Incidence and prevalence of systemic sclerosis in Sweden, 2004–2015, a register-based study

Objectives: we aim to present an in-depth report of the incidence and prevalence of systemic sclerosis (SSc) in Sweden in a nation-wide register-based study covering the entire Swedish population Methods: each individual residing in Sweden is given a unique personal identity number. We linked the National Patient Register and the Total Population Register to identify 1) patients with prevalent SSc on 2015–12–31 and 2) patients with incident SSc during the time period 2004–2015 based on ICD-10 codes. We estimated prevalence and incidence overall and stratified on age, sex, and county. Results: we identified 1774 prevalent cases, median age was 65 years (IQR 19.2) and 84% were women. The point prevalence estimate was 22.7 per 100,000 (95%CI 13.3–32.0). 1139 individuals were newly diagnosed with SSc during 2004–2015 with a median age of 60 years (IQR 20.6) and 80% were women. The mean standardized incidence was 11.9 per 1,000,000 person-years (95%CI 5.1–18.7). The annual incidence remained stable over the study period. Women had five times higher incidence and prevalence than men. The highest prevalence stratified by age strata was observed in the group aged 70–79. Conclusion: SSc incidence and prevalence in Sweden are comparable to estimates from southern Europe, as opposed to the previous assumption of lower occurrence in northern Europe. We further observe that SSc incidence has been rather constant throughout recent years in Sweden with no obvious increase.