Transepidermal water loss, serum IgE and beta-endorphin as important and independent biological markers for development of itch intensity in atopic dermatitis

BACKGROUND: Although itch is the predominant symptom of atopic dermatitis (AD), it is poorly characterized and subjective. The objective assessment of itch intensity is important for treatment and follow-up in patients with AD. OBJECTIVES: To determine what objective clinical parameter(s) could be used as biomarker(s) for itch intensity in patients with AD. METHODS: This is a retrospective and cross-sectional study. Seventy-five patients, aged 7 months-49 years with equal sex ratio, were enrolled in 2000 according to criteria proposed by Hanifin and Rajka. Thirty-five age- and sex-matched subjects who visited the dermatological clinic but were otherwise healthy served as controls. Subjective itch intensity was divided into four grades of severity. Disease severity was measured by SCORAD index, which also includes itch intensity as part of the measurement. Transepidermal water loss (TEWL) and skin surface pH were measured by noninvasive methods in clinically normal skin on the forearm. Serum beta-endorphin and vasoactive intestinal peptide (VIP) were determined by radioimmunoassay. Ordinal logistic regression was used to assess the trend of the subjective itch intensity and SCORAD index by serum IgE, beta-endorphin, VIP, TEWL and skin pH. RESULTS: There were significant trends for itch intensity with IgE, beta-endorphin and TEWL. After adjustment for sex, age and other variables, the odds ratio (OR) for itch intensity by log IgE, beta-endorphin and TEWL was 2.103 [95% confidence interval (CI) 1.222-3.618], 1.100 (95% CI 1.005-1.203) and 1.081 (95% CI 1.009-1.158), respectively. The OR for disease severity by log IgE, beta-endorphin and TEWL was 2.250 (95% CI 1.149-4.407), 1.156 (95% CI 1.086-1.231) and 1.071 (95% CI 0.971-1.182), respectively. In contrast, there was no association between serum VIP concentration and itch intensity. CONCLUSIONS: Beta-endorphin and IgE are both useful biomarkers for itch and disease severity in patients with AD, while TEWL is a good biomarker for itch intensity. These biomarkers provide a way to assess the itch intensity in patients with AD.