Characteristics of extrinsic vs. intrinsic atopic dermatitis in infancy: correlations with laboratory variables

Summary Background Atopic dermatitis (AD) has been divided into the extrinsic type (ADe) and the intrinsic type (ADi) according to the serum IgE levels and the presence or absence of allergen‐specific IgE. Although previous studies have demonstrated differences in the various immunological parameters, the characteristics of AD in infancy have rarely been reported. Objectives Our study was performed to analyse the correlations between the laboratory parameters of infantile ADe and ADi. Methods We recruited 237 infants with AD and checked the SCORAD index, the number of peripheral blood eosinophils, the serum eosinophil cationic protein (ECP) levels, the total serum IgE levels and the specific serum IgE levels in all the patients. We also checked the serum interleukin (IL)‐4 and IL‐5 levels in 20 patients with ADe and in 20 with ADi. Results This study showed many peculiar characteristics of infantile AD. In infancy, ADi was more prevalent than ADe. The eosinophil count, the ECP level and the SCORAD in ADi were lower than in ADe. Furthermore, a group of patients without characteristics of ADi or ADe could be identified. We tentatively classify this group as indeterminate type (ADind) and propose it as a separate entity. The clinical severity was well correlated with the eosinophil count and the serum ECP levels in ADe and ADi. Therefore these two parameters could be used as clinical severity markers in infancy. Infants are more allergic to food, and the variety of specific allergenic responses was connected with clinical severity. A higher eosinophil count, a higher ECP level and a higher detection rate of IL‐5 in the peripheral blood of infants with ADe means that eosinophils have a more prominent role in ADe than in ADi. Conclusions Infantile AD has many distinctive features in its laboratory variables as compared with AD in other age groups. Clinicians should recognize these facts when they deal with infants with AD, and further studies are warranted on the natural course of infantile AD.