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

Abstract

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