Defining Disease Activity in Systemic Sclerosis

Abstract Purpose of Review Systemic sclerosis (SSc) is a multisystem autoimmune disease characterised by the presence of fibrosis, microvasculopathy and inflammation. The complex pathogenesis and widespread organ involvement have made assessment and quantification of overall disease activity challenging. In this review, we present an update of the assessment of disease activity in SSc. Recent Findings There has been increasing interest in the use of composite outcome measures to assess the totality of SSc and measure multidimensional disease constructs such as activity and damage. Recently, the Scleroderma Clinical Trials Consortium (SCTC) published a new SSc Activity Index (SCTC-AI) to quantify disease activity across nine domains of disease. In this article, we discuss both the challenges of measuring disease activity in SSc and the rationale and clinical importance of accurate quantification of disease activity. Summary Heterogeneity in clinical presentation, variation in the tempo of disease and variable responsiveness to treatment at different disease stages has resulted in significant challenges in classification and assessment of SSc patients. However, two SSc-specific activity indices now exist to quantify states of high disease activity. Further work is required to establish whether composite outcome measures offer superior measures of treatment response in SSc clinical trials and what the role of the assessment of disease activity is in the recruitment and assessment of participants in trials of novel therapies.