It is estimated that there are between 700,000 and 780,000 people with Crohn's disease in the United States as of 2018. Another statistic given by some doctors is 3.2 cases per 1,000 people in the developed countries worldwide. Crohn's disease is primarily a disorder found in adults, most often beginning in late adolescence or the early adult years. The most common age at onset is between 15 and 30 years, although the disorder may begin at any age. Males and females are equally affected. In the United States, the rate of Crohn's disease has been increasing since the early 2000s, especially among those who are African American. Children who are African American often develop more severe disease than children from other racial or ethnic groups, but the reasons for this difference are still unclear.
The rate of Crohn's disease in North America has been increasing since the 1960s, although the reasons for the increase are not well understood. Southern Europe, South America, Africa, and Asia have considerably lower rates of the disease—as low as 0.08–0.5 cases per 100,000 people. Around the world, rates of Crohn's disease are higher in cities than in rural areas, higher in colder than in warmer climates, and higher among people with higher incomes than among lower-income groups.
One argument for the presence of a genetic factor in Crohn's disease is that it runs in some families; people who have a sibling with the disease are 30 times more likely to develop it than the normal population. Crohn's disease is also relatively common among certain ethnic groups, particularly those who are of Jewish and Eastern European origin. A two- to four-fold increase in the frequency of Crohn's disease has been found among the Jewish population in the United States, Europe, and South Africa compared to other ethnic groups.
Crohn's disease can affect any part of the digestive system, but it develops most often in the section of the small intestine just before the large intestine begins. This region is called the ileum, and Crohn's disease that develops there is sometimes called ileitis. The other common site for Crohn's disease is in the colon or large intestine.
Crohn's disease is one of several inflammatory bowel diseases. It can be mistaken for ulcerative colitis, as both these diseases cause watery or bloody diarrhea and abdominal cramps or pain. Ulcerative colitis, however, affects only the layer of cells that line the intestine, forming sores or ulcers on this surface. Crohn's disease begins in these same surface cells, but eats its way inward, damaging all four layers of the intestine and sometimes creating an opening (fistula) through the intestine and into other tissue. Another major difference between Crohn's disease and ulcerative colitis is that Crohn's disease can develop simultaneously in several spots in the digestive tract, resulting in damaged areas with patches of healthy tissue in between. Ulcerative colitis, on the other hand, spreads uniformly across an area. Crohn's disease is somewhat treatable, but not curable, and can cause many complications beyond the digestive system. Eventually, the walls of the intestine thicken, and blockages may occur that can be corrected only by surgery.
Another subtype of Crohn's disease is called stricturing disease. Stricture is the medical term for an abnormal narrowing of a hollow organ like the bowel. In stricturing disease, the inflammation and swelling of tissue inside the bowel leads to changes in the size of the patient's stools and eventual blockage of the intestinal passages. Severe abdominal cramping is often an indication of stricturing disease, as are nausea and vomiting.
Risk factors for Crohn's disease include a family history of the disorder, a history of heavy smoking, and Eastern European Jewish ethnicity.
At one time, researchers thought that stress and diet caused Crohn's disease, particularly high-fat foods. Now researchers know that these are not causative factors, although both stress and diet can worsen symptoms in people who already have the disease. What researchers do know is that Crohn's disease is caused by an inappropriate immune-system reaction that affects cells in the digestive tract. Beyond that, the reasons some people develop the disease are not clear, although smoking does increase the risk, especially among people with a family history.
Some medications have been suggested to increase risk (for example, antibiotics and nonsteroidal anti-inflammatory drugs [NSAIDs]), but the evidence is not clear.
There is almost certainly an inherited component that predisposes some people to the disease. Individuals who are blood relatives of a parent, sibling, or child with Crohn's disease are 30 times more likely to develop the disease than the general population. Scientists believe multiple genes are involved in development of the disease. More than genetics, however, determines who gets Crohn's disease, because only about 44% of identical twins both develop the disease, and according to 2018 research, about 80% of patients diagnosed with Crohn's do not have any of the genetic mutations linked to the disease. Researchers have found genetic mutations in many, but not all, patients with Crohn's disease, but they do not yet have a clear understanding of the effects of any of these mutations.
The current theory is that interactions among genes, environment, health, and body chemistry affect a person's risk of developing Crohn's disease. When foreign materials (antigens) enter the body, the immune system produces antibodies, which are proteins that neutralize the foreign invader. One theory is that a foreign organism or material stimulates an immune system response in the digestive system, and then, through an error in genetic control, the response cannot be “turned off.” A second theory suggests that the cells of the immune system mistake beneficial bacteria, food, or some other substance that is normally present in the digestive tract as a foreign substance and make antibodies against this material. Either way, an inappropriate immune system response occurs that appears to be the root cause of the symptoms people with Crohn's disease experience.
Symptoms of Crohn's disease vary, depending on the location of the damaged cells and the length of time the individual has had the disease. Symptoms can be mild or severe. They can develop suddenly or gradually, and they may improve or even disappear and then worsen many times throughout an individual's life. Some people may have only occasional episodes of diarrhea, for example, while others may have 20–30 bowel movements in a single day that interfere with sleep, work, school, or other activities. In general, symptoms can be divided into those that affect the digestive tract and those that affect the rest of the body.
