Confocal laser endomicroscopy for the differential diagnosis of ulcerative colitis and Crohn s disease: a pilot study

Transcription

1 Confocal laser endomicroscopy for the differential diagnosis of ulcerative colitis and Crohn s disease: a pilot study Authors Gian Eugenio Tontini 1, 2, Jonas Mudter 1, Michael Vieth 3, Raja Atreya 1, Claudia Günther 1, Yurdagül Zopf 1, Dane Wildner 1, Ralf Kiesslich 4, Maurizio Vecchi 2, 5, Markus F. Neurath 1, Helmut Neumann 1 Institutions Institutions are listed at the end of article. submitted 8. October 2013 accepted after revision 27. October 2014 Bibliography DOI /s Published online: 2014 Endoscopy Georg Thieme Verlag KG Stuttgart New York ISSN X Corresponding author Helmut Neumann, MD, PhD Department of Medicine I University of Erlangen- Nuremberg Ulmenweg Erlangen Germany Fax: helmut.neumann@uk-erlangen. de Background and study aim: The differential diagnosis of ulcerative colitis from Crohn s disease is of pivotal importance for the management of inflammatory bowel diseases, as both entities involve specific therapeutic management strategies. Confocal laser endomicroscopy (CLE) allows on-demand, in vivo characterization of architectural and cellular details during endoscopy. The aim of this study was to assess the efficacy of CLE to differentiate between ulcerative colitis and Crohn s disease. Patients and methods: This was a prospective study involving consecutive patients with a wellestablished diagnosis of ulcerative colitis or Crohn s disease who underwent colonoscopy with fluorescein-aided confocal imaging. Results: Overall, 79 patients were included (40 Crohn s disease, 39 ulcerative colitis). CLE findings in patients with Crohn s disease, showed significantly more discontinuous inflammation (87.5 % vs. 5.1%), focal cryptitis (75.0 % vs %), and discontinuous crypt architectural abnormality (87.5 % vs. 10.3%) than in ulcerative colitis (P <0.0001). Conversely, ulcerative colitis was associated with severe, widespread crypt distortion (87.2 % vs % in Crohn s disease), decreased crypt density (79.5 % vs %), and frankly irregular surface (89.7 % vs %; P< for all comparisons). Statistically significant differences were not seen for heavy, diffuse lamina propria cell increase or mucin preservation. No granulomas were visible. Based on these findings, a CLE scoring system was developed that revealed excellent accuracy (93.7 %) when compared with the historical clinical diagnosis and the histopathological gold standard. Conclusions: CLE could visualize several diseasespecific microscopic features, which are conventionally used in standard histopathology to differentiate between ulcerative colitis and Crohn s disease. However, because of the limited penetration depth of CLE, submucosal details or granulomas were not visible. The new scoring system may allow in vivo diagnosis of ulcerative colitis or Crohn s disease. Trial registered at ClinicalTrials.gov: NCT Introduction Inflammatory bowel disease (IBD) encompasses two major entities ulcerative colitis and Crohn s disease [1]. The differential diagnosis of the two diseases is of paramount importance to the optimization of clinical management, as modern therapies and reliable prognostic indices often involve disease-specific strategies [2 4]. The differential diagnosis is currently based on clinical evaluation and a combination of endoscopic, histological, radiological, and biochemical investigations [4, 5]. However, in about 3% 6% of all initial IBD diagnoses made in adult patients, a distinctive diagnosis is not possible, leading to the term of IBD type unclassified [5 7]. In 2004, confocal laser endomicroscopy (CLE) was introduced, enabling real-time histology during ongoing endoscopy (i. e. in vivo histology) [8]. Recent data have suggested that CLE enables in vivo confirmation of histological changes associated with ulcerative colitis and Crohn s disease [5, 9 12]. CLE has been utilized in a few studies to assess IBD diagnosis [9, 13, 14], disease activity [10, 11], and prediction of disease relapse [15]. Taken together, these studies have underscored the potential usefulness of CLE for the in vivo diagnosis of IBD. However, no study has evaluated the potential of CLE for the in vivo differentiation of ulcerative colitis and Crohn s disease. The aim of this prospective study, therefore, was to assess the efficacy of CLE to define the differential diagnosis between ulcerative colitis and Crohn s disease. In addition, variables allowing the differentiation of the two disease entities

