A 68-year-old Indian woman presents with a 3-week history of tense, fluid-filled blisters on the flexural surfaces of her forearms, lower abdomen, and inner thighs. The blisters are painful and do not rupture easily. On examination, there is no oral mucosal involvement. Nikolsky sign is negative. Laboratory investigations show normal hemoglobin and white cell count. Direct immunofluorescence (DIF) of perilesional skin reveals linear IgG and C3 deposits along the basement membrane zone. What is the most likely diagnosis?

Explanation

## Diagnosis: Bullous Pemphigoid ### Clinical Presentation **Key Point:** Bullous pemphigoid presents with large, tense, intact blisters on flexural and lower abdominal skin, typically in elderly patients (>60 years). - Blisters are **non-flaccid** and do **not rupture easily** (unlike pemphigus) - **Negative Nikolsky sign** — pathognomonic for subepidermal blistering - **Absence of oral involvement** — oral mucosa is spared (cf. pemphigus vulgaris) - Urticarial or eczematous lesions may precede blisters ### Immunofluorescence Pattern **High-Yield:** DIF shows **linear IgG and C3 deposits at the basement membrane zone** — this is the gold standard for diagnosis. | Feature | Bullous Pemphigoid | Pemphigus Vulgaris | |---------|-------------------|--------------------| | Blister type | Tense, intact | Flaccid, ruptures easily | | Nikolsky sign | Negative | Positive | | Oral involvement | Rare | Common, often first site | | DIF pattern | Linear at BMZ | Intercellular IgG ("tombstone") | | Autoantigen | BP180, BP230 (hemidesmosomes) | Desmoglein 3 ± 1 | ### Pathophysiology **Key Point:** Autoantibodies against hemidesmosomal proteins (BP180 and BP230) cause subepidermal blistering at the dermal–epidermal junction. ### Treatment Approach 1. **First-line:** Topical or intralesional corticosteroids for localized disease 2. **Systemic:** Oral corticosteroids (prednisolone 0.5–1 mg/kg/day) for extensive disease 3. **Steroid-sparing agents:** Azathioprine, mycophenolate mofetil for long-term control **Clinical Pearl:** Bullous pemphigoid has a better prognosis than pemphigus vulgaris; many patients achieve remission or low-dose maintenance therapy.