The Eczema Area and Severity Index: An important update on validity and reliability

Atopic dermatitis (AD) is a common chronic inflammatory disease that places a large burden on the patients, their families and society.¹

For all clinical trials for AD, the Harmonizing Outcome Measures for Eczema (HOME) initiative recommended the Eczema Area and Severity Index (EASI) for assessing signs of AD.² An objective measure to evaluate treatment effect is usually required from regulatory agencies. EASI is therefore commonly used in addition to instruments which assess other domains such as symptoms, control of AD and quality of life.

Recently, EASI has been recommended for clinical practice and is used in numerous AD registries globally.

The study of Jacobson et al.³ summarizes the current evidence of the validity and reliability of EASI, assessing all relevant measurement properties across different populations. The authors have conducted this important work in a methodologically excellent manner. Their research adheres to COSMIN⁴ guidelines for patient-reported outcome measures.

The study of Jacobson et al.³ is therefore of great importance, as the worldwide widespread use of the EASI requires in depth knowledge of its validity across varying groups of individuals with AD, as well as awareness of the possible limitations in certain populations in order to ensure correct interpretation of outcomes.

Despite the initial selection of EASI by the HOME group, the need of further validation studies had been pointed out.² For example, there was a lack of evidence on the interpretability and feasibility of EASI.² The recent paper by Jacobson et al.³ explores whether these questions still persist; and answer new occurring questions about the validity in varying groups of individuals with AD defined by severity, age and skin phototype.

In severe AD, EASI is considered as valid, while in mild AD, changes in severity might be difficult to assess.⁵ In mild AD, the measurement error was greater than the MIC and a floor effect has been observed in this subset of patients with mild AD. For individuals with melanin-rich skin, further validation studies might be needed to correctly calculate and interpret the EASI, as the current evidence is still limited although promising. Questions pertain regarding the interpretability of the EASI. Although evaluated in studies with excellent study design, variations in severity strata across different studies suggest that the interpretation of EASI might benefit from further studies for developing strata. EASI is generally considered feasible, especially when performed by trained investigators. The increasing use of EASI in clinical trials, clinical practice and registries has created a demand for technological adaptations and applications.

The findings of the Jacobson et al.³ are of high importance for all clinical trials, registries and for clinicians treating children and adults with AD as they help to interpret results from the EASI and highlight remaining challenges.

This research fills existing validation gaps and highlights a few remaining questions which are needed to measure outcomes appropriately in children in both clinical trials and routine and thus promote excellence in research and patient care. The results of the current study will enable well-designed studies that are able to address questions which otherwise remain unsolved.

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The authors have no conflict of interest to declare.