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DEFINITION

Ankylosing spondylitis (AS) belongs to the family of spondyloarthritides that also includes reactive arthritis (Chap. 162), psoriatic arthritis (Chap. 161), enteropathic arthritis (Chap. 165) juvenile-onset spondyloarthritis, and undifferentiated spondyloarthritis. Classification criteria based on their main clinical features of axial spondyloarthritis (Table 160-1) and peripheral spondyloarthritis (Table 160-2) have been developed that aide in early identification. AS is a chronic and progressive inflammatory disease of the axial skeleton with sacroiliitis (usually bilateral) as its hallmark. Peripheral joints and extra-articular structures may also be affected. Most frequently presents in second or third decade more commonly in men; strong association with histocompatibility antigen HLA-B27.

TABLE 160-1ASAS CRITERIA FOR CLASSIFICATION OF AXIAL SPONDYLOARTHRITIS (TO BE APPLIED FOR PATIENTS WITH BACK PAIN ≥3 MONTHS AND AGE OF ONSET <45 YEARS)a
TABLE 160-2ASAS CRITERIA FOR PERIPHERAL SPONDYLOARTHRITISa

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