Autoimmune thyroiditis in benign and malignant thyroid nodules: 16-year results.

BACKGROUND It is controversial whether autoimmune thyroiditis is associated with higher frequency of papillary thyroid carcinoma (PTC). METHODS This was a cross-sectional, retrospective study. PTCs were compared to benign nodules regarding the prevalence of autoimmune thyroiditis over 16 years. RESULTS A similar proportion of autoimmune thyroiditis was observed in both benign and/or malignant nodules. Mean nodule size in cases with autoimmune thyroiditis was smaller than those without autoimmune thyroiditis. Multivariate analysis showed a negative association between the coexistence of autoimmune thyroiditis and lymph node and/or distant metastases. Lymph nodes involvement and distant metastases were lower in the PTC with autoimmune thyroiditis compared to those without autoimmune thyroiditis. Capsular invasion was a strong predictor for distant metastases attenuated by the presence of autoimmune thyroiditis. CONCLUSION Thyroid nodules with autoimmune thyroiditis are not more likely to be malignant than those without autoimmune thyroiditis. The coexistent autoimmune thyroiditis may be beneficial as a decreased incidence of lymph nodes involvement and distant metastasis was seen in those patients.