Mary Sherlock

Pediatric modification of the Montreal classification for inflammatory bowel disease: The Paris classification†‡

Background: Crohns disease and ulcerative colitis are complex disorders with some shared and many unique predisposing genes. Accurate phenotype classification is essential in determining the utility of genotype‐phenotype correlation. The Montreal Classification of IBD has several weaknesses with respect to classification of children. The dynamic features of pediatric disease phenotype (change in disease location and behavior over time, growth failure) are not sufficiently captured by the current Montreal Classification. Methods: Focusing on facilitating research in pediatric inflammatory bowel disease (IBD), and creating uniform standards for defining IBD phenotypes, an international group of pediatric IBD experts met in Paris, France to develop evidence‐based consensus recommendations for a pediatric modification of the Montreal criteria. Results: Important modifications developed include classifying age at diagnosis as A1a (0 to <10 years), A1b (10 to <17 years), A2 (17 to 40 years), and A3 (>40 years), distinguishing disease above the distal ileum as L4a (proximal to ligament of Treitz) and L4b (ligament of Treitz to above distal ileum), allowing both stenosing and penetrating disease to be classified in the same patient (B2B3), denoting the presence of growth failure in the patient at any time as G1 versus G0 (never growth failure), adding E4 to denote extent of ulcerative colitis that is proximal to the hepatic flexure, and denoting ever severe ulcerative colitis during disease course by S1. Conclusions: These modifications are termed the Paris Classification. By adhering to the Montreal framework, we have not jeopardized or altered the ability to use this classification for adult onset disease or by adult gastroenterologists. (Inflamm Bowel Dis 2011)

Interleukin-10 receptor signaling in innate immune cells regulates mucosal immune tolerance and anti-inflammatory macrophage function

Intact interleukin-10 receptor (IL-10R) signaling on effector and T regulatory (Treg) cells are each independently required to maintain immune tolerance. Here we show that IL-10 sensing by innate immune cells, independent of its effects on T cells, was critical for regulating mucosal homeostasis. Following wild-type (WT) CD4(+) T cell transfer, Rag2(-/-)Il10rb(-/-) mice developed severe colitis in association with profound defects in generation and function of Treg cells. Moreover, loss of IL-10R signaling impaired the generation and function of anti-inflammatory intestinal and bone-marrow-derived macrophages and their ability to secrete IL-10. Importantly, transfer of WT but not Il10rb(-/-) anti-inflammatory macrophages ameliorated colitis induction by WT CD4(+) T cells in Rag2(-/-)Il10rb(-/-) mice. Similar alterations in the generation and function of anti-inflammatory macrophages were observed in IL-10R-deficient patients with very early onset inflammatory bowel disease. Collectively, our studies define innate immune IL-10R signaling as a key factor regulating mucosal immune homeostasis in mice and humans.

NADPH oxidase complex and IBD candidate gene studies: identification of a rare variant in NCF2 that results in reduced binding to RAC2

Objective The NOX2 NADPH oxidase complex produces reactive oxygen species and plays a critical role in the killing of microbes by phagocytes. Genetic mutations in genes encoding components of the complex result in both X-linked and autosomal recessive forms of chronic granulomatous disease (CGD). Patients with CGD often develop intestinal inflammation that is histologically similar to Crohns colitis, suggesting a common aetiology for both diseases. The aim of this study is to determine if polymorphisms in NOX2 NADPH oxidase complex genes that do not cause CGD are associated with the development of inflammatory bowel disease (IBD). Methods Direct sequencing and candidate gene approaches were used to identify susceptibility loci in NADPH oxidase complex genes. Functional studies were carried out on identified variants. Novel findings were replicated in independent cohorts. Results Sequence analysis identified a novel missense variant in the neutrophil cytosolic factor 2 (NCF2) gene that is associated with very early onset IBD (VEO-IBD) and subsequently found in 4% of patients with VEO-IBD compared with 0.2% of controls (p=1.3×10−5, OR 23.8 (95% CI 3.9 to 142.5); Fisher exact test). This variant reduced binding of the NCF2 gene product p67phox to RAC2. This study found a novel genetic association of RAC2 with Crohns disease (CD) and replicated the previously reported association of NCF4 with ileal CD. Conclusion These studies suggest that the rare novel p67phox variant results in partial inhibition of oxidase function and are associated with CD in a subgroup of patients with VEO-IBD; and suggest that components of the NADPH oxidase complex are associated with CD.