2 were identified, and a prediction model was developed to enable the in vivo diagnosis of IBD. Patients and methods Patient enrollment, inclusion, and exclusion Consecutive patients with a well-established diagnosis of ulcerative colitis or Crohn s disease underwent screening or surveillance colonoscopy for the evaluation of disease activity. Patients were prospectively included between October 2009 and April 2013 at the endoscopy unit of the Department of Medicine I at the University of Erlangen-Nuremberg. All patients signed informed consent after the endoscopist or the attending physician had explained the procedure to them in detail. The study was approved by the local ethical committee of the University of Erlangen-Nuremberg and government authorities, and was conducted in accordance with the declaration of Helsinki. (ClinicalTrials Registration number NCT ) Patients were included if they met the following inclusion criteria: age 18 years, ability to provide written informed consent, and a well-established diagnosis of ulcerative colitis or Crohn s disease. Patients with one or more of the following criteria were excluded from the study: history of IBD reclassification in the last 3 years, Boston Bowel Preparation Scale score <2 in at least one of the three segments of the colon (i. e. rectum plus left-sided colon, transverse colon plus left and right flexures, right colon) [16], inability to provide written informed consent, severe uncontrolled coagulopathy, impaired renal function, pregnancy or breast feeding, active gastrointestinal bleeding, known allergy to fluorescein, and residence in institutions. Endoscopic and endomicroscopic procedure All colonoscopies were performed after the patient had undergone standard bowel preparation using either oral sodium phosphate or polyethylene glycol electrolyte lavage solution. CLE was performed using two European Conformity-certified and Food and Drug Administration-approved CLE systems (icle, Pentax, Tokyo, Japan; and pcle, Cellvizio, Mauna Kea Technologies, Paris, France). Conscious sedation with constant monitoring of vital signs was employed (e. g. midazolam hydrochloride and pethidine hydrochloride). Initially, the endoscope was advanced to the colon. On withdrawal, all parts of the colon were evaluated. The Boston Bowel Preparation Scale and inflammation changes were recorded. In patients with ulcerative colitis, inflammatory lesions were classified according to the Mayo Ulcerative Endoscopic Score of Severity (Mayo score), and Crohn s disease was classified according to the Crohn s Disease Endoscopic Index of Severity (CDEIS). Briefly, the Mayo score considers four degrees of severity: 0=normal or inactive disease; 1 = mild disease (erythema, decreased vascular pattern, mild friability); 2 = moderate disease (frank friability, marked erythema, absent vascular pattern, erosions); 3 = severe disease (mucopus, spontaneous bleeding, and ulceration) [17]. The CDEIS calculates disease activity according to five endoscopically visualized segments (rectum, sigmoid/left colon, transverse colon, right colon, terminal ileum), and findings, including ulcer size, extent of disease (surface with disease involvement and surface with ulcer involvement), and stenosis. The CDEIS score ranges from 0 to 44, with a higher score indicating more severe disease [18]. In the current study, a CDEIS score of <3 suggested inactive disease, 3 to < 9 mildly active, 9 to < 12 moderately active, and 12 severely active disease [19]. For confocal imaging, 5 ml of fluorescein sodium 10 % (Alcon Laboratories, Texas, USA) was administered intravenously to optimize tissue contrast [20]. Endomicroscopy was performed at a minimum of five random sites in the colon after careful washing of the mucosa with water in order to prevent the inclusion of image artefacts from residual stool fragments. Careful attention was paid to ensure high-quality images in focus either by using icle or pcle. The confocal images were first analyzed during the endoscopy. Then, the images were digitally stored and reviewed after the procedure in order to zoom in on details (icle) for a higher magnification (approximately fold) or by using the Cellvizio Viewer for virtual staining of mucosal structures to