Influence Factors for Lymph Node Metastasis in Papillary Thyroid Carcinoma: Hashimoto's Thyroiditis Has a Weak Effect on Central or Lateral Lymph Node Metastasis

Purpose: To analyze the effect of Hashimoto's thyroiditis (HT) concurrent with papillary thyroid cancer (PTC) on cervical lymph node metastasis (LNM). Methods: Two thousand nine hundred twenty-six patients who underwent thyroidectomy and lymph node dissection between January 2015 and December 2018 were enrolled in this study. Patient demographics and clinicopathologic features were analyzed. Results: Of the total enrolled patients, 598 (20.4%) had concurrent HT. There were 1482 PTC cases with N0, 1033 cases with N1a, and 411 cases with N1b. Patients with HT had lower frequency of extrathyroidal extension (ETE), lymphatic vascular (LV) invasion, high pathological T stage (III+IV) and central LNM rate. Stratifying central LNM by non-ETE or without intrathyroidal spreading, it was further found that central LNM rate in patients with HT was lower than that of patients without HT. However, there was no significant difference in the central LNM rate in patients with PTC stratified by ETE or intrathyroidal spreading. HT with PTC played a weak protective role in N1a, reducing the risk of N1 a by 16.4%. Conversely, HT is a risk factor for Nlb, increasing the risk by 1.336 times compared to patients without HT. TgAb is an independent risk factor for N1b, which appears related to the promotion of N1b by HT. Conclusion: In PTC, HT has a protective effect on central LNM and a risk effect on lateral LNM, although the difference was not significant. This weak protective effect on N1a is more obvious in PTC with less aggressive clinicopathologic characteristics. The risk effect of HT on N1b may be associated with TgAb.