Tissue eosinophil levels as a marker of disease severity in bullous pemphigoid

Background Eosinophils play an important role in bullous pemphigoid (BP) pathogenesis. Although tissue infiltration with eosinophils has been known for a long time, there is a lack of knowledge about the relationship between tissue eosinophil levels and disease severity and clinical characteristics of the patients. Methods Fifty‐nine patients diagnosed with BP between January 2008 and December 2018 were reviewed. Haematoxylin–Eosin (H&E)‐stained preparations were re‐evaluated in terms of tissue eosinophil levels. For disease severity, Bullous Pemphigoid Disease Area Index (BPDAI) was used. The relationship between tissue eosinophil levels and disease severity and clinical features were evaluated. Results Erosion/blister and urticaria/erythema BPDAI scores were higher in the group with high tissue eosinophil level than the group with low tissue eosinophil level. Tissue and peripheral blood eosinophil count were correlated with total urticaria/erythema BPDAI scores. There was no correlation between blood and tissue eosinophil count. The mortality rate was 64.7% vs 44.0% in the high vs low tissue eosinophil groups. Tissue eosinophil levels were high in patients with BP accompanying neurological disease. Conclusions Tissue eosinophil count and peripheral blood eosinophil count were correlated with disease severity in BP. Tissue eosinophil levels were also high in patients with BP accompanying neurological disease.