enhance tissue contrast. icle images were collected at a frame rate of 0.8 /second at pixels or 1.6/second at pixels. Normal mucosa and pathological lesions were evaluated according to the Mainz confocal pattern classification for icle [21] and the Miami classification for pcle [22]. Colonoscopy with CLE was performed in vivo by two expert endoscopists who were aware of the patients history and endoscopic results. The digitally stored confocal images were reviewed blinded to the true diagnosis. Based on previous histological studies that focused on the diagnosis of ulcerative colitis and Crohn s disease, the CLE examination aimed at evaluating the following features: severe and widespread architectural distortion, frankly irregular surface, decreased crypt density, discontinuous crypt architecture, focal cryptitis, heavy and diffuse cell infiltration within the lamina propria, mucin preservation at active sites, discontinuous inflammation, and granulomas [5, 12]. Multiple biopsies were taken from both macroscopically normal and abnormal mucosa after confocal examination. Specimens were retrieved and fixed in 4% buffered formalin for subsequent histopathological analysis to confirm the diagnosis. Patients diagnoses, defined according to the Montreal classification [6], were based on medical history, endoscopy, and histopathology. CLE scoring system for prediction of IBD diagnosis A simplified scoring system was developed based on CLE findings that showed a significant difference between patients with ulcerative colitis and those with Crohn s disease. The score was initially developed based on the method proposed by Pera et al. for ileo-colonoscopy [23], which used the likelihood ratios of the individual endoscopic findings. However, we found that the use of likelihood ratios or any similar method based on accuracy ratios, greatly increased the CLE score range and complexity with no impact on either accuracy or variability. Because of this, for the current study a number of simulations were performed, which involved the allocation of 1 5 points for each CLE finding with a positive likelihood ratio for ulcerative colitis, and 1to 5 points for those with a higher sensitivity for Crohn s disease. Finally, each score system was tested using all possible cutoff levels and assessed for sensibility, specificity, and accuracy. The overall best performance was provided by the endoscopic score system that involved the allocation of 3 points for the presence of each ulcerative colitis-related sign and one additional point for the absence of each Crohn s disease-related sign, with the diagnosis cutoff level set at 6 points. The score scale ranged from the minimum value of 0 (highly predictive for Crohn s disease) to the maximum value of 12 points (highly predictive for ulcerative co- Tontini Gian Eugenio et al. Confocal laser endomicroscopy in inflammatory bowel disease Endoscopy

3 litis). The score has been called the IBD Differentiation based on Endomicroscopic Assessment (IDEA) scoring system. Statistical analysis All statistical analyses were performed using PASW Statistics 18 (SPSS, Inc., Chicago, USA). A two-sided P value of < 0.05 was considered to be significant. For comparisons of proportions between ulcerative colitis and Crohn s colitis, such as crypt architecture, presence of microerosions, and vascular pattern between the different groups, the Fisher s exact test was used. The median is presented for non-normally distributed variables, and the mean is shown for normally distributed variables. The ranges presented indicate the minimum and maximum values. Results Patient characteristics The endoscopic disease activity was prospectively evaluated in 105 patients with a previous well-established diagnosis of colonic IBD. A total of 79 of them fulfilled the inclusion criteria and underwent a complete colonoscopic examination using CLE ( " Fig. 1). There were 40 patients with Crohn s disease (median age 35.5 ± 12.7 years [range 18 73]; 17 females) and 39 with ulcerative colitis (median age 39.9 ± 12.0 years [range 21 63]; 10 females). The demographic and clinical data of patients are shown in " Table 1 and " Table2. A total of 26 patients were excluded because of suboptimal bowel preparation, IBD-type reclassification in the last 3 years, or poor historical documentation addressing the previous disease classification. Endomicroscopic evaluation