Incidence of clinically important 10-year health status and disease activity levels in population-based cohorts with rheumatoid arthritis.

OBJECTIVE: To calculate the average age- and sex-specific annual incidence of rheumatoid arthritis (RA) linked to clinically important levels of health status after 10 years, and to study time trends in 10-year disease status during a 6-year period.
METHODS: Patients between 20 and 79 years of age with onset of RA from 1988 to 1993 (n = 550) were asked to participate in a 10-year followup examination. Two hundred sixteen patients in different age and sex groups from 6 different annual cohorts met during the period 1998-2003. Study variables included demographic variables, medication, swollen, tender and deformed joint counts, erythrocyte sedimentation rate, Disease Activity Score (DAS28), Health Assessment Questionnaire, and pain and fatigue on a 100 mm visual analog scale and Arthritis Impact Measurement Scale 2. Age- and sex-specific incidences of RA exceeding clinically important levels 10 years after disease onset were calculated using the Poisson distribution with 95% confidence intervals. Analysis of covariance and logistic regression were used to test the influence of time on 10-year DAS28 and presence of deformed joints.
RESULTS: The average annual incidence of cases exceeding clinically important levels in disease activity and health status 10 years after disease onset increased with higher age and was highest among women. There was a tendency to lower disease activity 10 years after disease onset in the latest cohorts compared to the earliest cohorts.
CONCLUSION: These results from population-based RA incidence cohorts provide important information to healthcare planners and support findings of secular decline in disease burden.