After forty years of decline, rheumatoid arthritis may be on the rise in women, according to research presented this week at the American College of Rheumatology Annual Scientific Meeting in San Francisco, Calif.

Rheumatoid arthritis is a chronic disease that causes pain, stiffness, swelling, and limitation in the motion and function of multiple joints. Though joints are the principal body parts affected by RA, inflammation can develop in other organs as well. An estimated 1.3 million Americans have RA, and the disease typically affects women twice as often as men.

The overall incidence, or occurrence, of newly diagnosed RA in a given year, declined between 1955 and 1994. Researchers recently set out to examine the incidence, as well as the prevalence, or number of persons affected by RA in a population at any given time,

This study identified a group of patients with RA (who were at least 18 years old and fulfilled the ACR’s 1987 criteria for RA) first diagnosed between January 1, 1995 and January 1, 2005 and a group of patients with prevalent RA on January 1, 2005 living in Olmsted County, Minn.

A total of 350 patients were identified with new-onset RA between 1995 and 2005. Of these patients, 242 were women with an average age of 56.5 years old. Researchers found that the overall incidence of RA was 41.8 per 100,000 people. Among women, the incidence was 54 per 100,000 people, a significant increase when compared to the incidence of 36.4 per 100,000 people in the decade 1985-1994. In contrast, among men, the incidence of RA was 28.6 per 100,000 people, which was consistent with the incidence for men in the previous decade.

The overall prevalence of RA in 2005 was 950 per 100,000 people, which was higher than the 1995 estimate of 850 per 100,000 people.

“Over the past decade, more people have become affected with RA, and we do not yet understand the reasons why,” explains Sherine Gabriel, MD; Mayo Clinic rheumatologist and lead author of the study. “This worrisome increase in occurrence of RA not only offers us clues into the causes of RA, but also highlights the need for more research into the causes and treatment of this devastating disease.”

The ACR is an organization of and for physicians, health professionals, and scientists that advances rheumatology through programs of education, research, advocacy and practice support that foster excellence in the care of people with or at risk for arthritis and rheumatic and musculoskeletal diseases. For more information on the ACR’s annual meeting, see http://www.rheumatology.org/annual.

Editor’s Notes: Sherine Gabriel, MD will present this research during the ACR Annual Scientific Meeting at the Moscone Center from 9:00 – 11:00 AM on Monday, October 27, in Hall A. Dr. Kremers will be available for media questions and briefing at 8:30 AM on Tuesday, October 28 in the on-site press conference room, 114.

Presentation Number: 773

The Rising Incidence of Rheumatoid Arthritis

Sherine Gabriel, Cynthia S. Crowson, Hilal Maradit Kremers, Terry M. Therneau. Mayo Clinic, Rochester, MN

Purpose: Incidence of RA declined from 1955 to 1994, but little is known about the incidence of RA in more recent years. Due to declining incidence and lack of improvement in survival of RA patients, the prevalence of RA was also declining up to 1995. The purpose of this study is to examine the trends in incidence and prevalence of rheumatoid arthritis (RA) from 1995 to 2005.

Methods: To augment our previously assembled inception cohort of RA patients from 1955 to 1994, we assembled a population-based inception cohort of individuals (aged ≥18 years) who fulfilled ACR 1987 criteria for RA between 1/1/1995 and 1/1/2005 and a cohort of patients with prevalent RA on 1/1/2005. Incidence and prevalence rates were estimated and were age- and sex-adjusted to the 2000 white population of the US. Trends in incidence rates were examined using Poisson regression methods.

Results: The incidence cohort from 1995 through 2004 comprised 350 patients with a mean age at incidence of 56.5 years. Of these, 242 (68.9%) were female. The overall age- and sex-adjusted annual incidence of RA was 41.8/100,000 population (95% confidence interval [CI] 37.4 - 46.3) The age adjusted incidence in females was 54.0/100,000 population (95% CI 47.2 - 60.9), which represents a significant increase compared to incidence for females in the previous decade (1985-1994) of 36.4/100,000 population (95% CI 27.4 - 45.5; p=0.015). In contrast, age adjusted incidence in males was 28.6/100,000 population (95% CI 23.1 - 34.1), which was consistent with incidence for males in the previous decade of 29.5/100,000 population (95% CI 22.8 - 36.2; p=0.23). In addition, the overall age- and sex- adjusted prevalence in 2005 was 0.95% (95% CI 0.88 - 1.03) up from the 1995 estimate of 0.85% (95% CI 0.75 - 0.95).

Conclusion: Incidence of RA appears to be rising in females after 4 decades of decline. The reasons for this increase are unknown, but it suggests that an environmental factor may play a role in the etiology of RA. This recent increase in incidence also appears to be precipitating an increase in the prevalence of RA.

Disclosure Block: S. Gabriel, None; C.S. Crowson, None; H. Maradit Kremers, Pfizer, 2; Amgen, 5; Amgen, 2; T.M. Therneau, None.

Source: American College of Rheumatology (ACR)