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What Causes Crohn's Disease and Ulcerative Colitis?

Ulcerative Colitis Description and Symptoms

Crohn's Disease Description and Symptoms


Inflammatory bowel disease (IBD) is a term used to describe two related diseases that involve inflammation of the small intestine and the colon. These two diseases are Crohn’s disease and ulcerative colitis.  Men and women are equally affected. IBD most commonly begins during adolescence and early adulthood, but it can also begin during childhood and later in life.

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What causes Crohn's disease and Ulcerative Colitis?

The causes of Crohn's disease and ulcerative colitis are unknown. To date, there has been no convincing evidence that these two diseases are caused by infection. Neither disease is contagious.

Crohn's disease and ulcerative colitis are caused by abnormal activation of the immune system in the intestines. The immune system is composed of immune cells and the proteins that these cells produce. These cells and proteins serve to 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, in fact, 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 Crohn's disease and ulcerative colitis, however, the immune system is abnormally and chronically activated in the absence of any known invader. The continued abnormal activation of the immune systems causes chronic inflammation and ulceration. The susceptibility to abnormal activation of the immune system is genetically inherited. First degree relatives (brothers, sisters, children, and parents) of patients with IBD are thus more likely to develop these diseases.

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Ulcerative Colitis?

Ulcerative colitis involves inflammation of the inner lining of the colon and the rectum that causes rectal bleeding and diarrhea. There is a wide range of symptoms and disease severity among patients with this disease. Variation in symptoms and disease severity reflects differences in the extent of disease (the amount of surface areas of the colon and the rectum inflamed) and the intensity of inflammation. Generally, patients with inflammation confined to the rectum and a short segment of the colon adjacent to the rectum have milder symptoms and a better prognosis than patients with more widespread inflammation of the colon. The different types of ulcerative colitis are classified according to the location and the extent of inflammation:

  1. Ulcerative proctitis refers to inflammation that is limited to the rectum. In many patients with ulcerative proctitis, mild intermittent rectal bleeding may be the only symptom. Other patients with a higher degree (intensity) of rectal inflammation may, in addition, experience rectal pain, urgency (sudden feeling of having to defecate, and need to rush to the bathroom for fear of soiling), and tenesmus (constant urge to move one’s bowels).
  2. Proctosigmoiditis involves inflammation of the rectum and the sigmoid colon (a short segment of the colon contiguous to the rectum). Symptoms of proctosigmoiditis, like that of proctitis, include rectal bleeding, urgency, and tenesmus. Some patients with proctosigmoiditis also develop bloody diarrhea and cramps.
  3. Left-sided colitis involves inflammation that starts at the rectum and extends up the left colon (sigmoid colon and the descending colon). Symptoms of left-sided colitis include bloody diarrhea, abdominal cramps, weight loss, and left-sided abdominal pain.
  4. Pancolitis or universal colitis refers to inflammation affecting the entire colon (right colon, left colon, transverse colon and the rectum). Symptoms of pancolitis include bloody diarrhea, abdominal pain and cramps, weight loss, fatigue, fever, and night sweats. Some patients with pancolitis have low-grade inflammation and mild symptoms that respond readily to medications. Generally, however, patients with pancolitis suffer more severe disease and are more difficult to treat than those with more limited forms of ulcerative colitis.
  5. Fulminant colitis is a rare but severe form of pancolitis. Patients with fulminant colitis are extremely ill with dehydration, severe abdominal pain, protracted diarrhea with bleeding, and even shock. They are at risk of developing toxic megacolon (marked dilatation of the colon due to severe inflammation) and colon rupture (perforation). Patients with fulminant colitis and toxic megacolon are treated in the hospital with potent intravenous medications. Unless they respond to treatment promptly, surgical removal of the diseased colon is necessary to prevent colon rupture.

The risk of a patient with ulcerative colitis of developing colon cancer is related to the location and the extent of their disease. Patients with only ulcerative proctitis probably do not have increased colon cancer risk compared to the general population. Among patients with active pancolitis of 10 years or longer, their risk of colon cancer is 10-20 times that of the general population. In patients with chronic left-sided colitis, the risk of colon cancer is increased, but not as high as in patients with chronic pancolitis.

