Validation of the Cutaneous Dermatomyositis Disease Area and Severity Index: characterizing disease severity and assessing responsiveness to clinical change

Summary Background The Cutaneous Dermatomyositis Disease Area and Severity Index (CDASI) was developed for use in clinical trials and longitudinal patient assessment. Objectives To characterize disease severity using the CDASI and assess the responsiveness of this instrument to clinically meaningful changes in disease activity. Methods Patients with cutaneous dermatomyositis at the University of Pennsylvania (UPenn, n = 93) and Stanford University (Stanford, n = 106) were prospectively evaluated using the CDASI, physician global assessment (PGA) Likert scales and a visual analogue scale (VAS). Data was analysed using logistic regression models and receiver operating characteristic curves to select cut‐offs. Results Baseline CDASI activity scores for the patients evaluated at UPenn ranged from 0 to 47 (median 17), and baseline PGA VAS scores ranged from 0 to 9·6 (median 1·1). At UPenn a CDASI activity score of 19 differentiated mild from moderate and severe disease. At Stanford baseline CDASI scores ranged from 0 to 48 (median 21), baseline PGA VAS scores ranged from 0 to 9·7 (median 4·2) and CDASI activity scores of 14 or less characterized mild disease. When a 2‐cm change in the PGA VAS was regarded as a clinically significant improvement, a 4‐point (UPenn) or 5‐point (Stanford) change in CDASI reflected a minimal clinically significant response. Conclusions The CDASI is a valid and responsive measure that can be used to characterize cutaneous dermatomyositis severity and detect improvement in disease activity. Variations in cut‐offs may be due to differences in disease severity between the two populations or inter‐rater variations in the use of the external gold measures. What's already known about this topic? Validated outcome measures are essential for comparative trials. The Cutaneous Dermatomyositis Disease Area and Severity Index (CDASI) was created for the assessment of cutaneous dermatomyositis in clinical trials, translational research and clinical practice. Previous studies have demonstrated the validity and reliability of this instrument. What does this study add? Cutaneous dermatomyositis disease severity can be characterized with the CDASI. Clinical change can be assessed by changes in CDASI activity scores. Practical and standardized use of the CDASI is now possible. Linked Comment: Volc‐Platzer, Br J Dermatol 2015; 173: 890–891.