Nationwide Incidence of Thyroid Eye Disease and Cumulative Incidence of Strabismus and Surgical Interventions in Denmark

IMPORTANCE: Thyroid eye disease (TED) is a serious condition that can cause proptosis and strabismus and, in rare cases, lead to blindness. Incidence data for TED and strabismus and surgical interventions after TED are sparce. OBJECTIVE: To investigate the nationwide incidence of TED, strabismus, and surgical interventions associated with TED. DESIGN, SETTING, AND PARTICIPANTS: A Danish nationwide registry-based cohort study between 2000, which marks the beginning of uniform coding for the decompression surgery nationwide, and 2018. The cohort consisted of a mean 4.3 million people aged 18 to 100 years with no prior TED diagnosis each year. Total observation time was 8.22 × 10(7) person-years (women, 4.18 × 10(7) person-years; men, 4.04 × 10(7) person-years). MAIN OUTCOME MEASURES: The annual numeric and age-standardized incidence of hospital-treated TED and cumulative incidence of strabismus, strabismus surgery, and orbital decompression surgery in patients with TED. The incidence was stratified by sex, thyroid diagnosis, and age. RESULTS: A total of 4106 incident diagnoses of TED were identified during 19 years among 3344 women (81.4%) and 762 men (18.6%). The mean numeric annual nationwide incidence rate of TED was 5.0 per 100 000 person-years overall, 8.0 per 100 000 person-years in women, and 1.9 per 100 000 person-years in men, resulting in a 4:1 ratio of women to men with TED. The age-standardized incidence was similar. The mean (SD) age at onset was 51.3 (14.5) years. At the time of TED diagnosis, 611 patients (14.9%) were euthyroid, 477 (11.6%) were hypothyroid, and 3018 (73.5%) were hyperthyroid. In patients with TED who were euthyroid, the 4-year cumulative incidence was 41% for antithyroid medication and 13% for L-thyroxine. In patients with TED, the 4-year cumulative incidence for strabismus was 10%. The 4-year cumulative incidence of surgical interventions after TED was 8% for strabismus surgery and 5% for orbital decompression. At 4 years, strabismus surgery was more common in men (13.3%; 95% CI, 10.75-15.86) than in women (7.2%; 95% CI, 6.24-8.08), and the absolute difference was 6.1% (95% CI, 3.42-8.14; P