Pitfalls in cytological diagnosis of autoimmune thyroiditis.

The aims of this study are to document pitfalls in cytologic diagnosis of autoimmune thyroiditis (AT) and highlight possible ways to minimize them. One hundred consecutive thyroid aspirates with features diagnostic or suggestive of AT, performed and reported by the first author, were included in the study. Follow-up was traced and cytologic features responsible for indecisiveness were re-assessed in those reported as suggestive of AT. The features were then correlated with the results of serologic and thyroid function tests and clinical features, and an attempt was made to amend the final diagnosis using an integrated approach. Seventy eight were diagnostic and 22 were suggestive of AT. In the latter 22, features responsible for the indecisiveness were: cytologic atypia, in the form of nuclear enlargement, irregularity and grooves and altered chromatin texture, in 14 (64%); nucleoli with suspicion of a coexisting neoplasm in three (13.6%), two of which showed epithelial preponderance, crowding and discohesion; sparse inflammation in four (18%); a predominant lymphoid population without epithelial cells resembling a reactive lymph node in one (4.5%); co-existing toxic features in two (9%); and scanty smears in one (4.5%). Eighteen of the 22 suspected of AT had follow-up. Six had been assessed histologically; three with features suspicious of a neoplasm were diagnosed respectively as a papillary carcinoma (PC), Hurthle cell carcinoma (HCC) and a multinodular goitre (MNG) with degenerate changes. The other three were confirmed as AT; one with cytologic atypia, one with sparse inflammation and the third as cytologically resembling a reactive lymphnode. In ten of the remaining 12, the final diagnosis could be revised following an integrated approach with possible reduction of the indecisiveness. Potential pitfalls are: cytologic atypia occurring in AT; abundance or scarcity of background inflammation; low cell yield; and co-existing toxicity and malignancies. Epithelial preponderance over inflammation, nuclear crowding, severe atypia and cell discohesion should raise the possibility of a neoplasm in spite of other features of AT. Awareness of possible pitfalls and adopting an integrated approach, especially in difficult situations, will minimize pitfalls.