Contemporary epidemiology of systemic sclerosis: A population-based cohort study in the United Kingdom

Abstract

Objective: To estimate the contemporary epidemiology of systemic sclerosis (SSc) in the UK and to explore the validity of using The Health Improvement Network (THIN) primary care database to study SSc.

Methods: 4,520,299 individuals (2000-2012) aged 1-99 years were followed to identify potential incident cases of SSc; potential prevalent cases were identified at start of follow-up. Patient profiles, including free-text comments, were manually reviewed to verify cases of SSc, and case validation was undertaken for a sample (n = 100) using questionnaires to primary care physicians. Incidence, prevalence and mortality rates were calculated.

Results: Following manual review, we identified 1321 cases of SSc (689 incident and 632 prevalent) over a mean follow-up of 7.6 years; mean age at diagnosis 59.1 years. Using information from 91/100 valid questionnaires returned, the positive predictive value of SSc diagnoses in THIN following manual review was 94%. Incidence rates of SSc per 100,000 person-years (95% CI) were 2.02 (1.87-2.17) overall, [3.36 (3.09-3.64) in females, 0.61 (0.49-0.74) in males], ranging from 1.53 (1.11-2.06) to 2.56 (1.78-3.56) across calendar years. Prevalence of SSc per 100,000 (95% CI) increased from 17.13 (14.97-19.51) to 25.38 (23.68-27.16) over the study period, and was higher in females. Using Poisson regression, the adjusted mortality rate ratio was 2.82 (95% CI: 2.55-3.13) among SSc cases versus the general population.

Conclusions: THIN enables precise and valid estimates of SSc occurrence to be determined. The observed increase in SSc prevalence has not been driven by increasing incidence.

Keywords: Epidemiology; Incidence; Mortality; Prevalence; Systemic sclerosis.