Considerations for a combined index for limited cutaneous systemic sclerosis to support drug development and improve outcomes

Systemic sclerosis (SSc; systemic scleroderma) is characterized by a heterogeneous range of clinical manifestations. SSc is classified into limited cutaneous SSc (lcSSc) and diffuse cutaneous subgroups (dcSSc) based on the extent of skin involvement. Randomized controlled trials in scleroderma have mainly focused on dcSSc partly because the measurement of skin involvement, critical for evaluating a therapeutic intervention is more dynamic in this subset. Nonetheless, lcSSc, the most common cutaneous subset (about 2/3), is also associated with significant morbidity and detrimental impact on health-related quality of life. The lack of interventional studies in lcSSc is partly due to a lack of relevant outcome measures to evaluate this subgroup. Combining several clinically meaningful outcomes selected specifically for lcSSc may improve representativeness in clinical trials and responsiveness of outcomes measured in randomized controlled trials. A composite index dedicated to lcSSc combining such relevant outcomes could advance clinical trial development for lcSSc by providing the opportunity to test and select among candidate drugs that could act as disease-modifying treatments for this neglected subgroup of SSc. This proposed index would include items selected by expert physicians and patients with lcSSc across domains grounded in the lived experience of lcSSc. This article reviews the reasons behind the relative neglect of lcSSc, discusses the current state of outcome measures for lcSSc, identifies challenges, and proposes a roadmap for a combined lcSSc-specific treatment response index.