CLE enabled a clear characterization of seven out of the eight architectural and inflammatory changes investigated in the present study: severe and widespread architectural distortion, frankly irregular surface, decreased crypt density, discontinuous crypt architectural abnormality, focal cryptitis, heavy and diffuse cell infiltration within the lamina propria, mucin preservation at active sites, and discontinuous inflammation ( " Fig. 2a c). No granulomas were detected by CLE. " Table 3 shows the CLE findings in patients. In ulcerative colitis, CLE images showed higher prevalence of severe and widespread architectural distortion (87.2 %, P< ), frankly irregular surface (89.7 %, P < ), and decreased crypt density (79.5 %, P < ) compared with Crohn s disease patients (17.5 %, 17.5%, and 22.5%, respectively). Conversely, CLE images collected from patients with Crohn s disease showed a greater amount of discontinuous crypt architectural abnormality (87.5 %, P< ), focal cryptitis (75.0 %, P <0.0001), and discontinuous inflammation (87.5 %, P <0.0001) compared with patients with ulcerative colitis (10.3 %, 12.8 %, and 5.1 %, respectively). In both groups of patients, CLE images presented heavy and diffuse infiltration within the lamina propria (85.0 % in Crohn s disease and 89.7% in ulcerative colitis; P = ) and low grade of mucin preservation at active site (7.5 % and 12.8 %, respectively; P =0.4814). There were no meaningful differences in the frequencies of CLE findings according to either the Montreal classification or the endoscopic disease severity (i. e. Mayo or CDEIS) for both ulcerative colitis patients and those with Crohn s disease ( " Table 4, " Table5). Fig. 1 Assessed for eligibility: Patients with ulcerative colitis or Crohn s disease submitted for colonoscopy (n = 105) Excluded patients (n = 26): Suboptimal bowel preparation (n = 7) IBD-type reclassification within the last 3 years (n = 6) Poor historical documentation addressing the previous disease classification (n = 13) Clinical, endoscopic, and histopathological definition of ulcerative colitis (n = 39) and Crohn s disease (n = 40) Confocal laser endomicroscopy (n = 79) Analysis CONSORT 2010 flow diagram. Table1 Baseline characteristics of patients with Crohn sdiseaseand ulcerative colitis. Baseline characteristics Crohn s disease Ulcerative colitis Patients, n Females, n (%) 17 (42.5) 10 (25.6) Age, median (range), years 35.5 (18 73) 39.9 (21 63) Years from diagnosis, median (range) 10 (3 30) 11 (3 23) Table2 Characterization of Crohn s disease and ulcerative colitis study populations based on clinical data. Clinical data Crohn sdisease,n=40 Montreal classification L2 11 L3 27 L3 /L4 2 CDEIS score < 3 (mean CRP 11 mg/dl) 8 3 to <9 (mean CRP 4 mg/dl) 16 9to<12(meanCRP24mg/dL) 5 12 (mean CRP 41mg/dL) 11 Ulcerative colitis, n =39 Montreal classification E1 3 E2 12 E3 24 Mayo endoscopic subscore Number of patients CDEIS, Crohn s Disease Endoscopic Index of severity; CRP, C-reactive protein. The mean procedure time was 10 minutes for the in vivo CLE examination and 10 minutes to review the digitally stored confocal images after the endoscopy procedure. No differences in image interpretation were observed between the icle and pcle CLE systems, although this was not an aim of the study. CLE scoring system for prediction of IBD diagnosis Based on the IDEA scoring system and its performance characteristics in the study population, a diagnosis of ulcerative colitis was

4 Fig. 2 Confocal laser endomicroscopy findings. a Normal colonic crypts in a healthy individual. b Focal cryptitis in a patient with active Crohn s colitis. c Crypt architectural distortion in a patient with active ulcerative colitis. Table3 Confocal laser endomicroscopy findings in patients with Crohn s disease or ulcerative colitis. CLE findings Ulcerative colitis, % Crohn s disease, % P Odds ratio 95%CI Severe and widespread architectural distortion < Frankly irregular surface < Decreased crypt density < Discontinuous crypt architectural abnormality < Focal cryptitis < Discontinuous inflammation < Heavy and diffuse infiltration within lamina propria Mucin preservation at active sites Granulomas 0 0 CLE, confocal laser endomicroscopy; CI, confidence interval. Table4 Confocal laser endomicroscopy findings in Crohn s disease population according to Montreal classification and Crohn s disease endoscopic index of severity. CLE findings Overall Montreal classification CDEIS score L2 L3 1 B1 B2 B3 < 3 3 to<9 9 to<12 12 Number of patients Severeandwidespreadarchitecturaldistortion Franklyirregular surface Decreasecryptsdensity Discontinuous crypts architectural abnormality Focalcryptitis Discontinuous inflammation Heavy and diffuse infiltration in lamina propria Mucinpreservationatactivesites Granulomas CLE, confocal laser endomicroscopy; CDEIS, Crohn s disease endoscopic index of severity. 