A 48-year-old man of Indian descent presents with a 2-month history of recurrent oral ulcers and blisters on the palate and gingiva. Over the past month, he has developed flaccid blisters on his neck, chest, and groin that rupture easily, leaving painful erosions. He reports no preceding trauma or drug exposure. Laboratory investigations show serum anti-desmoglein 3 antibodies (high titre) and anti-desmoglein 1 antibodies (negative). Histopathology reveals suprabasal acantholysis. What is the expected pattern of cutaneous involvement in this patient?

Explanation

## Pemphigus Vulgaris: Serotype and Clinical Phenotype ### Serologic Classification **Key Point:** Pemphigus vulgaris is classified into two main serotypes based on autoantibody profile, which correlates with clinical phenotype and disease severity. | Serotype | Anti-Dsg 3 | Anti-Dsg 1 | Clinical Type | Oral Involvement | Cutaneous Involvement | Prognosis | |----------|-----------|-----------|---------------|------------------|----------------------|----------| | **Mucosal-dominant** | ✓ (High) | ✗ | Oral-only or mucocutaneous | Severe, early | Limited or progressive | Better if oral-only | | **Mucocutaneous** | ✓ (High) | ✓ (High) | Generalized | Severe | Extensive | Requires aggressive therapy | | **Cutaneous-dominant** | ✗ | ✓ | Cutaneous-only | Absent/minimal | Extensive | Variable | **High-Yield:** Anti-desmoglein 3 (Dsg 3) antibodies alone → mucosal-dominant or mucocutaneous type. Anti-desmoglein 1 (Dsg 1) antibodies alone → cutaneous-dominant type. Both antibodies → mucocutaneous (generalized) type. ### Clinical Phenotype in This Patient **Clinical Pearl:** This patient has **anti-Dsg 3 only (high titre) and negative anti-Dsg 1**, indicating the **mucosal-dominant type**. He currently presents with oral involvement (palate, gingiva) and early cutaneous lesions (neck, chest, groin), representing the **mucocutaneous phenotype** (progression from mucosal-dominant). ### Pathophysiology 1. **Dsg 3 distribution:** Expressed predominantly in oral mucosa and lower epidermis 2. **Dsg 1 distribution:** Expressed in superficial epidermis and stratum corneum 3. **Dsg 3 antibodies alone** → acantholysis in lower epidermis (suprabasal) → oral and intertriginous involvement 4. **Addition of Dsg 1 antibodies** → superficial acantholysis → widespread cutaneous disease ### Histologic Correlation **Key Point:** Suprabasal acantholysis (as seen in this patient) is typical of mucosal-dominant pemphigus vulgaris, where Dsg 3 is the primary target. This contrasts with subcorneal acantholysis seen in pemphigus foliaceus (anti-Dsg 1 only). ### Expected Disease Course - **Mucosal-dominant (anti-Dsg 3 only):** May remain oral-only or progress to mucocutaneous disease - **Risk of progression:** Approximately 50% of mucosal-dominant cases progress to mucocutaneous type over months to years - **Favorable prognostic factor:** Absence of anti-Dsg 1 antibodies suggests lower risk of extensive cutaneous involvement [cite:Robbins 10e Ch 25]