Virtual reality simulation training for health professions trainees in gastrointestinal endoscopy

BACKGROUNDnTraditionally, training in gastrointestinal endoscopy has been based upon an apprenticeship model, with novice endoscopists learning basic skills under the supervision of experienced preceptors in the clinical setting. Over the last two decades, however, the growing awareness of the need for patient safety has brought the issue of simulation-based training to the forefront. While the use of simulation-based training may have important educational and societal advantages, the effectiveness of virtual reality gastrointestinal endoscopy simulators has yet to be clearly demonstrated.nnnOBJECTIVESnTo determine whether virtual reality simulation training can supplement and/or replace early conventional endoscopy training (apprenticeship model) in diagnostic oesophagogastroduodenoscopy, colonoscopy and/or sigmoidoscopy for health professions trainees with limited or no prior endoscopic experience.nnnSEARCH METHODSnHealth professions, educational and computer databases were searched until November 2011 including The Cochrane Central Register of Controlled Trials, MEDLINE, EMBASE, Scopus, Web of Science, Biosis Previews, CINAHL, Allied and Complementary Medicine Database, ERIC, Education Full Text, CBCA Education, Career and Technical Education @ Scholars Portal, Education Abstracts @ Scholars Portal, Expanded Academic ASAP @ Scholars Portal, ACM Digital Library, IEEE Xplore, Abstracts in New Technologies and Engineering and Computer & Information Systems Abstracts. The grey literature until November 2011 was also searched.nnnSELECTION CRITERIAnRandomised and quasi-randomised clinical trials comparing virtual reality endoscopy (oesophagogastroduodenoscopy, colonoscopy and sigmoidoscopy) simulation training versus any other method of endoscopy training including conventional patient-based training, in-job training, training using another form of endoscopy simulation (e.g. low-fidelity simulator), or no training (however defined by authors) were included.xa0 Trials comparing one method of virtual reality training versus another method of virtual reality training (e.g. comparison of two different virtual reality simulators) were also included. Only trials measuring outcomes on humans in the clinical setting (as opposed to animals or simulators) were included.nnnDATA COLLECTION AND ANALYSISnTwo authors (CMS, MES) independently assessed the eligibility and methodological quality of trials, and extracted data on the trial characteristics and outcomes. Due to significant clinical and methodological heterogeneity it was not possible to pool study data in order to perform a meta-analysis. Where data were available for each continuous outcome we calculated standardized mean difference with 95% confidence intervals based on intention-to-treat analysis. Where data were available for dichotomous outcomes we calculated relative risk with 95% confidence intervals based on intention-to-treat-analysis.nnnMAIN RESULTSnThirteen trials, with 278 participants, met the inclusion criteria. Four trials compared simulation-based training with conventional patient-based endoscopy training (apprenticeship model) whereas nine trials compared simulation-based training with no training. Only three trials were at low risk of bias. Simulation-based training, as compared with no training, generally appears to provide participants with some advantage over their untrained peers as measured by composite score of competency, independent procedure completion, performance time, independent insertion depth, overall rating of performance or competency error rate and mucosal visualization. Alternatively, there was no conclusive evidence that simulation-based training was superior to conventional patient-based training, although data were limited.nnnAUTHORS CONCLUSIONSnThe results of this systematic review indicate that virtual reality endoscopy training can be used to effectively supplement early conventional endoscopy training (apprenticeship model) in diagnostic oesophagogastroduodenoscopy, colonoscopy and/or sigmoidoscopy for health professions trainees with limited or no prior endoscopic experience. However, there remains insufficient evidence to advise for or against the use of virtual reality simulation-based training as a replacement for early conventional endoscopy training (apprenticeship model) for health professions trainees with limited or no prior endoscopic experience. There is a great need for the development of a reliable and valid measure of endoscopic performance prior to the completion of further randomised clinical trials with high methodological quality.

