A 52-year-old Indian woman presents with a 3-week history of painful oral erosions and blistering of the oral mucosa. She reports that the blisters rupture easily, leaving painful ulcers. Two weeks later, flaccid blisters appear on the flexural surfaces of the arms and in the axillae. On examination, gentle pressure on apparently normal skin results in separation of the epidermis (positive Nikolsky sign). Oral mucosa shows erosions with surrounding erythema. A skin biopsy shows intraepidermal acantholysis with a "tombstone" appearance of basal cells. Immunofluorescence reveals IgG and C3 deposits in an intercellular pattern. What is the most likely diagnosis?

Explanation

## Diagnosis: Pemphigus Vulgaris ### Clinical Features **Key Point:** Pemphigus vulgaris classically presents with oral mucosal involvement (80–90% of cases) as the first manifestation, followed by cutaneous blisters on flexural surfaces. **Clinical Pearl:** The oral erosions in pemphigus vulgaris are often the presenting complaint and may precede skin lesions by weeks to months. Patients report severe pain due to the superficial nature of the erosions. ### Diagnostic Criteria | Feature | Pemphigus Vulgaris | Bullous Pemphigoid | |---------|-------------------|-------------------| | **Oral involvement** | 80–90% (common, early) | Rare (< 10%) | | **Nikolsky sign** | Positive (intraepidermal) | Negative | | **Blister level** | Intraepidermal (acantholysis) | Subepidermal | | **Histology** | Tombstone appearance, acantholysis | Subepidermal cleft, intact basal layer | | **Direct IF** | Intercellular IgG + C3 | Linear IgG + C3 at BMZ | | **Blister fragility** | Flaccid, rupture easily | Tense, firm | ### Histopathology **High-Yield:** The "tombstone" or "row of tombstones" appearance is pathognomonic: basal cells remain attached to the basement membrane while overlying keratinocytes are separated by acantholysis (loss of cell-to-cell adhesion due to anti-desmoglein antibodies). ### Immunofluorescence Pattern **Mnemonic: INTER-cellular = PEMphigus** (intercellular IgG deposition in pemphigus; contrast with linear BMZ pattern in pemphigoid) - **Direct immunofluorescence (DIF):** IgG and C3 in intercellular spaces (acantholytic zones) - **Indirect immunofluorescence (IIF):** Circulating anti-desmoglein antibodies (anti-Dsg3 in mucosal-dominant; anti-Dsg1 + Dsg3 in mucocutaneous form) ### Pathophysiology 1. Autoantibodies against desmogleins (Dsg3, Dsg1) disrupt desmosomes 2. Loss of cell-to-cell adhesion → acantholysis 3. Intraepidermal blister formation (suprabasal in vulgaris) 4. Nikolsky sign positive due to shallow epidermal split **Warning:** Do not confuse the intercellular pattern with the linear pattern at the basement membrane zone (BMZ) seen in bullous pemphigoid and linear IgA disease. ### Clinical Variants - **Mucosal-dominant:** Anti-Dsg3 only; oral involvement predominates - **Mucocutaneous:** Anti-Dsg1 + Dsg3; both oral and skin involvement **Clinical Pearl:** The presence of anti-Dsg3 antibodies alone predicts oral-dominant disease; addition of anti-Dsg1 antibodies predicts more extensive cutaneous involvement.