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Arthritis Rheum. 1999 Jul;42(7):1339-46.

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

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1
University of Manchester Medical School, UK.

Abstract

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.

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