done as an outpatient procedure, showed atypical epithelial cells on a background of amyloid. Considering these findings we gave a diagnosis of medullary carcinoma. Histology of the total thyroidectomy specimen showed an extensive infiltration of neoplastic plasma cells against a background of Hashimoto's thyroiditis, with a bizarre Hurthle cell change. Immunohistochemistry on the histology sections confirmed the diagnosis of solitary plasmacytoma of thyroid against a background of Hashimoto's thyroiditis.