Dose-dependent relationship between levothyroxine and health-related quality of life in survivors of differentiated thyroid cancer.

Background: Long-term survival for patients with differentiated (papillary, follicular, and Hürthle cell) thyroid cancer exceeds 95% but self-reported health-related quality of life scores remain low compared with survivors of cancers with worse prognoses. There are reports that thyroid hormone replacement therapy is associated with lower health-related quality of life. This hypothesis was tested in a sample of Medicare Advantage survivors of differentiated thyroid cancer.

Methods: Data were obtained from the linked 2007-2017 Surveillance, Epidemiology and End Results-Medicare Health Outcomes Survey for patients with differentiated thyroid cancer to conduct a cross-sectional study. Levothyroxine 6-month defined daily dose was calculated from claims data. Defined daily dose was classified as low, average, or high on the basis of standard deviations around body mass index-specific means. Veterans RAND 12-item Quality of Life Survey measures were categorized by T score as low health-related quality of life (T scores ≤25), moderately low (25< T scores ≤50), and high (T scores >50). The association of defined daily dose and health-related quality of life was tested using multinomial logistic regression.

Results: Among patients with differentiated thyroid cancer (n = 782), 67.5% were prescribed levothyroxine for thyroid hormone replacement therapy (mean defined daily dose 123 μg; standard deviation 44.1 μg). Greater defined daily dose was associated with greater relative risk of low (compared with moderately low) health-related quality of life on several measures including Role Limitation (relative risk, 4.9, 95% confidence interval, 2.1-11.6) and Social Functioning (relative risk, 5.6, 95% confidence interval, 2.5-12.5), as well as greater relative risk of multiple low-scoring health-related quality of life measures.

Conclusion: Results suggest greater-than-average thyroid hormone replacement therapy dosages may be associated with lower health-related quality of life among survivors of differentiated thyroid cancer. Given the prevalence of thyroid hormone replacement therapy among survivors of differentiated thyroid cancer, thyroid hormone replacement therapy dose adjustment warrants close attention to address the functional and psychosocial well-being of patients.