1 Two L3+L4 patients were included in the L3 group. assigned for scores of 6 points and a diagnosis of Crohn s disease was made for scores <6 ( " Fig. 3, " Table6). This cutoff resulted in the following validity measures: sensitivity 97.4 % for ulcerative colitis and 90.0 % for Crohn s disease; specificity 90.0 % and 97.4 %, respectively; positive predictive value 90.5 % and 97.3 %, respectively; negative predictive value 97.3 % and 90.5%, respectively; accuracy 93.7 % for both groups ( " Table 7). Discussion This prospective pilot study showed that the variables detected by CLE allow the in vivo diagnosis of ulcerative colitis or Crohn s disease. Based on these findings, it was possible to develop a prediction score (the IDEA score) that potentially allowed the diagnosis of both ulcerative colitis and Crohn s disease with a high overall accuracy (93.7 %). Obtaining a specific diagnosis of ulcerative colitis or Crohn s disease is particularly important because it enables tailored medical treatment to be provided, and affects prognostic evaluation and potential surgical approaches [1 5, 24, 25]. In addition, exact dif- Tontini Gian Eugenio et al. Confocal laser endomicroscopy in inflammatory bowel disease Endoscopy

5 Table5 Confocal laser endomicroscopy findings in ulcerative colitis population according to Montreal classification and Mayo ulcerative endoscopic score of severity. CLE findings Overall Montreal classification Mayo endoscopic score E1 E2 E Number of patients Severe and widespread architectural distortion Frankly irregular surface Decrease crypts density Discontinuous crypts architectural abnormality Focal cryptitis Discontinuous inflammation Heavy and diffuse infiltration in lamina propria Mucin preservation at active sites Granulomas CLE, confocal laser endomicroscopy. Endomicroscopy score ( IDEA ) for differential diagnosis between Crohn s disease and ulcerative colitis Add 3 points for the presence of each CLE finding correlated with UC Severe and widespread architectural distortion Frankly irregular surface Decreased crypt density Add 1 point for the absence of each CLE finding correlated with CD Discontinuous crypts architectural abnormality Focal cryptitis Discontiuous inflammation < 6 points: Crohn s disease 6 points: ulcerative colitis Fig. 3 Endomicroscopy score IBD Differentiation based on Endomicroscopic Assessment (IDEA) for the differential diagnosis of Crohn s disease and ulcerative colitis. UC, ulcerative colitis; CD, Crohn s disease; CLE, confocal laser endomicroscopy. Table6 Confocal laser endomicroscopy score IBD Differentiation based on Endomicroscopic Assessment (IDEA) 1 for the differential diagnosis between Crohn s disease and ulcerative colitis. CLE findings Corresponding score Presence Absence Severe and widespread architectural distortion 3 0 Frankly irregular surface 3 0 Decreased crypt density 3 0 Discontinuous crypts architectural abnormality 0 1 Focal cryptitis 0 1 Discontinuous inflammation 0 1 CLE, confocal laser endomicroscopy. 1 The scoring system assigns a value of 3 points for the presence of each of the three CLE findings typically associated with ulcerative colitis, and 1 additional point for the absence of each of the three Crohn s disease-related findings. Final score=0 12 ferentiation between the various IBD entities is mandatory for patient inclusion into clinical trials. Growing efforts are being made to identify molecular targets, which play a pivotal role within the inflammatory cascade of both diseases, in order to develop highly specific drugs [2, 3, 26 29]. It is therefore anticipated that the importance of differentiating between ulcerative colitis and Crohn s disease will increase as new, disease-specific medical therapies become available in clinical practice. The increasing interest in mucosal healing has also made it necessary to discriminate between ulcerative colitis and Crohn s disease [25]. Specifically, mucosal healing in patients with ulcerative colitis plays a pivotal role as the clinical parameter used to assess early response to anti-tumor necrosis factor antibody therapy [30]. In addition, mucosal healing is used to lead the decision of dose escalation, or the switching or stopping of biological therapies [31]. Conversely, in patients with Crohn s disease, the clinical relevance of mucosal healing has to be weighed against signs of transmural bowel inflammation and disease complications [24, 25]. In addition, there are substantial differences between ulcerative colitis and Crohn s disease in the effect of different drugs on mucosal healing [25, 32]. A specific diagnosis is particularly relevant for surgical therapy. The vast majority of patients with ulcerative colitis who undergo ileal pouch anal anastomosis (IPAA) do well, whereas 50 % of patients with Crohn s disease who undergo IPAA require revision or diversion [33, 34]. However, the reclassification of a patient s diagnosis after surgery is common (4 % 9%), even in referral IBD centers [34, 35]. It has already been shown that the in vivo diagnosis of IBD is feasible by using an optical biopsy system [9, 13, 14]. Recent data have also shown that CLE can be used to identify epithelial cell shedding and epithelial gap density during in vivo imaging [13, 15]. However, it was concluded that the assessment of these parameters cannot differentiate patients with Crohn s disease from those with ulcerative colitis [13]. Crohn s disease Ulcerative colitis Sensitivity, % [95%CI] 90.0 [ ] 97.4 [ ] Specificity, % [95 %CI] 97.4 [ ] 90.0 [ ] Positive predictive value, % [95 %CI] 97.3 [ ] 90.5 [ ] Negative predictive value, % [95 %CI] 90.5 [ ] 97.3 [ ] Accuracy, % [95 %CI] 93.7 [ ] 93.7 [ ] 95%CIs according to normal approximation and correction for continuity. Table7 Results of in vivo differentiation between Crohn sdisease and ulcerative colitis using the IBD Differentiation based on Endomicroscopic Assessment (IDEA) score.

6 The current study focused on the in vivo characterization of several microscopic architectural structures and inflammatory changes currently regarded as hallmarks for histopathological evaluation in IBD [5]. Based on these well-established distinctive features of IBD, a scoring system the IDEA score was proposed. Although this score represents a unique opportunity to immediately predict the diagnosis of either ulcerative colitis or Crohn s disease during ongoing endoscopy, offering a time-saving option, its potential limitations need to be acknowledged. First, this is only a pilot study evaluating patients with well-characterized ulcerative colitis or Crohn s disease. Patients with indeterminate colitis were excluded. However, we believe that this potential deficit strengthens the results of the scoring system, as patients with other types of colitis were excluded. This pilot study defined a potential classification that will need to be perfected and validated in larger, prospective studies. Second, it was not possible to diagnose granulomas. This was due to the limited penetration depth of the laser scanning system. The maximum scanning depth of CLE is 250 µm, whereas granulomas appear in the deeper parts of the mucosa at about 500 µm. Although previous data have shown that granulomas are present in approximately 30 % of surgical specimens from patients with Crohn s disease [36, 37], with wide variability ranging from 7 % to 100 % [37, 38], in endoscopic cohorts the granuloma detection is much lower [37 39]. Furthermore, epithelioid granulomas are regarded as a hallmark for IBD differentiation only if they appear well formed, isolated, noncaseating, and basally oriented in the mucosa and distant from the colonic crypts. Otherwise, granuloma specificity decreases and other potential granulomatous conditions, such as tuberculosis, acute bacterial enterocolitis, complicated diverticular disease, diversion colitis, sarcoidosis, and even ulcerative colitis, should be ruled out [5, 38]. Third, fluorescein-guided CLE does not allow for a detailed analysis of the cellular infiltrate, as no differentiation between single inflammatory cells (e. g. eosinophilic granulocytes or neutrophilic granulocytes) is feasible. In addition, the current study was performed at a tertiary referral center that specialized in advanced endoscopic imaging techniques. Nevertheless, one