IntroductionCrohn's disease [CD] is a chronic inflammatory bowel disease [IBD] that can result in progressive bowel damage and disability 1 . CD can affect individuals of any age, from children to the elderly, 2,3 and may cause significant morbidity and impact on quality of life. Up to one-third of patients present with complicated behaviour [strictures, fistula, or abscesses] at diagnosis 4 . Most patients over time will develop a complication, with roughly 50% of patients requiring surgery within 10 years of diagnosis [5][6][7] . As the precise aetiology of CD remains unknown, a curative therapy is not yet available 8 . Several agents are available for the medical treatment of CD. Medical agents include mesalazine [5-ASA], locally active steroids [such as budesonide], systemic steroids, thiopurines such as azathioprine [AZA] and mercaptopurine [MP], methotrexate [MTX], and biological therapies [such as anti-TNF, anti-integrins, and anti-IL12/23].The European Crohn's and Colitis Organisation [ECCO] produces and regularly updates several guidelines aimed at providing evidence-based guidance on critical aspects of IBD care to all healthcare professionals who manage patients with IBD. To provide high-quality evidence-based recommendations on medical and surgical treatment in CD, ECCO decided to develop these guidelines by adopting the GRADE [Grading of Recommendations Assessment, Development, and Evaluation] approach 9 . GRADE is a systematic process for developing guidelines that addresses how to frame the healthcare questions, summarize the evidence, formulate the recommendations, and grade their strength and the quality of the associated evidence. GRADE increases transparency at all levels of this process and makes explicit the three considerations that lead to a particular recommendation: the quality of the evidence, the balance of benefits and harms, and the patients' values and preferences. Therefore, ECCO reviewed the available high-quality evidence on the medical management of CD and developed evidence-based recommendations on the medical treatment of adult patients with CD. These guidelines do not cover specific situations, such as post-operative management of adult patients with CD, which was already covered in the last ECCO Guidelines on Crohn's disease 10 . MethodsBased on the GRADE workflow, the Guidelines Committee of ECCO [GuiCom] selected a panel of 48 experts supported by a team of methodologists and librarians. Selection was based on IBD expertise, scientific background, and knowledge of the GRADE methodology. All panellists received adequate training in GRADE before starting the process.Additionally, four patients with CD representing the European Federation of Crohn's and Colitis Associations [EFCCA] were invited to participate in all face-to-face meetings and to provide their experiences and state their preferences.Three domains for medical treatment of CD were identified: 1) induction therapy 2) maintenance therapy 3) therapy of fistulizing perianal disease.All panellists were assigned to...

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This article is the second in a series of two publications relating to the European Crohn’s and Colitis Organisation [ECCO] evidence-based consensus on the management of Crohn’s disease. The first article covers medical management; the present article addresses surgical management, including preoperative aspects and drug management before surgery. It also provides technical advice for a variety of common clinical situations. Both articles together represent the evidence-based recommendations of the ECCO for Crohn’s disease and an update of previous guidelines.

Our study protocol was registered with PROSPERO (registration number: CRD42018112214). We followed a standardized methodology 7 and report findings according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (ie, PRISMA) 8 and Meta-analyses of Observational Studies in Epidemiology (ie, MOOSE) 9 recommendations. Search Strategy We systematically searched PubMed, Embase, and Scopus from inception through September 28, 2018, to identify metaanalyses of studies assessing the association between environmental factors and IBD. Search terms included inflammatory bowel disease, Crohn's disease, or ulcerative colitis, combined with systematic review or meta-analysis. We excluded conference abstracts, letters, editorials, and articles published in languages other than English. The reference lists of the identified meta-analyses were screened for additional eligible articles. No other restrictions were imposed.