Prior appendectomy and the phenotype and course of Crohn’s disease

Prior Appendectomy Is Associated With a Milder Clinical Course in Crohn's Disease: A Nationwide Population-based Cohort Study

BACKGROUND

Appendectomy may affect the clinical course of Crohn's disease (CD), but rigorous evidence is sparse and contradicting. The aim of this study was to examine the association between appendectomy and the clinical course of CD.

METHODS

All patients diagnosed with CD in Denmark in the period from 1977 to 2017 were identified from the Danish National Patient Registry. Patients with appendectomy were matched with up to 10 comparators with CD and no appendectomy; and rates of CD-related hospital admissions were compared between CD patients with and without appendectomy using incidence rate ratios (IRRs). We used stratified Cox regression analysis to calculate adjusted hazard ratios (aHRs) of initiating treatment with biologics or undergoing intestinal resections.

RESULTS

In all, 21 189 CD patients (1936 with appendectomy and 19 253 without) were identified and followed for a median of 13.6 years. Crohn's disease patients who had undergone appendectomy experienced a lower rate of CD-related hospital admissions (appendectomy before CD: IRR = 0.83; 95% confidence interval [CI], 0.81-0.85; appendectomy after CD: IRR = 0.85; 95% CI, 0.81-0.88) compared with CD patients without appendectomy. For patients with appendectomy before CD diagnosis, the rate of initiating biologics was lower compared with CD patients with no appendectomy (aHR1-<5 years = 0.61; 95% CI, 0.46-0.81; aHR5-<10 years 0.47; 95% CI, 0.33-0.66; aHR10-20 years = 0.61; 95% CI, 0.47-0.79), as was the risk of undergoing colorectal resections (aHR1-<5 years = 0.94; 95% CI, 0.77-1.15; aHR5-<10 years 0.63; 95% CI, 0.47-0.85; aHR10-20 years = 0.75; 95% CI, 0.54-1.04). Rates of small bowel resections were comparable for CD patients with or without appendectomy prior to CD. Appendectomy performed after CD did not influence the rate of initiating treatment with biologics or undergoing intestinal resections.

CONCLUSION

The clinical course of CD is milder for those who have previously undergone appendectomy.

MICDnet: Multimodal information processing networks for Crohn's disease diagnosis

Crohn's disease (CD) is a chronic inflammatory disease with increasing incidence worldwide and unclear etiology. Its clinical manifestations vary depending on location, extent, and severity of the lesions. In order to diagnose Crohn's disease, medical professionals need to comprehensively analyze patients' multimodal examination data, which includes medical imaging such as colonoscopy, pathological, and text information from clinical records. The processes of multimodal data analysis require collaboration among medical professionals from different departments, which wastes a lot of time and human resources. Therefore, a multimodal medical assisted diagnosis system for Crohn's disease is particularly significant. Existing network frameworks find it hard to effectively capture multimodal patient data for diagnosis, and multimodal data for Crohn's disease is currently lacking. In addition,a combination of data from patients with similar symptoms could serve as an effective reference for disease diagnosis. Thus, we propose a multimodal information diagnosis network (MICDnet) to learn CD feature representations by integrating colonoscopy, pathology images and clinical texts. Specifically, MICDnet first preprocesses each modality data, then uses encoders to extract image and text features separately. After that, multimodal feature fusion is performed. Finally, CD classification and diagnosis are conducted based on the fused features. Under the authorization, we build a dataset of 136 hospitalized inspectors, with colonoscopy images of seven areas, pathology images, and clinical record text for each individual. Training MICDnet on this dataset shows that multimodal diagnosis can improve the diagnostic accuracy of CD, and the diagnostic performance of MICDnet is superior to other models.

Association between prior appendectomy and the risk and course of Crohn's disease: A systematic review and meta-analysis

BACKGROUND AND AIMS

The appendix has an important immune function in both health and disease, and appendectomy may influence microbial ecology and immune function. This meta-analysis aims to assess the association between appendectomy and the risk and course of Crohn's disease (CD).

