Epidemiology of systemic sclerosis in Quebec, Canada: a population-based study.

Background: Systemic sclerosis (SSc) is a systemic life-threatening autoimmune rheumatic disease. We aimed to assess the incidence, prevalence, mortality and spatiotemporal trends of SSc in Quebec, Canada with stratification by sex and age.

Methods: SSc cases were identified from Quebec populational databases from 1989 to 2019. Negative Binomial (NB) Generalized Linear Models were used for age-standardized incidence rates (ASIR) analyses and NB random walk for prevalence and mortality. A Poisson Besag-York-Mollié regression model was used for spatial analysis.

Findings: 8180 incident SSc cases were identified between 1996 and 2019 with an average age of 57.3 ± 16.3 years. The overall ASIR was 4.14/100,000 person-years (95%, Confidence Interval (CI) 4.05-4.24) with a 4:1 female predominance. ASIR increased steadily over time with an Average Annual Percent Change (AAPC) of 3.94% (95% CI 3.49-4.38). While the highest incidence rates were in those aged 60-79 years old among females and >80 years old among males, the highest AAPC (∼10%) was seen in children. Standarized incidence ratios varied geographically between 0.52 to 1.64. The average prevalence was 28.96/100,000 persons (95% CI 28.72-29.20). The Standardized Mortality Ratio (SMR) decreased from 4.18 (95% CI 3.64-4.76) in 1996 to 2.69 (95% CI 2.42-2.98) in 2019. Females had a greater SMR until 2007 and males thereafter. The highest SMR was in children and young adults [31.2 (95% CI 8.39-79.82) in the 0-19-year age group].

Interpretation: We showed an increasing trend in SSc incidence and prevalence and a decline in SMR over a 25-year period in Quebec. An uneven geographic distribution of SSc incidence was demonstrated.

Funding: National Scleroderma Foundation, Canadian Dermatology Foundation/Canadian Institutes of Health Research.