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What is Most specific for diagnosing Ankylosing spondyliti? and explain in detail?
According to Modified New York criteria, the diagnosis of definite AS requires the following: established sacroiliitis on radiographs (unilateral or bilateral) and at least one of the following clinical criteria: (1) low back pain and stiffness for more than 3 months improving with activity, (2) reduced chest expansion (3) limited lumbar movements. HLA B27 is present in > 90% cases of ankylosing spondylitis but it is not specific for AS.