Dear Mayo CLINIC: What exactly is ischemic colitis? Do doctors know what causes it?

Reply: Ischemic colitis occurs when blood flow to part of the large intestine (colon) is reduced due to one of two reasons: either there is a blocked or narrowed blood vessel (occlusive), or there is a temporary decrease in blood flow to the colon (nonocclusive). Ninety-five percent of cases of ischemic colitis are due to a nonocclusive mechanism. When this occurs, cells in the digestive system don’t receive sufficient oxygen, which then leads to areas of colon inflammation and ulceration. While the exact cause of ischemic colitis is often unclear, with proper medical care, most people diagnosed with ischemic colitis typically recover in a day or two and never have another episode.

Even under normal circumstances, the colon receives less blood flow than any other portion of the gastrointestinal tract. As a result, if the colon is suddenly subjected to reduced blood flow – whatever the reason – its tissues may be damaged. The severity of damage varies depending on the amount of time that the blood flow was interrupted and the degree to which it was decreased. In rare cases, patients can suffer a perforation (tear) of the colon, which requires surgical treatment.

Reduced blood flow to the colon may occur for a variety of reasons. One cause is narrowing of arteries serving the colon, which is often associated with the buildup of fatty deposits (atherosclerosis). More commonly, decreased blood pressure due to heart disease, severe illness, various medications, cocaine use or hemodialysis can decrease blood flow to the colon and cause an episode of ischemic colitis. Patients who participate in strenuous exercise can develop ischemia, likely due to a combination of dehydration and diversion of blood away from the colon to more vital parts of the body.

In addition, abdominal surgeries that require clamping off arteries that supply the colon with blood – such as during repair of an aortic aneurysm – may result in ischemic colitis. Blood clots in the vessels supplying the colon may be due to an underlying clotting disorder or could have traveled from another part of the body, such as the heart.

While the vast majority of people who develop ischemic colitis are older than 55, younger patients also can develop this condition. When it occurs in younger patients, a potential clotting disorder should be investigated.

The most common symptoms of ischemic colitis are abdominal pain – typically on the left side of the abdomen – and bloody diarrhea, which usually develops within 24 hours of the onset of pain. If a CT scan is performed, results can be normal or can show typical findings of bowel wall thickening (often in the left, but occasionally involving the right colon). Bowel wall thickening is a nonspecific finding, however, that could also be the result of a bacterial infection of the colon, diverticulitis, or due to an autoimmune condition called inflammatory bowel disease.

The gold standard to diagnose ischemic colitis is an evaluation with either flexible sigmoidoscopy or colonoscopy. These tests can directly evaluate the lining of the colon, and also can be used to obtain samples (biopsies) of the colon tissue.

Ischemic colitis tends to improve without treatment in 24 to 48 hours. In more severe cases, however, treatment may involve a day or two in the hospital for observation, intravenous fluids, and supportive care. Antibiotics also may be given in severe cases. For most people, the colon heals completely in about two weeks; healing in a small percentage of people may take longer.

 – Sarah Umar, M.D., Gastroenterology & Hepatology, Mayo Clinic, Scottsdale, Ariz.