Assessment of SpondyloArthritis Society (ASAS) Classification and Diagnostic Criteria for Early Axial Spondyloarthritis (SpA)

Background: Existing criteria for AS/SpA such as mod. New York, ESSG, or Amor criteria for classification and/or diagnosis of spondyloarthritis have limitations when applied to early disease. Moreover, MRI is not part of any of the established criteria and the precise role of MRI in early axial disease has not been fully defined yet. Even less is known about sacroiliac (SI) changes in SpA patients with peripheral symptoms. A pilot study using data from 'paper patients' led to new candidate criteria for early spondyloarthritis. Subsequently, the members of the ASAS International Working Group decided to conduct a prospective multi-centre study to evaluate (validate) the new candidate criteria, and to assess their performance as diagnostic criteria. Aims of the study: 1. To evaluate the new candidate criteria for axial SpA in a multi-centre setting. 2. To assess the potential role of the new candidate criteria to be used as diagnostic criteria. To accomplish this, inclusion of consecutive and undiagnosed patients is mandatory as are longer periods of follow-up . 3. To compare criteria encompassing the whole group of SpA such as ESSG and Amor criteria against criteria which are tailored to either predominant axial disease or predominant peripheral disease. To accomplish this, both patients with predominant axial disease (back pain) but also patient with predominant peripheral disease (arthritis/enthesitis) will be included.