METHODS

PubMed, EMBASE, and the Cochrane Library were used to identify all studies published until June 2022. Data from studies evaluating the association between appendectomy and CD were reviewed.

RESULTS

A total of 28 studies were included in the final analysis, comprising 22 case-control and 6 cohort studies. A positive relationship between prior appendectomy and the risk of developing CD was observed in both case-control studies (odds ratio [OR]: 1.59, 95% confidence interval [CI]: 1.22-2.08) and cohort studies (relative risk [RR]: 2.28, 95% CI: 1.66-3.14). The elevated risk of CD persisted 5 years post-appendectomy (RR = 1.24, 95% CI: 1.12-1.36). The risk of developing CD was similarly elevated regardless of the presence (RR = 1.64, 95% CI: 1.17-2.31) or absence (RR = 2.77, 95% CI: 1.84-4.16) of appendicitis in patients. Moreover, significant differences were found in the proportion of terminal ileum lesions (OR = 1.63; 95% CI: 1.38-1.93) and colon lesions (OR = 0.70; 95% CI: 0.5-0.84) between CD patients with appendectomy and those without appendectomy.

CONCLUSIONS

The risk of developing CD following an appendectomy is significant and persists 5 years postoperatively. Moreover, the elevated risk of CD may mainly occur in the terminal ileum.

Long-term effects of appendectomy in humans: is it the optimal management of appendicitis?

INTRODUCTION

Appendectomy remains the gold standard for treating uncomplicated and complicated appendicitis. However, the vermiform appendix may play a significant role in the immune system (secondary immune function) and maintain a reservoir of the normal microbiome for the human body. The aim of this study was to summarize the long-term effects after appendectomy and discuss whether appendectomy is suitable for all appendicitis patients.

AREAS COVERED

A comprehensive and unbiased literature search was performed in PubMed. The terms 'appendix,' 'appendicitis,' 'appendectomy,' and 'endoscopic retrograde appendicitis therapy' were searched in the title and/or abstract. This review summarizes the long-term effects of appendectomy on some diseases in humans and describes three methods including appendectomy, medical treatment, and an 'organ-sparing' technique, named endoscopic retrograde appendicitis therapy (ERAT) to treat appendicitis.

EXPERT OPINION

Appendectomy remains the first-line therapy for appendicitis. The patient's problem is appendix, not appendicitis. If we treat appendicitis, the problem should be resolved. During COVID-19, an initial antibiotic treatment of mild appendicitis represents a promising strategy. For patients who are worried about the long-term adverse effect after appendectomy and have a strong desire to preserve the appendix and are aware of the risk of appendicitis recurrence, medical treatment, or ERAT could be proposed.

Environmental factors associated with biological use and surgery in inflammatory bowel disease

BACKGROUND AND AIM

While major efforts were made studying the complex etiology of inflammatory bowel disease (IBD) including environmental factors, less is known about underlying causes leading to the heterogeneous and highly variable course of disease. As cigarette smoking cessation is the best-known environmental factor with beneficial effect in Crohn's disease (CD), more exposome factors are likely involved. Further insights into the role of the exposome in heterogeneity of disease might not only further knowledge of underlying pathways, but also allow for better risk stratification.

METHODS

Seven hundred twenty-eight IBD patients completed the validated Groningen IBD Environmental Questionnaire, collecting exposome data for 93 exposome factors. Associations with disease course, that is, for need for surgery or biological therapy, were evaluated using univariate and multivariate-adjusted logistic regression modeling.

RESULTS

No significant associations were seen after Bonferroni correction. However, 11 novel exposome factors were identified with P < 0.05. Two factors were associated with course of CD and ulcerative colitis (UC): beer (CD OR0.3/UC OR0.3) and cannabis (0.5/2.2). While in CD, carpet flooring (0.5) was associated with biological use, and four factors were associated with surgery: working shifts (1.8), appendectomy (2.4), frequent tooth brushing (2.8), and large household size (0.1). For UC, migrants more often required biologicals (10.2). Childhood underweight (3.4), amphetamine use (6.2), and cocaine use (4.8) were associated with surgery. Five factors were replicated.

