Prognostic Factors Affecting Outcomes in Fistulating Perianal Crohn's Disease: a Systematic Review

Background: One in three patients with Crohn's disease will develop a perianal fistulae, and one third of these will achieve long-term healing or closure. A barrier to conducting well-designed clinical trials for these patients is a lack of understanding of prognostic factors. This systematic review sets out to identify factors associated with prognosis of perianal Crohn's fistulae.

Methods: This review was registered on the PROSPERO database (CRD42016050316) and conducted in line with PRISMA guidelines along a predefined protocol. English-language studies assessing baseline factors related to outcomes of fistulae treatment in adult patients were included. Searches were performed on MEDLINE and Embase databases. Screening of abstracts and full texts for eligibility was performed prior to extraction of data into predesigned forms. Bias was assessed using the QUIPS tool.

Results: Searches identified 997 papers. Following removal of duplicates and secondary searches, 923 were screened for inclusion. Forty-seven papers were reviewed at full-text level and 13, 2 of which were randomised trials, were included in the final qualitative review. Two studies reported distribution of Crohn's disease as a prognostic factor for healing. Two studies found that CARD15 mutations decreased response of fistulae to antibiotics. Complexity of fistulae anatomy was implicated in prognosis by 4 studies.

Conclusions: This systematic review has identified potential prognostic markers, including genetic factors and disease behaviour. We cannot, however, draw robust conclusions from this heterogeneous group of studies; therefore, we recommend that a prospective cohort study of well-characterised patients with Crohn's perianal fistulae is undertaken.