Objective: This study aimed to assess the minimal clinically important differences (MCIDs) for the modified Rodnan skin score (mRSS) using combined data from the Scleroderma Lung Studies (I and II).
Methods: MCID estimates for the mRSS at 12 months were calculated using three anchors: change in scores on the Health Assessment Questionnaire- Disability Index from baseline to 12 months, change in scores on the Patient Global Assessment from baseline to 12 months, and answer at 12 month for the Short Form-36 health transition question "Compared to one year ago, how would you rate your health in general now?" We determined the mRSS MCID estimates for all participants and for those with diffuse cutaneous systemic sclerosis (dcSSc). We then assessed associations between MCID estimates of mRSS improvement and patient-reported outcomes, using Student's t test to compare the mean differences in patient outcomes between those who met the MCID improvement criteria versus those who did not meet the improvement criteria.
Results: The mean (SD) mRSS at baseline was 14.75 (10.72) for all participants and 20.93 (9.61) for those with dcSSc. The MCID estimate for mRSS improvement at 12 months ranged from 3 to 4 units for the overall group (improvement of 20-27% from baseline) and was 5 units for those with dcSSc (improvement of 24% from baseline). Those who met the mRSS MCID improvement criteria had statistically significant improvements in scores on the Short Form-36 Physical Component Summary, the Transition Dyspnea Index, and joint contractures at 12 months.
Conclusion: MCID estimates for the mRSS were 3-4 units for all participants and 5 units for those with dcSSc. These findings are consistent with previously reported MCID estimates for systemic sclerosis.
Trial registration: ClinicalTrials.gov NCT00004563 NCT00883129.
Keywords: Interstitial lung disease; Minimal clinically important difference; Modified Rodnan skin score; Scleroderma; Skin thickness; Systemic sclerosis.