Association of Peripheral Blood and Cutaneous Eosinophils With Bullous Pemphigoid Disease Severity and Treatment Outcomes

A dermal inflammatory infiltrate rich in eosinophils is a prominent histological feature of bullous pemphigoid (BP) and peripheral blood eosinophilia has been documented in 50-60% of BP patients. Nevertheless, the impact of circulating and dermal infiltrate eosinophil levels on BP remains poorly understood. The main objective of this work was to investigate the association of peripheral blood and dermal infiltrate eosinophil levels with clinical and immunological characteristics of the disease.Retrospective cohort study including all patients diagnosed with BP between 2011 and 2020.The study cohort included 233 patients with BP. The mean baseline peripheral blood eosinophil count was 956.3±408.6×106/L and the mean number of tissue eosinophils at the dermal hot spot area was 30.5±19.0. Patients with disseminated presentation (i.e. BSA>50%) had significantly higher peripheral blood eosinophil counts (P=0.028). Mucosal involvement was significantly associated with lower dermal eosinophil count (P=0.001). Requiring inpatient care and relapsing were significantly associated with high peripheral blood eosinophil count (P=0.025; P=0.020, respectively). Among the 68 patients who experienced a relapse, 31 had peripheral blood eosinophilia (i.e. >500×106/L) at relapse (44.2%). Peripheral blood eosinophil counts at baseline and at relapse were significantly correlated (r=0.82, P<0.001).Peripheral blood and cutaneous eosinophils levels may be useful biomarkers for disease activity and treatment outcomes in BP. Monitoring peripheral blood eosinophil counts may allow early detection of relapse.