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Rheumatoid Arthritis May Be Up in Women

New Study Suggests an Increase in RA Cases Among Women
WebMD Health News
Reviewed by Louise Chang, MD

Oct. 27, 2008 -- Rheumatoid arthritis appears to be increasing among women, but not men, after 40 years of decline, according to Mayo Clinic researchers.

"We don't know why," says Hilal Maradit-Kremers, MD, associate professor of epidemiology at the Mayo Clinic in Rochester, Minn., who is presenting the finding this week at the annual meeting of the American College of Rheumatology and the Association of Rheumatology Health Professionals in San Francisco.

She suspects an environmental factor, possibly hormonal, she tells WebMD.

Rheumatoid arthritis (RA) is an inflammatory arthritis triggered by the immune system. RA most often affects the small joints in the hands and feet, causing pain, stiffness, swelling, and limitations of movement. Treatment includes medication and physical therapy.

Rheumatoid Arthritis Trends

For years, the incidence of RA has been reported to be declining, Kremers says. The incidence refers to the number of new cases diagnosed in a specific time period, such as per year.

In fact, a report published earlier this year by the National Arthritis Data Workgroup, of which Kremers and other Mayo Clinic researchers are a part, found that rheumatoid arthritis affects an estimated 1.3 million U.S. adults, down from the estimate of 2.1 million for 1995.

But Kremers says her group wanted to take a look at more recent data than that used by the Workgroup report. So they found 350 patients with RA in Olmstead County, Minn., diagnosed from 1995 to 2005. Then they looked at the population as a whole to compute the incidence.

When they took into account the entire population of the county, they found that 54 women of every 100,000 developed RA each year, compared to just 36 women of every 100,000 for the decade before. The incidence for men stayed about the same -- 29 men per 100,000.

Overall, the percentage of the population as a whole with the condition rose from 0.85 to 0.95, they found.

"These rates would apply to the entire U.S. population," Kremers says. "Based on this new data, the estimated number of people with RA in the U.S. is probably higher than 1.2 million."

The increase in incidence, the researchers say, appeared to be leading to an increase in prevalence -- defined as the current number of people affected by an illness.

The finding was somewhat surprising, Kremers says. "But for a disease like this, it takes awhile to show what the real trend is," she says.

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