Influenza Vaccine as a Potential Trigger for Urticarial Phase Bullous Pemphigoid: A Case Report.

Introduction: Bullous pemphigoid (BP) is a chronic autoimmune blistering disorder that primarily affects older adults. While typically associated with tense bullae, its urticarial phase presents diagnostic challenges due to its nonspecific features, often mimicking other pruritic dermatoses. Case Presentation: This report presents a unique case of urticarial phase BP triggered by influenza vaccination in a 58-year-old male, with a clinical course marked by widespread intensely pruritic annular erythematous plaques. Notably, no vesicles, bullae, or erosions were observed during the early phase. Histopathological analysis revealed subepidermal eosinophilic infiltration and characteristic direct immunofluorescence findings, confirming the diagnosis. Treatment with systemic corticosteroids and topical therapies resulted in clinical remission. Conclusion: This case contributes to the growing evidence of vaccine-triggered autoimmune diseases, highlighting potential mechanisms such as molecular mimicry and immune dysregulation. By comparing this case with previous reports, we underscore the importance of recognizing vaccination as a potential BP trigger. Clinicians should maintain vigilance in diagnosing and managing this rare but significant complication. Further research is needed to elucidate the immunopathogenesis and establish guidelines for vaccination in high-risk individuals.