104 - Classification and epidemiology of juvenile idiopathic arthritis

Abstract

Juvenile idiopathic arthritis (JIA) is an umbrella term for a heterogeneous group of diseases that are characterized by chronic arthritis of unknown cause with onset in childhood. In the absence of diagnosis-assuring parameters and a yet insufficiently understood etiopathogenesis, classification systems are used for a uniform case definition and categorization of the different arthritis forms. Based on the classification of the International League of Associations for Rheumatology, six defined JIA onset types and one undifferentiated JIA as well as two oligoarthritis course types are distinguished. The JIA categories have distinct phenotypes, genetic predispositions, pathophysiology, disease courses, and outcomes. The JIA classification will continue to change as the pathogenesis underlying the defined phenotypes is further uncovered. JIA is the most common chronic inflammatory rheumatic disease of childhood. Incidence rates range from 3 to 23 per 100,000 children and prevalence rates from 15 to 167 per 100,000 in North American and European populations. The picture of JIA differs around the world in terms of the frequency and clinical phenotypes of JIA. The risk for JIA is attributed to a complex combination of environmental and genetic factors. Genetic variation within the HLA region defines the strongest known genetic risk factor. Environmental influences have also been implicated in the pathogenesis of JIA, but no consistentlystrong risk factors have been identified so far. This chapter aims to provide an overview of the current classification system of childhood-onset arthritis, the characteristics of the different JIA categories, the frequency of JIA, and the risk factors for JIA.