recent study highlighted that CLE is easy to learn as a diagnostic method for the in vivo analysis and diagnosis in IBD, suggesting that this technique could be disseminated into general clinical practice in the near future [40]. In addition, there are few data on the use of CLE in IBD, and no previous study to date had addressed whether it would be possible to differentiate between ulcerative colitis and Crohn s disease. Thus, no published evidence was available to allow a thorough sample size calculation prior to the current study. Other investigators can now use the current findings to perform power calculations when evaluating CLE prospectively. In the current study, the endoscopists performing CLE were not blinded to the patient s previous diagnosis. However, the digitally stored confocal images were reviewed blinded to both the true diagnosis as well as to the previous CLE evaluation. Notably, no relevant difference in confocal image interpretation was observed between the in vivo and post-procedural CLE evaluations, although this was not an aim of the study. Finally, the inter- and intraobserver validity of the IDEA score were not evaluated. This is a topic of a separate study in patients with Crohn s disease [11]. In conclusion, CLE parameters that differentiate ulcerative colitis from Crohn s disease have been described. These features were proven to be highly specific to differentiate between the two disease entities. Because the proposed new IDEA CLE score seems to allow the accurate discrimination between patients with ulcerative colitis and Crohn s disease, it may impact on future diagnostic algorithms for patients with IBD. We believe that this study sets the stage for larger, prospective, controlled trials to evaluate the validity and reproducibility of the score for CLE in the diagnosis of IBD. Competing interests: None Institutions 1 Department of Medicine, University of Erlangen-Nuremberg, Erlangen, Germany 2 Gastroenterology and Digestive Endoscopy Unit, IRCCS Policlinico San Donato, San Donato Milanese, Italy 3 Institute of Pathology, Klinikum Bayreuth, Bayreuth, Germany 4 St. Marienkrankenhaus Katharina-Kasper, Frankfurt am Main, Germany 5 Department of Biomedical Sciences for the Health, University of Milan, Milan, Italy Acknowledgments Gian Eugenio Tontini is the recipient of a grant from the Italian Group for the study of IBD (IG-IBD) to support his research work at the Department of Medicine I, University of Erlangen-Nuremberg. References 1 Abraham C, Cho JH. Inflammatory bowel disease. N Engl J Med 2009; 361: Dignass A, Lindsay JO, Sturm A et al. Second European evidence-based consensus on the diagnosis and management of ulcerative colitis part 2: current management. J Crohns Colitis 2012; 6: Dignass A, Van Assche G, Lindsay JO et al. The second European evidence-based Consensus on the diagnosis and management of Crohn s disease: current management. J Crohns Colitis 2010; 4: (Erratum in: J Crohns Colitis 2010; 4: 353) 4 Mowat C, Cole A, Windsor A et al. Guidelines for the management of inflammatory bowel disease in adults. Gut 2011; 60: Magro F, Langner C, Driessen A et al. European consensus on the histopathology of inflammatory bowel disease. J Crohns Colitis 2013; 7: Silverberg MS, Satsangi J, Ahmad T et al. Toward an integrated clinical, molecular and serological classification of inflammatory bowel disease: report of a working party of the 2005 Montreal World Congress of Gastroenterology. Can J Gastroenterol 2005; 19: 5 36 (Suppl A) 7 Meucci G. What is the incidence, prevalence, and natural history of indeterminate colitis? Inflamm Bowel Dis 2008; 14: Erratum in: Inflamm Bowel Dis 2009; 15: Neumann H, Kiesslich R, Wallace MB et al. Confocal laser endomicroscopy: technical advances and clinical applications. Gastroenterology 2010; 139: Watanabe O, Ando T, Maeda O et al. Confocal endomicroscopy in patients with ulcerative colitis. J Gastroenterol Hepatol 2008; 23: Li CQ, Xie XJ, Yu T et al. Classification of inflammation activity in ulcerative colitis by confocal laser endomicroscopy. Am J Gastroenterol 2010; 105: Neumann H, Vieth M, Atreya R et al. Assessment of Crohn s disease activity by confocal laser endomicroscopy. Inflamm Bowel Dis 2012; 18: Geboes K. What histologic features best differentiate Crohn s disease from ulcerative colitis? Inflamm Bowel Dis 2008; 14: Liu JJ, Wong K, Thiesen AL et al. Increased epithelial gaps in the small intestines of patients with inflammatory bowel disease: density matters. Gastrointest Endosc 2011; 73: Trovato C, Sonzogni A, Fiori G et al. Confocal laser endomicroscopy for the detection of mucosal changes in ileal pouch after restorative proctocolectomy. Dig Liver Dis 2009; 41: Tontini Gian Eugenio et al. Confocal laser endomicroscopy in inflammatory bowel disease Endoscopy