While the intensity of colon inflammation in ulcerative colitis wax and wane over time, the location and the extent of disease in a patient generally stays constant. Therefore, when a patient with ulcerative proctitis develops disease relapse, the inflammation usually is confined to the rectum. But a small number of patients (less than 10%) with ulcerative proctitis or proctosigmoiditis can later develop more extensive colitis. Thus, patients who initially only have ulcerative proctitis can later develop left-sided colitis or even pancolitis.

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Crohn's Disease?

Crohn's disease involves chronic inflammation of the intestines. 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. Like ulcerative colitis, the symptoms and the prognosis of Crohn's disease are dependent on the location and the intensity of the inflammation.

While ulcerative colitis appears only in the colon and the rectum, Crohn’s disease affects the colon, the rectum, and the small intestine. In rare instances, Crohn’s disease can also involve the stomach, the mouth, and the esophagus (the food pipe between the mouth and the stomach). Like ulcerative colitis, there are different types of Crohn’s disease based on disease locations:

  1. Crohn’s colitis is inflammation that appears only in the colon. Abdominal pain and bloody diarrhea are the common symptoms. Anal fistulae and perirectal abscesses can also occur.
  2. Crohn’s enteritis refers to inflammation only of the small intestine. Abdominal pain and diarrhea are the common symptoms. Obstruction of the small intestine (small intestinal obstruction) can also occur.
  3. Crohn’s terminal ileitis is inflammation that affects only the part of the small intestine closest to the colon (terminal ileum). Abdominal pain and diarrhea are the common symptoms. Small intestinal obstruction can also occur.
  4. Crohn’s enterocolitis or ileocolitis is a condition involving both the small intestine and the large intestine. Bloody diarrhea and abdominal pain are the common symptoms. Small intestinal obstruction can also occur. Crohn's terminal ileitis and ileocolitis are the most common locations of the disease.

The patterns of inflammation in Crohn’s disease are different from ulcerative colitis. Except in the most severe cases, the inflammation in ulcerative colitis tends to involve the superficial layers of the inner wall. The inflammation tends also to be diffuse and uniform (all the mucosa in the affected segment of the bowel is inflamed). Unlike ulcerative colitis, the Crohn’s disease inflammation is more localized and involve deeper layers of the intestinal wall. Therefore, the affected segment(s) of bowel in Crohn’s disease is usually studded with ulcers (sometimes deep ulcers) with normal mucosa in between these ulcers.

The deep ulcers and inflammation of Crohn’s disease, along with chronic scarring, can decrease the inner diameter of the intestine (the size of the opening of the intestine). The inner diameter of the small intestine is normally smaller than that of the colon. When Crohn’s enteritis and terminal ileitis cause further narrowing of the small intestine, intestinal obstruction can occur. When the intestine is obstructed, the digested food, fluid and gas from the stomach and the upper intestines cannot pass into the colon. Symptoms of small intestinal obstruction include severe abdominal cramping pain, nausea, vomiting, abdominal distention, and dehydration.

Deep ulcers can puncture holes in the walls of the small intestine and the colon, and create a tunnel between the intestine and the adjacent organs. If the ulcer tunnel reaches an adjacent empty space inside the abdominal cavity, a collection of infected pus (abdominal abscess) is formed. Patients with abdominal abscesses can develop high fevers, abdominal pain, and tender abdominal masses. When the ulcer tunnels into an adjacent organ, a fistula (channel) is formed. The formation of a fistula between the intestine and the bladder can cause recurrent urinary 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 a mucous discharge emerges from a small painful opening on the skin of the abdomen. The development of a fistula between the colon and the vagina causes gas and intestinal contents to emerge through the vagina. The presence of a fistula in the anus (anal fistula) leads to mucous and pus discharge from the fistula opening.

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.
  2. Development of anal ulcers and fissures on the anal sphincter. These ulcers and fissures can cause bleeding and pain with defecation.
  3. Development of anal fistulae (abnormal channels between the anus and the skin surrounding the anus). Mucous and pus can drain out of the fistulae.
  4. Development of perirectal abscesses (collections of pus around the anal area). Perirectal abscesses can cause fever, pain and tenderness around the anus.

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Last updated on 16/04/99


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