Variations in risk of asthma and seasonal allergies between early- and late-onset pediatric atopic dermatitis: A cohort study.

BACKGROUND: Atopic dermatitis is associated with other allergic conditions, but variations in this "atopic march" are poorly understood.

OBJECTIVE: To determine the impact of the age of atopic dermatitis onset on the risk for asthma and seasonal allergies.

METHODS: A cohort study was performed using the Pediatric Eczema Elective Registry, which is an observational cohort of subjects with pediatric onset atopic dermatitis.

RESULTS: In total, 3966 children were included, and 73% reported atopic dermatitis onset before age 2 years. At baseline, subjects with atopic dermatitis onset at ages 3 to 7 or 8 to 17 years had significantly lower rates of seasonal allergies and asthma than those with onset before age 2. During follow-up, the adjusted relative risks for incident seasonal allergies were 0.82 (95% confidence interval, 0.72-0.91) and 0.64 (95% CI confidence interval, 0.47-0.83) in the 3- to 7- and 8- to 17-years-old at onset groups compared with the age 2 years or younger at onset group. The adjusted risk for incident asthma was not significantly different between the older onset groups and the earliest onset group.

LIMITATIONS: Misclassification bias may arise from using self-reported onset age data.

CONCLUSIONS: The timing of atopic dermatitis onset may explain part of the variation in the atopic march. These findings may improve future risk stratification of patients for treatment.