Figure 3: The Assessment of SpondyloArthritis international Society (ASAS) classification criteria for axial and peripheral SpA. Peripheral arthritis is usually asymmetric or predominantly of the lower limbs. Sacroiliitis on X-ray is defined as in the 1984 modified New York criteria for AS. This set of criteria allows differentiation between axial and exclusively peripheral SpA. SpA: spondyloarthropathy MRI: magnetic resonance imaging, NSAIDs: non-steroidal anti-inflammatory drugs, CRP: C-reactive protein. (Adapted from: Ann Rheum Dis. 2011;70: 25-31).