Thyroid plasmacytoma mimicking medullary carcinoma: A potential pitfall inaspiration cytology

Extramedullary plasmacytoma (EMP), a malignant neoplasm of the soft tissues composed of plasma cells, may occur either as a solitary plasma-cell tumor (primary EMP) or as a manifestation of multiple myeloma (secondary EMP). W e report on the aspiration cytology findings of an intriguing case of EMP o f the thyroid that was initially misinterpreted as medullary carcinoma on c linical and cytologic examination. A major contributing cause for the cytol ogic misinterpretation was the presence of amyloid in the aspirate and the clinical impression of a "thyroid mass." Based on this experience, we sugge st that EMP should be considered in the differential diagnosis of a neck ma ss that yields discohesive cells associated with amyloid/amyloid-like mater ial. Clinical correlation and immunocytochemistry are crucial in avoiding p itfalls in this situation. Diagn. Cytopathol. 2000;23:354-358. (C) 2000 Wil ey-Liss, Inc.