Measuring disability of women with systemic sclerosis: validation of the italian version of the systemic sclerosis questionnaire.

BACKGROUND

The aim of this study was to validate the Italian version of Systemic Sclerosis Questionnaire (SySQ) and to evaluate its psychometric characteristics on a sample of inpatient and outpatient women with systemic sclerosis (SSc).

METHODS

Internal and external validity of the Italian version of SySQ were analyzed. Internal validity included: 1) construct validity by means of factor analysis; 2) internal consistency for each category of SySQ through Cronbach's alpha; and 3) reproducibility over time with test-retest using both Pearson's correlation and Intraclass Correlation Coefficient. External validity included: 1) concurrent validity, i.e. correlation with Skindex-17; and 2) discriminant validity, through comparison of scores for different groups of patients.

RESULTS

We obtained data on 115 patients with SSc: 68 had the limited clinical form (lSSc) and 47 had the diffuse clinical form (dSSc). The structure of SySQ was confirmed by factor analysis. The questionnaire showed optimal internal consistency for all SySQ categories (Cronbach's alpha >0.84) and very good reproducibility over time (0.79-0.93, P<0.001). Regarding external validity, SySQ showed good correlation with Skindex-17 (P<0.01) and a satisfactory power of discrimination between groups affected by different clinical conditions.

CONCLUSIONS

The study confirmed that the SySQ maintains good psychometric properties also in a language different from the original. It is a disease-specific tool that can be routinely used in clinical practice for the evaluation of the level of disability in patients with SSc.