A 52-year-old woman presents with painful oral erosions and flaccid blisters on the flexural areas of the trunk. Histopathology shows acantholysis with suprabasal clefting. Direct immunofluorescence reveals IgG and C3 deposits in an intercellular pattern. All of the following are characteristic features of pemphigus vulgaris EXCEPT:

Explanation

## Characteristic Features of Pemphigus Vulgaris **Key Point:** Pemphigus vulgaris is an intraepidermal acantholytic disorder with suprabasal blister formation — NOT subepidermal. The basement membrane zone remains intact. ### Correct Answer Analysis Option 3 (subepidermal blister formation) is INCORRECT and therefore the right answer to an "EXCEPT" question. Pemphigus vulgaris shows **intraepidermal acantholysis** with blister formation within the epidermis, typically at the suprabasal level. The basement membrane zone (BMZ) is preserved and intact — this is a cardinal distinguishing feature from bullous pemphigoid and other subepidermal blistering disorders. ### Why the Other Options Are Correct | Feature | Explanation | |---------|-------------| | **Nikolsky sign** | Positive on clinically normal skin due to widespread acantholysis; indicates poor cell-to-cell adhesion | | **Antibody targets** | IgG autoantibodies against desmogleins (Dsg3 ± Dsg1); Dsg3 alone = mucosal type; Dsg3 + Dsg1 = mucocutaneous type | | **Oral involvement** | Occurs in ~50% at presentation; may be the sole manifestation initially; painful erosions are characteristic | ### Pathophysiology ```mermaid flowchart TD A[Autoantibodies against desmogleins]:::outcome --> B[Loss of keratinocyte adhesion]:::action B --> C[Acantholysis]:::action C --> D{Blister location?}:::decision D -->|Suprabasal| E[Pemphigus vulgaris<br/>Intraepidermal]:::outcome D -->|Subepidermal| F[Bullous pemphigoid<br/>Subepidermal]:::outcome E --> G[Intact BMZ<br/>Correct for PV]:::action F --> H[Disrupted BMZ<br/>Incorrect for PV]:::urgent ``` **High-Yield:** The distinction between intraepidermal (pemphigus) and subepidermal (pemphigoid) blistering is fundamental. Pemphigus = acantholysis = intraepidermal. Pemphigoid = antibodies to BMZ = subepidermal. **Clinical Pearl:** Direct immunofluorescence in pemphigus shows "tombstone" or intercellular IgG deposition around acantholytic cells, whereas bullous pemphigoid shows linear IgG/C3 along the BMZ. [cite:Robbins 10e Ch 25]