A 68-year-old man presents with tense, firm bullae on the flexural surfaces of the forearms and inner thighs for 3 weeks. Histopathology shows subepidermal blister with eosinophil-rich infiltrate. Direct immunofluorescence reveals linear IgG and C3 deposits along the basement membrane zone. Which of the following is NOT a characteristic feature of bullous pemphigoid?

Explanation

## Pathophysiology of Bullous Pemphigoid **Key Point:** Bullous pemphigoid (BP) is characterized by **subepidermal blister formation WITHOUT acantholysis**. The primary mechanism is loss of dermal-epidermal adhesion, not intraepidermal cell separation. ### Correct Answer Analysis **Acantholysis is NOT a feature of BP.** Acantholysis (loss of cell-to-cell adhesion) is the hallmark of pemphigus vulgaris, not BP. In BP, the blister forms at the dermal-epidermal junction (subepidermal), and the epidermis remains intact above the blister. ### Pathogenic Mechanism in BP 1. **Autoantibodies** bind to hemidesmosomal proteins (BP180 and BP230) 2. **Complement activation** (C3 deposition) occurs 3. **Eosinophil infiltration** and release of proteolytic enzymes 4. **Disruption of anchoring filaments** → loss of adhesion 5. **Subepidermal blister** forms with intact epidermis above ### Clinical Features of BP | Feature | Details | | --- | --- | | **Lesion type** | Tense, firm bullae (do not rupture easily) | | **Distribution** | Flexural surfaces, lower abdomen, inner thighs | | **Oral involvement** | Rare (< 10% of cases) — spares mucosa | | **Prodrome** | Urticarial, eczematous, or pruritic lesions | | **Age of onset** | Elderly (> 60 years) | **High-Yield:** BP is a **non-acantholytic** autoimmune blistering disorder — this is the key distinction from pemphigus vulgaris. **Clinical Pearl:** The **tense, firm nature** of BP bullae (vs. flaccid bullae in pemphigus) reflects the subepidermal location and intact epidermis above the blister. ### Why the Other Options Are Correct - **BP180 and BP230 antigens:** These are transmembrane and intracellular hemidesmosomal proteins; antibodies against them are pathognomonic for BP [cite:Robbins 10e Ch 25] - **Oral mucosa sparing:** BP rarely involves mucous membranes (< 10% of cases), unlike pemphigus vulgaris - **Urticarial/eczematous prodrome:** 1–2 weeks of pruritic urticarial or eczematous lesions commonly precede frank bullae [cite:Robbins 10e Ch 25]