IBDanswers

By Karla Gale
Fri Apr 2, 5:18 PM ET

NEW YORK (Reuters Health) - The occurrence of ulcerative colitis -- an inflammatory bowel disease -- is reduced after people have their appendix removed, studies from Denmark show, suggesting that the surgery confers genuine protection.

However, "for patients who already have ulcerative colitis, their clinical course is not altered by performing an appendectomy," lead investigator Dr. Jesper Hallas at Odense University Hospital told Reuters Health.

Many studies have established that people who have undergone appendectomy are less likely to develop ulcerative colitis, Hallas and his colleagues explain in the medical journal Epidemiology. Why this is so is not clear, but genetic traits or factors related to childhood hygiene have been suggested, rather than a direct effect of appendectomy.

Using the Danish National Registry of Patients, Hallas' group identified approximately 230,000 individuals who had their appendix taken out between 1997 and 1999.

In this group, the incidence rates of ulcerative colitis were 17.6 per 100,000 persons per year before surgery and 13.0 per 100,000 person-years after surgery.

Based on the rates of ulcerative colitis in entire Danish population, 496 cases would have been expected in the study group in the period after they had had an appendectomy, but the actual number of cases was just 330.

"The known inverse association between appendectomy and ulcerative colitis cannot be explained by a mutual genetic determinant, childhood hygiene, or some other factor that is stable over time," the authors conclude.

Instead, something in the way the appendix processes bacteria may explain how the appendix promotes the development of colitis, they suggest.

But these findings do not justify appendectomy as a preventive measure, even among individuals at high risk of developing ulcerative colitis, Hallas said, because it is not currently possible to identify such patients. "Even in patients with a known risk factor, such as family history, ulcerative colitis is rare," he explained.

Meanwhile, in the gastroenterology journal Gut, Hallas and his team report that appendectomy has no significant effect on hospitalization rates in patients already diagnosed with ulcerative colitis.

In a group of 202 patients with ulcerative colitis who underwent appendix removal, the rate of admissions decreased by 47 percent after surgery. However, in a reference group of colitis patients who still had their appendixes, the rate of admissions similarly decreased by 49 percent.

"So even if you can prevent ulcerative colitis by doing an appendectomy, you cannot modify the clinical course by performing appendectomy once it is established," Hallas concluded.

SOURCES: Epidemiology, March 2004, and Gut, March 2004.