People who have diverticulosis, or pouches in the lining of the colon, often worry that they will eventually develop a painful and sometimes serious condition called diverticulitis, as previous research has shown that one in four, or up to 25 percent, of those with the condition will.

Now, in a 15-year study that contradicts the common wisdom on rate of progression from diverticulosis to diverticulitis, UCLA researchers show that the risk is significantly lower than previously thought, about 1 percent over seven years. Researchers also found that those diagnosed with diverticulosis at a younger age are more likely to progress to diverticulitis than those diagnosed at an older age.

The study will help inform patients with diverticulosis – particularly those diagnosed at a younger age – and their physicians about the risks of developing acute diverticulitis, said study senior author Dr. Brennan Spiegel, an associate professor of medicine at the David Geffen School of Medicine at UCLA.

“These colon pouches are commonly detected during colonoscopy, and patients wonder if they are important and what to do with them,” Spiegel said. “In short, diverticulosis is not something to worry much about. Chances are low that something will happen.”

The study appears in the December edition of the peer-reviewed journal Clinical Gastroenterology and Hepatology.

As they age, most people develop diverticulosis. More than half of people over 60 and two-thirds of those over 70 have the condition, but the pouches usually don’t cause any problems. Occasionally, the pouches become inflamed, leading to diverticulitis, which causes pain and infection in the abdomen. Doctors usually treat the condition with antibiotics, or in more severe cases, surgery.

Spiegel said the research predicting that one in four patients with diverticulosis would develop diverticulitis is based on limited data pulled from a time when population-based colonoscopy was not performed.

“These risk figures have been widely quoted throughout the literature and appear in multiple research publications, prominent review articles, textbooks and public guidelines,” Spiegel said. “Because the data are from before the advent of routine colonoscopy, many cases of diverticulosis may have gone undiscovered, skewing the risk predictions.”

The retrospective UCLA study identified 2,222 patients from the Veterans Affairs Health System with chart-confirmed diverticulosis and followed them over a median of 6.75 years. Of those 2,222 patients, 95 patients, or 4.3 percent, developed diverticulitis using a liberal definition of the condition not requiring CT scan confirmation. Of those 95, 23 patients, or only 1 percent, developed diverticulitis that met a very rigorous definition of the condition requiring CT scan or surgery to confirm the diagnosis.

And although the younger patients were more likely to develop diverticulitis, their risk was nowhere near the traditionally-cited 25 percent level, Spiegel said.

“With an aging population and greater use of colonoscopy for colorectal cancer screening, more and more people are going to be told they have diverticulosis,” Spiegel said. “Patients often question the significance of this. If providers had more accurate information regarding the risk of diverticulosis complications, they then could make better decisions about the timing of interventions such as surgery.”

Spiegel said the study had limitations. It was a retrospective, single-center study in a Veterans Affairs hospital where the patients were primarily Western and predominantly male. Also, the researchers relied on administrative data to identify diverticulitis cases, and some cases may have been missed. However, the team did perform extensive reviews of medical records to confirm the chart evidence of diverticulitis.

Going forward, Spiegel and his team will study diverticulosis in other, more diverse populations to confirm these findings.

Diverticular disease accounts for more than 300,000 hospital admissions, 1.5 million inpatient care days and $2.4 billion in direct costs annually in the United States.

“These data may help to re-frame discussions with patients regarding their probability of developing clinically significant diverticulitis,” the study states. “Future research should identify individual predictors of diverticulitis in a prospective analysis to better risk-stratify among patients and further study why younger patients may harbor a higher risk of progression than do older patients.”

The study was funded by Shire Pharmaceuticals.