Abstract
The spondyloarthritis (SpA) complex embraces ankylosing spondylitis (AS), reactive arthritis (ReA), psoriatic arthritis (PsA), arthritis related to inflammatory bowel disease (IBD), and forms that do not fulfil established criteria, which are labelled as undifferentiated SpA (uSpA). In the early 1990s, 2 sets of classification criteria were suggested to encompass the clinical spectrum of SpA: the Amor criteria and the European Spondylarthropathy Study Group (ESSG) criteria.