The disturbance of epidermal barrier function in atopy patch test reactions in atopic eczema

Atopic eczema (AE) is a common skin disorder. Eczematous lesions showing macroscopic, microscopic and immunopathological resemblance to lesional AE can be induced by aeroallergens by epicutaneous testing (atopy patch test, APT). Altered epidermal barrier function, as determined by transepidermal water loss (TEWL), is a typical feature of patients with AE. The present investigation was performed to define the differences in the epidermal barrier function between positive APT reactions to aeroallergens and positive patch test reactions to contact allergens in AE patients. Allergen extracts from grass pollen, birch pollen, cat dander and house dust mite (Dermatophagoides pteronyssinus) were applied in large Finn chambers on Scanpor for 48 h on the clinically unaffected and untreated skin of the back, in 11 patients with AE. The same procedure was done with 27 contact allergens of a standard test battery. Test reactions were read and TEWL was measured after 48 and 72 h. Eight of the 11 patients developed positive APT reactions to D. pteronyssinus, two to cat dander and one to birch pollen. Seven of the 11 patients showed positive patch test reactions to nickel sulphate, two to potassium dichromate, one to thiuram-mix and one to paraphenylenediamine. Vehicle controls were negative. The TEWL of the positive APT reactions was significantly higher, both after 48 h (mean ± standard deviation 10.0 ± 6.5 g/m² h) and after 72 h (9.7 ± 5.4 g/m² h) as compared with the control site (48/72 h: 4.4 ± 1.5/4.1 ± 1.4 g/m² h) (P < 0.01). In contrast, TEWL of the positive patch test reactions to contact allergens (48/72 h: 5.4 ± 2.2/5.4 ± 1.9 g/m² h) was similar to that of the control site (48/72 h: 5.2 ± 2.1/5.0 ± 1.8 g/m² h) (not significant). The relative TEWL at 48 h and 72 h, expressed as the ratio between the positive patch test and the control site, was significantly higher in the positive APT reactions (48/72h: 218.8 ± 80.4%/232.0 ± 85.9%) compared with positive patch test reactions to contact allergens (48/72 h: 102.1 ± 12.0%/107.1 ± 9.5%) (P < 0.01). It is concluded that the epidermal barrier function in AE patients is altered only in positive APT reactions, in contrast to positive patch test reactions to contact allergens. As a consequence of this aeroallergen-induced altered epidermal barrier function, further allergens can more easily penetrate the skin, inducing a vicious circle and perpetuating the eczematous lesions.