Background: To estimate the incident risk of surgical intervention for nasolacrimal duct obstruction after radioactive iodine (RAI) treatment and elucidate the high-risk group of patients with thyroid cancer (TC). Methods: This is a nationwide, population-based cohort study using data from the Korean National Health Claims database. Among the entire South Korean population aged between 20 and 80 years from 2007 to 2019, all patients with TC were included. Among all TC patients, a cohort was established by classifying it into the RAI and non-RAI groups according to whether RAI treatment was performed during the recruitment period. A log-rank analysis was used to evaluate the risk of nasolacrimal duct obstruction surgery in the RAI group compared with that in the non-RAI group. The Cox proportional hazards regression analysis was performed to calculate the adjusted hazard ratio (HR). The analysis was performed stratified by the age group, sex, frequency of RAI treatment, and cumulative dose of 131I. Results: Among 55,371 TC patients, who received RAI treatment, 515 (0.93%) underwent nasolacrimal duct obstruction surgeries, and among 56,950 TC patients, who did not receive RAI treatment, 72 (0.13%) underwent the surgeries. The average timing of incident nasolacrimal duct obstruction surgery was 3.8 ± 2.1 years after the first exposure to RAI. The incidence rate of nasolacrimal duct obstruction surgery was 104.04/100,000 person-years in the RAI group. There was a significantly higher risk of nasolacrimal duct obstruction surgery (HR 7.50 [confidence interval, CI: 5.86-9.60], p < 0.001) in the RAI group than in the non-RAI group. The risks significantly increased in the high-dose group (HR 14.15 [CI: 10.88-18.39]) and those younger than 50 years (HR 15.54 [CI: 9.76-24.72]). Conclusion: We quantified the risk of RAI-induced nasolacrimal duct obstruction surgery through a long-term follow-up of 9 years, which may contribute to estimating the general health care burden related to RAI treatment for TC patients in a practical setting. Great attention should be paid to its risk in patients younger than 50 years, especially in those treated with high doses.
Keywords: cohort; nasolacrimal duction obstruction; radioactive iodine; surgery; thyroid cancer.