Psychometric Evaluation of the Scleroderma Skin Questionnaire: A Novel Patient-Reported Outcome for Skin Disease in Patients With Systemic Sclerosis.

OBJECTIVE

We aimed to evaluate the psychometric properties of the Scleroderma Skin Questionnaire (SSQ), a novel patient-reported outcome (PRO) to assess systemic sclerosis (SSc)-related skin symptoms.

METHODS

Participants were recruited from the SSc Collaborative National Quality and Efficacy Registry (CONQUER). Internal consistency was determined using Cronbach α and McDonald ω total (ωt). The correlation of the SSQ was assessed with the modified Rodnan skin score (mRSS), physician global assessment (PGA), Scleroderma Health Assessment Questionnaire, 29-item Patient-Reported Outcomes Measurement Information System (PROMIS-29), and patient global assessment to assess criterion, convergent, and divergent validity. Correlations were also assessed between patients' self-reported recall of skin changes over the past 6 months ("SSQ 6-Month") and 6-month change in mRSS.

RESULTS

The SSQ was administered to 799 adults (mean age 52.7; 83% female) enrolled in CONQUER. Cronbach α was 0.90 and ωt was 0.92, indicating high internal consistency. The SSQ was moderately correlated with mRSS (r 0.56), with stronger correlations in diffuse (r 0.54) vs limited cutaneous subtypes (r 0.24; all P < 0.05). The SSQ was also moderately-to-strongly correlated with PROMIS-29 physical function (r -0.50) and pain interference subscales (r 0.61), strongly with Health Assessment Questionnaire score (r 0.63) and severity subscale (r 0.62), and moderately with PGA SSc activity score (r 0.48; all P < 0.05). SSQ 6-Month correlated weakly with the 6-month change in mRSS (r 0.26; P < 0.05).

CONCLUSION

SSQ demonstrated high reliability and moderate correlation with mRSS and legacy PROs. This study provides initial support for SSQ, but not SSQ 6-Month, to assess skin symptoms in patients with SSc.