Crohn’s disease and ulcerative colitis are the two major chronic inflammatory bowel diseases, together known as IBD. These two diseases, while similar in many ways, can differ in location, symptoms, and the character of the inflammation and ulcerations. Crohn’s disease, named after one of the physicians who described it in 1932 and also known as regional enteritis, results in ulcers, or sores in the gastrointestinal tract. It may involve any part of the gastrointestinal system from the mouth to the anus. However, it most often involves the lower part of the small intestine, known as the ileum, and the large intestine (the colon). In contrast, ulcerative colitis causes ulcers only in the large intestine.

The symptoms of Crohn’s disease and ulcerative colitis include diarrhea, abdominal pain, blood in the stool, anemia, weight loss, malnutrition, and fever. Patients with ulcerative colitis more often complain of diarrhea and blood in their stools andpatients with Crohn’s disease more often complain of diarrhea and abdominal pain. Crohn’s disease also may present with delayed growth in adolescence or childhood, intestinal obstruction (severe painful cramping, vomiting, nausea, and abdominal distention), bowel perforation, fistulas (abnormal passages or tunnels from one part of the intestine to another, or to the skin, or less commonly to the abdominal wall, vagina, bladder or other nearby organs), or abscesses. In both UC and Crohn’s, patients can experience periods of remission from symptoms and periods of relapse or “flares”. About one-quarter of patients for both types of IBD may have extra-intestinal disease manifestations, most commonly arthritis, eye inflammation (uveitis, iritis or episcleritis), and skin inflammation, typically pyoderma gangrenosum and erythema nodosum. Unfortunately, once IBD occurs it tends to be present for life. Ulcerative colitis can be cured by surgical removal of the entire colon including the rectum. Crohn’s disease, however, most often returns even after the involved sections of the intestine are surgically removed.

Both diseases appear to be caused by a dysfunctional inflammatory response in the gastrointestinal tract. Inflammation is the body’s natural attempt to heal by sending immune cells to the site of an injury or invader. Researchers hypothesize that this immune system response in both ulcerative colitis and Crohn’s disease may be triggered by bacteria or viruses, material in the intestinal contents (such as products from food digestion or intestinal bile), or a defective signal from the body’s own cells, called an autoimmune response. Inflammation results in pain, heat, redness, and swelling of the tissue, known as edema. Chronic inflammation can impair the proper function of tissues and organs.

Microscopically, ulcerative colitis presents as continuous, shallow ulcers located in the superficial layer of the colon (known as the epithelium). The colon becomes swollen (edematous) and loses the shape of its normal folds. In contrast, Crohn’s disease results in discontinuous, “transmural” ulcerations, which typically extend through all layers of the bowel. The formation of large, deep ulcers results in the classic “cobblestone” appearance of the involved intestine. These deep ulcers can form abscesses or scar to cause narrowing of the bowels.It is important to note that, at this time, scientists do not know what triggers Crohn’s disease and that there is no cure. The goals of medical therapy for Crohn’s disease are to control the active disease and to prevent relapses and complications. Sometimes surgery is recommended for removing inflamed segments of the intestines that do not respond to medical therapy or to treat complications such as abscesses, blockages, perforations, and fistulas. About two-thirds of patients will require surgery to remove a portion of their intestines at some point during the course of their disease. New drugs and research on the genetic and environmental basis of the disorder offer the promise of improved future treatments for Crohn’s disease.