Development and validation of the dermatomyositis skin severity index

Background Dermatomyositis is an autoimmune inflammatory muscle disease with characteristic cutaneous findings of heliotrope eruption, Gottron's papules and a photodistributed eruption with poikiloderma. Objectives To develop and validate a tool to assist with objective assessment of the skin disease of dermatomyositis. Methods A skin severity index was developed; content validity was evaluated by a panel of experts, and construct validity was assessed by convergence with other measures of disease severity including physician's global assessment of disease, specific skin disease changes (ulceration, poikiloderma and pruritus), and quality of life. Test and retest reliability and interobserver reproducibility were determined. Results In total, 98 subjects were enrolled. The Dermatomyositis Skin Severity Index (DSSI) showed significant correlation to the physician's global assessment, assessments of poikiloderma and self-assessment of pruritus. Inter-rater reliability showed strong correlations from 0.73 to 1. Test-retest (intrarater reliability) was completed on 33 subjects, and showed correlations above 0.75. The ability of this tool to detect clinical changes with treatment has not been fully evaluated. Conclusions The DSSI is a valid and reliable measure of skin disease severity in dermatomyositis and can be used in future clinical trials as an assessment tool.