Crohn's Disease

What is Crohn's disease?

Crohn's disease is a chronic inflammatory disease of the intestines. It primarily causes ulcerations (breaks in the lining) of the small and large intestines, but can affect the digestive system anywhere from the mouth to the anus. It is named after the physician who described the disease in 1932. It also is called granulomatous enteritis or colitis, regional enteritis, ileitis, or terminal ileitis.

Crohn's disease is related closely to another chronic inflammatory condition that involves only the colon called ulcerative colitis. Together, Crohn's disease and ulcerative colitis are frequently referred to as inflammatory bowel disease (IBD). Ulcerative colitis and Crohn's disease have no medical cure. Once the diseases begin, they tend to fluctuate between periods of inactivity (remission) and activity (relapse). They affect approximately 500,000 to two million people in the United States. Men and women are equally affected. IBD most commonly begins during adolescence and early adulthood, but it also can begin during childhood and later in life.

Crohn's disease tends to be more common in relatives of patients with Crohn's disease. It also is more common among relatives of patients with ulcerative colitis.

What causes Crohn's disease?

The cause of Crohn's disease is unknown. Some scientists suspect that infection by certain bacteria, such as strains of mycobacterium, may be the cause of Crohn's disease. To date, however, there has been no convincing evidence that the disease is caused by infection. Crohn's disease is not contagious. Although diet may affect the symptoms in patients with Crohn's disease, it is unlikely that diet is responsible for the disease.

Activation of the immune system in the intestines appears to be important in IBD. The immune system is composed of immune cells and the proteins that these immune cells produce. Normally, these cells and proteins defend the body against harmful bacteria, viruses, fungi, and other foreign invaders. Activation of the immune system causes inflammation within the tissues where the activation occurs. (Inflammation is an important mechanism of defense used by the immune system.)

Normally, the immune system is activated only when the body is exposed to harmful invaders. In patients with IBD, however, the immune system is abnormally and chronically activated in the absence of any known invader. The continued abnormal activation of the immune system results in chronic inflammation and ulceration. The susceptibility to abnormal activation of the immune system is genetically inherited. Thus, first degree relatives (brothers, sisters, children, and parents) of patients with IBD are more likely to develop these diseases. Recently a gene called NOD2 has been identified as being associated with Crohn's disease. This gene is important in determining how the body responds to some bacterial products. Individuals with mutations in this gene are more susceptible to developing Crohn's disease.
How does Crohn's disease affect the intestines?

In the early stages, Crohn's disease causes small, scattered, shallow, crater-like areas (erosions) on the inner surface of the bowel. These erosions are called aphthous ulcers. With time, the erosions become deeper and larger, ultimately becoming true ulcers (which are deeper than erosions) and causing scarring and stiffness of the bowel. As the disease progresses, the bowel becomes increasingly narrowed, and ultimately can become obstructed. Deep ulcers can puncture holes in the wall of the bowel, and bacteria from within the bowel can spread to infect adjacent organs and the surrounding abdominal cavity.

When Crohn's disease narrows the small intestine to the point of obstruction, the flow of the contents through the intestine ceases. Sometimes, the obstruction can be caused suddenly by poorly-digestible fruit or vegetables that plug the already-narrowed segment of the intestine. When the intestine is obstructed, digesting food, fluid and gas from the stomach and the small intestine cannot pass into the colon. The symptoms of small intestinal obstruction then appear, including severe abdominal cramps, nausea, vomiting, and abdominal distention. Obstruction of the small intestine is much more likely since the small intestine is much narrower than the colon to begin with.

Deep ulcers can puncture holes in the walls of the small intestine and the colon, and create a tunnel between the intestine and adjacent organs. If the ulcer tunnel reaches an adjacent empty space inside the abdominal cavity, a collection of infected pus (an abdominal abscess) is formed. Patients with abdominal abscesses can develop tender abdominal masses, high fevers, and abdominal pain.

When the ulcer tunnels into an adjacent organ, a channel (fistula) is formed. The formation of a fistula between the intestine and the bladder (enteric-vesicular fistula) can cause frequent urinary tract infections and the passage of gas and feces during urination. When a fistula develops between the intestine and the skin (enteric-cutaneous fistula), pus and mucous emerge from a small painful opening on the skin of the abdomen. The development of a fistula between the colon and the vagina (colonic-vaginal fistula) causes gas and feces to emerge through the vagina. The presence of a fistula from the intestines to the anus (anal fistula) leads to a discharge of mucous and pus from the fistula's opening around the anus.

How is Crohn's disease different from ulcerative colitis?

