Epidemiology of Antiphospholipid Syndrome in Korea: a Nationwide Population-based Study.

Background: Antiphospholipid syndrome (APS) is a systemic autoimmune disorder characterized by arterial and venous thrombosis or pregnancy morbidity in patients with persistent antiphospholipid antibodies. However, nationwide population-based epidemiology studies regarding APS are still unavailable. Methods: We analyzed claims data extracted from the Korean Health Insurance and Review Agency (HIRA) covering more than 52 million Koreans, between January 1, 2008, and December 31, 2017. Patients diagnosed with APS, as determined by the Korean Classification of Disease, 7th edition (D68.6), and a rare intractable disease program (V253), were identified in HIRA. Results: A total of 3,088 newly diagnosed incident cases of 1,215 men and 1,873 women were identified during 2009-2016. The mean age was 44.6 +/- 16.6 (men, 47.4 +/- 16.3; women, 42.8 +/- 16.6) years. The incidence was 0.75 per 10(5) person-year (95% confidence interval, 0.73-0.78). The prevalence in 2016 was 6.19 per 10(5) people. For incident cases, women showed incidence peak at ages of 30-39 years and 70-79 years, whereas for men, it was highest at ages of 70-79 years only. Of all patients, 1,766 (57%, 810 men and 956 women) had primary APS, 1,322 (43%, 405 men and 917 women) had secondary APS, and 845 (27%, 216 men and 629 women) were associated with systemic lupus erythematosus (SLE). Conclusion: The incidence of APS differs according to age groups and gender. The incidence of primary APS was higher than that of secondary APS in both gender. Furthermore, as already reported, secondary APS is highly associated with SLE; however, we observed that rheumatoid arthritis is also highly related.