P123 The association of (hyper)eosinophilia with atopic dermatitis severity and treatment response: evidence from the UK-Irish Atopic eczema Systemic TherApy Register (A-STAR)

Abstract

Atopic dermatitis (AD) is often accompanied by elevated blood eosinophils. While eosinophils are central in asthma pathophysiology, their role and clinical relevance in AD is poorly characterized. The aim of this study was to assess the relationship between baseline eosinophil levels and AD severity, clinical characteristics and treatment response. A-STAR is a prospective longitudinal study of patients with AD receiving systemic therapy in the UK. Patients enrolled between October 2018 and May 2025 with baseline eosinophil counts were included. Eosinophil levels were stratified as normal (< 0.5 × 109 cells L−1), moderately raised (0.5–1.5 × 109 cells L−1) or hypereosinophilia (> 1.5 × 109 cells L−1). The eosinophil-to-lymphocyte ratio (ELR) was split into four categories (0 to < 0.15, 0.15 to < 0.29, 0.29 to < 0.49, ≥ 0.49). Clinical scores were normalized to 0–100. Treatment response outcomes were evaluated through achieving EASI 75 and EASI 90 (≥ 75% and ≥ 90% improvement in Eczema Area and Severity Index score from baseline, respectively) for each patient censored at 1 year. Multivariable regression was performed using R 4.4.1. In total, 719 patients were included; the mean age was 27.6 years (SD 15.5), 56.1% were male, 9.3% had prior dupilumab exposure and 47.1% received dupilumab during A-STAR follow-up. Patients with hypereosinophilia (n = 64, 8.9%) were younger, with earlier AD onset and erythrodermic phenotype. Compared with those with normal eosinophil count, hypereosinophilia was associated with asthma [odds ratio (OR) 2.4, 95% confidence interval (CI) 1.1–2.1] and higher AD severity with, EASI +15% (95% CI 9.5–20.5), Dermatology Life Quality Index (DLQI) +14.4% (95% CI 5.2–23.6), Peak Pruritus Numerical Rating Scale (PP-NRS) +8.8% (95% CI 0.4–17.1) and Patient-Oriented Eczema Measure (POEM) +8.3 (95% CI −0.3 to 17). ELR ≥ 0.49 correlated with asthma (OR 3.2, 95% CI 1.7–6.0) and higher EASI (+11.2%, 95% CI 6.7–15.7), but not DLQI, PP-NRS or POEM. Baseline eosinophil counts were not associated with treatment response to any systemic therapy, including both conventional agents and biologics or small molecule. High eosinophil counts are associated with more severe AD, independently of asthma, yet baseline eosinophil counts or ELR do not impact treatment response.