Rheumatoid arthritis and incidence

by Nathan Wei, MD, FACP, FACR

Nathan Wei is a nationally known board-certified rheumatologist and author of the Second Opinion Arthritis Treatment Kit. It's available exclusively at this website... not available in stores.

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Incidence is defined as the number of times an event occurs.

It is the number of new cases that develop in a particular period of time. Prevalence is known as the number of all new cases and old cases of a disease during a given time. Most researchers who study rheumatoid arthritis have concluded that the disease occurs twice as often in women than in men.

In most populations, this statement may be changing.

It is reported that the incidence may increase if there is a long period of follow up for the first appearance of symptoms.

Also, as the population ages, the prevalence of RA may increase even though the incidence tends to decline. This could be because the American population that has rheumatoid arthritis is living longer. In men the occurrence of RA rises during adulthood.

Prevalance of Rheumatoid arthritis: 2.5 million Americans (NWHIC); 1% of US population (NIAMS)

Prevalance Rate: approx 1 in 108 or 0.92% or 2.5 million people in USA

Prevalance of Rheumatoid arthritis: Scientists estimate that about 2.1 million people, or 1 percent of the U.S. adult population, have rheumatoid arthritis.1 ... About 1 percent of the U.S. population (about 2.1 million people) has rheumatoid arthritis. 2

Prevalance statistics about Rheumatoid arthritis: The following statistics relate to the prevalence of Rheumatoid arthritis:

• 2.1 million people with rheumatoid arthritis (NIAMS)
• 1,736,099 people with rheumatoid arthritis in the USA 1996 3
• 2.1 million cases of RA in the US (NIH, The National Women’s Health Centre, 2004)
• 2 to 3 times more common in women than men in the US (NIH, The National Women’s Health Center, 2004)
• About 2.5 million people in the US (American Medical Women’s Association)
• Affects women 3 times more than men in the US (American Medical Women’s Association)

1. excerpt from Handout on Health Rheumatoid Arthritis: NIAMS
2. excerpt from Questions and Answers About Arthritis and Rheumatic Diseases: NIAMS
3. Rose and Mackay, 1998, The Autoimmune Diseases, Third Edition
Arthritis Rheum. 1999 Jul;42(7):1339-46.

Estimating the incidence of rheumatoid arthritis: trying to hit a moving target?

Wiles N, Symmons DP, Harrison B, Barrett E, Barrett JH, Scott DG, Silman AJ.

University of Manchester Medical School, UK.

OBJECTIVE: To examine the effect of delay between symptom onset and notification to an arthritis register and the effect of application of the American College of Rheumatology (ACR; formerly, the American Rheumatism Association) 1987 criteria in a cumulative manner on estimates of the incidence of rheumatoid arthritis (RA). METHODS: General practitioners and/or hospital consultants in the Norwich Health Authority, Norfolk, UK, notified the Norfolk Arthritis Register (NOAR) of all patients who had onset of inflammatory polyarthritis (swelling of > or =2 joints) during 1990. The patients were assessed within 2 weeks of notification and annually thereafter. The ACR 1987 criteria for RA were applied at each assessment. Age- and sex-specific incidence rates were calculated. RESULTS: If up to 12 months elapsed from symptom onset to notification to NOAR and the ACR criteria were applied at the baseline assessment, RA incidence estimates, age-adjusted to the population of England and Wales, were 30.8/100,000 for women and 12.7/100,000 for men. If up to 5 years elapsed from symptom onset to notification, these estimates rose by 45% for women and 36% for men. If up to 5 years elapsed between symptom onset and notification and the criteria were applied cumulatively, the estimates rose by 75% and 93% for women and men, respectively, compared with the 1-year data, reaching 54.0/100,000 for women and 24.5 per 100,000 for men. CONCLUSION: Accurate estimation of the incidence of RA requires long-term followup of patients who present with undifferentiated inflammatory polyarthritis. The highest age-adjusted estimates from this study are probably the best that are available.

PMID: 10403260 [PubMed - indexed for MEDLINE]

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