Performance of the 2017 EUSTAR activity index in an scleroderma cohort

Assessment of disease activity in systemic sclerosis (SSc) is limited by the absence of a fully validated, multisystem measure of disease activity. The European Scleroderma Trials and Research Group (EUSTAR) SSc activity index (EScSG-AI) was recently revised, and a validation study within the EUSTAR cohort was performed. In this study, we evaluated the performance of the revised EScSG-AI in an external Australian cohort. The association between the EScSG-AI and the physician global assessment of disease activity (PhGA), both collected prospectively at each annual visit over up to 12 years follow-up, was evaluated using Pearson’s correlation coefficient and Cohen’s kappa coefficient. Generalized linear modelling and time-dependent Cox regression analysis were performed to determine the association of disease activity measured by the EScSG-AI and the summed Medsger Severity Scale (MSS) and death, respectively. There was a moderate correlation between EScSG-AI and PhGA scores (r 0.42, p < 0.001) and moderate association between rising EScSG-AI and summed MSS (r 0.60, p < 0.001). High disease activity, measured by the EScSG-AI at any time during follow-up, was associated with a hazard ratio of 2.07 (95% CI 1.51–2.79) for mortality. The EScSG-AI has a moderate correlation with physician-assessed SSc disease activity. This suggests that the criterion and construct validity of the EScSG-AI are yet to be demonstrated in an external cohort of SSc patients.