Crohn's Disease

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Crohn's Disease

Definition

Crohn's disease is a type of inflammatory bowel disease (IBD) caused by inflammation along any portion of the alimentary canal (the mouth to the anus).

Description

Although Crohn's disease may involve any part of the alimentary canal, it most commonly affects the small intestine. There is evidence that the inflammation is an autoimmune response—when products of the immune system attack the body itself instead of attacking a foreign substance such as a virus or bacteria.

The part of the small intestine most commonly affected is the last part of the ileum, also known as the terminal ileum. The colon (large intestine ) is less commonly involved. Inflammation may also occur in other areas of the alimentary canal, less frequently affecting the mouth, esophagus, or stomach.

Crohn's disease differs from ulcerative colitis, the other major type of IBD, in the following ways:

The inflammation of Crohn's disease may be discontinuous, meaning that areas of involvement in the intestine may be separated by normal, unaffected segments of intestine. The affected areas are called "regional enteritis," while the normal areas are called "skip areas."
The inflammation of Crohn's disease is transmural; this means it affects all the layers of the intestinal wall, while ulcerative colitis affects only the lining of the intestine.
Ulcerative colitis does not usually involve the small intestine; in rare cases it involves the terminal ileum (so-called "backwash" ileitis).

In addition to inflammation, Crohn's disease causes ulceration. These ulcers occur because the inflammation has caused areas of tissue destruction.

Crohn's disease may be diagnosed at any age, although most diagnoses are made between the ages 15-35. About 0.02-0.04% of the population suffers from this disorder. It affects equal numbers of males and females. Whites are more frequently affected than other racial groups, and people of Jewish origin are between three and six times more likely to suffer from IBD. IBD runs in families; an IBD patient has a 20% chance of having other relatives who are fellow sufferers.

Crohn's disease is a chronic disorder. Though symptoms can be effectively controlled, patients are not completely cured of the underlying disease.

Causes and symptoms

The cause of Crohn's disease is unknown. No infectious agent has been positively identified as the cause of Crohn's disease. Some researchers have theorized that a certain bacterium may have originally been responsible for triggering the immune system, resulting in the abnormal activation of the immune system in the intestines that occurs in Crohn's disease.

Symptoms of Crohn's disease depend on which section of the alimentary canal is affected. Symptoms may include diarrhea, fever, abdominal pain, loss of appetite, weight loss, and fatigue. Some patients experience severe pain that mimics appendicitis. Unlike patients with ulcerative colitis, it is rare for patients with Crohn's disease to notice blood in their bowel movements. Because Crohn's disease severely limits the ability of the affected intestine to absorb the nutrients from food, a patient may have signs of malnutrition, depending on the amount of intestine affected and the duration of the disease.

The combination of severe inflammation, ulceration, and scarring that occurs in Crohn's disease can result in serious complications, including intestinal obstruction, intra-abdominal abscess formation, and fistula formation.

An obstruction is a mechanical blockage in the intestine. This obstruction, called a stricture, prevents the intestinal contents from passing beyond the point of the blockage. The intestinal contents "back up," resulting in constipation, vomiting, and intense pain. Although rare in Crohn's disease (because of the increased thickness of the intestinal wall due to swelling and scarring), severe bowel obstruction can result in an intestinal wall perforation (a hole in the intestine). A hole in the intestinal wall would allow the intestinal contents, containing bacteria, to enter the abdominal cavity, causing a severe, life-threatening infection known as peritonitis.

Abscess formation is the development of a walled-off pocket of pus. A patient with an abscess in the abdomen will have fever, abdominal pain, and may have a lump or mass that can be palpated (felt) through the wall of the abdomen.

Fistula formation is the formation of abnormal channels. These channels may connect one loop of the intestine to a neighboring section of intestine. Fistulas may connect an area of the intestine to the vagina or urinary bladder, or may drain an area of the intestine through the skin. Abscesses and fistulas commonly affect the area around the anus and rectum. These abnormal connections allow the bacteria normally present in the intestine to enter other areas of the body, causing potentially serious infections.

Patients suffering from Crohn's disease are at increased risk of other disorders. Some of these may relate specifically to the intestinal disease, and others appear to have some relationship to the compromised immune system. The faulty absorption of the bowel can result in gallstones and kidney stones. Inflamed areas in the abdomen may compress and block the ureter (the tube that drains urine from the kidney to the bladder) causing failure of the kidney on the affected side. Patients with Crohn's disease also frequently suffer from extraintestinal manifestations such as:

arthritis (inflammation of the joints)
spondylitis (inflammation of the vertebrae, the bones of the spine)
ulcers of the mouth and skin
erythema nodosum (painful, red bumps on the skin)
inflammation of several eye areas
inflammation of the liver, gallbladder, and/or the ducts that carry bile between and within the liver, gallbladder, and intestine

The risk of developing cancer of the intestine is greater than average among patients with Crohn's disease, although the cancer risk is not as high as it is for patients with ulcerative colitis.

Diagnosis

Diagnosis is first suspected based on a patient's symptoms. Blood tests may reveal an increase in white blood cells, an indication that some type of inflammation is occurring in the body. The blood tests may also reveal anemia and other signs of malnutrition due to malabsorption, such as low blood protein; low calcium, potassium, and magnesium present in the blood; and indications of liver inflammation. Stool samples may be examined to rule out various infectious agents, and to see if the stool contains blood.

During a colonoscopic exam, a physician passes a flexible tube with a tiny, fiber-optic camera (called an endoscope ) through the rectum and into the colon. The physician carefully examines the lining of the intestine for signs of inflammation and ulceration that might suggest Crohn's disease. A biopsy of the intestine can also be taken through the colonoscope, and the tissue will be examined under a microscope for evidence of Crohn's disease.

