1 Introduction
Trajectories of allergic diseases follow the paradigm of the atopic march, which describes the idea of sequential development of allergic diseases, namely atopic dermatitis (AD), food allergy (FA), allergic asthma (AA) and allergic rhinitis (AR), in early life.1 AD, also known as eczema, is a chronic, recurrent skin disease, characterized by chronic skin barrier impairment, inflammation of the skin, eczematous lesions and pruritus.2 AD usually emerges in infancy, arising in the first year in about 60 % of affected children.3Similarly, primary FA, characterized by IgE-mediated responses to foods,4 generally arises during infancy and early childhood.5 AA and AR typically show a later onset and are thus viewed as the latter manifestations in the trajectory of allergic diseases.1,5
Dysfunction of the skin barrier, a hallmark of AD, plays an important role in the aetiology of comorbid allergic diseases. The systemic sensitization against food allergens and inhalant allergens at a young age are thought to be promoted by skin barrier impairment (epicutaneous sensitization), increasing the likelihood for later development of FA, AA and AR.6
Lately, studies focusing on childhood AD have established the importance of differentiating between phenotypic subclasses of AD. Typically, these disease phenotypes are being stratified according to age of onset, persistence and severity of AD.7-10 Differences in underlying pathophysiological pathways which might cause this heterogeneity of AD are yet to be described.8 However, pinpointing the phenotype at highest risk for developing allergic multimorbidity and identifying phenotype-specific risk factors is needed for developing personalized prevention and treatment strategies for children with AD.
Thus, we hypothesize that children with early onset and persistent eczema are at highest risk for sensitization against food and/or inhalant allergens and the subsequent development of allergic multimorbidity. The current TRACKER (Trajectories of Allergy in Children in Real Life Databases) study aims to identify the associations of eczema phenotypes with presence of FA, asthma and hay fever. In addition, we aimed to describe the trajectories of eczema, asthma and hay fever, differentiating between children with and without FA.