Oral budesonide for induction of remission in ulcerative colitis

BACKGROUNDnCorticosteroids are first-line therapy for induction of remission in ulcerative colitis. Although corticosteroids may improve symptoms, they have significant adverse effects. Steroids which act topically, with less systemic side-effects may be more desirable. Budesonide is a topically acting corticosteroid with extensive first pass hepatic metabolism. There are currently three formulations of budesonide: two standard formulations including a controlled-ileal release capsule and a pH-dependent capsule both designed to release the drug in the distal small intestine and right colon; and the newer Budesonide-MMX® capsule designed to release the drug throughout the entire colon.nnnOBJECTIVESnThe primary objective was to evaluate the efficacy and safety of oral budesonide for the induction of remission in ulcerative colitis.nnnSEARCH METHODSnWe searched MEDLINE, EMBASE, CENTRAL, and the Cochrane IBD Group Specialised Register from inception to April 2015. We also searched reference lists of articles, conference proceedings and ClinicalTrials.gov.nnnSELECTION CRITERIAnRandomised controlled trials comparing oral budesonide to placebo or another active therapy for induction of remission in ulcerative colitis were considered eligible. There were no exclusions based on patient age or the type, dose, duration or formulation of budesonide therapy.nnnDATA COLLECTION AND ANALYSISnTwo independent investigators reviewed studies for eligibility, extracted data and assessed study quality. Methodological quality was assessed using the Cochrane risk of bias tool. The overall quality of the evidence supporting the outcomes was evaluated using the GRADE criteria. The primary outcome was induction of remission (as defined by the primary studies) at week eight. Secondary outcomes included clinical, endoscopic and histologic improvement, adverse events and early withdrawal. We calculated the risk ratio (RR) and corresponding 95% confidence interval (CI) for each dichotomous outcome and the mean difference (MD) and corresponding 95% CI for each continuous outcome. Data were analysed on an intention-to-treat basis.nnnMAIN RESULTSnSix studies (1808 participants) were included. Four studies compared budesonide-MMX® with placebo, one small pilot study looked at clinical remission at week four, and was subsequently followed by three large, studies that assessed combined clinical and endoscopic remission at week eight. Although two placebo-controlled studies had mesalamine and Entocort (standard budesonide) treatment arms, these studies were not sufficiently powered to compare Budesonide-MMX® with these active comparators. One small study compared standard budesonide with prednisolone and one study compared standard budesonide to mesalamine. Four studies were rated as low risk of bias and two studies had an unclear risk of bias. A pooled analysis of three studies (900 participants) showed that budesonide-MMX® 9 mg was significantly superior to placebo for inducing remission (combined clinical and endoscopic remission) at 8 weeks. Fifteen per cent (71/462) of budesonide-MMX® 9 mg patients achieved remission compared to 7% (30/438) of placebo patients (RR 2.25, 95% CI 1.50 to 3.39). A GRADE analysis indicated that the overall quality of the evidence supporting this outcome was moderate due to sparse data (101 events). A subgroup analysis by concurrent mesalamine use suggests higher efficacy in the 442 patients who were not considered to be mesalamine-refractory (RR 2.89, 95% CI 1.59 to 5.25). A subgroup analysis by disease location suggests budesonide is most effective in patients with left-sided disease (RR 2.98, 95% CI 1.56 to 5.67; 289 patients). A small pilot study reported no statistically significant difference in endoscopic remission between budesonide and prednisolone (RR 0.75, 95% CI 0.23 to 2.42; 72 patients). GRADE indicated that the overall quality of the evidence supporting this outcome was very low due to unclear risk of bias and very sparse data (10 events). Standard oral budesonide was significantly less likely to induce clinical remission than oral mesalamine after 8 weeks of therapy (RR 0.72, 95% CI 0.57 to 0.91; 1 study, 343 patients). A GRADE analysis indicated that the overall quality of the evidence supporting this outcome was moderate due to sparse data (161 events). Another study found no difference in remission rates between budesonide-MMX® 9 mg and mesalamine (RR 1.48, 95% CI 0.81 to 2.71; 247 patients). GRADE indicated that the overall quality of the evidence supporting this outcome was low due to very sparse data (37 events). One study found no difference in remission rates between budesonide-MMX® 9 mg and standard budesonide 9 mg (RR 1.38, 95% CI 0.72 to 2.65; 212 patients). A GRADE analysis indicated that the overall quality of the evidence supporting this outcome was low due to very sparse data (32 events). Suppression of plasma cortisol was more common in prednisolone-treated patients (RR 0.02, 95% CI 0.0 to 0.33). While budesonide does appear to suppress morning cortisol to some extent, mean morning cortisol values remained within the normal range in 2 large studies (n = 899) and there was no difference in glucocorticoid-related side-effects across different treatment groups. Further, study withdrawal due to adverse events was not more common in budesonide compared with placebo treated patients (RR 0.85, 95% CI 0.53 to 1.38). Common adverse events included worsening ulcerative colitis, headache, pyrexia, insomnia, back pain, nausea, abdominal pain, diarrhoea, flatulence and nasopharyngitis.nnnAUTHORS CONCLUSIONSnModerate quality evidence to supports the use of oral budesonide-MMX® at a 9 mg daily dose for induction of remission in active ulcerative colitis, particularly in patients with left-sided colitis. Budesonide-MMX® 9 mg daily is effective for induction of remission in the presence or absence of concurrent 5-ASA therapy. Further, budesonide-MMX® appears to be safe, and does not lead to significant impairment of adrenocorticoid function compared to placebo. Moderate quality evidence from a single study suggests that mesalamine may be superior to standard budesonide for the treatment of active ulcerative colitis. Low quality evidence from one study found no difference in remission rates between budesonide MMX® and mesalamine. Very low quality evidence from one small study showed no difference in endoscopic remission rates between standard budesonide and prednisolone. Low quality evidence from one study showed no difference in remission rates between budesonide-MMX® and standard budesonide. Adequately powered studies are needed to allow conclusions regarding the comparative efficacy and safety of budesonide versus prednisolone, budesonide-MMX® versus standard budesonide and budesonide versus mesalamine.

