A 52-year-old woman presents with flaccid blisters on the oral mucosa and flexural skin. Histopathology shows intraepidermal acantholysis with a suprabasal cleft. Direct immunofluorescence reveals IgG and C3 deposits in an intercellular pattern. Which single feature best distinguishes pemphigus vulgaris from bullous pemphigoid?

Explanation

## Distinguishing Pemphigus Vulgaris from Bullous Pemphigoid ### Pathophysiology **Key Point:** Pemphigus vulgaris (PV) is an autoimmune disorder targeting **desmoglein 3** (mucosal-dominant) and **desmoglein 1** (mucocutaneous), while bullous pemphigoid (BP) targets **BP180 and BP230** at the basement membrane zone. ### Histological Distinction | Feature | Pemphigus Vulgaris | Bullous Pemphigoid | |---------|-------------------|-------------------| | **Blister level** | Intraepidermal (suprabasal acantholysis) | Subepidermal (at BMZ) | | **Acantholysis** | Present | Absent | | **Blister character** | Flaccid, rupture easily | Tense, intact | | **Mucosal involvement** | Frequent (80–90%) | Rare | ### Immunofluorescence Pattern **High-Yield:** - **PV:** IgG and C3 in **intercellular pattern** (between keratinocytes) - **BP:** IgG and C3 in **linear pattern** along basement membrane zone ### Autoantigen Specificity **Key Point:** The presence of **IgG antibodies against desmoglein 3** (and/or desmoglein 1) is the gold-standard discriminator for PV. These antibodies cause loss of cell-to-cell adhesion, leading to intraepidermal acantholysis. **Clinical Pearl:** Desmoglein 3 antibodies correlate with mucosal disease; desmoglein 1 antibodies correlate with cutaneous disease. In mucosal-dominant PV, only desmoglein 3 antibodies are present. ### Why Option 0 is Correct Autoantibodies against desmoglein 3 (and sometimes desmoglein 1) are **pathognomonic for PV** and directly cause the disease mechanism. This is the single most specific and discriminating feature.