House-dust mite hypersensitivity, eczema, and other nonpulmonary manifestations of allergy

The pathogenetic role of house-dust mites (HDM) in atopic dermatitis (AD) remains controversial, mainly because there is no common agreement on a provocation test that mimics ordinary exposure to HDM. This is related to the lack of knowledge of the mechanism of how HDM allergens enter the body. Theoretically, there are two possible routes: directly through the epidermis, or by inhalation. In "atopy patch testing", a concentrated HDM suspension is tested on the skin under occlusion. This method is frequently used as a model of the epidermal route. The clinical relevance of this method as a provocation test for AD is discussed. As opposed to atopy patch testing, we describe another method, namely, "allergen inhalation testing", as a model of the respiratory route. Twenty patients with AD underwent bronchial provocations with HDM extract in a double-blind, randomized, placebo-controlled study. In nine out of 20 AD patients, bronchial challenge with HDM evoked skin symptoms. All patients with HDM-induced dermatitis had a history of asthma, and as a group they had a higher mean total log-transformed IgE level than the "negative skin responders". Thus, the respiratory route may be relevant in the provocation of AD in a subset of AD patients and may represent an appropriate model of provocation in these patients. Furthermore, the role of HDM in urticaria and allergic rhinitis is discussed.