Medical Therapy for Pediatric Inflammatory Bowel Disease

Pediatric inflammatory bowel disease encompasses a spectrum of disease phenotype, severity, and responsiveness to treatment. Intestinal healing rather than merely symptom control is an especially important therapeutic goal in young patients, given the potential for growth impairment as a direct effect of persistent chronic inflammation and the long life ahead, during which other disease complications may occur. Corticosteroids achieve rapid symptom control, but alternate steroid-sparing strategies with greater potential to heal the intestine must be rapidly adopted. Exclusive enteral nutrition is an alternate short-term treatment in pediatric Crohn’s disease. The results of multi-center pediatric clinical trials of both infliximab and adalimumab in Crohn’s disease and of infliximab in ulcerative colitis (all in children with unsatisfactory responses to other therapies) have now been reported and guide treatment regimens in clinical practice. Optimal patient selection and timing of anti-TNF therapy requires clinical judgment. Attention must be paid to sustaining responsiveness safely.

Severe neutropenia following infliximab treatment in a child with ulcerative colitis.

To the Editor: Infusion reactions, skin eruptions, and the potential for infectious complications are recognized adverse events associated with tumor necrosis factor alpha (TNF-a) antagonist therapy. Blood dyscrasias are infrequently reported in the medical literature. We report a case of profound neutropenia developing in a pediatric patient with ulcerative colitis (UC) treated with a single infliximab infusion. A previously healthy 8-year-old boy presented with a 5-week history of bloody diarrhea, abdominal pain, and weight loss. Past medical history was unremarkable and the family history was negative for inflammatory bowel disease (IBD) and autoimmune disorders. Initial laboratory parameters revealed a normal hemoglobin of 132 g/L, total white cell count of 15.8 10/L, neutrophils of 3.45 10/L, and platelets 569 10/L. The erythrocyte sedimentation rate (ESR) was 11 mm/h and albumin 42 g/L. Investigations were negative for infection. Upper endoscopy was normal, macroscopically and histologically. Colonoscopy demonstrated a moderate to severe pancolitis with a normal terminal ileum. On histology, there was chronic active colitis, with no granulomata. A diagnosis of UC was made. The Pediatric Ulcerative Colitis Activity Index (PUCAI) score was 80, indicating severe colitis. He responded to treatment with intravenous corticosteroids. Subsequent attempts to wean oral prednisone were unsuccessful, despite the addition of sulfasalazine (60 mg/kg/day in divided doses). Repeat colonoscopy demonstrated continuous colonic inflammation. To manage his steroid-dependent UC, infliximab was initiated 2 months after the initial diagnosis. Our plan was to administer a standard induction regimen with 5 mg/kg at 0, 2, and 6 weeks with regularly scheduled infusions thereafter. Complete blood count (CBC) and differential were entirely normal prior to the first infliximab infusion, to which he had an excellent clinical response, with a PUCAI score of 10 at week 2, indicating remission. Routine labwork immediately prior to the second infusion revealed a severe neutropenia (0.03 10/L). The infliximab infusion was withheld and the patient was admitted for further investigation. Sulfasalazine, which was commenced 35 days earlier, was discontinued in light of the known association between sulfasalazine and blood dyscrasias. Infectious work-up was negative. He was positive for p-ANCA antibodies. A bone marrow biopsy revealed normal cell line precursors with active granulopoeisis. No further infliximab infusions were administered and the neutrophil count slowly recovered over the following 2–3 months (Fig. 1). The child remained well for 4 months but has since had a colitis exacerbation requiring corticosteroid therapy. The severity and duration of his neutropenia following a single infliximab infusion has precluded further anti-TNF therapy. Agranulocytosis, occurring in association with anti-TNF-a therapy, has only rarely been described in the medical literature. In contrast, observational studies and several case reports describe an association between sulfasalazine use and the development of