What is the most appropriate management for a 36-year-old male with Crohn's disease (inflammatory bowel disease), treated with infliximab (chimeric monoclonal antibody) and azathioprine (immunosuppressive medication), presenting with perianal pain, purulent discharge, induration, and erythema, with stable vital signs, no fever, and leukocytosis (high white blood cell count)?

Management of Perianal Abscess in Crohn's Disease

Percutaneous drainage of the perianal abscess is the most appropriate initial management for this patient with Crohn's disease presenting with perianal pain, purulent discharge, induration, and erythema.

Initial Assessment and Management Algorithm

1. First Step: Drainage of Perianal Abscess

   • The patient presents with classic signs of perianal abscess (pain, purulent discharge, induration, erythema) with elevated WBC count
   • Drainage is essential to control sepsis before any adjustment to immunosuppressive therapy 1
   • The presence of purulent discharge indicates an active infection requiring drainage

2. Antibiotic Therapy

   • Following drainage, broad-spectrum antibiotics should be initiated 1
   • Recommended regimens:
     • Metronidazole 400mg three times daily and/or ciprofloxacin 500mg twice daily 1
     • Target both aerobic and anaerobic bacteria commonly found in perianal infections

3. Microbiological Assessment

   • Obtain perianal swab and culture during drainage procedure 1
   • Adjust antibiotics based on culture results

Comprehensive Management Plan

Post-Drainage Medical Management

• Continue current immunosuppressive therapy (infliximab and azathioprine) after drainage and control of sepsis 1, 2
• Consider optimization of infliximab therapy:
  • Higher trough levels (>10 μg/mL) may be beneficial for perianal fistulizing disease 2
  • The combination of infliximab and azathioprine is effective for complex perianal disease 1, 3

Surgical Considerations

• Evaluation for seton placement if fistula tract is identified during drainage 1, 2
• Surgical management combined with medical therapy improves healing rates and reduces recurrence 2

Rationale for Recommended Approach

The British Society of Gastroenterology guidelines clearly state that "the initial aim should be to treat active disease and sepsis" in perianal Crohn's disease 1. The World Society of Emergency Surgery guidelines emphasize that "in complex perianal fistulizing disease, adequate surgical drainage is indicated" before continuing immunosuppressive therapy 1.

Increasing the infliximab dose (option A) without addressing the underlying abscess would be inappropriate and potentially dangerous, as it could worsen the infection by further suppressing the immune system 4.

Starting broad IV antibiotics alone (option B) without drainage is insufficient for an established abscess.

Obtaining a perianal swab and culture (option C) is important but should be done during the drainage procedure, not as the sole intervention.

Potential Complications and Monitoring

• Monitor for:

  • Recurrent abscess formation
  • Development of fistula tracts
  • Adverse effects of antibiotics (e.g., C. difficile infection)
  • Systemic infection while on immunosuppression

• Caution: Combined treatment with infliximab and azathioprine can induce severe immunosuppression, increasing risk for opportunistic infections 4

Follow-up Plan

• Reassess in 1-2 weeks after drainage and antibiotic therapy
• Consider MRI pelvis to evaluate for fistula tracts if symptoms persist
• Long-term management should include optimization of medical therapy for Crohn's disease to prevent recurrence

The evidence strongly supports that in a patient with Crohn's disease presenting with perianal abscess, drainage is the critical first step before any adjustment to immunosuppressive therapy.