The diagnostic accuracy of fine-needle aspiration cytology for thyroid nodules is not affected by coexistent chronic autoimmune thyroiditis: results from a cyto-histological series of patients with indeterminate cytology.

Indeterminate cytological result at fine-needle aspiration cytology (FNAC) remains a clinical challenge for endocrinologists. Aim of the present study was to evaluate whether a coexistent chronic autoimmune thyroiditis (CAT) might affect the diagnostic accuracy of fine-needle aspiration cytology for thyroid nodules. A retrospective cohort study was designed including all nodules receiving an indeterminate cytology result (TIR3A or TIR3B) undergoing thyroid surgery and subsequent histological confirmation. Patients were stratified into two groups according to the presence or absence of CAT. The hypothesis to be tested was whether follicular cell alterations induced by CAT might increase the rate of indeterminate cytological results in histologically benign thyroid nodules. Additional control groups were represented by nodules with determinate cytology, either benign (TIR 2) or malignant (TIR5). One hundred and eighty-nine indeterminate thyroid nodules were included (67 TIR3A and 122 TIR3B). At post-surgical histology, 46 nodules (24.3%) were malignant. No significant differences were observed in the rate of histologically proven malignancy between patients without CAT and patients with CAT in the TIR3B (29.4% vs 32.4%; P = 0.843) nor TIR3A (13.0% vs 11.4%; P = 1.000) nodules. The rate of coexistent CAT was similar between TIR3B and TIR5 nodules harboring PTC at histology (30.4% vs 39.4%, P = 0.491) and between indeterminate nodules and a control group of TIR2 nodules (39.2% vs 37.0%; P = 0.720). The similar rates of histologically proven malignancy found in cytologically indeterminate nodules in the presence or absence of concomitant CAT would not support that CAT itself affects the diagnostic accuracy of fine-needle aspiration cytology.