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Introduction: A perianal fistula occurring after proctocolectomy and ileal pouch-anal anastomosis (IPAA) for ulcerative (UC) or indeterminate colitis (IC) may herald a change in diagnosis to Crohn’s disease (CD). However evidence for this association is limited. The aim of this study is to assess how often a perianal fistula following IPAA indicates the presence of CD.
Methods: Patients developing a perianal fistula after IPAA for UC or IC were identified from a prospective database and their medical record reviewed. Demographics, date of pouch surgery, colectomy histopathology, date of fistula diagnosis, clinical or pathological evidence of CD and follow-up were abstracted. Patients with anastomotic leak or fistula only to the abdominal wall or vagina were excluded.
Results: 105 patients were identified, 32 were female. 68 had an initial diagnosis of UC and 37 IC. Mean follow up was 118+/-70 months. 43 (41%) patients with perianal fistulas were subsequently diagnosed with CD. This diagnosis was based on complex perianal disease in 18 patients, characteristic inflammation of the pouch and/or anal canal in 16, small bowel disease in 4, additional fistulas in 2 and Prometheus testing in 2. 11/43 (25%) had histological evidence of CD in the pouch, perianal area or small bowel. The median age of these patients was 28 +/- 8 years compared with 34 +/- 12 in those without CD (p=0.007). Of those with an initial diagnosis of UC, 38% (26/68) were subsequently diagnosed with CD compared with 51% (19/37) who had an initial diagnosis of IC (p=0.2).Smoking was not a significant risk factor for change of diagnosis with 4/12 smokers (33%) diagnosed with CD compared with 8/12 (66%) who were not (p=0.51)Management of the fistula is presented in Table 1. Four patients with CD were treated with infliximab and 3 of these 4 were able to retain their pouches.
Conclusion: Perianal fistula complicating IPAA for UC or IC is associated with a change in diagnosis to CD, with all the therapeutic and prognostic implications inherent in such a change. This is especially so in younger patients and those without pouchitis. While medical management continues to improve, this complication results in a significant incidence of pouch loss.

Table 1: Management of fistula

Outcome	CD (n=43)	Non-CD (n=62)	p value
Seton	15	2	<0.001
Fistulotomy	7	23	0.02
Flap repair or Pouch advancement	1	9	0.04
Plug	1	0	0.41
Diversion	2	2	0.7
Abscess drainage alone	0	3	0.27
Pouch Excision	9	1	0.001

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