OBJECTIVE: Perianal fistuliing Crohn\'s disease [PFCD] is an aggressive phenotype of Crohn\'s disease defined by frequent relapses and disabling symptoms. A novel consensus classification system was recently outlined by the TOpCLASS consortium, which seeks to unify disease severity with patient-centred goals but has not yet been validated. We aimed to apply this to a real-world cohort and to identify factors that predict transition between classes over time.
METHODS: We identified all patients with PFCD and at least one baseline and one follow-up pelvic MRI [pMRI]. TOpCLASS classification, disease characteristics, and imaging indices were collected retrospectively at time periods corresponding with respective MRIs.
RESULTS: We identified 100 patients with PFCD, of whom 96 were assigned TOpCLASS Classes 1-2c at baseline. Most patients [78.1%] started in Class 2b, but changes in classification were observed in 52.1% of all patients. Male sex [72.0%, 46.6%, 40.0%, p = 0.03] and prior perianal surgery [52.0% vs 44.6% vs 40.0%, p = 0.02] were more frequently observed in those with improved class compared to unchanged and worsened class. Baseline pMRI indices were not associated with changes in classification; however, greater improvements in mVAI, MODIFI-CD, and PEMPAC were seen among those who improved. Linear mixed effect modelling identified only male sex [-0.31, 95% CI -0.60 to -0.02] with improvement in class.
CONCLUSIONS: The TOpCLASS classification highlights the dynamic nature of PFCD over time. However, our ability to predict transitions between classes remains limited and requires prospective assessment. Improvement in MRI index scores over time was associated with a transition to lower TOpCLASS classification.

OBJECTIVE: Treatment of perianal fistula has evolved with the introduction of new techniques and biologicals in Crohn\'s disease (CD). Several guidelines are available worldwide, but many recommendations are controversial or lack high-quality evidence. The aim of this work was to provide an overview of the current available national and international guidelines for perianal fistula and to analyse areas of consensus and areas of conflicting recommendations, thereby identifying topics and questions for future research.
METHODS: MEDLINE, EMBASE and PubMed were systematically searched for guidelines on perianal fistula. Inclusion was limited to papers in English less than 10 years old. The included topics were classified as having consensus (unanimous recommendations in at least two-thirds of the guidelines) or controversy (fewer than three guidelines commenting on the topic or no consensus) between guidelines. The highest level of evidence was scored as sufficient (level 3a or higher of the Oxford Centre for Evidence-based Medicine Levels of Evidence 2009, http://www.cebm.net/oxford-centre-evidence-based-medicine-levels-evidence-march-2009/) or insufficient.
RESULTS: Twelve guidelines were included and topics with recommendations were compared. Overall, consensus was present in 15 topics, whereas six topics were rated as controversial. Evidence levels varied from strong to lack of evidence.
CONCLUSIONS: Evidence on the diagnosis and treatment of perianal fistulae (cryptoglandular or related to CD) ranged from nonexistent to strong, regardless of consensus. The most relevant research questions were identified and proposed as topics for future research.