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 Crohns 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.
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.
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:
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.
Crohn's disease involves chronic inflammation of the intestines. Common symptoms of Crohns 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, Crohns disease affects the colon, the rectum, and the small intestine. In rare instances, Crohns 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 Crohns disease based on disease locations:
The patterns of inflammation in Crohns 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 Crohns disease inflammation is more localized and involve deeper layers of the intestinal wall. Therefore, the affected segment(s) of bowel in Crohns disease is usually studded with ulcers (sometimes deep ulcers) with normal mucosa in between these ulcers.
The deep ulcers and inflammation of Crohns 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 Crohns 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:
Last updated on 16/04/99