SUN-396 - Fracture Risk after Total Thyroidectomy Versus Lobectomy in Patients with Thyroid Cancer: A Nationwide Cohort Study

Introduction: After thyroid cancer surgery, TSH suppression therapy is commonly administered; however, long-term exposure to high-dose levothyroxine may increase the risk of osteoporosis. Patients undergoing total thyroidectomy generally require higher doses of levothyroxine than those undergoing lobectomy. This study aimed to evaluate whether fracture risk differs according to the extent of thyroid surgery.

Method: We conducted a retrospective cohort study using data from the Korean National Health Insurance Service. Patients who underwent surgery for thyroid cancer between 2010 and 2017 were identified, and 76,532 patients were included in the final analysis. The study population was categorized into two groups: 56,029 patients who underwent total thyroidectomy and 21,183 patients who underwent lobectomy. Patients were followed from the date of surgery until December 31, 2021, to identify incident fractures, including site-specific fractures. Cox proportional hazards regression models were used to evaluate the association between fracture risk and surgical extent. Secondary analyses were performed by stratifying patients according to levothyroxine dose categories and age groups.

Results: The mean daily dose of levothyroxine was higher in the total thyroidectomy group than in the lobectomy group (116 μg vs. 89 μg). When all fracture types were considered, the incidence rate(IR) per 1,000 person-years(PYs) was 6.46 in the lobectomy group and 7.43 in the total thyroidectomy group. In unadjusted analyses, total thyroidectomy was associated with a higher fracture risk (hazard ratio [HR] 1.13, 95% confidence interval [CI] 1.05-1.22). However, this association was attenuated after adjustment for age and sex (HR 0.95, 95% CI 0.88-1.03) and remained non-significant after further multivariable adjustment for age, sex, income, smoking, drinking, regular exercise, diabetes, hypertension, dyslipidemia, CKD, and obesity (HR 0.95, 95% CI 0.88-1.03). Site-specific fracture analyses showed results consistent with those of all-fracture analyses. No significant differences in fracture IR were observed across levothyroxine dose categories. In age-stratified analyses, fracture IR per 1,000 PYs did not differ significantly according to surgical extent in either age group. However, patients aged 50 years or older had significantly higher fracture IR compared with those younger than 50 years(IR per 1000 PYs, 10.96-10.99 vs. 2.67-3.04), regardless of surgical type.

Conclusion: Fracture risk did not differ according to the extent of thyroid surgery or levothyroxine dose in patients with thyroid cancer. However, fracture risk was significantly higher in older patients. These findings suggest that bone mineral density assessment and management should be considered before initiating TSH suppression therapy in older patients after thyroid cancer surgery.

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