High prevalence and incidence of systemic sclerosis in Reunion Island, a French multi-ethnical and tropical territory

Systemic sclerosis' (SSc) prevalence varies according to geographical location, presumably in link with environmental and genetic factors. We sought to determine SSc prevalence and incidence on Reunion Island, a southern hemisphere territory characterised by multi-ethnic background.

We conducted a retrospective review of SSc cases defined according to ACR/EULAR 2013 classification criteria. Cases were retrieved over the 2005-2021 period through multiple sources, mainly community and hospital follow-up. Patients were assigned to three clinical subsets: sine scleroderma (normal skin) (ss), limited cutaneous (lc) or diffuse cutaneous (dc) SSc. Prospective submission of questionnaires to patients in 2021 enabled determination of patients' self-declared ethnicity and physician-assessed phototype group. Prevalence was calculated for 2021 and mean annual incidence between 2005 and 2021 after adjustment with WHO's standards.

Overall, 207 patients were included in the retrospective cohort, including 175 SSc (108 lcSSc, 58 dcSSc and 9 ssSSc) and 32 mixed connective tissue disease. Prevalence and mean annual incidence were estimated to be 30.9 (95 %IC: 26.1-35.8) per 100,000 inhabitants in 2021 and 2.13 (95 %IC: 1.81-2.45) per 100,000 inhabitants/year respectively. The 5- and 10-year survival rates after diagnosis were 0.93 and 0.82 respectively. Phototypes and ethnicity were determined in 102 and 86 patients, respectively. Darker phototypes presented more frequently with pulmonary hypertension, while lighter phototypes had more severe gastro-intestinal manifestations and anti-centromere antibodies positivity.

Our study revealed high prevalence and incidence of SSc in Reunion Island which is consistent with the frequently described higher frequency among patients of African origin.