X rays can be helpful for diagnosis, and to determine how much of the intestine is involved in the disease. For these x rays, the patient must either drink a chalky solution containing barium, or receive a barium enema. Barium helps to "light up" the intestine, allowing more detail to be seen on the resulting x rays.

Crohn's disease and ulcerative colitis are similar, but they are distinct conditions. Although it may be difficult to determine whether a patient has Crohn's disease or ulcerative colitis, it is important to make every effort to distinguish between these two diseases because the long-term complications of the diseases are different, as is the treatment.

Treatment

Treatment for Crohn's disease aims to reduce the underlying inflammation, the resulting malabsorption/malnutrition, and relieve symptoms of abdominal pain and diarrhea. Treatment is also intended to prevent potential complications such as obstructions, abscesses, and fistulas.

Inflammation can be treated with a drug called sulfasalazine. Sulfasalazine is in part related to the sulfa antibiotics; its other component is a form of the anti-inflammatory chemical, salicylic acid (related to aspirin). Sulfasalazine is not well absorbed from the intestine, so it remains largely within the intestine, where it is broken down into its components. It is believed that the salicylic acid component actively treats Crohn's disease by fighting inflammation. Some patients do not respond to sulfasalazine and require corticosteroids such as prednisone. Corticosteroids, however, must be used carefully to avoid the various complications of these drugs, including an increased risk of infection and osteoporosis (weakening of the bones).

Patients with intra-abdominal abscesses or those with disease in the large bowel or ileum may be given antibiotics such as metronidazole or ciprofloxacin. Potent immunosuppressive drugs, such as 6-mercaptopurine, azathioprine, cyclosporine, and infliximab, which block the immune system and thereby reduce inflammation, may be prescribed for patients who do not respond to corticosteroids.

Serious cases of malabsorption/malnutrition may require treatment with nutritional supplements. These supplements must be in a form that can be absorbed from the damaged, inflamed intestine. Some patients find that certain foods are hard to digest, including milk, large quantities of fiber, and spicy foods. When patients are suffering from an obstruction, or during periods of time when symptoms of the disease are at their worst, they may need to drink specially formulated, high-calorie liquid supplements. Those patients who are severely ill may need total parenteral nutrition (TPN). TPN patients receive their nutrition intravenously, or through a catheter inserted directly into a major vein in the chest.

A number of medications are available to help decrease the cramping and pain associated with Crohn's disease. These include loperamide, tincture of opium, and codeine. Fiber preparations (methylcellulose or psyllium) are helpful for some patients; others do not tolerate them well.

The first step in treating an obstruction involves general efforts to decrease inflammation with sulfasalazine, steroids, or immunosuppressive drugs. A patient with a severe obstruction is given no food or drink by mouth, allowing the bowel to "rest." Abscesses and other infections require antibiotics. Surgery may be required to repair an obstruction that does not resolve on its own, to drain an abscess, or to repair a fistula. Such surgery may involve the resection (removal) of the diseased length of the intestine.

In extremely severe cases of Crohn's disease that do not respond to treatment, patients may require a colostomy. In this procedure, a piece of the remaining small intestine is pulled through an opening in the abdomen. This segment of intestine is fashioned surgically to allow a special bag to be placed over it. This bag collects the stool, which can no longer pass through the large intestine and out of the anus.

KEY TERMS

Abscess— A walled-off pocket of pus caused by infection.

Endoscope— An instrument that can be passed into an area of the body (the bladder or intestine, for example) to allow examination of that area. The endoscope usually has a fiber-optic camera, which allows a greatly magnified image to be shown on a television screen viewed by the operator. Many endoscopes also allow the operator to retrieve a biopsy of the area examined.

Fistula— An abnormal channel that creates an open passageway between two structures that do not normally connect.

Gastrointestinal tract— The entire length of the digestive system, running from the mouth to the stomach, through the small intestine, large intestine, rectum, and anus.

Immune system— The body system responsible for combating infection by viruses, bacteria, fungi, and other foreign invaders. In autoimmune disease, these cells and chemicals turn against the body itself.

Inflammation— The result of the body's attempts to fight off and wall off an area that is infected. Inflammation results in the classic signs of redness, heat, swelling, and loss of function.

Obstruction— A blockage.

Ulceration— A pitted area or break in the continuity of a surface such as skin or mucous membrane.

Prognosis

Crohn's disease is a chronic, lifelong illness. The severity of the disease may vary, and patients may experience periods of time when the disease is not active and they are symptom free. Still, the complications and risks of Crohn's disease tend to increase over time. More than 60% of all patients with Crohn's disease will require surgery, and about half of these will require more than one operation over time. Approximately 5-10% of all Crohn's patients die of their disease, primarily due to massive infection.

Health care team roles

Crohn's disease is often diagnosed by primary care practitioners or gastroenterologists. In many instances, patients require surgical intervention. Imaging studies to assist in diagnosis are performed by x-ray technologists, and laboratory technologists may be involved in obtaining blood and stool samples for analysis.

Nurses, dieticians, and nutritional counselors have important roles in teaching patients about dietary changes to manage symptoms. Nurses, social workers, and ostomy specialists may also be involved in educating patients pre- and postoperatively about ostomy care.

Prevention

Presently, there is no way to prevent the development of Crohn's disease.

Resources

BOOKS

Glickman, Robert. "Inflammatory Bowel Disease: Ulcerative Colitis and Crohn's Disease." In Harrison's Principles of Internal Medicine, edited by Anthony S. Fauci, et al. New York: McGraw-Hill, 1998.

Long, James W. The Essential Guide to Chronic Illness. New York: Harper Perennial, 1997.

Saibil, Fred. Crohn's Disease and Ulcerative Colitis. Buffalo, NY: Firefly Books, 1997.