CONCLUSIONS

We identified 16 environmental factors nominally associated with biological use and surgery in established IBD. These new insights form an important stepping stone to guide research on biological pathways involved, risk stratification, tailor-made interventions, and preventive strategies in IBD.

Impact of Appendectomy on Gut Microbiota

Background: Considered vestigial from the classic point of view, the vermiform appendix has long been the subject of intensive studies. The recent understanding of appendix function in the context of unique architecture and bacterial complexity and density allows considering it as a safehouse for intestinal biodiversity. Methods: This review analyzes and assesses the current state of scientific knowledge regarding the role of the vermiform appendix in normal gut microbiota maintenance as a crucial factor of host homeostasis. It also highlights the difference in microbial composition between the large bowel and the appendix, as well as the association between the surgical excision, appendectomy, and dysbiosis-induced diseases. In addition, the review discusses the results of epidemiologic studies on appendectomy as a risk factor for the initiation of gastrointestinal carcinogenesis. It also highlights the association between appendectomy and a series of chronic inflammatory and neurologic disorders, including inflammatory bowel disease.

Prior Appendectomy and the Onset and Course of Crohn's Disease in Chinese Patients

Background and Aim

The relationship between prior appendectomy and Crohn's disease (CD) has previously revealed conflicting findings. The present study investigates the relationship between prior appendectomy and CD development in Chinese patients.

Methods

A retrospective case-control study was performed to compare prior appendectomy rate between CD patients and age- and gender-matched controls at two Chinese hospitals. The clinical course of CD was determined in patients who underwent and did not undergo appendectomies before CD diagnosis.

Results

A total of 617 CD patients and 617 controls were included. The appendectomy rate before CD diagnosis in patients was higher, when compared to controls (6.65% versus 3.73%, P = 0.033). Appendectomy was a risk factor for the onset of CD independent of smoking in the multivariate analysis (OR: 1.878; 95% CI: 1.111–3.174; P = 0.019). Appendectomies were performed closer to the date of CD diagnosis in the trend test (P = 0.039). The rate of appendectomy within one year or 1-5 years before CD diagnosis was higher in patients when compared to that in controls (0.97% versus 0%, P = 0.031; 1.13% versus 0.32%, P = 0.180). However, the rate of appendectomy over five years before CD diagnosis was close to controls (4.54% versus 3.40%, P = 0.392). No significant differences in disease location, behavior, medication, and intestinal resection between appendectomy and nonappendectomy CD patients were found, even in the subgroup analysis by age of appendectomy.

Conclusion

Prior appendectomy is a risk factor for the onset of CD. However, the appendectomy rate only increased for a short duration before CD diagnosis, likely reflecting a diagnostic bias. Prior appendectomy did not influence the features or course of CD.

Emerging trends and risk factors for perianal surgery in Crohn's disease: a 20-year national population-based cohort study

BACKGROUND

Little is known about the rates of perianal surgery (PAS) in Crohn's disease (CD). Our aim was to determine trends in PAS, the timing of surgery relative to the diagnosis of CD and to identify subgroups at risk of PAS.

MATERIALS AND METHODS

We identified 9391 incident cases of CD between 1989 and 2009. We defined three eras: era 1 (1989-1995), era 2 (1996-2002) and era 3 (2003-2009), and determined trends in procedure type and the time to first PAS relative to the date of diagnosis. We used Kaplan-Meier analysis to calculate the rate of first PAS and performed Cox regression to determine subgroups at risk of PAS.

RESULTS

Among the 9391 incident cases of CD, 405 (4.3%) underwent PAS. The overall rate of PAS was 5.5% [95% confidence interval (CI): 4.9-6.2%] 10 years after diagnosis. 34% (n=137) of all patients undergoing PAS had surgery in the 5 years before CD diagnosis. Abscess drainage increased from 34 to 58%, whereas proctectomy decreased from 16 to 6% between eras 1 and 3, respectively. Men [hazard rate (HR) 1.51, 95% CI: 1.24-1.84], those aged 17-40 years (HR 1.69, 95% CI: 1.09-2.02 vs. those aged >40 years) and those with a history of previous intestinal resection (HR 28.5, 95% CI: 22.2-36.5) were more likely to have PAS.

