Large Thymus Size at 2 Months Is Associated With Increased Risk of Atopic Dermatitis at Age 2

Atopic dermatitis (AD) is driven by a complex interplay of skin barrier dysfunction and immune dysregulation, including a significant T-cell-mediated immune response. The thymus is the key organ of T cell receptor gene rearrangement and T-cell maturation in early life. This study investigated whether infant thymus size is associated with incident AD during the first 2 years of life.

Three hundred term newborns were followed clinically from birth until 2 years of age. Trans-sternal ultrasound scans of the thymus were performed at birth, 2 months, and 12 months. The thymic index was calculated and dichotomized at ≥ 90th percentile. Skin tape strips from the dorsal hand were analyzed for immune biomarkers. Hazard ratios (HR) with 95% confidence intervals (95% CI) were calculated for AD risk and early-onset AD. Multivariate analyses (aHR) were adjusted for sex, weight, height, breastfeeding, FLG mutation, and parental atopy.

Of the 300 enrolled children, 290 (97%) were eligible for analyses. The 2-year cumulative prevalence of AD was 34.1% (95% CI: 28.7%-39.6%). A higher thymic index at 2 months was associated with increased AD risk during the first 2 years of life (HR: 3.51; 95% CI: [1.73-7.12]; p < 0.001), (aHR: 6.32; 95% CI: [2.81-14.20]; p < 0.001) and increased early-onset AD before 6 months (HR: 2.95; 95% CI: [1.29-6.76]; p = 0.01), (aHR: 5.35; 95% CI: [2.05-13.90]; p < 0.001). A moderate correlation between thymic index and EASI (Eczema Area and Severity Index) was observed at 2 months of age (r = 0.39).

Our findings indicate that increased thymic activity and T-cell development may be associated with a higher risk of AD onset, suggesting a potential role of early-life T-cell maturation in disease pathogenesis.