5.5 Additional Reading:Crohn’s Disease
Definition
Crohn’s disease is a type of inflammatory bowel disease（IBD），resulting in swelling and dysfunction of the intestinal tract.
Epidemiology
The incidence of Crohn’s disease is thought to be similar in Europe but lower in Asia and Africa.It also has a higher incidence in Ashkenazi Jews and smokers.Crohn’s disease begins most commonly in people in their teens and 20s，and people in their 50s through to their 70s.It is rarely diagnosed in early childhood.It usually affects female children more severely than males.However，only slightly more women than men have Crohn’s disease.Parents，siblings or children of people with Crohn’s disease are 3 to 20 times more likely to develop the disease.
The incidence of Crohn’s disease is increasing in Europe and in newly industrialized countries.For example，in Brazil，there has been an annual increase of 11%in the incidence of Crohn’s disease since 1990.
Signs and symptoms
Because of the“patchy”nature of the gastrointestinal disease and the depth of tissue involvement，initial symptoms can be more subtle than those of ulcerative colitis.People with Crohn’s disease experience chronic recurring periods of flare-ups and remission.Abdominal pain is a common initial symptom of Crohn’s disease，especially in the lower right abdomen.It is often accompanied by diarrhea，which may or may not be bloody.Inflammation in different areas of the intestinal tract can affect the quality of the feces.Ileitis typically results in large-volume，watery feces，while colitis may result in a smaller volume of feces of higher frequency.Fecal consistency may range from solid to watery.In severe cases，an individual may have more than 20 bowel movements per day，and may need to awaken at night to defecate.Visible bleeding in the feces is less common in Crohn’s disease than in ulcerative colitis，but is not unusual.Bloody bowel movements are usually intermittent，and may be bright or dark red in color.In severe Crohn’s colitis，bleeding may be copious.Flatulence，bloating，and abdominal distension are additional symptoms and may also add to the intestinal discomfort.
Like many other chronic，inflammatory diseases，Crohn’s disease can cause a variety of systemic symptoms.Among children，growth failure is common.Many children are first diagnosed with Crohn’s disease based on inability to maintain growth.As it may manifest at the time of the growth spurt in puberty，up to 30%of children with Crohn’s disease may have retardation of growth.Fever may also be present，though fevers greater than 38.5℃（101.3℉）are uncommon unless there is a complication such as an abscess.Among older individuals，Crohn’s disease may manifest as weight loss，usually related to decreased food intake，since individuals with intestinal symptoms from Crohn’s disease often feel better when they do not eat and might lose their appetite.People with extensive small intestine disease may also have malabsorption of carbohydrates or lipids，which can further exacerbate weight loss.
Causes(https://www.daowen.com)
While the exact cause is unknown，Crohn’s disease seems to be due to a combination of environmental factors and genetic predisposition.Crohn’s is the first genetically complex disease in which the relationship between genetic risk factors and the immune system is understood in considerable detail.Each individual risk mutation makes a small contribution to the overall risk of Crohn’s（approximately 1∶200）.The genetic data and direct assessment of immunity indicate a malfunction in the innate immune system.In this view，the chronic inflammation of Crohn’s is caused when the adaptive immune system tries to compensate for a deficient innate immune system.
Diagnosis
A colonoscopy is the best test for making the diagnosis of Crohn’s disease，as it allows direct visualization of the colon and the terminal ileum，identifying the pattern of disease involvement.On occasion，the colonoscopy can travel past the terminal ileum，but it varies from person to person.During the procedure，the gastroenterologist can also perform a biopsy，taking small samples of tissue for laboratory analysis，which may help confirm a diagnosis.As 30%of Crohn’s disease involves only the ileum，cannulation of the terminal ileum is required in making the diagnosis.Finding a patchy distribution of disease，with involvement of the colon or ileum，but not the rectum，is suggestive of Crohn’s disease.A“cobblestone”-like appearance is seen in approximately 40%of cases of Crohn’s disease upon colonoscopy，representing areas of ulceration separated by narrow areas of healthy tissue.
CT and MRI scans are useful for looking for intraabdominal complications of Crohn’s disease，such as abscesses，small bowel obstructions，or fistulae.MRI is an option for imaging the small bowel as well as looking for complications，though it is more expensive and less readily available.MRI techniques such as diffusion-weighted imaging and high-resolution imaging are more sensitive in detecting ulceration and inflammation than CT.
Management
The treatment of patients with Crohn’s disease depends on disease severity，patient risk stratification，patient preference，and clinical factors，including age of onset and penetrating complications，and includes treatment with steroids，monoclonal antibody therapies，immunomodulators，and surgery.Vaccinations to prevent infections，such as influenza，pneumonia，and herpes zoster，are important components of health maintenance for patients with Crohn’s disease，although live vaccines are contraindicated for patients receiving immune suppression therapy.Crohn’s disease may result in anxiety or mood disorders，especially in young people who may have stunted growth or embarrassment from fecal incontinence.Counselling as well as antidepressant or anxiolytic medication may be helpful for some cases.Physicians should be familiar with the advantages and disadvantages of each therapy to best counsel their patients.
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Task 9 Identify the word elements and define the meaning of each medical term.
