The Atopy Patch Test in Atopic Dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease; its diagnosis is made by a combination of clinical features. AD is characterized by recurrent intense pruritus and a typically age-related distribution and skin morphology [1, 2]. The role of allergy in eliciting and maintaining the eczematous skin lesions has been controversial, partially due to the lack of specificity of the classic tests for IgE-mediated hypersensitivity. On the other hand, the most recent encouraging results of specific immunotherapy studies in AD patients with IgE-mediated allergies represent another line of evidence for the role of aeroallergens in AD. Among the allergens found to be relevant in AD, aeroallergens and food allergens (in children) are most important. As therapeutical consequences of the diagnosis of an allergy are based upon avoidance strategies, the relevance of (often multiple) IgE-mediated sensitizations in patients with AD must be evaluated.

Environmental substances such as aeroallergens produce flares in some patients with AD. Also, aeroallergen avoidance, especially with regard to house dust mites, can result in marked improvement of skin lesions [3]. Patients with AD often have elevated serum levels of IgE, which may correlate with the disease severity. The hypothesis is that Langerhans’ cells bind and present “immediate type” allergens [4], which penetrate the impaired epidermal barrier in AD patients [5]. This concept is derived from studies showing IgE and IgE-binding structures on the surface of epidermal Langerhans’ cells [5] together with mite allergen [6]. From atopy patch test biopsies, allergen-specific T cells have been cloned [7]. These T cells showed a characteristic TH2 (T-helper cell subpopulation) secretion pattern initially, while after 48 h a TH1 pattern was predominant. This same pattern is also found in chronic lesions of AD.