Association Between Disease Severity and Clinical, Histopathological, and Eosinophilic Markers in Patients With Bullous Pemphigoid (BP-EPIC)

Bullous pemphigoid (BP) is the most common autoimmune subepidermal blistering disease and is characterized by autoantibodies directed against hemidesmosomal proteins. Eosinophils and eosinophil-associated mediators are believed to play a central role in disease pathogenesis. Periostin and eosinophilic cationic protein (ECP) have been implicated in eosinophilic inflammation; however, their relationship with clinical disease severity in BP remains incompletely understood.

This single-center retrospective observational study will include patients diagnosed with bullous pemphigoid at the University of Health Sciences, Istanbul Training and Research Hospital. Clinical, laboratory, and histopathological data will be collected from medical records.

The study will evaluate demographic characteristics, disease severity measured by BPDAI, serum IgE levels, peripheral eosinophil counts, hospitalization history, relapse frequency, and other clinicopathological parameters. Archived skin biopsy specimens will undergo immunohistochemical staining for periostin and ECP. Staining intensity will be assessed using semi-quantitative scoring methods and correlated with clinical and laboratory findings.

The primary objective is to determine whether periostin and ECP expression levels are associated with disease severity. Secondary objectives include evaluating correlations between tissue biomarker expression and serum IgE levels, eosinophil counts, hospitalization, and disease recurrence.

Inclusion criteria

• Age ≥18 years.
• Diagnosis of bullous pemphigoid confirmed by compatible clinical, histopathological, and/or direct immunofluorescence findings.
• Availability of archived skin biopsy specimens suitable for immunohistochemical evaluation of periostin and eosinophilic cationic protein (ECP).
• Availability of clinical and laboratory data, including BPDAI score, serum IgE level, and peripheral eosinophil count.

Exclusion criteria

• Age <18 years.
• Diagnosis other than bullous pemphigoid.
• Inadequate or unavailable biopsy specimens for immunohistochemical analysis.
• Missing clinical, histopathological, or laboratory data required for study analyses.