The characteristics of patients with atopic dermatitis demonstrating a positive reaction in a scratch test after 48 hours against house dust mite antigen.

The clinical characteristics of patients in whom an IgE-mediated reaction against house dust mite (HDM) antigens that contribute to the pathogenesis of atopic dermatitis (AD) remain unclear. This study attempted to elucidate the characteristics of patients who exhibit a positive reaction 48 hr or later against HDM in scratch tests. The reactions after epi-cutaneous application of the allergen to skin with prior scratching were observed for one week in sixteen AD patients showing positive immediate-type hypersensitivity reactions for HDM. Fifty percent of the patients demonstrated positive reactions at 48 hours after epi-cutaneous application of HDM. Significantly higher values were demonstrated in the group positive for HDM after 48 h in serum total IgE, specific IgE for Der f 1, and lactate dehydrogenase, peripheral eosinophil counts, eruption score, and the area of eruption than in the group negative for HDM after 48 h. Domestic exposure to Der f 1 was also higher in the group positive for HDM after 48 h than in the negative group. These results indicate that the patients in whom the HDM-induced reaction continuing more than 48 h and contributing to their real eczematous eruptions are characterized by considerably increased levels of specific IgE for HDM antigens, high disease activity in AD, and increased exposure to domestic HDM.