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Overview of Inflammatory Bowel Disease
Inflammatory bowel disease (IBD), which includes Crohn disease and ulcerative colitis (UC), is a relapsing and remitting condition characterized by chronic inflammation at various sites in the GI tract, which results in diarrhea and abdominal pain.
Inflammation results from a cell-mediated immune response in the GI mucosa. The precise etiology is unknown, but evidence suggests that the normal intestinal flora trigger an abnormal immune reaction in patients with a multifactorial genetic predisposition (perhaps involving abnormal epithelial barriers and mucosal immune defenses). No specific environmental, dietary, or infectious causes have been identified. The immune reaction involves the release of inflammatory mediators, including cytokines, interleukins, and TNF.
Although Crohn disease and UC are similar, they can be distinguished in most cases (see Table: Differentiating Crohn Disease and Ulcerative Colitis). About 10% of colitis cases are not initially distinguishable and are termed unclassified; if a surgical pathologic specimen cannot be classified, it is called indeterminate colitis. The term colitis applies only to inflammatory disease of the colon (eg, ulcerative, granulomatous, ischemic, radiation-induced, infectious). Spastic (mucous) colitis is a misnomer sometimes applied to a functional disorder, irritable bowel syndrome.
Differentiating Crohn Disease and Ulcerative Colitis
Inflammatory bowel disease affects people of all ages but usually begins before age 30, with peak incidence from 14 to 24. IBD may have a second smaller peak between ages 50 and 70; however, this later peak may include some cases of ischemic colitis.
IBD is most common among people of Northern European and Anglo-Saxon origin and is 2 to 4 times more common among Ashkenazi Jews than non-Jewish whites from the same geographic location. The incidence is lower in central and southern Europe and lower still in South America, Asia, and Africa. However, the incidence is increasing among blacks and Latin Americans living in North America. Both sexes are equally affected. First-degree relatives of patients with IBD have a 4- to 20-fold increased risk; their absolute risk may be as high as 7%. Familial tendency is much higher in Crohn disease than in UC. Several gene mutations conferring a higher risk of Crohn disease (and some possibly related to UC) have been identified.
Cigarette smoking seems to contribute to development or exacerbation of Crohn disease but decreases risk of UC. Appendectomy done to treat appendicitis also appears to lower the risk of UC. NSAIDs may exacerbate IBD. Oral contraceptives may increase the risk of Crohn disease. Some data suggest that perinatal illness and the use of antibiotics in childhood may be associated with an increased risk of IBD.
Crohn disease and UC both affect organs other than the intestines. Most extraintestinal manifestations are more common in UC and Crohn colitis than in Crohn disease limited to the small bowel. Extraintestinal manifestations of inflammatory bowel disease are categorized in 3 ways:
1. Disorders that usually parallel (ie, wax and wane with) IBD flare-ups: These disorders include peripheral arthritis, episcleritis, aphthous stomatitis, erythema nodosum, and pyoderma gangrenosum. Arthritis tends to involve large joints and be migratory and transient. One or more of these parallel disorders develops in more than one third of patients hospitalized with IBD.
2. Disorders that are clearly associated with IBD but appear independently of IBD activity: These disorders include ankylosing spondylitis, sacroiliitis, uveitis, and primary sclerosing cholangitis. Ankylosing spondylitis occurs more commonly in IBD patients with the HLA-B27 antigen. Most patients with spinal or sacroiliac involvement have evidence of uveitis and vice versa. Primary sclerosing cholangitis, which is a risk factor for cancer of the biliary tract, is strongly associated with UC or Crohn colitis. Cholangitis may appear before or concurrently with the bowel disease or even 20 yr after colectomy. Liver disease (eg, fatty liver, autoimmune hepatitis, pericholangitis, cirrhosis) occurs in 3 to 5% of patients, although minor abnormalities in liver function tests are more common. Some of these conditions (eg, primary sclerosing cholangitis) may precede IBD by many years and, when diagnosed, should prompt an evaluation for IBD.
3. Disorders that are consequences of disrupted bowel physiology: These disorders occur mainly in severe Crohn disease of the small bowel. Malabsorption may result from extensive ileal resection and cause deficiencies of fat-soluble vitamins, vitamin B12, or minerals, resulting in anemia, hypocalcemia, hypomagnesemia, clotting disorders, and bone demineralization. In children, malabsorption retards growth and development. Other disorders include kidney stones from excessive dietary oxalate absorption, hydroureter and hydronephrosis from ureteral compression by the intestinal inflammatory process, gallstones from impaired ileal reabsorption of bile salts, and amyloidosis secondary to long-standing inflammatory and suppurative disease.
Thromboembolic disease may occur as a result of multiple factors in all 3 categories.
Biologic agents (anticytokine drugs)
Several classes of drugs are helpful for IBD. Details of their selection and use are discussed under each disorder.
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