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.