The most common symptoms that affect the digestive tract are:
Symptoms of Crohn's disease also appear in other systems in the body. Some are the result of infection when fistulae develop. Others come from poor absorption of nutrients in the intestine over a long period. Some symptoms that occur outside the digestive tract include:
Several gastrointestinal diseases can resemble the more common symptoms of Crohn's disease. These include ulcerative colitis, irritable bowel syndrome, intestinal parasites, and intestinal obstruction. Thus in diagnosing Crohn's disease, it is important to distinguish it from other disorders. Normally, the physician will begin with recording a medical and family history, and performing standard blood and stool tests. The next step toward diagnosis is usually doing imaging studies, most often an upper GI series. An upper GI series, sometimes called a barium swallow, includes x-rays of the esophagus, stomach, and upper part of the intestine. The patient drinks a solution of a barium compound to improve contrast on the x-rays, thus the name barium swallow.
An upper endoscopy or a colonoscopy is another routine part of the diagnostic procedure. An upper endoscopy is done if abnormalities appear to be in the esophagus, stomach, or upper part of the small intestine (the duodenum). A colonoscopy uses the same technique to examine the colon. These procedures are usually performed in a doctor's office or an outpatient clinic under light sedation. A tube called an endoscope is inserted down the throat and into the stomach and duodenum, or up through the rectum and into the colon. At the end of the endoscope is a tiny camera that allows the doctor to see whether there is damage to the cells lining the digestive tract. During this procedure, the doctor also removes small tissue samples (biopsies) to look for abnormal cells under the microscope.
No cure is available for Crohn's disease. Treatment is aimed at controlling inflammation, preventing vitamin and mineral deficiencies, and relieving symptoms. Treatment options include a combination of drugs, biologic therapies, nutritional supplements, and surgery.
Individuals with mild to moderate Crohn's disease are usually treated first with such anti-inflammatory drugs as sulfasalazine (Azulfidine) or mesalamine (Asacol, Rowasa, Canasa). Individuals with moderate to severe Crohn's disease often are prescribed corticosteroid drugs. Prednisone (Deltasone, Orasone, Meticorten) is often the corticosteroid of choice. These drugs have significant side effects, however, and cannot be used for long-term suppression of symptoms. Antibiotics are used to treat infection that may develop, for example, from fistula formation. The antibiotics most often used are metronidazole and ciprofloxacin.
Biologic therapies use human-made antibodies to fight disease. Infliximab (Remicade) is a laboratorymade antibody that blocks the production of an immune system factor that causes inflammation. This treatment is relatively new, but appears to have a good success rate for relieving symptoms. Additional biologic therapies for Crohn's disease were approved by the Food and Drug Administration; they include adalimumab (Humira), natalizumab (Tysabri), and certolizumab pegol (Cimzia).
Several investigational drugs for the treatment of Crohn's disease are undergoing clinical trials in Europe, the United States, and Japan. These drugs are presently identified only as E6011, ABT-494, AMG 161, and MT-1303.
Medical treatment becomes less effective over time. When medical treatment fails, or if the intestine becomes so thickened that blockages occur, surgery may be necessary. About 80% of all people with Crohn's disease eventually require surgery. Surgery to remove part of the intestine usually relieves symptoms for a few years, but surgery is not a cure for Crohn's disease, and symptoms almost always return within a few years. In cases in which the disease is located in the large intestine (colon), the surgeon may have to remove the entire colon in a procedure called a colostomy. In this procedure, an opening called a stoma is made in the wall of the abdomen and a portion of the remaining colon is attached to the stoma. The person's bodily wastes pass through the stoma and are collected in a special bag attached to the outside of the body.
Although such alternative therapies as acupuncture, hypnosis, fish oil, and herbal remedies have been tried in patients with Crohn's disease, no evidence indicates that these treatments are effective.
People with Crohn's disease tend to have vitamin and mineral deficiencies because damage to the lining of the intestine interferes with the absorption of nutrients, and chronic diarrhea hastens the loss of other nutrients. These deficiencies can cause specific disorders in other parts of the body. In addition, children with Crohn's disease also may need special highcalorie, high-nutrient liquid supplements to maintain normal growth. A nutritionist consulting with the patient's gastroenterologist can help determine the best diet and supplements to prevent nutritional deficiencies.
Although eating certain foods does not cause Crohn's disease, specific foods can worsen symptoms. Many people with Crohn's disease become lactoseintolerant and must limit or eliminate dairy products from their diet. Alcohol, high-fiber foods (such as popcorn, crackers, etc.), and spicy foods can worsen diarrhea and abdominal cramping. Individuals must be alert to the effect of food on their symptoms until they can decide which foods to avoid.
The Academy of Nutrition and Dietetics offers some suggestions for healthful eating for patients with Crohn's disease:
Crohn's disease can be very disruptive. Individuals may be reluctant to travel or attend concerts or sporting events because frequent diarrhea requires them to be near a toilet. The Crohn's and Colitis website suggests that patients with the disease carry a special restroom request card that allows them to ask discreetly for access to employees-only or other restricted restrooms. Support groups, either on the Internet or in person, help many people adjust to the difficulties of living with this chronic disease. Other people find that psychotherapy (talk therapy), guided by a psychologist or psychiatrist experienced in the stresses of chronic illness, can help them make a better adjustment to life with Crohn's disease.
Crohn's disease is a lifelong disease. Symptoms may improve or disappear for periods, but overall, symptoms and complications tend to worsen. Most people with Crohn's disease eventually need surgery as the disease becomes less and less responsive to medication. Living with Crohn's disease can be a difficult challenge that requires major lifestyle adjustments. The chance of a shortened life span or serious complications increase with the duration of the illness; patients with Crohn's disease also have an increased risk of colorectal cancer. The disease itself, however, is rarely fatal.
Crohn's disease cannot be prevented as of 2018.
See also Digestive diseases ; Gut microbiota ; Inflammatory bowel disease ; Irritable bowel syndrome ; Malnutrition ; Prebiotics and probiotics ; Ulcers .
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Rebecca J. Frey, PhD