Background Estimates of the prevalence and incidence of chronic juvenile inflammatory arthritis vary widely between studies. Reasons include source population, differences in case ascertainment, and evolving classification criteria.
Objectives To determine the incidence and prevalence of juvenile idiopathic arthritis (JIA) in Olmsted County, MN, via the Rochester Epidemiology Project utilizing the ILAR classification from 1994 through 2013, and identify trends in these parameters incorporating data from an earlier cohort from the same population to span 1960-2013.1,2
Methods For screening purposes, residents of Olmsted County, MN aged <18 years old between January 1, 1994 and December 31, 2013 were identified using diagnostic codes.1 The complete medical records of all identified patients were reviewed to confirm fulfillment of ILAR criteria for JIA and, separately, ACR criteria for juvenile rheumatoid arthritis (JRA).2,3 Overall rates were age- and sex-adjusted to the 2000 United States white population, as obtained from decennial censuses, with linear interpolation for the intercensal years. Trends in incidence rates were analyzed using Poisson regression analysis. Prevalence was determined on January 1, 2000 and January 1, 2010.
Results Ninety cases of JIA were identified in 1994-2013. Seventy-one of these were incident cases; 42 (59%) were female. Median follow-up time of the incident cases was 7.0 years (interquartile range 3.3, 12.4). Oligoarticular subtype was the most common (45, 63%). Of the oligoarticular subtype, 36 had ≤4 joints affected throughout their course (persistent), 7 had >4 joints (extended) 6 or more months after diagnosis, and 2 patients did not have follow-up beyond 6 months. Nine (12%) presented with polyarticular disease. Systemic disease occurred in 2 (3%). Psoriatic arthritis was diagnosed in 2 (3%) and 1 (1%) had enthesitis-related arthritis. Twelve (17%) were undifferentiated.
The overall age and sex-adjusted incidence rate was 10.3 per 100,000 population (95% confidence interval [CI] 7.9, 12.7). Of the 71 incident cases identified in 1994-2013, 59 (83%) met criteria for JRA. A total of 118 incident cases of JRA occurred in 1960-2013. Following the previously reported decline in incidence in the 1960-1993 time period, there were no significant trends in incidence during 1994-2013 (Fig 1). However, cyclical changes were present throughout the entire time course with peaks in incidence occurring approximately every 10 years. There were no differences in the age of diagnosis, sex, or time from symptom onset to diagnosis when comparing 1960-1993 to 1994-2013. Prevalence rates were 41.0 (95% CI 17.8, 64.3) and 54.4 (95% CI 28.5, 80.2) per 100,000 in 2000 and 2010, respectively.
Conclusions In this population based cohort, incidence of JIA was 10.3 (95% CI 7.9, 12.7) per 100,000. There were no changes in overall incidence rates over the past 20 years using a subgroup meeting JRA criteria, although there was cyclic variation of incidence during the entire 1960-2013 time period.
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Peterson LS, et al. Arthritis Rheum 1996;39(8):1385-90.
Brewer EJ, et al. Arthritis Rheum 1977;20(2 Suppl):195-9.
Disclosure of Interest None declared
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