Suprabasal Blistering as a Diagnostic Pitfall in Bullous Pemphigoid: Histopathologic-Immunofluorescence Discordance Complicated by Sepsis.

Bullous pemphigoid is the most common autoimmune subepidermal blistering disease, typically diagnosed through a combination of clinical features, histopathology, and direct immunofluorescence (DIF). However, histopathological findings can be misleading when re-epithelialization shifts the blister plane from subepidermal to suprabasal, mimicking pemphigus vulgaris. We present the case of a 58-year-old woman with type 2 diabetes mellitus, diabetic neuropathy, and a sacral pressure ulcer admitted with a three-week history of generalized tense bullae in a symmetric distribution across the trunk and extremities, with subsequent oral mucosal involvement. The disease was classified as severe bullous pemphigoid. Skin biopsy revealed a suprabasal blister with eosinophilic infiltrate, a pattern classically associated with pemphigus vulgaris; however, DIF demonstrated linear immunoglobulin G and complement C3c deposition at the dermoepidermal junction, confirming bullous pemphigoid and categorically ruling out pemphigus. Initial treatment with systemic corticosteroids and immunosuppressants was complicated by septic shock secondary to a catheter-related bloodstream infection, hospital-acquired pneumonia, and urinary tract infection, requiring vasopressor support, adjustment of the immunosuppressive regimen, and antimicrobial escalation. The patient also developed progressive multifactorial anemia, sepsis-associated coagulopathy, and upper gastrointestinal bleeding. Following multidisciplinary management, she achieved near-complete resolution of skin lesions and clinical recovery, and was discharged with plans for rituximab as definitive steroid-sparing therapy.  This case highlights two critical lessons: first, a suprabasal blister on histopathology does not exclude bullous pemphigoid, as re-epithelialization can alter the apparent cleavage plane, making DIF indispensable for an accurate diagnosis; second, severe bullous pemphigoid requiring intensive immunosuppression carries a substantial risk of sequential nosocomial infections warranting close microbiological surveillance, early source control, and timely modulation of immunosuppressive regimens.