A 62-year-old man presents with tense blisters on the flexural surfaces of the forearms and inner thighs for 3 weeks. Histopathology shows subepidermal blister with eosinophilic infiltrate, and direct immunofluorescence reveals linear IgG and C3 deposits along the basement membrane zone. What is the drug of choice for initial management?

Explanation

## Diagnosis & Pathophysiology **Key Point:** The clinical presentation (tense blisters on flexural surfaces), histology (subepidermal blister with eosinophilic infiltrate), and linear IgG + C3 at the basement membrane zone are pathognomonic for bullous pemphigoid (BP). ## First-Line Treatment of Bullous Pemphigoid **High-Yield:** Systemic corticosteroids are the gold standard first-line therapy for moderate-to-severe BP. Prednisolone 0.5–1 mg/kg/day is the standard starting dose, with gradual tapering over weeks to months as lesions heal. ### Rationale for Systemic Corticosteroids 1. **Rapid suppression of autoimmune response** — Corticosteroids inhibit T-cell activation and reduce IgG and IgE production against BP180 and BP230 antigens. 2. **Effective for extensive disease** — When >10% of body surface area is involved or lesions are in high-friction areas (flexures, genitals), systemic therapy is mandatory. 3. **Proven efficacy** — 80–90% of patients achieve remission within 4–8 weeks with appropriate dosing. ### When to Use Steroid-Sparing Agents | Scenario | Agent | Rationale | |----------|-------|----------| | Mild localized disease (<10% BSA) | Topical corticosteroids | Class III–IV potency (clobetasol, betamethasone dipropionate) sufficient | | Steroid-dependent or resistant | Dapsone | Inhibits neutrophil migration; useful in pemphigoid gestationis and some BP cases | | Severe, refractory disease | Azathioprine, mycophenolate mofetil, or cyclosporine | Reserved for steroid-refractory cases or when tapering fails | **Clinical Pearl:** Dapsone is NOT first-line for BP; it is reserved for steroid-sparing or in combination therapy. Cyclosporine is a second-line agent for refractory disease. **Warning:** Topical corticosteroids alone are insufficient for this patient's extensive distribution and severity. They are adequate only for localized disease affecting <10% BSA. ## Treatment Algorithm ```mermaid flowchart TD A[Bullous Pemphigoid diagnosed]:::outcome --> B{Extent of disease?}:::decision B -->|Localized <10% BSA| C[Potent topical corticosteroids]:::action B -->|Moderate 10-30% BSA| D[Systemic corticosteroids ± topical]:::action B -->|Extensive >30% BSA| E[Systemic corticosteroids 0.5-1 mg/kg/day]:::action D --> F{Response at 4-6 weeks?}:::decision E --> F F -->|Good remission| G[Taper prednisolone over 3-6 months]:::action F -->|Inadequate/steroid-dependent| H[Add steroid-sparing agent: dapsone, azathioprine, or MMF]:::action H --> I[Reduce corticosteroid dose gradually]:::action ``` **High-Yield:** Prednisolone 0.5–1 mg/kg/day is the standard starting regimen; most patients respond within 2–4 weeks. Maintenance therapy involves gradual tapering to the lowest effective dose to minimize long-term corticosteroid toxicity.