Delayed-Onset Localized Bullous Pemphigoid on an Umbilical Hernia Repair Scar: An Example of Ruocco's Immunocompromised Cutaneous District.

Bullous pemphigoid (BP) represents the most prevalent autoimmune subepidermal blistering condition, disproportionately affecting the elderly and frequently manifesting as a widespread disease. Localized variants are considerably rare and tend to emerge at sites subjected to prior trauma, surgical intervention, or persistent inflammation. Herein, we describe a 62-year-old male who developed bullous lesions restricted to an umbilical hernia repair scar, with onset occurring 15 years following open surgical repair involving prosthetic mesh. Clinical evaluation revealed a single, intact linear bulla along the scar without any mucosal or systemic involvement; the Nikolsky sign was absent. Histopathological analysis identified a subepidermal blistering pattern, and direct immunofluorescence demonstrated linear IgG deposits along the dermoepidermal junction, confirming the diagnosis of BP. Treatment with topical corticosteroids resulted in full resolution within approximately two weeks, with no recurrence detected during the follow-up period. Review of previously reported surgically triggered localized BP cases indicates that a 15-year latency is exceeded by only two prior reports, both at non-abdominal sites, underscoring the exceptional duration observed here. The extended latency period observed in this case is consistent with the concept of an immunocompromised cutaneous district, wherein localized immune dysregulation may persist well beyond the initial tissue insult. To the best of our knowledge, this constitutes the first reported case of localized BP arising on an umbilical hernia repair scar.