Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is among the mostcommon diseases of gastrointestinal system and includestwo chronic relapsing diseases: ulcerative colitisand Crohn s disease. These diseases are the result of dysregulatedimmune response to the gastrointestinal bacteriain people with genetic background (1). There areclinical and microscopic differences between ulcerativecolitis and Crohn s disease in terms of pattern of intestinalinvolvement and involvement of layers of bowel.Although these differences make the differentiation ofthe two mentioned diseases possible, there is also grayzone; meanwhile, indeterminate colitis (recently knownas IBD of undetermined etiology, IBDU) includes 10-15% ofthe cases. Ulcerative colitis generally starts in the rectumand spreads continuously to the proximal areas. Inflammationis limited to mucosa and sub- mucosa and diffuseand uniform involvement of the affected area. The characteristichistological finding for this disease is definedas destruction and irregularity of colon crypts. Crohn sdisease affects most of the gastrointestinal system fromthe mouth to the anus. The characteristic for this diseaseis the existence of skip areas and transmural involvement.Granuloma, fissure ulcer and several lymphoid folliclesare evident in histology. There may be three factorsleading to ulcerative colitis and Crohn s disease:- Genetic background,- Immune response, that is not able to down- regulatethe dysregulated immune reaction,- Changes in response to intestinal bacteria,Totally, these factors result in persistent inflammationin gastrointestinal system. Other environmental factorsincluding smoking (especially in Crohn s disease) andnutrition play an important role in this regard. The geneticbackground is considered as an effective factor inresponses of the host to the invading bacteria. Autophagygenes, nucleotide oligomerization domain 2, NOD2(now called CARD15) and interleukin-23-type 17 helper Tcell (Th17) pathways are among the main discussed geneticfactors (1, 2). CARD15 is a polymorphic gene playingan important role in both innate immune system andprogression of the disease (2). In addition, familial caseshighlight the role of genetic factor particularly in Crohn sdisease. However, environmental factors and genetics areeffective in both incidence of the disease and characteristicsof the disease. Some of genetic factors such as CARD15and ATG16L1 are Crohn’s disease specific factors; whereas,some others like 1L23 signaling pathway are common inboth diseases. It is estimated that the known genetic factorscomprise only 20% of the involved genetic factors(1). Diagnosis of inflammatory bowel diseases is basedon the histological, colonoscopic and clinical findings.One of the most important issues in IBD is list of differentialdiagnoses which is vitally important either in termsof clinical approach or histological approach. Developinga good relation between clinical physician, radiologist,colonoscopic and pathologic findings may lead toa proper diagnosis in most cases. However, a full list ofdifferential diagnoses should be considered including:Gastrointestinal infections, functional diarrhea, irritablebowel syndrome, Behcet’s disease, ischemia, AIDS, NSAIDuse, diverticulitis, Celiac disease, malignancy, tuberculosisand eosinophilic gastroenteritis. One of the mainpoints about diagnosis of IBD (especially in crohn’s disease)in some parts of the world like Middle East region isconsidering tuberculosis as a differential diagnosis. PPDtest, interferon- gamma based tests and PCR based moleculartests are among the associated diagnostic studies.Laboratory tests have an important role in diagnosis ofIBD; however, there are no specific tests in this regard.Some tests such as CBC (assessment of anemia), VitaminB12 level (especially in terminal ileum involvement), andfolate level (especially in treatment by sulfasalazine) areused in management of these patients. Nowadays, oneof the tests being discussed is measurement of fecal calprotectinas bowel inflammation index. Combined test ofpANCA and ASCA are being used for differentiating thesetwo diseases but there is no general agreement on it.Perideaux et al. have conducted a comprehensive studyabout serologic factors of pANCA, ASCA, Anti-OmpC, anti-CBir1, anti-12, ALCA, ACCA, AMCA, anti-L and anti-C (3). Oneof the important applications of serologic factors is in diagnosisof indeterminate colitis. Another factor in examinationof IBD patients is considering CMV infection especiallyin patients with steroid-resistance.

Keywords:

Inflammatory Bowel Disease , Digestive System