Classification of juvenile spondyloarthritis: enthesitis-related arthritis and beyond

Spondyloarthritis (SpA) refers to a spectrum of immune-mediated inflammatory diseases with overlapping features, which differ from other types of inflammatory arthritis in genetic predisposition, pathogenesis and outcome. SpA frequently involves the axial skeleton, and can result in abnormal bone formation with eventual ankylosis of the spine, resulting in substantial disability. SpA often begins as an 'undifferentiated' disease, the presentation of which differs in children and adults; most notably, spinal involvement is uncommon, while hip arthritis and enthesitis are frequently seen in juvenile-onset disease. Currently, the classification of SpA in adults and children is approached differently. Using the International League of Associations for Rheumatology (ILAR) system for juvenile idiopathic arthritis, most childhood SpA is classified as enthesitis-related arthritis. However, in contrast to adult SpA classification, the presence of, or a family history of, psoriasis dictates a separate category of juvenile idiopathic arthritis. More importantly, the ILAR system does not specifically recognize the presence of axial disease in juvenile SpA. Resolution of these issues will improve communication and the transitioning of patients from pediatric to adult clinics, will facilitate research in genetics and pathogenesis, and will be particularly important in the evaluation of tumor necrosis factor inhibitors and other biologic agents for early, axial SpA.