Validation of IGA*BSA in Assessing Disease Severity and Response in Patients with Atopic Dermatitis: A Retrospective Cohort Study in China

Background: Accurate evaluation of atopic dermatitis (AD) severity is crucial to determine and adjust treatment options. Previous studies have found the product of Investigator's Global Assessment (IGA) and affected body surface area (BSA) to be a simple tool, which requires further verification. Objective: To determine the validity of IGA*BSA in assessing the severity of AD across all age, sex, BMI and disease severity groups. Method: We performed a retrospective study of AD using data from a national cohort (China Type II Inflammatory Skin Disease Clinical Research and Standardized Diagnosis and Treatment Project). Results: Overall, 3051 participants were included in the final analysis. IGA*BSA correlated better with objective measures than with subjective measures. IGA*BSA significantly correlated with Eczema Area and Severity Index (EASI) (r = 0.81), which was stronger than either IGA or BSA alone with EASI, regardless of age, sex, Body Mass Index (BMI), and disease severity groups. Besides, IGA*BSA mild, moderate, and severe groups were associated with significantly higher scores of other assessments and had moderate to fair concordance with other assessments severity strata. At follow-up, the concordance of improvement between IGA*BSA 50/75/90 and EASI 50/75/90 was observed (ĸ = 0.65, 0.62, 0.58, respectively). Conclusion: IGA*BSA appears to be a valid objective assessment of AD severity and improvement over time across all age, sex, BMI, and disease severity subgroups in the clinical practice.