The role of C4d expression in the diagnosis of bullous pemphigoid: a clinical and histopathological study.

Inflammatory processes play a crucial role in both autoimmune and non-autoimmune skin diseases. The complement system contributes to these processes, with both well-established and yet-to-be-confirmed effects. The relationship between C4d, an intermediate product of the complement system, and skin diseases remains an area of ongoing investigation. While the presence and role of C4d in autoimmune and non-autoimmune skin diseases have been explored using immunohistochemical methods, the topic remains inconclusive. Bullous pemphigoid is an autoimmune skin disorder characterized by subepidermal blistering, predominantly affecting the elderly population. This study aims to evaluate the potential of C4d as an alternative immunohistochemical marker to the gold-standard diagnostic method, direct immunofluorescence, in diagnosing Bullous pemphigoid. Additionally, C4d staining patterns were analyzed in correlation with clinical data to assess its prognostic significance. In this retrospective study, the histomorphological, clinical, and demographic data of 43 patients diagnosed with Bullous pemphigoid were analyzed. Immunohistochemical assessment of C4d expression and staining patterns was conducted. The findings suggest that C4d may serve as a potential diagnostic and prognostic marker. C4d expression was significantly more frequent in lesions located on the upper extremities and in patients with higher eosinophil scores. Furthermore, patients with high eosinophil scores were more likely to receive systemic treatment. This study demonstrates that C4d could contribute significantly to the diagnostic process, particularly in cases where immunofluorescence studies are limited.