While ulcerative colitis causes inflammation only in the colon (colitis) and/or the rectum (proctitis), Crohn's disease may cause inflammation in the colon, rectum, small intestine (jejunum and ileum), and, occasionally, even the stomach, mouth, and esophagus.

The patterns of inflammation in Crohn's disease are different from ulcerative colitis. Except in the most severe cases, the inflammation of ulcerative colitis tends to involve the superficial layers of the inner lining of the bowel. The inflammation also tends to be diffuse and uniform. (All of the lining in the affected segment of the intestine is inflamed.) Unlike ulcerative colitis, the inflammation of Crohn's disease is concentrated in some areas more than others and involves layers of the bowel that are deeper than the superficial inner layers. Therefore, the affected segment(s) of bowel in Crohn's disease often is studded with deeper ulcers with normal lining between these ulcers.
What are the complications of Crohn's disease?

Complications of Crohn's disease may be related or unrelated to the inflammation within the intestine (such as intestinal or extra-intestinal). Intestinal complications of Crohn's disease include obstruction and perforation of the small intestine, abscesses (collections of pus), fistulae, and intestinal bleeding. Massive distention or dilatation of the colon (megacolon), and rupture (perforation) of the intestine are potentially life-threatening complications. Both generally require surgery, but, fortunately, these two complications are rare. Recent data suggest that there is an increased risk of cancer of the small intestine and colon in patients with long-standing Crohn's disease.

Extra-intestinal complications involve the skin, joints, spine, eyes, liver, and bile ducts. Skin involvement includes painful red raised spots on the legs (erythema nodosum) and an ulcerating skin condition generally found around the ankles called pyoderma gangrenosum. Painful eye conditions (uveitis, episcleritis) can cause visual difficulties. Arthritis can cause pain, swelling, and stiffness of the joints of the extremities. Inflammation of the low back (sacroiliac joint arthritis) and of the spine (ankylosing spondylitis) can cause pain and stiffness of the spine. Inflammation of the liver (hepatitis) or bile ducts (primary sclerosing cholangitis) also can occur. Sclerosing cholangitis causes narrowing and obstruction of the ducts draining the liver and can lead to yellow skin (jaundice), recurrent bacterial infections, and liver cirrhosis with liver failure. Sclerosing cholangitis with liver failure is one of the reasons for performing liver transplantation. Sclerosing cholangitis frequently is complicated by the development of cancer of the bile ducts.
What are the symptoms of Crohn's disease?

Common symptoms of Crohn's disease include abdominal pain, diarrhea, and weight loss. Less common symptoms include poor appetite, fever, night sweats, rectal pain, and rectal bleeding. The symptoms of Crohn's disease are dependent on the location, the extent, and the severity of the inflammation. The different subtypes of Crohn's disease and their symptoms are:

1. Crohn's colitis is inflammation that is confined to the colon. Abdominal pain and bloody diarrhea are the common symptoms. Anal fistulae and peri-rectal abscesses also can occur.

2. Crohn's enteritis refers to inflammation confined to the small intestine (the first part, called the jejunum or the second part, called the ileum). Involvement of the ileum alone is referred to as Crohn's ileitis. Abdominal pain and diarrhea are the common symptoms. Obstruction of the small intestine also can occur.

3. Crohn's terminal ileitis is inflammation that affects only the very end of the small intestine (terminal ileum), the part of the small intestine closest to the colon. Abdominal pain and diarrhea are the common symptoms. Small intestinal obstruction also can occur.

4. Crohn's entero-colitis and ileo-colitis are terms to describe inflammation that involve both the small intestine and the colon. Bloody diarrhea and abdominal pain are the common symptoms. Small intestinal obstruction also can occur.

Crohn's terminal ileitis and ileo-colitis are the most common types of Crohn's disease. (Ulcerative colitis frequently involves only the rectum or rectum and sigmoid colon at the distal end of the colon. These are called ulcerative proctitis and procto-sigmoiditis, respectively.)

Up to one third of patients with Crohn's disease may have one or more of the following conditions involving the anal area:

1. Swelling of the tissue of the anal sphincter, the muscle at the end of the colon that controls defecation.

2. Development of ulcers and fissures (long ulcers) within the anal sphincter. These ulcers and fissures can cause bleeding and pain with defecation.

3. Development of anal fistulae (abnormal tunnels) between the anus or rectum and the skin surrounding the anus). Mucous and pus may drain from the openings of the fistulae on the skin.

4. Development of peri-rectal abscesses (collections of pus in the anal and rectal area). Peri-rectal abscesses can cause fever, pain and tenderness around the anus.