Epidemiology of juvenile idiopathic arthritis in Oman

Background: There is a worldwide variation in the prevalence and subtype distribution of juvenile idiopathic arthritis (JIA) which may be affected by ethnicity and genetic factors. The purpose of this study is to determine the prevalence, subtype distribution and characteristic features of JIA among Omani children and to compare our results with other ethnic populations worldwide. Methods: A population-based, multicenter study among pediatric rheumatology clinics in the Sultanate over a 10 year period between 2004-2013. The diagnosis of JIA and identification of JIA subtypes was based on the ILAR 2004 revised criteria. The hospital charts of these patients were retrospectively reviewed and information was collected. All patients were screened for uveitis by an ophthalmologist using slit lamp examination during regular follow up visits. Results: The study included a total of 107 cases of JIA in Oman over the study period. Among the 107 patients, 71 % (n = 77) were girls with a female: male ratio of 2.5:1. The mean age of disease onset was 6.85 +/- 3.86 years (range 1-13years) while the mean disease duration of 4.8 +/- 2.9 years (range 1-11 years). The incidence of JIA was estimated at 2/100,000 with a prevalence of JIA of 20/100,000. The prevalence of JIA in girls was 28/100,000 while the prevalence in boys was 12/100,000. According to disease distribution, the most frequent subtype was polyarticular JIA rheumatoid factor negative (39.2 %) followed by oligoarthritis (31.8 %), systemic (17.8 %), polyarticular JIA rheumatoid factor positive (7.5 %). The unique feature of the Omani cohort is the lack of occurrence of uveitis. Conclusions: This is the first epidemiological JIA study conducted in Oman that highlights unique geographical disease phenotype. Compared to Western counties, there were higher frequency of polyarticular disease and lack of occurrence of uveitis. Further studies are needed to evaluate the implications of genetic, ethnic and environmental differences of disease expression.