Quality of life in systemic sclerosis: Psychometric properties of the World Health Organization Disability Assessment Schedule II

Abstract

To determine the validity of the World Health Organization Disability Assessment Schedule II (WHODAS II) in systemic sclerosis (SSc). Patients enrolled in the Canadian Scleroderma Research Group registry participated in a standardized evaluation and completed the WHODAS II. Criterion validity was assessed by comparing the WHODAS II with the Medical Outcomes Study Short Form 36 (SF-36), construct validity was assessed by examining how it relates to common measures of outcome in SSc, and discriminative validity was assessed by examining how it distinguishes patients with more severe disease from those with less severe disease. A total of 402 patients with SSc were included (mean +/- SD age 55 +/- 13 years, 87% women, mean +/- SD disease duration 11 +/- 9 years). The mean +/- SD WHODAS II score was 24.6 +/- 17.4, and the greatest impairments were in life activities and mobility. There were moderate to good correlations between the WHODAS II and the SF-36 Physical Component Summary score (r = -0.44), the SF-36 Mental Component Summary score (r = -0.41), and measures of function (r = 0.54), depression (r = 0.44), pain (r = 0.40), and fatigue (r = -0.49, P < 0.0001 for all). The WHODAS II was able to consistently distinguish patients with milder disease from those with more severe disease. The WHODAS II had good psychometric properties in patients with SSc and should be considered a valid measure of health-related quality of life in SSc.