CONCLUSION

Around one-third of patients have a PAS in the 5 years preceding their diagnosis of CD. Surgical practice has changed over 20 years, with a decrease in proctectomy and a concurrent increase in abscess drainage that is likely to reflect improvements in therapeutic practice.

How to predict clinical relapse in inflammatory bowel disease patients

Inflammatory bowel diseases have a natural course characterized by alternating periods of remission and relapse. Disease flares occur in a random way and are currently unpredictable for the most part. Predictors of benign or unfavourable clinical course are required to facilitate treatment decisions and to avoid overtreatment. The present article provides a literature review of the current evidence on the main clinical, genetic, endoscopic, histologic, serologic and fecal markers to predict aggressiveness of inflammatory bowel disease and discuss their prognostic role, both in Crohn’s disease and ulcerative colitis. No single marker seems to be reliable alone as a flare predictor, even in light of promising evidence regarding the role of fecal markers, in particular fecal calprotectin, which has reported good results recently. In order to improve our daily clinical practice, validated prognostic scores should be elaborated, integrating clinical and biological markers of prognosis. Finally, we propose an algorithm considering clinical history and biological markers to intercept patients with high risk of clinical relapse.

Impact of early thiopurines on surgery in 2770 children and young people diagnosed with inflammatory bowel disease: a national population-based study

BACKGROUND

The role of early thiopurine treatment in inflammatory bowel disease (IBD) is unproven.

AIM

To quantify the impact of timing and duration of thiopurines on the risk of first surgery in children and young people with IBD using a population-based cohort.

METHODS

We constructed an incident cohort of children and young people aged <25 years, diagnosed with Crohn's disease (CD) or ulcerative colitis (UC) from 1990 to 2009. We used Cox proportional hazards modelling to determine the impact of early thiopurine use, commenced within a year of diagnosis on risk of first surgery.

RESULTS

We identified 1595 and 1175 incident cases of CD and UC respectively with a mean length of follow-up of 4.3 years/person. There were 216 (13.5%) and 73 (6.2%) surgeries for CD and UC patients between 1990 and 2009 respectively. In CD among thiopurine users, the absolute risk of surgery at 5 years for early thiopurine use vs. late was 15.3% (95% CI: 10.5-22.1) vs. 22.1% (95% CI: 18.1-26.9) respectively. After adjustment, the early use of thiopurines was associated with a reduction in risk of first surgery of 39% (HR 0.61, 95% CI: 0.41-0.91) over the 20-year study period. In UC, early thiopurine use offered no additional benefit.

CONCLUSIONS

In Crohn's disease, early treatment with thiopurines in children and young people is associated with an appreciable reduction in the risk of surgery, but early treatment does not reduce surgical risk in UC.

Epidemiology and risk factors for IBD

IBD, comprising Crohn's disease and ulcerative colitis, is a chronic immunologically mediated disease at the intersection of complex interactions between genetics, environment and gut microbiota. Established high-prevalence populations of IBD in North America and Europe experienced the steepest increase in incidence towards the second half of the twentieth century. Furthermore, populations previously considered 'low risk' (such as in Japan and India) are witnessing an increase in incidence. Potentially relevant environmental influences span the spectrum of life from mode of childbirth and early-life exposures (including breastfeeding and antibiotic exposure in infancy) to exposures later on in adulthood (including smoking, major life stressors, diet and lifestyle). Data support an association between smoking and Crohn's disease whereas smoking cessation, but not current smoking, is associated with an increased risk of ulcerative colitis. Dietary fibre (particularly fruits and vegetables), saturated fats, depression and impaired sleep, and low vitamin D levels have all been associated with incident IBD. Interventional studies assessing the effects of modifying these risk factors on natural history and patient outcomes are an important unmet need. In this Review, the changing epidemiology of IBD, mechanisms behind various environmental associations and interventional studies to modify risk factors and disease course are discussed.