agranulocytosis. In the experience of our consultant hematologist and hematopathologist, a diagnosis of sulfasalazine-induced agranulocytosis requires demonstration of impaired granulocytopoeisis and/or granulocyte maturation on bone marrow examination. Similarly, Keisu and Ekman describe either sparse or absent granulocytopoeisis or maturation arrest in patients undergoing bone marrow examination in the setting of sulfasalazine associated agranulocytosis. Our patient’s normal bone marrow biopsy excludes sulfasalazine as the primary cause for the neutropenia. We hypothesize that the neutropenia may instead have developed as a consequence of infliximab-induced anti-neutrophil antibodies causing peripheral destruction of neutrophils. TNF-a antagonists are well known to be associated with autoantibody formation, most commonly antinuclear antibody (ANA) and anti-double-stranded DNA (anti-dsDNA). Regrettably, we were unable to identify a laboratory capable of testing for anti-bodies to neutrophil surface antigens. Our hypothesis of infliximab-induced anti-neutrophil antibody formation is indirectly supported, however, by the presence of anti-platelet antibodies, which were confirmed in this patient following infliximab exposure. Additional supporting evidence for our hypothesis was the timeline for recovery of the neutrophil count, which was 2–3 months. This timeline is consistent with the metabolism of infliximab, which has a mean half-life of 18 days. We hypothesize that the clearance of infliximab from the circulation removed any further stimulus for autoantibody formation, thus allowing the neutrophil count to return to normal.

W1177 Infliximab-Induced Psoriasis in Pediatric Crohn Disease; Experience of This Paradoxical Skin Manifestation At a Tertiary Centre and a Potential Association with a Variation in the IL-23r Gene

Background: Infliximab, a chimeric anti-tumour necrosis factor alpha antibody, is now an established therapy for both Crohn disease (CD) and psoriasis. Among patients treated for CD, however, the paradoxical development of new-onset psoriasis has been reported in up to 15% of adult patients. We reviewed the prevalence of psoriasis developing in pediatric CD patients during infliximabmaintenance therapy, and examined the role of polymorphisms in the interleukin 23-receptor (IL-23R) gene, known to contribute to CD and psoriasis susceptibility. Methods: The medical records of all CD patients with documented skin abnormalities following the instigation of infliximab, at our center, were reviewed. DNA from patients developing psoriasis following infliximab was compared with that of diseasematched controls to examine the association of Il-23R polymorphisms with this paradoxical event. Results: 118 children received infliximab from January 2000 to August 2008. Thirteen children (11%), (9 males), developed new onset psoriasis following infliximab therapy. Persistent luminal disease despite conventional therapy (n=10) and perianal disease (n=3) were the indications for initiation of infliximab. The median duration of infliximab exposure at the time of psoriasis onset was 1.0 year (IQR 0.6 2.1). The median age at diagnosis of psoriasis or psoriasiform lesions was 14.7 years (IQR 14.2 15.2). 11 of 13 responded well to topical steroid therapy. 2 patients discontinued infliximab, both with resolution of their psoriasis. DNA was available on 8 of the 13 patients who developed psoriasis, 137 diseasematched controls and 86 ulcerative colitis (UC) patients. 75% of cases were homozygous for the Il-23R rs10489629 single nucleotide polymorphism (SNP) compared with 42% of CD controls and 28% of UC controls, with an allele frequency of 88%, 65% and 53% for cases, CD controls and UC controls respectively. The odds ratio for an infliximab-exposed patient developing psoriasis was 3.8 for heterozygotes and 14 for homozygotes (p=0.07). Conclusion: The frequency of new-onset psoriasis in this pediatric cohort of CD patients treated with infliximab mirrors that reported in adult series. Most patients respond well to topical therapy and in the majority of cases, anti-TNF therapy can be continued. We found a trend towards association of this adverse event with a variation in the Il-23R gene. However, the true significance of this variation warrants further investigation in large, adequately powered, studies.

