Crohn's disease overview

# Overview
Crohn's disease is a chronic, episodic, inflammatory bowel disease (IBD) that affects the entire wall of the bowel or intestines. Crohn's disease can affect any part of the gastrointestinal tract from mouth to anus; as a result, the symptoms of Crohn's disease vary among afflicted individuals. The disease is characterized by areas of inflammation with areas of normal lining between in a symptom known as skip lesions. The main gastrointestinal symptoms are abdominal pain, diarrhea (which may be bloody or the blood may not be seen by the naked eye), constipation, vomiting, weight loss or weight gain.  Crohn's disease can also cause complications outside of the gastrointestinal tract such as skin rashes, arthritis, and inflammation of the eye. Diagnosis of Crohn's disease requires an endoscopic evaluation of the colon followed by biopsy. Treatment for Crohns disease depends on the location and severity of disease, complications, and the persons response to previous medical treatments when treated for recurring symptoms. 

# Historical Perspective
The first case of Crohn's disease was reported by Combe and Sanders, physicians of royal college London in 1806. The first detailed explanation of inflammatory bowel disease (IBD) was done by Giovanni Battista Morgagni and by Scottish physician T. Kennedy Dalziel.

# Classification
Crohn's disease almost invariably affects the gastrointestinal tract. As a result, most gastroenterologists classify the disease by the affected areas and behavior of disease as it progresses. The disease can attack any part of the digestive tract, from mouth to anus.

# Pathophysiology
Genetic and environmental factors play a key role in the pathogenesis of Crohn's disease. Mutations in the CARD15 gene (also known as the NOD2 gene) are associated with Crohn's disease and with susceptibility to certain phenotypes of disease location and activity. Environmental factors include autoimmune disease and dysregulated immune response to commensal bacteria. Characteristic features of the pathology that point toward Crohn's disease are transmural pattern of inflammation and skip lesions. Under microscopy granulomas are seen, which are aggregates of macrophage derivatives known as giant cells, are found in 50% of cases and are most specific for Crohn's disease.

# Causes
Several theories exist about what causes Crohns disease, but none have been proven. The human immune system is made from cells and different proteins that protect people from infection. The most popular theory is that the bodys immune system reacts abnormally in people with Crohns disease, mistaking bacteria, foods, and other substances for being foreign. The immune systems response is to attack these invaders. During this process, white blood cells accumulate in the lining of the intestines, producing chronic inflammation, which leads to ulcerations and bowel injury.

# Differentiating Crohn's Disease from Other Diseases
The most common disease that mimics the symptoms of Crohn's disease is ulcerative colitis, as both are inflammatory bowel diseases that can affect the colon with similar symptoms. It is important to differentiate these diseases, since the course of the diseases and treatments may be different. In some cases, however, it may not be possible to tell the difference, in which case the disease is classified as indeterminate colitis.

# Epidemiology and Demographics
The incidence of Crohn's disease has been ascertained from population studies in Norway and the United States and is similar at 6 to 7.1 per 100,000 people. Prevalence estimates for Northern Europe have ranged from 2748 per 100,000. Crohn's disease tends to present initially in the teens and twenties, with another peak incidence in the fifties to seventies, although the disease can occur at any age. Crohn's disease affects between 400,000 and 600,000 people in North America. Crohn's disease has a bimodal distribution in incidence as a function of age. There is no association with gender, social class or occupation.

# Risk Factors
Common risk factors in the development of crohns disease include white ancestry, age between 15-40 or 60-80 years, family history of crohns disease and cigarette smoking.

# Natural History, Complications and Prognosis
Crohn's disease increases the risk of cancer in the area of inflammation. For example, individuals with Crohn's disease involving the small bowel are at higher risk for small intestinal cancer. Similarly, people with Crohn's colitis have a relative risk of 5.6 for developing colon cancer.There are many complications that can come with Crohn's disease like: obstructions, abscesses, free perforation, and hemorrhage. With treatment, most people achieve a healthy life, and the mortality rate for the disease is low.

# Diagnosis

## History and Symptoms
Many people with Crohn's disease have symptoms for years prior to the diagnosis. The usual onset is between 15 and 30 years of age but can occur at any age. Abdominal pain may be the initial symptom of Crohn's disease. Crohn's disease, like many other chronic, inflammatory diseases, can cause a variety of systemic symptoms. In addition to systemic and gastrointestinal involvement, Crohn's disease can affect many other organ systems

## Physical Examination
Physical examination findings in crohn's disease include fever, fatigue, weakness, bloody diarrhea, abdominal pain, hypotension and tachycardia.

## Laboratory Findings
The laboratory findings in a patient with Crohn's disease include anemia, low albumin, elevated ESR, elevated serum alkaline phosphatase, deranged LFTs and electrolyte abnormalities.

## Abdominal X Ray
Xray of the abdomen is not required for the diagnosis of Crohn's disease. Xray may sometimes be one in case colitis is suspected. Xray is normal in mild to moderate disease and can show dilation and/or "thumb printing sign" in fulminant cases.

## CT Scan
CT and MRI scans are useful for evaluating the small bowel with enteroclysis protocols. Findings include skip lesions, bowel wall thickening, surrounding inflammation, abscess, and fistulae.

## MRI Scan
Magnetic resonance imaging (MRI) is another option for imaging the small bowel as well as looking for complications, though it is more expensive and less readily available.

## Other Diagnostic Studies
The diagnosis of Crohn's disease can sometimes be challenging, and a number of tests are often required to assist the physician in making the diagnosis. Sometimes even with all the tests the Crohn's does not show itself. A colonoscopy has about a 70% chance of showing the disease and the rest of the tests go down in percentage.  Disease in the small bowel can not be seen through some of the regular tests; for example, a colonoscopy can't get there.

## Other Imaging Findings
Other imaging findings for Crohn's disease can be seen by the help of barium enema. Barium enema may show ulcerations and skip lesions. Barium enema must be avoided in severe cases as it can lead to the manifestation of toxic megacolon.

# Treatment

## Medical Therapy
Treatment may include drugs, nutrition supplements, surgery, or a combination of these options. The goals of treatment are to control inflammation, correct nutritional deficiencies, and relieve symptoms likeabdominal pain, diarrhea, and rectal bleeding. At this time, treatment can help control the disease by lowering the number of times a person experiences a recurrence, but there is no cure. Treatment for Crohns disease depends on the location and severity of disease, complications, and the persons response to previous medical treatments when treated for recurring symptoms. Some people have long periods of remission, sometimes years, when they are free of symptoms. However, the disease usually recurs at various times over a persons lifetime. This changing pattern of the disease means one cannot always tell when a treatment has helped. Predicting when a remission may occur or when symptoms will return is not possible.

## Surgery
Two-thirds to three-quarters of patients with Crohns disease will require surgery at some point in their lives. Surgery becomes necessary when medications can no longer control symptoms. Surgery is used either to relieve symptoms that do not respond to medical therapy or to correct complications such as blockage, perforation, abscess, or bleeding in the intestine. Surgery to remove part of the intestine can help people with Crohns disease, but it is not a cure. Surgery does not eliminate the disease, and it is not uncommon for people with Crohns Disease to have more than one operation, as inflammation tends to return to the area next to where the diseased intestine was removed.

## Prevention
Smoking cessation is the only lifestyle modification shown to have an effect on the prevention of recurrence in Crohn's disease. There is no specific guidelines for colorectal cancer screening in patients with CD, it is widely accepted to perform surveillance colonoscopy every 1 to 2 years, starting at 8 years after establishing the diagnosis of pancolitis and 15 years in the case of left-sided colitis.