Initial Management of Perianal Fistulas

Diagnostic Approach

The European Crohn's and Colitis Organisation recommends contrast-enhanced pelvic MRI as the initial imaging procedure of choice for assessment of perianal fistulas, with endoscopic anorectal ultrasound (EUS) being a good alternative if rectal stenosis is excluded 1, 2
Proctosigmoidoscopy should be routinely performed during initial evaluation to assess for concomitant rectosigmoid inflammation, which has significant prognostic and therapeutic implications 1, 3
Examination under anesthesia (EUA) is considered the gold standard for definitive diagnosis and classification of perianal fistulas when performed by an experienced surgeon 1, 2

For simple perianal fistulas, the European Crohn's and Colitis Organisation recommends first-line medical treatment including antibiotics (metronidazole 400 mg three times daily and/or ciprofloxacin 500 mg twice daily) 4, 3
Seton placement in combination with antibiotics is the preferred initial strategy for symptomatic simple perianal fistulas 1, 3
For complex perianal fistulas, imaging before surgical drainage is strongly recommended, and EUA for surgical drainage of sepsis is mandatory, with abscess drainage and loose seton placement as the initial step 1

For simple fistulas not responding to antibiotics, thiopurines (azathioprine 1.5-2.5 mg/kg/day or mercaptopurine 0.75-1.5 mg/kg/day) or anti-TNF agents can be used as second-line therapy 1, 4
For complex fistulas, anti-TNF therapy (particularly infliximab) combined with immunomodulators is considered first-line medical treatment after surgical drainage and seton placement 5, 3

Clinical assessment (decreased drainage) is usually sufficient to evaluate response to treatment, but MRI or anal endosonography in combination with clinical assessment is recommended to evaluate improvement of fistula track inflammation 1, 3
It's essential to note that clinical closure does not always equal MRI closure, with high risk of recurrence without complete fibrotic tract on MRI 3

The American Gastroenterological Association recommends avoiding fistulotomy in patients with high fistulas and active inflammation of the rectosigmoid colon due to high risk of incontinence 6, 7
Non-cutting setons are the treatment of choice for high fistulas with active rectal inflammation, as recommended by the American Gastroenterological Association 6, 7
The presence of active proctitis is associated with lower rates of fistula healing and necessitates a more conservative surgical approach, according to the American Gastroenterological Association 6, 7

The American Gastroenterological Association recommends treating any active proximal luminal Crohn's disease with appropriate therapy, including budesonide, conventional corticosteroids, azathioprine, 6-mercaptopurine, methotrexate, or infliximab 7, 8
Reducing stool liquidity with loperamide, diphenoxylate and atropine, codeine, cholestyramine, and a low-fat diet can decrease fistula drainage, as suggested by the American Gastroenterological Association 7, 8
The American Gastroenterological Association advises monitoring for development of malignancy in chronic perianal fistula tracts, as squamous cell carcinoma, basal cell carcinoma, and adenocarcinoma have been reported 6, 8

The American Gastroenterological Association recommends that antibiotics (metronidazole and ciprofloxacin) improve fistula symptoms and may reduce drainage but do not achieve fistula healing when used alone, with a weak evidence base from only one small randomized controlled trial (n=25) comparing ciprofloxacin, metronidazole, and placebo for perianal Crohn's disease fistulas, showing no significant difference in fistula closure at 10 weeks 9, 10, 11
The European Crohn’s and Colitis Organisation suggests antibiotics are indicated for treating perianal sepsis and controlling infection, but not for closing fistulas as monotherapy 12

The American College of Gastroenterology recommends ciprofloxacin combined with anti-TNF therapy (infliximab or adalimumab) improves short-term outcomes for complex perianal fistulas 13, 14
Typical dosing from clinical trials: metronidazole 750-1500 mg/day or ciprofloxacin 500-1000 mg/day for 6-8 weeks, though relapse is common after discontinuation 9, 11

Ciprofloxacin plus infliximab achieved 73% fistula response at 18 weeks versus 39% with infliximab alone (p=0.12) 9
Ciprofloxacin plus adalimumab reduced draining fistulas by ≥50% in 70.6% of patients versus 47.2% with adalimumab alone (p=0.002) 9, 11

If perianal abscess is present, surgical drainage with examination under anesthesia (EUA) is mandatory before any medical therapy, according to the Society of American Gastrointestinal and Endoscopic Surgeons 9, 10

Antibiotics should be continued for the duration determined by clinical response and inflammatory markers (CRP), typically 6-12 weeks when used adjunctively, as recommended by the Infectious Diseases Society of America 13
Clinical assessment (decreased drainage) is usually sufficient to evaluate response; MRI is recommended to confirm fistula tract improvement if considering discontinuation of therapy 9, 10