Objective: To ascertain the incidence and prevalence of juvenile idiopathic arthritis (JIA) in Catalonia (autonomous region in northeast Spain), examined according to the currently established disease subtypes.
Methods: Before initiating the study, we conducted an educational programme on paediatric rheumatology, addressed to all general paediatricians in Catalonia. A 2-year (2004-2006), prospective, population-based study was then carried out to determine the incidence of JIA. Prospective and retrospective data retrieval was performed to calculate prevalence. The International League of Associations for Rheumatology (ILAR, Edmonton revision) classification criteria were applied.
Results: Over the study period, 145 new cases of JIA were diagnosed. The mean annual incidence was 6.9/10⁵ children aged less than 16 years (range 5.8-8.1 years; 9.0 years for girls and 4.8 years for boys). On separate analysis of patients ≤ 6 and > 6 years, the distribution in younger children was found to be similar for both girls and boys, whereas in older children, most girls belonged to the oligoarthritis and polyarthritis subgroups, and boys to the enthesitis-related arthritis and undifferentiated subgroups. The calculated prevalence of JIA (31 October 2006) was 39.7 (36.1-43.7)/10⁵ children younger than 16. The relative risk of girls having JIA was 2.1 [95% confidence interval (CI) 1.7-2.7, p < 0.001]. In 70% of patients, the diagnosis was established before the age of 7. Subgroup distribution of prevalent cases mirrored that of incident cases.
Conclusion: This is the first population-based study on the epidemiology of JIA in Catalonia. Incidence and prevalence rates are lower than those reported for several areas in Nordic countries of Europe. Oligoarthritis was the most common subtype.