Figure 2: The European Spondyloarthropathy Study Group (ESSG) preliminary classification criteria for spondyloarthropathy. Sacroiliitis on X-ray is defined as in the 1984 modified New York criteria for AS. AS: ankylosing spondylitis, ReA: reactive Arthritis. (Adapted from: Arthritis Rheum. 1991;34:1218-27).