A 52-year-old Indian woman presents with a 3-week history of painful blisters in the oral cavity, followed by flaccid blisters on the trunk and flexural areas of the skin. On examination, positive Nikolsky sign is noted on the buccal mucosa and forearm. Histopathology shows intraepidermal acantholysis with suprabasal clefting. Direct immunofluorescence (DIF) reveals IgG and C3 deposits in an intercellular pattern. What is the most likely diagnosis?

Explanation

## Diagnosis: Pemphigus Vulgaris ### Clinical Presentation **Key Point:** Pemphigus vulgaris classically presents with oral mucosal involvement (80–90% of cases) preceding cutaneous lesions by weeks to months. - Painful blisters and erosions on buccal mucosa, palate, gingiva - Flaccid blisters on skin (trunk, flexural areas, face) - Positive Nikolsky sign (intraepidermal acantholysis) - Lesions are fragile and rupture easily, leaving erosions ### Histopathology **High-Yield:** Suprabasal acantholysis with "tombstone" appearance (basal cells remain attached to basement membrane, creating a characteristic pattern). - Intraepidermal blister formation - Loss of cell-to-cell adhesion (desmoglein-3 dysfunction) - Acantholytic cells (rounded keratinocytes) in blister fluid ### Immunofluorescence Pattern | Finding | Pemphigus Vulgaris | Bullous Pemphigoid | | --- | --- | --- | | **DIF Pattern** | Intercellular IgG + C3 ("chicken wire") | Linear IgG + C3 at basement membrane zone | | **IIF** | Circulating IgG antibodies (anti-desmoglein-3) | Circulating IgG against BP180/BP230 | | **Blister Level** | Intraepidermal (suprabasal) | Subepidermal | **Clinical Pearl:** The intercellular "chicken wire" pattern on DIF is pathognomonic for pemphigus vulgaris and distinguishes it from subepidermal bullous disorders. ### Autoantigen Involvement **Mnemonic: DES-3** — Desmoglein-3 (mucosal type) and Desmoglein-1 (mucocutaneous type) - Anti-desmoglein-3 antibodies → oral and lower trunk involvement (mucosal-dominant) - Anti-desmoglein-1 antibodies → widespread cutaneous involvement (mucocutaneous) [cite:Robbins 10e Ch 25]