A 68-year-old man presents with tense, fluid-filled blisters on the flexural surfaces of both forearms and inner thighs for 3 weeks. On examination, the blisters are intact, do not rupture easily, and the surrounding skin is erythematous. Direct immunofluorescence shows linear IgG and C3 deposits along the basement membrane zone. What is the most appropriate next step in management?

Explanation

## Diagnosis Confirmation **Key Point:** The clinical presentation (tense blisters, intact bullae, flexural distribution) combined with linear IgG and C3 at the basement membrane zone on DIF is diagnostic of bullous pemphigoid (BP). ## Management Algorithm for Bullous Pemphigoid ```mermaid flowchart TD A[Bullous Pemphigoid Confirmed]:::outcome --> B{Extent & Severity?}:::decision B -->|Localized/Mild| C[Topical/Intralesional Corticosteroids]:::action B -->|Generalized/Moderate| D[Oral Corticosteroids 0.5-1 mg/kg/day]:::action B -->|Severe/Refractory| E[Add Steroid-sparing Agent]:::action E --> F[Azathioprine, Mycophenolate, or Dapsone]:::action D --> G[Taper as lesions heal]:::action C --> H[Monitor for progression]:::action ``` ## First-Line Management **High-Yield:** Oral corticosteroids are the gold standard for moderate-to-generalized bullous pemphigoid. The standard starting dose is **prednisolone 0.5–1 mg/kg/day** (typically 40–60 mg/day), which achieves remission in 60–80% of patients within 4–6 weeks. **Clinical Pearl:** The patient has generalized disease (bilateral forearms and thighs) with multiple intact blisters—this is moderate-to-generalized BP requiring systemic therapy, not localized disease. ## Steroid-Sparing Agents | Agent | Indication | Onset | Notes | |-------|-----------|-------|-------| | Azathioprine | Steroid-dependent or refractory | 4–8 weeks | Requires TPMT testing; monitor LFTs | | Mycophenolate mofetil | Alternative to azathioprine | 2–4 weeks | Better tolerated; no genetic testing needed | | Dapsone | Rapid control; IgA-mediated BP | 1–2 weeks | Risk of hemolysis; requires G6PD screening | **Key Point:** Steroid-sparing agents are added if the patient is steroid-dependent (unable to taper below 10–15 mg/day) or if remission is not achieved within 6–8 weeks. ## Why Not the Other Options? - **Intralesional injections:** Appropriate only for localized disease (few lesions in one area); this patient has generalized involvement. - **Plasmapheresis:** Reserved for severe, rapidly progressive, or refractory cases; not indicated as first-line. - **Topical antibiotics and observation:** Ignores the autoimmune nature of BP; spontaneous remission is rare without systemic therapy.