Enhanced TH17 Responses in Patients with IL10 Receptor Deficiency and Infantile-onset IBD

Background: IL10 receptor (IL10R) deficiency causes severe infantile-onset inflammatory bowel disease. Intact IL10R-dependent signals have been shown to be important for innate and adaptive immune cell functions in mice. We have previously reported a key role of IL10 in the generation and function of human anti-inflammatory macrophages. Independent of innate immune cell defects, the aim of the current study was to determine the role of IL10R signaling in regulating human CD4+ T-cell function. Methods: Peripheral blood mononuclear cells and intestinal biopsies cells were collected from IL10/IL10R-deficient patients and controls. Frequencies of CD4+ T-cell subsets, naive T-cell proliferation, regulatory T cell (Treg)-mediated suppression, and Treg and TH17 generation were determined by flow cytometry. Transcriptional profiling was performed by NanoString and quantitative real-time polymerase chain reaction. RNA in situ hybridization was used to determine the quantities of various transcripts in intestinal mucosa. Results: Analysis of 16 IL10- and IL10R-deficient patients demonstrated similar frequencies of peripheral blood and intestinal Tregs, compared with control subjects. In addition, in vitro Treg suppression of CD4+ T-cell proliferation and generation of Treg were not dependent on IL10R signaling. However, IL10R-deficient T naive cells exhibited higher proliferative capacity, a strong TH17 signature, and an increase in polarization toward TH17 cells, compared with controls. Moreover, the frequency of TH17 cells was increased in the colon and ileum of IL10R-deficient patients. Finally, we show that stimulation of IL10R-deficient Tregs in the presence of IL1&bgr; leads to enhanced production of IL17A. Conclusions: IL10R signaling regulates TH17 polarization and T-cell proliferation in humans but is not required for the generation and in vitro suppression of Tregs. Therapies targeting the TH17 axis might be beneficial for IL10- and IL10R-deficient patients as a bridge to allogeneic hematopoietic stem cell transplantation.

Higher Postinduction Infliximab Serum Trough Levels Are Associated With Healing of Fistulizing Perianal Crohn’s Disease in Children

BackgroundnThere is some evidence in adults that higher serum infliximab (IFX) levels are needed to adequately treat fistulizing perianal Crohns disease (CD). However, data in children are lacking. We aimed to determine postinduction serum trough IFX levels that are associated with healing of fistulizing perianal CD (PCD) at week 24.nnnMethodsnIn a multicenter inception cohort study, consecutive children younger than age 17 years with fistulizing perianal CD treated with IFX between April 2014 and June 2017 who had serum trough IFX titers measured before the fourth infusion were included. Area under the receiver operating characteristic curve (AUROC) was calculated to determine the best cutoff to predict fistula healing.nnnResultsnA total of 667 children with Crohns disease were recruited, with 85 (12.7%) patients diagnosed with fistulizing PCD. There were 27 of 52 (52%) children in whom pre-fourth infusion IFX levels were measured (mean age, 12.57 ± 5.12 years). At week 24, 14 of 27 (52%) patients responded with healing/healed PCD, whereas the rest had ongoing active fistulizing disease. The median IFX pre-fourth dose level in the responders was 12.7 ug/mL, compared with 5.4 ug/mL in the active disease group (P = 0.02). There was a strong correlation between IFX levels and healing of fistulizing PCD at week 24 (r = 0.65; P < 0.001). The AUROC was 0.80 (95% confidence interval, 0.64-0.97; P = 0.007) for pre-fourth IFX level to predict response of fistulizing PCD at week 24, and a level of 12.7 ug/mL best predicted fistula healing.nnnConclusionsnHigher trough IFX levels are associated with healing of fistulizing perianal CD.