What is the next step in managing a patient with Crohn's disease on azathioprine and infliximab (anti-tumor necrosis factor-alpha inhibitor) presenting with anal pus, stable vital signs, and no fever?

Management of Perianal Discharge in Crohn's Disease Patient on Azathioprine and Infliximab

The next step in managing a patient with Crohn's disease on azathioprine and infliximab presenting with anal pus discharge, stable vital signs, and no fever should be a pelvic MRI (option A).

Rationale for Pelvic MRI

• Perianal discharge in a Crohn's disease patient suggests possible perianal fistulizing disease with potential abscess formation, which requires accurate anatomical assessment before treatment decisions 1.
• Pelvic MRI has high diagnostic accuracy for classifying perianal fistulas and detecting occult abscesses, which is crucial for proper management 1.
• The World Journal of Emergency Surgery guidelines specifically recommend imaging investigations in cases of suspected anorectal abscesses, particularly when there's suspicion of complex fistulas or perianal Crohn's disease 1.

Why Other Options Are Less Appropriate

• Broad IV Antibiotics (Option B): While antibiotics are important in perianal Crohn's disease, they should not be routinely administered without first establishing the presence and extent of perianal sepsis 1. The guidelines state: "We recommend not routinely administrating antibiotics in IBD patients but only in the presence of superinfection, intra-abdominal abscesses, and sepsis" 1.

• Swab and Culture (Option C): While microbiological assessment may be useful, it does not provide the anatomical information needed to guide management decisions. The primary concern is to identify potential abscesses or fistulae that require drainage before adjusting medical therapy 1.

• Increasing Infliximab Dose (Option D): Escalating anti-TNF therapy without first addressing potential perianal sepsis could worsen the condition. Guidelines state: "Infliximab should be considered...following adequate resolution of intra-abdominal abscesses" 1. Additionally, "In complex perianal fistulizing disease infliximab or adalimumab can be used as first line therapy...following adequate surgical drainage if indicated" 1.

Management Algorithm

1. First step: Obtain pelvic MRI to assess for presence of perianal abscess and define fistula anatomy 1

2. If abscess is detected:

   • Surgical drainage is required before adjusting medical therapy 1
   • After adequate drainage, consider antibiotics (ciprofloxacin and/or metronidazole) 1

3. If no abscess but fistula present:

   • Consider examination under anesthesia with possible seton placement 1, 2
   • Continue current infliximab therapy or optimize dose 3
   • Consider adding antibiotics (ciprofloxacin improves short-term outcomes when combined with anti-TNF therapy) 1

4. If neither abscess nor fistula:

   • Consider other causes of perianal discharge
   • Maintain current therapy and monitor closely

Important Considerations

• The patient is already on combination therapy with azathioprine and infliximab, which is the recommended approach for complex perianal fistulizing disease 1.
• Stable vital signs and absence of fever suggest that this is not an emergency requiring immediate broad-spectrum antibiotics, allowing time for proper imaging assessment 1.
• Prior to any escalation of immunosuppressive therapy, it's essential to rule out perianal sepsis, which would require drainage 1, 2.

Potential Pitfalls

• Increasing immunosuppression without addressing underlying sepsis can worsen outcomes and lead to systemic infection 1.
• Failing to obtain proper imaging can result in missed abscesses that require drainage before medical therapy can be effective 1.
• Relying solely on clinical examination without imaging may miss deep or complex perianal disease that requires specific intervention 1.