A 72-year-old man with a 2-month history of recurrent blisters on his shins, forearms, and lower abdomen is referred to dermatology. The blisters are preceded by urticarial lesions and pruritus. On examination, some blisters have ruptured, leaving erosions. Oral mucosa is uninvolved. Indirect immunofluorescence (IIF) on patient serum is positive at 1:40 dilution. Histopathology shows subepidermal blistering with eosinophil-rich infiltrate in the dermis. What is the most appropriate next step in management?

Explanation

## Management of Bullous Pemphigoid: Systemic Corticosteroids ### Clinical Context **Key Point:** This patient has extensive bullous pemphigoid (multiple body sites, ruptured blisters, 2-month duration) requiring systemic therapy, not topical management alone. ### Why Systemic Corticosteroids? **High-Yield:** Extensive or progressive bullous pemphigoid requires **oral corticosteroids as first-line systemic therapy**. | Extent of Disease | First-Line Treatment | |-------------------|----------------------| | Localized (<10% BSA) | Topical corticosteroids, intralesional injections | | Moderate (10–30% BSA) | Systemic corticosteroids ± topical | | Extensive (>30% BSA) | Systemic corticosteroids + steroid-sparing agent | ### Dosing & Monitoring 1. **Initial dose:** Prednisolone 0.5–1 mg/kg/day (typically 40–60 mg/day) 2. **Taper:** Reduce by 5–10 mg every 2–4 weeks once lesions cease 3. **Maintenance:** Long-term low-dose (5–10 mg/day) or alternate-day dosing 4. **Follow-up:** Clinical review in **2 weeks** to assess response and adjust dose **Clinical Pearl:** Most patients achieve disease control within 2–4 weeks of systemic corticosteroids. Early response is a good prognostic sign. ### Why This Patient Needs Systemic Therapy - Multiple body sites involved (shins, forearms, abdomen) - Blisters have ruptured → risk of secondary infection - 2-month duration suggests progressive disease - Topical therapy alone is insufficient for this extent ### Pathophysiology Reminder **Key Point:** Autoantibodies (IgG) against BP180 and BP230 (hemidesmosomal proteins) activate complement and recruit eosinophils, causing subepidermal blistering. Corticosteroids suppress this immune response. ### Steroid-Sparing Agents (Second-Line) If disease is extensive or steroid-dependent: - **Azathioprine** (1–2 mg/kg/day) — takes 4–8 weeks to work - **Mycophenolate mofetil** (1–3 g/day) - **Methotrexate** (15–25 mg/week) **Mnemonic:** **AZAM** — Azathioprine, Azathioprine, Methotrexate, Mycophenolate (steroid-sparing agents for BP). ### Monitoring During Therapy - Clinical response (new blister formation, erosion healing) - Steroid side effects (hyperglycemia, osteoporosis, infections) - Baseline DEXA scan if long-term corticosteroids anticipated