Detection of Anti-IgE Antibodies Against Basement Membrane Zone in Bullous Pemphigoid by Direct Immunofluorescence: Prevalence, Associations and Significance.

BACKGROUND: Considerable uncertainty exists regarding the prevalence and clinical significance of basement membrane zone (BMZ) anti-IgE antibodies in bullous pemphigoid (BP). OBJECTIVE: To assess the frequency of linear BMZ anti-IgE antibody deposition by direct immunofluorescence (DIF) and evaluate its association with disease severity and potential diagnostic utility in BP. METHODS: This prospective cross-sectional analytical study enrolled 50 patients with newly diagnosed BP, confirmed by DIF and serology, and 50 non-BP controls. Associations with clinical disease severity and laboratory parameters were analysed. An exploratory diagnostic performance analysis of anti-IgE positivity was also performed. RESULTS: The mean age of the study and control populations was 65.1 ± 17 and 58.2 ± 18.5 years, respectively. BMZ anti-IgE antibodies were detected in 27/50 BP patients (54%) and 1/50 (2%) controls [odds ratio (OR) 57.5, 95% confidence interval (CI), 7.4-449.7; p < 0.001]. Anti-IgE positivity was significantly associated with bullous pemphigoid disease area index (BPDAI) total and BPDAI-Erosion-Blister scores, total body surface area, high absolute eosinophil count (AEC), and increased serum IgE. In multivariate logistic regression, elevated AEC and increased serum IgE independently predicted anti-IgE positivity [adjusted-OR (95% CI): 1.004 (1.000-1.008); p = 0.037 and 1.003 (1.000-1.005); p = 0.033, respectively]. Anti-IgE positivity demonstrated 54% sensitivity, 98% specificity and a positive likelihood ratio of 27. CONCLUSIONS: BMZ anti-IgE antibody was present in over half of the patients with BP and was associated with greater disease severity, eosinophilia and elevated serum IgE. Given its high specificity but modest sensitivity, anti-IgE positivity may serve as a useful adjunctive marker to support, rather than exclude, the diagnosis of BP.