Utility of eosinophil cationic protein levels in the diagnosis of intrinsic atopic dermatitis.

Atopic dermatitis (AD) is a chronic-intermittent eczema-tous dermatitis that starts in early childhood (1). AD can be subdivided into extrinsic (ADe) and intrinsic (ADi) subtypes (2). Although 10–45% of patients with AD have been reported to have ADi, defined as AD with low serum immunoglobulin E (IgE) and no allergen-specific IgE, there are few laboratory markers to diagnose or evaluate the severity of ADi. Moreover, because AD is diagnosed based on its characteristic clinical features, it is difficult to diagnose when a patient is too young or in the early stage of the disease with subtle clinical features of AD. It is now widely accepted that AD is associated with elevated levels of eosinophil cationic protein (ECP) (3–5). ECP is a ribonuclease produced by eosinophils, which is elevated in many allergic diseases (3). However, reports are scarce and controversial regarding the age-related changes and diagnostic utility of ECP in AD. Moreover, with regards to evaluating ADi, only a few studies have been published (6–10). The aim of the present study was to compare the clinical and laboratory parameters between ADi and ADe and to assess the usefulness of ECP in diagnosing AD, including ADi. MATERIALS AND METHODS Retrospective chart review was carried out on subjects with AD whose total IgE, ECP and allergen-specific IgE were checked from January 2005 to August 2012 in our hospital. Disease severity was classified into 3 categories (mild, moderate and severe), according to the prescription at the patient's visit. The subjects were classified into the ADi group if their IgE levels were ≤ 183 U/ml and allergen-specific IgE was absent. Subgroup analysis was carried out for very young patients under the age of 2 years, the age range at which AD most commonly presents (11). Statistical analysis was performed with the SPSS 18.0 program. Fisher's exact test and Student's t-test were used to compare the mean values of the 2 groups. To analyse the correlation of categorical data, multivariate regression analysis was performed.