What is the initial management for a patient with a perianal fistula?

Initial Management of Perianal Fistula

The initial management of perianal fistula requires immediate classification as simple versus complex, followed by examination under anesthesia (EUA) with surgical drainage of any abscess and seton placement, combined with antibiotic therapy (metronidazole 400 mg three times daily and/or ciprofloxacin 500 mg twice daily). 1, 2

Immediate Diagnostic Steps

Clinical Assessment and Classification

• Perform EUA as the gold standard for definitive diagnosis and classification when performed by an experienced surgeon 1
• Classify the fistula as simple (low intersphincteric or trans-sphincteric with single external opening) versus complex (high intersphincteric, high trans-sphincteric, extrasphincteric, or suprasphincteric) 2
• Perform proctosigmoidoscopy during initial evaluation to assess for concomitant rectosigmoid inflammation, as the presence of proctitis significantly lowers fistula healing rates and changes management 1, 2

Imaging Requirements

• Order contrast-enhanced pelvic MRI as the initial imaging procedure of choice for assessment of perianal fistulas 1, 3
• Use endoscopic anorectal ultrasound (EUS) as an alternative if rectal stenosis is excluded 1, 3
• Obtain imaging before surgical drainage for complex fistulas to guide surgical planning 1, 3

Initial Treatment Algorithm

For Simple Perianal Fistulas

• Start first-line medical treatment with antibiotics: metronidazole 400 mg three times daily and/or ciprofloxacin 500 mg twice daily 1, 2
• Perform seton placement in combination with antibiotics as the preferred initial strategy for symptomatic simple perianal fistulas 1, 2
• Consider fistulotomy for uncomplicated low anal fistulas, which has the highest success rate for simple fistulas 2, 3

For Complex Perianal Fistulas

• Perform EUA for surgical drainage of sepsis as mandatory first step 1, 3
• Drain any abscess and place a loose (non-cutting) seton as the initial surgical intervention 1, 2
• Initiate anti-TNF therapy (particularly infliximab) combined with immunomodulators as first-line medical treatment after surgical drainage and seton placement 1, 2, 3
• Add adjunctive antibiotics (metronidazole and ciprofloxacin) to the anti-TNF regimen 2

Critical Pitfalls to Avoid

Do Not Perform Definitive Fistulotomy Initially for Complex Fistulas

• Avoid fistulotomy in patients with high fistulas and active inflammation of the rectosigmoid colon due to high risk of incontinence 4
• Non-cutting setons are the treatment of choice for high fistulas with active rectal inflammation 4

Screen for Crohn's Disease

• Obtain colonoscopy if multiple fistulas are present at different clock positions, as this suggests Crohn's disease rather than simple cryptoglandular disease 3
• Perianal fistulas occur in 13-27% of Crohn's disease patients and can be the initial manifestation in up to 81% of those who develop perianal disease 3
• Do not rely on absence of bowel symptoms to exclude Crohn's disease—perianal manifestations can be isolated 3

Assess for Active Rectal Disease

• The presence of active proctitis is associated with lower rates of fistula healing and necessitates more conservative surgical approach 4, 2
• Many experts advocate using a non-cutting seton rather than fistulotomy in patients with low fistulas and active inflammation of the rectosigmoid colon 4

Second-Line Treatment Options

If Simple Fistulas Do Not Respond to Antibiotics

• Use thiopurines (azathioprine 1.5-2.5 mg/kg/day or mercaptopurine 0.75-1.5 mg/kg/day) as second-line therapy 1, 2
• Consider anti-TNF agents as alternative second-line therapy 1

Monitoring Response

• Clinical assessment (decreased drainage) is usually sufficient to evaluate response to treatment 1, 3
• Use MRI or anal endosonography in combination with clinical assessment to evaluate improvement of fistula tract inflammation 1, 3
• Recognize that clinical closure does not equal MRI closure—there is high risk of recurrence without complete fibrotic tract on MRI 1, 2, 3

Concurrent Management Considerations

Treat Active Luminal Disease

• Treat any active proximal luminal Crohn's disease with appropriate therapy including budesonide, conventional corticosteroids, azathioprine, 6-mercaptopurine, methotrexate, or infliximab 4
• Reduce stool liquidity with loperamide, diphenoxylate and atropine, codeine, cholestyramine, and low-fat diet to decrease fistula drainage 4

Long-Term Monitoring

• Monitor for development of malignancy in chronic perianal fistula tracts, as squamous cell carcinoma, basal cell carcinoma, and adenocarcinoma have been reported 4, 2, 3