Time to first occurrence of erosions in inflammatory polyarthritis: Results from a prospective community-based study

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Abstract
Objective To examine the time of occurrence of first radiographic erosions in a cohort of patients with inflammatory polyarthritis. Methods Patients were recruited through the Norfolk Arthritis Register, which follows up patients annually. Patients with features of rheumatoid arthritis (other than erosions) sufficient, together with erosions, to meet the American College of Rheumatology (formerly, the American Rheumatism Association) 1987 revised criteria were requested to undergo radiographic examinations of the hands and feet at the first and/or second annual followup visits. All patients were requested to undergo radiographic examinations at the fifth annual followup visit. The most recent erosion‐free radiograph was identified for 416 eligible patients, and these data were used to derive the duration of disease since the recalled date of onset of first symptoms. The rate of occurrence of first erosions was then determined (as a cumulative prevalence and as an incidence rate using Poisson regression) from analysis of followup films. Patients were assumed to be free of erosions at symptom onset. Results The cumulative prevalence of erosions in patients whose first film was obtained 12–24 months after disease onset was 36%, equivalent to an incidence rate of 24.5/1,000 patient‐months. We identified 3 analysis groups of patients who were free of erosions based on films obtained 12–24 months, 24–36 months, and 36–60 months since the recalled date of onset of first symptoms. New erosions were observed in all 3 groups, with cumulative prevalences of 23%, 28%, and 47%, respectively. These were equivalent to first‐erosion incidence rates/1,000 patient‐months of 5.4 (95% confidence interval [95% CI] 3.8–8.3), 6.8 (95% CI 4.7–10.0), and 13.0 (95% CI 8.9–19.2), respectively. Conclusion Many patients with erosive disease first develop their erosions >2 years from disease onset.