Results of atopy patch tests with house dust mites in adults with 'intrinsic' and 'extrinsic' atopic dermatitis

Background The most frequently employed diagnostic criteria of atopic dermatitis (AD) can be fulfilled in the absence of elevated total circulating IgE or specific IgE to food allergens or environmental aeroallergens and/or in the absence of personal or familial history of atopy as well. Therefore a distinction between 'extrinsic' or 'allergic' and 'intrinsic' or 'non-allergic' AD has been suggested. Recently, a patch test with environmental aeroallergens, named atopy patch test (APT), has been proposed for use in the study of AD. Objective The aim of this study was to investigate the reactivity to APT in patients with 'extrinsic' and 'intrinsic' AD. Patients, materials and methods Two groups of adult male subjects with AD were examined consecutively in our department (Department of Dermatology, Italian Navy Main Hospital, Taranto, Italy) and patch tested with whole bodies of house dust mites (HDM) at a concentration of 20% in petrolatum (Dermatophagoides pteronyssinus 50%, D. farinae 50%). The groups included: (i) 95 patients affected by the adult clinical form of 'extrinsic' AD; (ii) 12 patients affected by the adult clinical form of 'intrinsic' AD; and (iii) a control group of 49 adult healthy male subjects with a negative anamnesis for eczema and atopy and negative skin prick test to aeroallergens/food allergens and/or normal level of total circulating IgE, also patch tested with the same allergen. The statistical differences were calculated by chi(2) test and 95% confidence intervals (CI) were provided. Results The APT was positive in 47.4% (Cl: 37-57%) of 'extrinsic' AD, in 66.6% (CI: 41-93%) of 'intrinsic' AD and in 12.2% (CI: 3-21%) of healthy subjects. The differences between the two AD subgroups and the control group were statistically significant (P < 0.001). Conclusions APT positivity is more frequent in both 'extrinsic' and 'intrinsic' AD than in unaffected subjects. Other studies are needed to confirm our data and to explain why the APT is positive in the 'intrinsic' form.