The Eczema Area and Severity Index: An update of progress and challenges in its measurement of atopic dermatitis after 20 years of use

The Eczema Area and Severity Index is an investigator-assessed instrument reporting clinical signs of atopic dermatitis. The instrument is extensively validated in both adult and paediatric populations and recommended as a core outcome measure to assess clinical signs by the Harmonising Outcome Measures for Eczema initiative in clinical trials and was recently recommended as an option to measure signs in clinical practice. Here, we review the validation of the instrument using standard assessment criteria, explore controversies and challenges to its universal applicability and highlight future electronic adaptations. We find that the instrument demonstrates adequate performance in the measurement properties recommended by the COnsensus-based Standards for the selection of health Measurement INstruments initiative for instruments reporting clinical signs, is clinically interpretable, and is suitable for all atopic dermatitis severities. Some validation gaps remain. Information reporting on its performance in diverse populations, with emphasis on deeply pigmented skin, is promising though limited. Technological adaptations are demonstrating promising initial validation results and may facilitate remote and/or automated assessments assisting clinical care and decentralized clinical trials in the future. We find no strong evidence limiting its use in trials or clinical practice although questions pertaining to the effect of investigator training remain. We recommend that the Eczema Area and Severity Index be used in all interventional atopic dermatitis trials and be considered alongside other recommended clinical practice severity instruments.