7 15 Kiesslich R, Duckworth CA, Moussata D et al. Local barrier dysfunction identified by confocal laser endomicroscopy predicts relapse in inflammatory bowel disease. Gut 2012; 61: Lai EJ, Calderwood AH, Doros G et al. The Boston bowel preparation scale: a valid and reliable instrument for colonoscopy-oriented research. Gastrointest Endosc 2009; 69: D Haens G, Sandborn WJ, Feagan BG et al. A review of activity indices and efficacy end points for clinical trials of medical therapy in adults with ulcerative colitis. Gastroenterology 2007; 132: Mary JY, Modigliani R. Development and validation of an endoscopic index of the severity for Crohn s disease: a prospective multicentre study. Groupe d Etudes Therapeutiques des Affections Inflammatoires du Tube Digestif (GETAID). Gut 1989; 30: Sipponen T, Nuutinen H, Turunen U et al. Endoscopic evaluation of Crohn s disease activity: comparison of the CDEIS and the SES-CD. Inflamm Bowel Dis 2010; 16: Wallace MB, Meining A, Canto MI et al. The safety of intravenous fluorescein for confocal laser endomicroscopy in the gastrointestinal tract. Aliment Pharmacol Ther 2010; 31: Kiesslich R, Burg J, Vieth M et al. Confocal laser endoscopy for diagnosing intraepithelial neoplasias and colorectal cancer in vivo. Gastroenterology 2004; 127: Wallace M, Lauwers GY, Chen Y et al. Miami classification for probebased confocal laser endomicroscopy. Endoscopy 2011; 43: Pera A, Bellando P, Caldera D et al. Colonoscopy in inflammatory bowel disease. Diagnostic accuracy and proposal of an endoscopic score. Gastroenterology 1987; 92: Tontini GE, Bisschops R, Neumann H. Endoscopic scoring systems for inflammatory bowel disease: pros and cons. Expert Rev Gastroenterol Hepatol 2014; 8: Neurath MF, Travis SP. Mucosal healing in inflammatory bowel diseases: a systematic review. Gut 2012; 61: Cominelli F. Inhibition of leukocyte trafficking in inflammatory bowel disease. N Engl J Med 2013; 369: Günther C, Martini E, Wittkopf N et al. Caspase-8 regulates TNF-alphainduced epithelial necroptosis and terminal ileitis. Nature 2011; 477: Günther C, Neumann H, Neurath MF et al. Apoptosis, necrosis and necroptosis: cell death regulation in the intestinal epithelium. Gut 2013; 62: Danese S, Peyrin-Biroulet L. IBD in 2013: enriching the therapeutic armamentarium for IBD. Nat Rev Gastroenterol Hepatol 2014; 11: Colombel JF, Rutgeerts P, Reinisch W et al. Early mucosal healing with infliximab is associated with improved long-term clinical outcomes in ulcerative colitis. Gastroenterology 2011; 141: Orlando A, Guglielmi FW, Cottone M et al. Clinical implications of mucosal healing in the management of patients with inflammatory bowel disease. Dig Liver Dis 2013; 45: Armuzzi A, Van Assche G, Reinisch W et al. Results of the 2nd scientific workshop of the ECCO (IV): therapeutic strategies to enhance intestinal healing in inflammatory bowel disease. J Crohns Colitis 2012; 6: Fazio VW, Kiran RP, Remzi FH et al. Ileal pouch anal anastomosis: analysis of outcome and quality of life in 3707 patients. Ann Surg 2013; 257: Shen B. Crohn s disease of the ileal pouch: reality, diagnosis, and management. Inflamm Bowel Dis 2009; 15: Moss AC, Cheifetz AS. How often is a diagnosis of ulcerative colitis changed to Crohn s disease and vice versa? Inflamm Bowel Dis 2008; 14: Freeman HJ. Granuloma-positive Crohn's disease. Can J Gastroenterol 2007; 21: Rubio CA, Orrego A, Nesi G et al. Frequency of epithelioid granulomas in colonoscopic biopsy specimens from paediatric and adult patients with Crohn s colitis. J Clin Pathol 2007; 60: Shepherd NA. Granulomas in the diagnosis of intestinal Crohn s disease: a myth exploded? Histopathology 2002; 41: Heresbach D, Alexandre JL, Branger B et al. Frequency and significance of granulomas in a cohort of incident cases of Crohn s disease. Gut 2005; 54: Neumann H, Vieth M, Atreya R et al. Prospective evaluation of the learning curve of confocal laser endomicroscopy in patients with IBD. Histol Histopathol 2011; 26: