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

Abstract

OBJECTIVE 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 The SSQ was administered to 799 adults (mean age 52.7; 82% female) enrolled in the SSc Collaborative National Quality and Efficacy Registry (CONQUER). Internal consistency was determined using Cronbach's α and McDonald's 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 (SHAQ), Patient-Reported Outcomes Measurement Information System-29 (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 six months ("SSQ 6-Month") and six-month change in mRSS. RESULTS Cronbach's 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) versus limited subtypes (r=0.24; all p<0.05). The SSQ was also moderately-to-strongly correlated with PROMIS-29 physical (r=-0.50) and pain interference subscales (r=0.61), strongly with SHAQ's HAQ score (r=0.63) and severity subscale (r=0.62), and moderately with PGA's scleroderma activity score (r=0.48; all p<0.05). SSQ 6-Month correlated weakly with the six-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.