Patients With IBS Not More Likely to Develop Polyps or Colon Cancer

Pauline Anderson

April 07, 2010

April 7, 2010 — The prevalence of common structural abnormalities of the colon, including polyps, hemorrhoids, colorectal cancer (CRC), and diverticulosis, is no higher in nonconstipated patients with irritable bowel syndrome (IBS) than in healthy control patients undergoing colonoscopy for CRC screening, according to a new study.

The findings lend support to the recent recommendation of the American College of Gastroenterology not to use routine colonic imaging in patients with typical IBS symptoms who have no alarm features such as unexplained weight loss, fever, or significant gastrointestinal bleeding.

Long-Standing Bias

"There has been a bias for a long time that patients with chronic abdominal complaints — diarrhea, constipation, bloating, and so forth — may somehow be at higher risk of harboring underlying malignancy," commented Brennan M.R. Spiegel, MD, to Medscape Gastroenterology.

However, he added, only about 1% of colonoscopies performed on patients with IBS will find something substantial; for example, colitis.

Dr. Spiegel is assistant professor of medicine, VA Greater Los Angeles Healthcare System, David Geffen School of Medicine at the University of California–Los Angeles, and director, University of California–Los Angeles/VA Center for Outcomes Research and Education.

The study, led by William D. Chey, MD, from the Division of Gastroenterology, University of Michigan Health System, Ann Arbor, was published online February 23 in the American Journal of Gastroentrology.

The prospective, observational, case-controlled, multicenter trial compared the prevalence of structural lesions of the colon found during colonoscopy in 466 patients with nonconstipated IBS with that of 451 healthy volunteers undergoing colonoscopy for routine CRC screening based on a personal history of adenomatous polyps.

Younger, Women

Patients in the group with suspected IBS were significantly younger and more likely to be women compared with those in the control group. There was no disparity in racial makeup of the 2 groups with equivalent numbers of white (80-85%) and black (roughly 10%) patients in each cohort.

During colonoscopies in patients with suspected IBS, investigators identified and recorded all abnormalities. They biopsied polyps and/or mucosal abnormalities and obtained at least 2 random biopsies from the sigmoid colon and rectum.

Abnormalities identified during colonoscopy in the control group were similarly recorded, but colon biopsies were only performed in this group when a visible abnormality was identified.

Most Common Lesions

The researchers found that the most common colonic lesions in patients with suspected IBS were hemorrhoids (18.2%), followed by polyps (14.6%), diverticuli (8.8%), and erythema or ulceration (4.9%). In the control group, the most common findings were polyps (34.4%), followed by diverticuli (21.3%) and hemorrhoids (16.4%). The control group had a significantly higher prevalence of polyps and diverticulosis compared with those patients with suspected IBS (34.4% vs 14.6% and 21.3% vs 8.8% respectively; both differences significant to the P < .0001 level).

The prevalence of macroscopically visible mucosal erythema or ulceration was significantly higher in patients with suspected IBS compared with control patients (4.9% vs 1.8%; P < .01).

The most common histologic findings in the IBS group were hyperplastic polyps (8.4%) and adenomas (7.7%), whereas in the control group the order was reversed -- adenomas were the most common (26.1%) followed by hyperplastic polyps (11.5%).

After adjusting for age, sex, race, level of education, smoking, and alcohol use, the odds ratio for the presence of adenomas in patients with suspected IBS compared with control patients was 0.33 (95% confidence interval [CI], 0.20 - 0.56). The adjusted odds ratios for the presence of diverticulosis and hemorrhoids in the IBS group compared with the control patients were 0.68 (95% CI, 0.42 - 1.1) and 1.2 (95% CI, 0.75 - 1.8), respectively.

The prevalence of adenomas was higher in the control group possibly because a substantial minority of control patients undergoing colonoscopy had a family history of colon polyps or cancer, whereas patients with IBS with a first-degree relative with colon cancer were not eligible for inclusion in the study, explained the authors.

Microscopic Colitis

Microscopic colitis, which can be mistaken for IBS, was identified in only about 1.5% of patients with suspected IBS, most of whom were women, and all of whom were older than 35 years. The prevalence increased to 2.3% in patients with IBS older than 45 years. "It is possible that our study underestimated the true prevalence of microscopic colitis in IBS patients as the protocol required the endoscopist to obtain only two biopsies from the sigmoid and rectum," wrote the authors. "The optimal number and location of colonic mucosal biopsies needed to diagnosis microscopic colitis remains controversial."

Physicians are concerned about missing colorectal cancer or inflammatory bowel disease in patients with suspected IBS and often use colonoscopy to evaluate IBS symptoms, wrote the authors. A recent national database analysis found that roughly one quarter of all colonoscopies performed in the United States are for IBS-related symptoms.

Dr. Spiegel called this figure "outrageous," especially when the technology is scarce and expensive. "We've got queues forming of individuals waiting for fixed resources, and if we start pushing other individuals who have IBS — something that affects up to 10% of the population — into those queues, then it's going to be very difficult to get proper screening."

Possible Limitations

Differences in demographics and indications for colonoscopy may have influenced the study results, said the authors. Another limitation is that the study did not collect information on complications rates, which would have contributed to a risk–benefit analysis. The results do not necessarily extend to other subgroups of patients with IBS.

According to the American College of Gastroenterology recommendations, in addition to being used to screen for colorectal cancer in those older than 50 years, colonoscopic imaging should be performed in patients with IBS only with alarm features, to rule out organic diseases. The college recommends that when performing colonoscopy in patients with IBS, physicians should consider obtaining random biopsies to rule out microscopic colitis.

"With IBS, time is on your side, so if someone's not following the script and isn't responding to the usual treatments, or the symptoms are a little bit off the beaten path, we should always reserve the right to do a colonoscopy; but we should still keep in mind that even in that situation, the yield remains very low," said Dr. Spiegel.

One of the rationales for using colonsocopy is to reassure IBS patients that there is nothing seriously wrong, said Dr. Spiegel. "I can tell them until I'm blue in the face that they do not have cancer, don't have colitis, and there's no worm inside, but some people, until we actually physically look in there, won't believe it; they need some confirmation."

However, negative results from a colonoscopy does not seem to offer the expected reassurance, he said. One published study found that such a negative result did not improve the quality of life for patients with IBS, and they tended to continue to believe that there was something seriously wrong.

Dr. Chey is a consultant for Albireo, Aryx, AstraZeneca, Ironwood, McNeil, Proctor & Gamble, Prometheus, Salix, Smart Pill Corporation, Takeda, and Xenosport and has been a speaker's bureau member for Axcan, Prometheus, Salix, and Takeda. For conflict of interest information on other authors, please refer to the original article. Dr. Spiegel receives grant support from Takeda Pharmaceuticals, Prometheus Laboratories, and Rose Pharmaceuticals. He is also an adviser for Prometheus and Ironwood Pharmaceuticals.

Am J Gastroenterol. Published online February 23, 2010. Abstract

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