Abstract: Background and purpose: Neck lymph node metastasis, most of which presents in central neck compartment, is common in patients with papillary thyroid carcinoma (PTC). The objective of this study was to investigate the relationship between the number of dissected central neck lymph nodes and clinical outcome after radioactive iodine (RAI) ablation in pN1a PTC with no more than 5 lymph nodes involvement. Methods: A total of 167 PTC patients who had 1-5 proven metastatic lymph nodes according to postoperative pathological diagnosis were retrospectively analyzed, all of whom underwent total or near total thyroidectomy and central lymph node dissection. After a median follow-up period of 26 months, the clinical outcome of each patient was evaluated as excellent response (ER), indeterminate response (IDR), biochemical incomplete response (BIR), or structural incomplete response (SIR) according to the new American Thyroid Association guidelines. The accumulative ER rate (ER_n) was calculated in patients with different numbers of dissected lymph nodes (ER_n was defined as the proportion of patients who achieved ER with the dissected lymph node number of ≤n). The relationship between the number of dissected central neck lymph nodes and ER_n were investigated. Results: As the increase in the number of dissected central neck lymph nodes，there was also an overall increase in ER_n, especially when n rose from 1 to 10. The values of ER₁, ER₅, ER₁₀ and ER₃₀ were 25.0%, 66.7%, 74.7% and 79.1%, respectively. Besides, the proportion of patients who achieved ER was higher in those with 10 or more dissected lymph nodes than in those with less than 10 (85.7% vs 73.3%, P=0.05). In the multivariate logistic regression analysis, both the dissected central lymph node number of ≥10 (OR=2.720, 95%CI: 1.052-7.033, P=0.039) and the level of preablation stimulated thyroglobulin (OR=0.955, 95%CI: 0.926-0.984, P=0.003) were shown to contribute independently to ER. Conclusion: As the increasing number of dissected central neck lymph nodes, the percentage of pN_1a PTC patients that achieved ER after RAI ablation generally rises. In pN_1a PTC patients with no more than 5 lymph nodes involvement, a central compartment dissection with 10 or more lymph nodes might help them achieve ER after RAI ablation.

Key words: Papillary thyroid carcinoma, Neck lymph node dissection, Clinical outcome, Lymph node metastasis