A 55-year-old woman with bullous pemphigoid has been on oral prednisolone 40 mg/day for 8 weeks. She has achieved 80% clearance of lesions and is now being tapered. However, after reducing to 30 mg/day, new blisters appear within 2 weeks. Repeat direct immunofluorescence confirms persistent linear IgG and C3 at the basement membrane. What is the most appropriate next step?

Explanation

## Clinical Scenario: Steroid-Dependent Bullous Pemphigoid **Key Point:** This patient demonstrates **steroid-dependent BP**—inability to taper systemic corticosteroids below a certain threshold without disease flare. This is an indication for steroid-sparing agent initiation. ## Definition of Steroid Dependence **High-Yield:** Steroid dependence in BP is defined as: - Inability to taper corticosteroids below **10–15 mg/day** without relapse, OR - Recurrence of lesions when attempting to reduce the maintenance dose This patient flared at 30 mg/day, indicating early steroid dependence. ## Management of Steroid-Dependent BP ```mermaid flowchart TD A[BP Flares on Steroid Taper]:::outcome --> B{Maintenance Dose?}:::decision B -->|>15 mg/day| C[Add Steroid-Sparing Agent]:::action B -->|<10 mg/day| D[Consider Plasmapheresis or Biologics]:::action C --> E[Azathioprine or Mycophenolate]:::action E --> F[Slow prednisolone taper over 3-6 months]:::action F --> G[Achieve remission off steroids]:::outcome ``` ## Steroid-Sparing Agents: First-Line Options | Agent | Dose | Onset | Monitoring | Advantage | |-------|------|-------|-----------|----------| | **Azathioprine** | 1–2 mg/kg/day (50–100 mg/day) | 4–8 weeks | TPMT, CBC, LFTs | Proven efficacy; long track record | | **Mycophenolate mofetil** | 1 g BD (2 g/day) | 2–4 weeks | CBC, LFTs | Faster onset; no genetic testing | | Dapsone | 50–100 mg/day | 1–2 weeks | G6PD, CBC | Rapid; use if IgA-mediated | **Clinical Pearl:** Azathioprine is the traditional first-line steroid-sparing agent in BP. It allows successful tapering of corticosteroids in 60–70% of steroid-dependent patients. Mycophenolate is an equally effective alternative with potentially faster onset. ## Why Azathioprine Is Chosen Here 1. **Proven efficacy:** Well-established in steroid-dependent BP with decades of clinical data. 2. **Appropriate timing:** Patient is at 30 mg/day prednisolone—ideal threshold for introducing a steroid-sparing agent. 3. **Synergistic effect:** Allows gradual corticosteroid reduction while maintaining disease control. 4. **Standard practice:** Recommended by major dermatology guidelines (AAD, EADV) as first-line steroid-sparing therapy. ## Expected Outcome Once azathioprine is initiated and reaches therapeutic levels (4–8 weeks), prednisolone can be tapered by 5–10 mg every 2–4 weeks, with the goal of achieving remission off steroids or at a minimal maintenance dose (<5 mg/day). ## Why Not the Other Options? - **Option A (Increase and slow taper):** Prolonged high-dose steroids increase infection, osteoporosis, and metabolic complications. Steroid-sparing agents are indicated at this point. - **Option C (Mycophenolate instead):** Both are valid steroid-sparing agents, but azathioprine is the traditional first-line choice in BP. Mycophenolate is reserved as a second-line option or for patients intolerant of azathioprine. - **Option D (Plasmapheresis):** Indicated for severe, rapidly progressive, or refractory disease unresponsive to corticosteroids and steroid-sparing agents. This patient still has good response to corticosteroids and has not failed conventional therapy.