Skin improvement is a surrogate for favourable changes in other organ systems in early diffuse cutaneous systemic sclerosis

Objectives. Skin improvement in diffuse cutaneous SSc (dcSSc), measured with modified Rodnan skin score (mRSS), is frequently used as a primary outcome in clinical trials, but it is uncertain whether mRSS changes reflect changes in other organ systems. This aim of this study was to explore if skin changes in early dcSSc over 1 and 2 years are associated with changes in severity of other organ involvement. Methods. Canadian Scleroderma Research Group database patients with dcSSc, disease duration of <= 5 years, no evidence of initial end-stage organ damage and/or significant comorbidity who had 1 year (n = 154) and 2 years (n = 128) of follow-up data were included. mRSS changes of 25% and/or >= 5 points were considered significant. Organ involvement was assessed by Medsger Disease Severity Score and Canadian Scleroderma Research Group definitions using bivariate, chi-square, ANOVA, adjusted regression and longitudinal mixed effect model analyses. Results. Improvement in mRSS was found in 41% of patients at 1 year and in 50% at 2 years. Improved patients showed less forced vital capacity decline (P = 0.012) and less frequent new cardiac involvement (P = 0.02) over 1 year, as well as better lung (by both Disease Severity Score, P = 0.006, and Delta forced vital capacity%, P = 0.026), peripheral vascular (P = 0.006) and joint/tendon (P = 0.002) involvement over 2 years. mRSS worsening was consistently linked to less favourable lung outcomes at both 1- and 2-year follow-up visits, and more severe gastrointestinal disease at 2 years. Conclusion. Changes in lung function in early dcSSc closely parallel skin changes. mRSS improvement reflects better prognosis for visceral disease and may be a reliable outcome measure in clinical trials.