Ask the doctors 7/9

Dear Doctors: My internist has recommended a colonoscopy. I dread having it, though, because I’m concerned about the liquid laxative prep it requires. I suffer from IBS, which is often painful. Is it possible that the prep will provoke a severe IBS occurrence, or might it make my condition worse?

Dear Reader: Unfortunately, there is no clear-cut answer. To explain why, let’s begin with some background.

Irritable bowel syndrome, or IBS, is a disorder that causes pain, discomfort and dysfunction in the large intestine. In addition to cramping, bloating, gas and abdominal pain, people with IBS experience ongoing episodes of diarrhea or constipation, and often both. There is no cure, which makes it a chronic condition.

Although the specific cause of the syndrome is not clear, recent research has linked it to certain changes that take place in the population of the gut microbiome. The vast majority of the microbiota that comprise the gut microbiome reside in the colon, which is also referred to as the large intestine. This is the portion of the gastrointestinal tract that is examined during a colonoscopy.

In order to perform an effective colonoscopy, the large intestine, which is where the body’s solid waste collects, must be free of all debris. That’s the only way for abnormalities to be visible. This necessitates the so-called colonoscopy prep, which entails a brief change of diet followed by the use of a laxative drink to completely void the bowel.

It’s here that the requirements of colonoscopy prep bump up against the challenges of IBS. While cleansing the bowel provides the clear field of vision needed to identify potential cancers, it also affects the intestinal flora. Studies show that this process alters the numbers, diversity and stability of the populations of microbes living in the gut, and that it takes several weeks for the microbiome to recover. How this affects people with IBS, whose gut microbiome may already be out of balance, is not clear. Research is scarce, and people’s experiences vary. Some say they are unaffected by the prep, and some experience a mild flare. Others report that their symptoms of IBS go away altogether for several weeks after the bowel is cleansed.

Another thing to keep in mind is that colonoscopy prep has made great strides in recent years. The gallon of liquid once required is now often just two small bottles. There is evidence that splitting the dose, with half consumed the night before the procedure and half the morning of, is easier on the gut. Each colonoscopy center has its own protocols, and you can check for the one you are most comfortable with.

Your reluctance to undergo a colonoscopy due to the potential effects of the prep is understandable, but it’s important to look at the big picture. The benefits of screening for colon cancer outweigh the risk of an IBS flare. A colonoscopy can identify precancerous polyps, which can be removed before they turn into cancer. When colorectal cancers are found early, they are highly treatable. And with normal results, you won’t need another colonoscopy for 10 years.

Send your questions to askthedoctors@mednet.ucla.edu.