[The new classification criteria for spondylarthritis: implications in clinical practice].

" Spondyloarthritis" consists of a group of several diseases sharing clinical, radiological and genetic similarities. Ankylosing spondylitis is the main representative of this group and is characterized by a predominant axial involvement. The presence of radiographic sacroiliitis is essential for the diagnosis of ankylosing spondylitis according to the modified New York criteria. Because the occurence of radiographic sacroiliitis takes 8 to 11 years, the diagnosis of spondyloarthritis is often delayed. Magnetic resonance imaging can depict sacroiliac joint inflammation before the appearance of radiographic damage thereby defining the concept of " non-radiographic axial spondylo-arthritis". This entity was defined by the axial spondyloarthritis classification criteria published by the Assessment of SpondyloArthritis international Society (ASAS). Some factors, such as elevated levels of C-reactive protein at baseline, have been identified as predictors of radiographic sacroiliitis progression, leading to a definite diagnosis of ankylosing spondylitis. These two entities show similar clinical expression (clinical features and activity levels), suggesting continuity between the two diseases. Non-radiographic forms most often affect women and patients with recent symptoms, and are therefore considered as a pre-radiographic status. If the use of magnetic resonance imaging is necessary for the identification of non-radiographic axial spondyloarthritis according to the ASAS criteria, the presumptive diagnosis is mainly based on complaints of inflammatory back pain. The presence of other typical clinical features, such as HLA B27 positivity and/or radiographic sacroiliitis increases the diagnostic probability and indicates the need for referral to a specialist.