Impact of timing and duration of thiopurine treatment on first perianal surgery in Crohn's disease: UK population-based study (1995-2009)

BACKGROUND

The impact of thiopurine (TP) use on perianal surgery is uncertain. Our aim was to determine trends in perianal surgery and the impact of timing and duration of TPs on the risk of first perianal surgery.

METHODS

We identified a population-based cohort of incident cases of Crohn's disease between 1995 and 2009. We used Kaplan-Meier analysis to determine trends in TP usage and first perianal surgery by era of diagnosis: era 1 (1995-2002) and era 2 (2003-2009). We quantified the impact of duration and timing of TPs on the risk of perianal surgery using a Cox regression model.

RESULTS

We identified a cohort of 5235 incident cases of Crohn's disease. The 5-year cumulative probability of first perianal surgery decreased from 2.7% to 1.7% between era 1 and era 2, respectively (P = 0.03). TP use for greater than 18 months was associated with a 40% risk reduction for first perianal surgery (hazard ratio: 0.60, 95% confidence interval: 0.39-0.95) and 49% if TPs were used for 2 years or more (hazard ratio: 0.51, 95% confidence interval: 0.32-0.99). There was no demonstrable additional benefit from early TP use within the first year after diagnosis (hazard ratio: 0.85, 95% confidence interval: 0.52-1.40, P = 0.53).

CONCLUSIONS

Over the past 15 years, TP use has increased by 50%, whereas perianal surgery rates have decreased by 37% among UK population with Crohn's disease. Sustained use for 18 months was associated with a reduced risk of perianal surgery by almost a half in the first 5 years after diagnosis.

The impact of timing and duration of thiopurine treatment on first intestinal resection in Crohn's disease: national UK population-based study 1989-2010

OBJECTIVES

The efficacy of thiopurines (TPs) in altering the risk of surgery in Crohn's disease (CD) remains controversial. We evaluated the impact of TP therapy, optimal timing, and duration of TP therapy on first intestinal resection rates using a population-based cohort.

METHODS

We constructed a population-based cohort of incident cases of CD between 1989 and 2005. We used the Kaplan-Meier analysis to calculate time trends in TP use and first intestinal resection in three groups defined by time period of diagnosis: 1989-1993, 1994-1999, and 2000-2005 groups A, B, and C, respectively. We quantified impact of duration and timing of TP treatment on likelihood of surgery using Cox regression and propensity score matching.

RESULTS

We identified 5,640 eligible patients with CD. The 5-year cumulative probability of TP use increased from 12, 18, to 25% ( P<0.0001) while probability of first intestinal resection decreased from 15, 12 to 9% (P<0.001) in groups A, B, and C, respectively. Patients treated with at least 6 months of TP therapy had a 44% reduction in the risk of surgery (hazards ratio (HR): 0.56; 95% confidence interval (CI): 0.37-0.85) and those receiving at least 12 months of TP therapy had a 69% reduction in the risk of surgery (HR: 0.31; 95% CI: 0.22-0.44). Early treatment (<12 months from diagnosis) vs. late treatment with TP showed no additional benefit in reducing risk of surgery (HR: 0.41; 95% CI: 0.27-0.61 vs. 0.21; 95% CI: 0.13-0.34).

CONCLUSIONS

Over the past 20 years, TP use has doubled, whereas intestinal surgery has fallen by one-third among the UK population of Crohn's patients. Prolonged exposure is associated with a reduced likelihood of surgery whereby more than 12 months TP therapy reduces the risk of first intestinal surgery two-fold; however, early initiation of TP treatment offered no apparent additional benefit.

