Incidence, prevalence, and mortality of localized scleroderma in Quebec, Canada: a population-based study

Localized scleroderma is an understudied autoimmune disease characterized by fibrosis of the skin and/or subcutaneous tissue. To date, only 6 articles reported on the incidence and/or prevalence estimates globally, with significant design limitations and risk of bias. None of the studies originated from Canada or investigated mortality/geospatial epidemiology. We aimed to study the incidence, prevalence, mortality and spatiotemporal trends of localized scleroderma in Quebec, Canada, stratified by sex and age.

Quebec populational health administrative databases were used to identify localized scleroderma cases from 1989 to 2019. Crude incidence rate, age-standardized incidence rate, prevalence and mortality analyses were conducted using negative binomial random walk models. Spatial analyses were conducted using a Poisson Besag-York-Mollié regression model.

There were 6063 incident localized scleroderma cases identified over the total period of the study (mean age 53.0, standard deviation [SD] 20.2 years at diagnosis). The overall age and sex-standardized incidence rate was 3.25/100,000 person-years [95% Confidence Interval (CI) 3.17-3.33]. Among 6063 incident cases, 4510 (74.4%) were female and 1553 (25.6%) were male, yielding a female-to-male ratio of approximately 3:1. In females, we noted an initial increase in age-standardized incidence rate followed by a plateau and a decrease after 2013 (average annual percent change -2.0 [95% CI -3.7 to -0.2]%). In males, a steady decrease in age-standardized incidence rate was observed (average annual percent change -3.3 [95% CI -5.0 to -1.8]%). The highest incidence rate was observed in the 60-79 year-old age group for females and the 80+ group for males. Age-standardized incidence rate varied geographically with hotspots identified in the south of Quebec. The average prevalence was 24.5/100,000 [95% CI 24.3-24.8]. The overall standardized mortality ratio was comparable for females (1.04 [95% CI 0.95-1.14]) and males (1.14 [95% CI 0.98-1.33]) and decreased steadily over time for both sexes (from 1.31 [95% CI 1.06-1.58] in 1996 to 0.81 [95% CI 0.66-0.98] in 2019). Standardized mortality ratio analysis revealed excess death only in females aged 40-59 years.

From 1989 onward, we report an initial increase in the age and sex-standardized incidence rate of localized scleroderma in Quebec followed by a recent decrease after 2013, as well as a generally increasing prevalence from 1996 to 2019. Standardized mortality ratio analysis confirmed the clinical observation that localized scleroderma is a morbid rather than life-threatening disease. We demonstrate an uneven geographic distribution of localized scleroderma incidence in Quebec.

This project was funded by Canadian Dermatology Foundation, National Scleroderma Foundation and Canadian Institutes of Health Research. Dr. Netchiporouk received FRQS Junior 1 Clinician Scientist Salary Award.