Objective: Many thyroid cancer patients are exposed to long-term thyroid stimulating hormone (TSH) suppression, in many cases as lifetime treatment, and are consequently subjected to risk for cardiovascular disease. We investigated incidence of coronary heart disease (CHD) and ischemic stroke among thyroid cancer patients compared to matched control subjects.
Design: Retrospective cohort study
Methods: A total of 182,419 subjects who received thyroidectomy for thyroid cancer during 2004-2012 were selected from the Korean National Health Insurance data, which covers approximately 97% of the entire Korean population. Propensity score matching was used to select non-cancer controls. Cox proportional hazards regression analysis was used to determine relative risk of coronary heart disease, and ischemic stroke. Mean follow-up was 4.32 years.
Results: Thyroid cancer patients had elevated risk for CHD and ischemic stroke with HR 1.15 (95% CI 1.10-1.22), and 1.15 (1.09-1.22), respectively. This risk was marked in those who took higher dosage of levothyroxine (HR 1.47, 95% CI 1.34-1.60 for CHD and HR 1.56, 95% CI 1.42-1.72 for ischemic stroke among those who took ≥170mcg/d). Atrial fibrillation risk was dose-dependently associated with levothyroxine dosage; however, it comprises only a small proportion of ischemic stroke incidence (4.4%, 128/2914).
Conclusions: The risk for CHD and ischemic stroke was higher in thyroid cancer patients who received thyroidectomy, and the dosage of levothyroxine administered appears to play a major role. More caution is suggested for the screening and treatment of thyroid cancer and subsequent TSH suppression therapy, as well as proper management for cardiovascular disease prevention.