Predictors of aggressive inflammatory bowel disease

Inflammatory bowel disease comprises a group of conditions characterized by idiopathic inflammation of the gastrointestinal tract. The natural course of disease can range from an indolent course with prolonged periods of remission to aggressive, incapacitating disease. Predicting which patients are more susceptible to developing severe disease is important, especially when choosing therapeutic agents and treatment strategies. This paper reviews current evidence on the main demographic, clinical, endoscopic, histologic, serologic, and genetic markers that predict aggressive inflammatory bowel disease. In ulcerative colitis, we considered disease to be aggressive when patients had a high relapse rate, need for admission and/or surgery, development of colon cancer, or extraintestinal manifestations. We defined aggressive Crohn's disease as having a high relapse rate, development of penetrating disease, need for repeat surgery, or multiple admissions for flares. In Crohn's disease, involvement of the upper gastrointestinal tract and ileum, penetrating disease, early age at diagnosis, smoking, extensive ulceration of the mucosa, high titers of serum antibodies, and mutations of the NOD2 gene are markers of aggressive disease. In ulcerative colitis, patients with more extensive involvement of the colon (pancolitis) have more symptomatology and are at higher risk for needing a colectomy and developing colon cancer. Also, plasmocytic infiltration of the colonic mucosa and crypt atrophy predict treatment failure. As with diagnosis, no single method can predict disease aggressiveness. Multiple serologic and genetic tests are being developed to refine the accuracy of prediction. Endoscopic findings can also predict the future course of disease. At present, clinical manifestations are the most useful way to make therapeutic decisions.

Epidemiology and natural history of inflammatory bowel diseases

In the West, the incidence and prevalence of inflammatory bowel diseases has increased in the past 50 years, up to 8-14/100,000 and 120-200/100,000 persons, respectively, for ulcerative colitis (UC) and 6-15/100,000 and 50-200/100,000 persons, respectively, for Crohn's disease (CD). Studies of migrant populations and populations of developing countries demonstrated a recent, slow increase in the incidence of UC, whereas that of CD remained low, but CD incidence eventually increased to the level of UC. CD and UC are incurable; they begin in young adulthood and continue throughout life. The anatomic evolution of CD has been determined from studies of postoperative recurrence; CD begins with aphthous ulcers that develop into strictures or fistulas. Lesions usually arise in a single digestive segment; this site tends to be stable over time. Strictures and fistulas are more frequent in patients with ileal disease, whereas Crohn's colitis remains uncomplicated for many years. Among patients with CD, intestinal surgery is required for as many as 80% and a permanent stoma required in more than 10%. In patients with UC, the lesions usually remain superficial and extend proximally; colectomy is required for 10%-30% of patients. Prognosis is difficult to determine. The mortality of patients with UC is not greater than that of the population, but patients with CD have greater mortality than the population. It has been proposed that only aggressive therapeutic approaches, based on treatment of early recurrent lesions in asymptomatic individuals, have a significant impact on progression of these chronic diseases.

The risk of developing Crohn's disease after an appendectomy: a meta-analysis

BACKGROUND

Studies exploring the association between appendectomy and Crohn's disease (CD) have reported conflicting findings. We conducted a systematic review of the literature and a meta-analysis to assess the risk of CD following an appendectomy and determine the effect of time between appendectomy and CD diagnosis.

METHODS

MEDLINE was used to identify observational studies evaluating the association between appendectomy and CD. Authors were contacted when data were insufficient. Relative risks (RR) with 95% confidence intervals (CI) were calculated using a random effects model. Studies that analyzed their data by the interval between the appendectomy and the diagnosis of CD were assessed separately. The Woolf chi(2) statistic was used to test for homogeneity. Egger's test was used to evaluate publication bias.

RESULTS

The summary RR estimate for CD following an appendectomy was significantly elevated (RR 1.61, 95% CI 1.28-2.02), though heterogeneity was observed (P < 0.0001). The risk was elevated within the first year following the operation (RR 6.69, 95% CI 5.42-8.25). The risk of CD was also significantly increased 1-4 yr following an appendectomy (RR 1.99, 95% CI 1.66- 2.38); however, after 5 yr or more, the risk fell to baseline levels (RR 1.08, 95% CI 0.99-1.18). Publication bias was not detected (P = 0.2).

CONCLUSION

The meta-analysis demonstrated a significant risk of CD following an appendectomy, though heterogeneity was observed between the studies. The elevated risk early after an appendectomy, which diminishes thereafter, likely reflects diagnostic problems in patients with incipient CD.

