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Wednesday, July 18, 2012

Sigmoidoscopy--might it be better than colonoscopy?

Sigmoidoscopy means visualization of the sigmoid colon, usually by a flexible fiberoptic scope. Colonoscopy is visualization of the whole colon by means of a longer fiberoptic scope. Both have been recommended as methods of detecting colon cancer early or preventing it by identifying abnormalities such as polyps that can lead to colon cancer.

Sigmoidoscopy looks at most of the left portion of the colon and can be done without anesthesia, in a doctor's office after an enema prep the morning of the procedure. After the procedure most people can go have breakfast and go back to work. A colonoscopy, when successful, looks at the entire colon after a patient is sedated by various intravenous medications, and follows a bowel prep that usual involves drinking 1/2-1 gallon of a polyethylene glycol solution that tastes a little like lemonade with baking soda in it and having many many bowel movements starting the afternoon before the procedure. The anesthesia, which is usually quite pleasant, leaves a hangover for a significant portion of the day and most people are unable to return to work. Because a person having a colonoscopy has a longer tube wending its way through their lower intestines and that person is pleasantly snoozing during the time this is happening, there is a higher risk that the operator, a gastroenterologist usually, will inadvertently push the long tube through the wall of the intestine, which can be a real mess and potentially fatal. This rarely happens, but most of us docs have heard of a few cases, often requiring surgery.

On June 21 the New England Journal of Medicine reported a study that looked at whether sigmoidoscopy really could reduce the risk of developing or dying from colorectal cancer. 154,900 patients were enrolled and randomized to either being offered sigmoidoscopy twice in 3-5 years or just seeing their primary care physicians and following or not following their recommendations for screening. 84% of the intervention patients had sigmoidoscopy once and a little over 50% had it done twice. Both groups were followed for 12 years. The incidence of colorectal cancer was 21% lower in the sigmoidoscopically screened group and mortality was 26% lower. If something was found on sigmoidoscopy the patient would get colonoscopy and have a biopsy or polyp removal done. In the control group ("usual care") screening colonoscopies happened, at about the rate that is reported nationwide, of a little below 50%.

So what happened? Most patients in the usual care group were probably offered colonoscopy, and the patients in the intervention group were offered colonoscopy's poor cousin, the sigmoidoscopy. Why did the poor cousin patients do better? It sounds like they did better not because the procedure (sigmoidoscopy) was necessarily better than full colonoscopy, but because it sounded more feasible to the patients so they actually had it done.

A couple of years ago at a table in a board meeting of my medical group a perfectly intelligent doctor colleague of mine said "does anyone here really recommend sigmoidoscopies anymore?" To which I said "yes." I offered them and performed them in my office during the many years I was in private practice and had no complications and discovered the occasional significant abnormality. None of the patients I screened in this way ever had a colon cancer that was clearly missed by the more limited procedure. As the standard of care in my community moved more and more to colonoscopy, I did fewer flexible sigmoidoscopies and referred more patients to the gastroenterologist for colonoscopies. There were occasional complications related to the fact that the colonoscopy was a more complex procedure.

So--is sigmoidoscopy better than colonoscopy? Maybe yes, maybe no. It is definitely cheaper to the uninsured, though now, with the passage of the health care reform bill, all insured patients have full coverage without copay for either sigmoidoscopy or colonoscopy. It is definitely less risky in terms of complications. It also can miss significant abnormalities in the part of the colon not screened, including precancerous polyps and cancers. For patients at average risk of colon cancer, looking for a minimally disruptive and adequate way to undergo screening, sigmoidoscopy should definitely be strongly considered instead of routine colonoscopy.

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