Modification of the Cutaneous Dermatomyositis Disease Area and Severity Index, an outcome instrument

Validated outcome measures play important roles in clinical practice and trials. In the field of dermatology, cutaneous scoring systems help to standardize disease management and to assess therapeutic response.1 These validated tools also allow new therapies for various diseases to be studied systematically, as well as aiding in studies of disease natural history and development of correlative biomarkers. Such outcome measures for the autoimmune dermatoses, specifically cutaneous lupus erythematosus (CLE) and dermatomyositis (DM), have recently been developed for the purpose of clinical trials.2,3 Gaines and Werth emphasize that the design process is equally as important as the availability of cutaneous scoring systems.4 According to Singer et al., the ideal clinical outcome measure is credible, comprehensive, sensitive to change, accurate, biologically sensible and feasible.5 The elements used to measure disease activity must be well established and responsive to changes in disease severity over time. The tool must be easy to use, especially in a busy clinical setting. Once developed, outcome measures need to demonstrate validity and reliability. The Cutaneous Lupus Disease Area and Severity Index (CLASI), an outcome instrument for CLE, exemplifies the process of developing a thorough but not burdensome tool. Albrecht et al. first presented the CLASI in 2005 and three studies have subsequently shown the tool to be valid and reliable, and also to demonstrate clinical responsiveness and reliability across two subspecialties, dermatology and rheumatology.3,6,7 Leading academic dermatologists and rheumatologists with an expertise in DM have similarly developed a one-page outcome measure for the cutaneous manifestations of DM, the Cutaneous Dermatomyositis Disease Area and Severity Index (CDASI). The CDASI has four activity (erythema, scale, excoriation, ulceration) and two damage (poikiloderma, calcinosis) measures over 15 anatomical sites and measures separately three specific areas: hands, periungual and alopecia. A total score ranges from 0 to 148 with an activity subscore ranging from 0 to 116 and a damage subscore ranging from 0 to 32. A recent study demonstrated the reliability and partial validity of the CDASI.2 Inter-rater reliability (as measured by the intraclass correlation coefficient) was excellent: 0.84 for the activity subscore [95% confidence interval (CI) 0.75–0.95], 0.53 for the damage subscore (95% CI 0.32–0.73) and 0.83 for the total score (95% CI 0.72–0.94). Similarly, test–retest intrarater reliability was excellent: r = 0.86 for the activity subscore (95% CI 0.73–0.99), r = 0.87 for the damage subscore (95% CI 0.74–0.99) and r = 0.89 for the total score (95% CI 0.77–1.0). Concurrent validation with the physician global measure (PGM) overall skin scale revealed statistically significant correlations: Spearman's rho rsp = 0.77 for the activity subscore, rsp = 0.40 for the damage subscore and rsp = 0.76 for the total score. However, since that analysis, minor changes have been made to the original CDASI in order to improve the tool for clinical use (Fig. 1a). Here we seek to validate the modified version of the CDASI, v2 (Fig. 1b). Fig 1 (a) Original Cutaneous Dermatomyositis Disease Area and Severity Index (CDASI): changes were made to circled elements. (b) Modified CDASI, v2.