The risk of developing Crohn's disease after an appendectomy: a population-based cohort study in Sweden and Denmark

BACKGROUND

The relationship between appendectomy and Crohn's disease is controversial. A Swedish-Danish cohort study was conducted to assess the risk of developing Crohn's disease after an appendectomy.

METHODS

709 353 appendectomy patients in Sweden (since 1964) and Denmark (since 1977) were followed for first hospitalisations for Crohn's disease to 2004. Standardised incidence ratios (SIR) served as relative risks.

RESULTS

Overall, 1655 Crohn's disease cases were observed during 11.1 million person-years of follow-up. Whereas appendectomy before the age of 10 years was not associated with the risk of Crohn's disease (SIR 1.00; 95% CI 0.80-1.25), the overall SIR of developing Crohn's disease was 1.52 (95% CI 1.45-1.59), being highest in the first 6 months (SIR 8.69; 95% CI 7.68-9.84). SIR diminished rapidly thereafter, with the risk of Crohn's disease reaching background levels after 5-10 years for Crohn's disease overall, as well as for Crohn's ileitis, ileocolonic Crohn's disease, Crohn's colitis and other/unspecified Crohn's disease. A long-term increased risk of Crohn's disease up to 20 years after the appendectomy was seen only in appendectomy patients without appendicitis or mesenteric lymphadenitis.

CONCLUSION

The transient increased risk of Crohn's disease after an appendectomy is probably explained by diagnostic bias.

Inflammatory bowel disease: cause and immunobiology

Crohn's disease and ulcerative colitis are idiopathic inflammatory bowel disorders. In this paper, we discuss how environmental factors (eg, geography, cigarette smoking, sanitation and hygiene), infectious microbes, ethnic origin, genetic susceptibility, and a dysregulated immune system can result in mucosal inflammation. After describing the symbiotic interaction of the commensal microbiota with the host, oral tolerance, epithelial barrier function, antigen recognition, and immunoregulation by the innate and adaptive immune system, we examine the initiating and perpetuating events of mucosal inflammation. We pay special attention to pattern-recognition receptors, such as toll-like receptors and nucleotide-binding-oligomerisation-domains (NOD), NOD-like receptors and their mutual interaction on epithelial cells and antigen-presenting cells. We also discuss the important role of dendritic cells in directing tolerance and immunity by modulation of subpopulations of effector T cells, regulatory T cells, Th17 cells, natural killer T cells, natural killer cells, and monocyte-macrophages in mucosal inflammation. Implications for novel therapies, which are discussed in detail in the second paper in this Series, are covered briefly.

Fibrogenesis in Crohn's disease

INTRODUCTION

Over one-third of patients with Crohn's disease (CD) will develop an intestinal stricture and the great majority of these will require at least one surgical procedure. While the pathogenesis of inflammation in CD has been extensively investigated, knowledge of stricture pathogenesis remains limited. The aim of this review is to discuss the current understanding of fibrogenesis in CD and to outline potential directions in research and therapeutics.

METHODS

The electronic literature (January 1966 to May 2006) on CD-associated fibrosis was reviewed. Further references were obtained by cross-referencing from key articles.

RESULTS

CD-associated fibrosis results from chronic transmural inflammation and a complex interplay among intestinal mesenchymal cells, cytokines, and local inflammatory cells. The fibroblast is the key cell type mediating stricture formation. The cytoarchitecure of the bowel wall is altered with disruption of the muscularis mucosa, thickening of the muscularis propria, and deposition of collagen throughout. The cytokine TGF-beta appears critical in this process, acting to increase growth factor and extracellular matrix (ECM) production and dysregulate ECM turnover. Potential therapeutic interventions are likely to concentrate on modulating down-stream targets of TGF-beta.

CONCLUSIONS

Greater understanding of the biology of fibrostenosis is likely to yield significant advances in our ability to care for patients with stricturing CD. Potential dividends of this approach include identification of novel therapeutic targets and biomarkers useful for prognostication and therapeutic monitoring.