Plasmacytoid morphology of poorly differentiated thyroid carcinoma: diagnostic approach with brief review of literature.

Poorly differentiated thyroid carcinoma (PDTC) is an uncommon neoplasm of thyroid accounting for 4-7% of all thyroid neoplasm's (1) that are rarely diagnosed accurately on cytology. Medullary thyroid carcinoma (MTC) is the most frequent primary thyroid neoplasm manifesting with plasmacytoid morphology possibly followed by Hürthle neoplasm (HCN) because of their high incidence compared to other subtypes of malignancy. The plasmacytoid morphology in other primary thyroid neoplasms is uncommon and distinguishing such neoplasm's from MTC is crucial for the clinical management of patients presenting with neoplastic thyroid nodules. PDTC may arises denovo from the follicular epithelium or may come from a background of well differentiated thyroid carcinoma (Papillary/ Follicular neoplasm). (1, 2) It affects individuals with a wide age range of 18-80 years with a male to female ratio of 1:2.7 (1). It has a typical cytology characterized by relatively monotonous epithelial cells having scant cytoplasm (high N:C ratio), prominent nucleoli and frequent mitoses in a necrotic background. Although rare, PDTC having plasmacytoid morphology of neoplastic cells pose diagnostic challenge on fine needle aspiration cytology (FNAC) and that forms the basis of this manuscript discussing the differential diagnoses with a brief review of relevant literature. This article is protected by copyright. All rights reserved.