Objectives American College of Rheumatology Composite Response Index in Systemic Sclerosis (ACR-CRISS) is a composite endpoint to assess the likelihood of improvement in diffuse systemic sclerosis. ACR-CRISS is a weighted score and includes five core set measures: modified Rodnan skin score, FVC% predicted, health assessment questionnaire–disability index, and patient and clinician global assessments.

Methods We analysed core set measures from 354 participants who participated in three placebo-controlled trials. We generated 10 development datasets, randomly selected from 2/3 of the participants, stratified by study and treatment group. The remaining participants (1/3 of the participants) formed the validation sets. Risk differences (RDs) between active and placebo treatments were calculated by averaging over the replicate datasets; bootstrap 95% CIs for the RDs to estimate the magnitude of treatment effects.

Results In the development sets (n=237), the proportion of participants in the active group had statistically higher improvement in >1 of 5 core set measures versus the placebo group. For example, the proportion who improved by ≥20% in ≥3 core set measures was 49.4% in the active versus338.9% in the placebo; RD: 10.5%, 95% CI4.9 % to 16.1%. In the validation sets (n=117), the proportion who improved by ≥20% in ≥3 core set measures was 50.3% in the active versus35.63% in the placebo (RD:114.8%, 95% CI 3.1% to225.7%). Similar trends were seen with larger percentage cut-offs.

Conclusion Revised CRISS, as assessed by the proportion of participants who improved by a certain percentage in ≥3 of 5 core set measures, is a potential new composite outcome measure.