A 68-year-old Indian man presents with a 3-week history of tense, fluid-filled blisters on the flexural aspects of both forearms and inner thighs. The blisters do not rupture easily and are preceded by urticarial lesions. On examination, there is no oral mucosal involvement. Nikolsky sign is negative. Serum IgG antibodies against BP180 are positive. What is the most likely diagnosis?

Explanation

## Diagnosis: Bullous Pemphigoid ### Clinical Presentation **Key Point:** Bullous pemphigoid (BP) presents with tense, intact blisters that do not rupture easily, typically on flexural surfaces and lower abdomen. ### Distinguishing Features in This Case | Feature | Bullous Pemphigoid | Pemphigus Vulgaris | Dermatitis Herpetiformis | |---------|-------------------|-------------------|------------------------| | **Blister type** | Tense, intact | Flaccid, ruptures easily | Vesicles, intensely pruritic | | **Nikolsky sign** | Negative | Positive | Negative | | **Oral mucosa** | Rarely involved | Commonly involved | Not involved | | **Autoantigen** | BP180, BP230 | Desmoglein 3 (mucosal), 1+3 (mucocutaneous) | Tissue transglutaminase | | **Antibody type** | IgG, IgE (circulating) | IgG (circulating) | IgA (granular, dermal-epidermal junction) | | **Age of onset** | Elderly (>60 years) | Variable, often middle-aged | Young adults, associated with celiac disease | ### Pathophysiology **High-Yield:** BP is an autoimmune blistering disorder where IgG and IgE antibodies target hemidesmosomal proteins (BP180 and BP230) at the dermal-epidermal junction, causing subepidermal blister formation. ### Immunofluorescence Pattern **Clinical Pearl:** Direct immunofluorescence (DIF) shows **linear IgG and IgE deposition along the basement membrane zone (BMZ)**, which is pathognomonic. Indirect immunofluorescence (IIF) detects circulating anti-BP180 and anti-BP230 antibodies. ### Why Negative Nikolsky Sign? Nikolsky sign is negative in BP because blisters form at the dermal-epidermal junction (subepidermal), not intraepidermally. In pemphigus, blisters are intraepidermal, so the epidermis separates easily with lateral pressure. ### Key Diagnostic Criteria Met 1. Age >60 years (typical for BP) 2. Tense, non-rupturable blisters 3. Flexural distribution 4. Negative Nikolsky sign 5. Positive serum IgG against BP180 (anti-BP180 antibodies) 6. No oral involvement **Mnemonic:** **BLISTERS** in BP are **BASEMENT** membrane-bound (subepidermal), **INTACT** (tense), and **ELDERLY** patients. [cite:Robbins 10e Ch 25]