What is the treatment for a posterior perianal fistula?

Treatment of Posterior Perianal Fistula

For posterior perianal fistulas, the initial treatment should be a short course of antibiotics followed by fistulotomy for simple fistulas that don't respond to antibiotics, while complex fistulas require a combination of medical therapy (primarily infliximab) and surgical intervention with non-cutting setons. 1

Classification of Perianal Fistulas

Before determining treatment, it's essential to classify the fistula:

• Simple fistulas: Low (superficial, intersphincteric, or low transsphincteric), single external opening, no pain/fluctuation suggesting abscess, no rectovaginal involvement, no anorectal stricture, and no active rectal disease
• Complex fistulas: High (high transsphincteric, extrasphincteric, or suprasphincteric), multiple external openings, associated abscess, rectovaginal involvement, anorectal stricture, or active rectal disease

Treatment Algorithm for Posterior Perianal Fistulas

Step 1: Drainage of Any Associated Abscess

• Surgical drainage of perianal abscesses is mandatory before initiating any medical therapy 1
• This prevents recurrent abscess formation and sepsis

Step 2: Treatment Based on Fistula Classification

For Simple Posterior Perianal Fistulas:

1. Initial treatment: Short course of antibiotics (ciprofloxacin or metronidazole) 1

   • Antibiotics are widely recommended in practice guidelines despite limited evidence from placebo-controlled trials
   • Ciprofloxacin appears better tolerated than metronidazole 2

2. If no response to antibiotics: Fistulotomy 1

   • Fistulotomy results in high rates of sustained healing for simple fistulas
   • This is the prevailing surgical approach for simple fistulas that don't respond to antibiotics

For Complex Posterior Perianal Fistulas:

1. Initial management: Placement of non-cutting setons 1

   • Prevents recurrent abscess formation
   • Should be placed during examination under anesthesia (EUA)

2. Medical therapy: Infliximab is the first-line biological therapy 1

   • Should be started as soon as adequate drainage of sepsis is achieved
   • Infliximab has proven efficacy in placebo-controlled trials for both reduction in draining fistulas and maintenance of that reduction 1
   • FDA-approved 3-dose induction regimen followed by maintenance every 8 weeks

3. Combination therapy: Consider adding immunosuppressants

   • Azathioprine or 6-mercaptopurine should be co-administered with infliximab 1
   • This helps prevent antibody formation against infliximab and maintains remission

4. Adjunctive antibiotic therapy: May be beneficial temporarily 1

   • Combination of antibiotics with biologics shows better results than biologics alone
   • However, benefits diminish after antibiotic discontinuation

Step 3: For Refractory Complex Fistulas

If initial treatments fail:

1. Re-evaluation: Perform anorectal EUA or pelvic MRI 1

2. Advanced medical options: Consider tacrolimus or cyclosporine in selected patients who fail multimodality treatment 1

3. Advanced surgical options: Consider only after endoscopic remission of proctitis 1

   • Options include mucosal advancement flaps, bioprosthetic plugs, or LIFT procedure
   • Success rates are variable and generally decline over time

4. Last resort options: Fecal diversion (temporary ileostomy or colostomy) or proctectomy 1

   • Patients should be counseled that rates of subsequent successful reversal are low

Special Considerations

1. Presence of proctitis: Assess rectal mucosa during examination as proctitis is associated with lower rates of fistula healing 1

2. Crohn's disease: If the fistula is associated with Crohn's disease:

   • Control any active luminal disease first
   • Infliximab is particularly effective for Crohn's-related fistulas 1

3. Rectovaginal fistulas: Require special consideration

   • Fistulotomy should rarely be used due to sphincter injury risk 1
   • Surgical repair should only be attempted after inflammation has resolved

Pitfalls to Avoid

1. Treating without adequate drainage: Never initiate medical therapy without first draining any associated abscess 1

2. Premature surgical repair: Attempting definitive surgical repair before controlling inflammation leads to poor outcomes 1

3. Overlooking rectal disease: Failure to assess for proctitis can lead to treatment failure 1

4. Discontinuing antibiotics too early: While antibiotics help reduce fistula drainage, they rarely lead to complete healing, and relapse rates are high after discontinuation 1

5. Performing fistulotomy for complex fistulas: This can lead to sphincter damage and incontinence

6. Relying solely on antibiotics: Recent evidence suggests antibiotics alone do not prevent fistula formation after perianal abscess drainage 3