Assessing disability and quality of life in systemic sclerosis: construct validities of the Cochin Hand Function Scale, Health Assessment Questionnaire (HAQ), Systemic Sclerosis HAQ, and Medical Outcomes Study 36-Item Short Form Health Survey.

Objective: To assess the construct validity of the Cochin Hand Function Scale (CHFS) and the relevance of using aggregate scores for the scleroderma Health Assessment Questionnaire (sHAQ) and Medical Outcomes Study 36-Item Short Form Health Survey (SF-36) in systemic sclerosis (SSc).

Methods: We evaluated 50 patients with SSc (mean +/- SD age and disease duration 54 +/- 12 years and 9 +/- 8 years, respectively), of which 26 had limited cutaneous SSc (lcSSc) and 23 diffuse SSc (dSSc). Quality of life was assessed by the SF-36, global disability by the Health Assessment Questionnaire (HAQ) and sHAQ, and hand disability by the CHFS. Construct validity was assessed by convergent and divergent validity (Spearman's rank correlation coefficient) and factor analysis.

Results: The CHFS had good construct validity and its total score explained 75% of the variance of the HAQ. The HAQ had better construct validity than the aggregate sHAQ and their scores correlated well (r = 0.88). The aggregate sHAQ was no better than the HAQ in discriminating between lcSSc and dSSc. SF-36 physical and mental components had acceptable convergent and divergent validity. Factor analysis of the 8 subscales extracted 3 factors explaining 72% of the variance, which differed from the a priori stratification with physical and mental subscales extracted in the same factor.

Conclusion: In patients with SSc, the CHFS has good construct validity, the HAQ should be preferred over the aggregate sHAQ for assessing physical functioning, and use of SF-36 physical and mental components aggregate scores is questionable.