So What Is Crohn’s Disease and Ulcerative Colitis? Pathophysiology of Crohn’s Disease and Ulcerative Colitis




© Springer International Publishing Switzerland 2015
Daniel J. Stein and Reza Shaker (eds.)Inflammatory Bowel Disease10.1007/978-3-319-14072-8_3


3. So What Is Crohn’s Disease and Ulcerative Colitis? Pathophysiology of Crohn’s Disease and Ulcerative Colitis



Viveksandeep Thoguluva Chandrasekar1 and Nanda Venu2  


(1)
Internal Medicine, SUNY Upstate Medical University, Syracuse, New York, USA

(2)
Digestive Diseases Institute, Virginia Mason Medical Center, Seattle, WA, USA

 



 

Nanda VenuConsultant Gastroenterologist

Email: nanda.venu@virginiamason.org


Keywords
Inflammatory bowel diseaseCrohn’s diseaseUlcerative colitisGeneticsImmune systemEnvironmentIntestinal microbiomeExtraintestinal manifestations



Suggested Response to the Patient


Crohn’s disease and ulcerative colitis make up a pair of diseases called inflammatory bowel disease. We do not fully understand the exact cause of IBD, but basically it is what we call an autoimmune disease. This means that your immune system, which normally fights infections, is attacking your intestines causing ulcers and sores inside your intestines leading to your symptoms. The cause of Crohn’s disease and ulcerative colitis is a result of several factors that we are just now starting to understand. It is most likely a result of several factors including genetics, environmental factors, immune system defects, and interactions with gut bacteria. Ultimately it is not one single factor that caused your inflammatory bowel disease, but rather an interaction of several factors that has caused your IBD.


Brief Review of the Literature


Inflammatory bowel disease (IBD) is an immune-mediated disease affecting the gastrointestinal tract. There are two main types of IBD, ulcerative colitis (UC) and Crohn’s disease (CD). Crohn’s disease (CD) can affect any part of the gastrointestinal tract from the mouth to anus, while ulcerative colitis (UC) typically affects only the large intestines. These are mainly diseases of the Western world, suggesting that the lifestyle and dietary factors play an important role in these disorders. But on closer look, they are much more complex in nature with multiple factors such as heredity also playing a part.


Incidence and Prevalence


The incidence of IBD is increasing worldwide. The largest number of IBD patients live in North America. IBD affects nearly 1.4 million people in the USA. The incidence of ulcerative colitis ranges from 2.2 to 19.2 cases per 100,000 person years and that of CD 3.1–20.2 cases per 100,000 person years. The prevalence of UC is 238 per 100,000 and CD is 201 per 100,000 population [1].


Symptoms


Most common symptoms of IBD are nausea, vomiting, abdominal pain, diarrhea, pain or discomfort in the rectum, urgency and blood mixed with mucus in the stools. Other symptoms include night sweats, fever, chills and weight loss. Extraintestinal manifestations such as arthralgia, skin lesions like pyoderma gangrenosum and eye involvement (iritis/uveitis) can also occur in IBD.


Diagnosis


Colonoscopy or endoscopy with biopsy is often needed to make the diagnosis. Colonoscopy is only 70 % effective in CD as the lesions can involve other areas of the GI tract such as the small bowel. In these situations, modalities like capsule endoscopy, CT scan and MRI scans are needed to make a diagnosis.


Pathophysiology


To understand the pathophysiology of these disorders, an understanding of the disease process is essential as multiple factors alone or in combination may play a role in the causation of both CD and UC. These factors include:

1.

Genetic factor

 

2.

Immune system

 

3.

Intestinal microbiome

 

4.

Environment

1.

Genetic factors:

The first IBD-associated gene identified was the NOD2 gene within the IBD1 gene locus in 2001. Since then extensive genome-wide analysis studies have identified more than 160 genes linked to IBD and these numbers are constantly growing. Familial clustering and racial and ethnic differences also suggest a role for genetics in IBD. Ten to twenty percentage of the affected individuals have a family history of IBD. Caucasians have the highest rates of IBD. Ethnic predisposition is also a feature with highest rates of disease in the Jewish population especially the Ashkenazi Jews. All these associations suggest a role for genetic factors in the development of IBD [2].

 

2.

Immune system:

The immune system has three basic components, which must act in coordination to protect the human body from microbes and foreign particles called antigens. The immune system consists of:

(a)

The mucosal lining or the epithelium of the GI tract. In addition to being a physical barrier, the epithelium also secretes mucus and other anti-bacterial substances. This in combination with intestinal peristalsis helps in clearing harmful microbes.

 

(b)

The innate immune system comprising mainly of white blood cells (neutrophils, eosinophils, basophils and macrophages) and the natural killer cells. These cells have receptors which bind to specific receptors on the microbes or their products to neutralize them.

 

(c)

The adaptive (memory) immune system comprises of the B lymphocytes, T lymphocytes and the dendritic cells. The B lymphocytes secrete substances called antibodies and the T lymphocytes on interaction with the antigens elicit immune response through substances called cytokines. The dendritic cells help T and B lymphocytes recognize harmful antigens.

 




  • It is hypothesized that a dysfunction in the immune system contributes to IBD as follows:


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Jun 5, 2017 | Posted by in GASTROENTEROLOGY | Comments Off on So What Is Crohn’s Disease and Ulcerative Colitis? Pathophysiology of Crohn’s Disease and Ulcerative Colitis

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