Axial spondyloarthritis

**Long definition:** Experts from the Assessment of SpondyloArthritis international Society (ASAS) developed classification criteria for axSpA and peripheral SpA. Axial spondyloarthritis (SpA) criteria consist of two arms: the 'imaging arm' and the 'clinical arm.' Both arms require that the patient experience chronic back pain before the age of 45 years that persists for approximately 3 months. To fulfill the imaging arm, a patient should have sacroiliitis on either MRI images or conventional radiographs, and have at least one feature of SpA. To fulfill the clinical arm, the patient should be HLA-B27 positive and have at least two other SpA-associated features; sacroiliitis is not mandatory for fulfillment of the ASAS axSpA criteria when the criteria for the clinical arm are met.

**Inclusions:** - Ankylosing spondylitis

**Exclusions:** - Behçet disease