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What is A 22-year-old man has symptoms of low back pain and stiffness. After several months of mild symptoms, he notes more severe stiffness at night and hip pain. On physical examination, there is paravertebral muscle tenderness and limited flexion of the lumbar spine. Figure shows an x-ray of the lumbar spine. Which of the following is the most likely diagnosis? and explain in detail?
(c) Source: (Kasper, p. 1993) AS occurs in 1-6% of adults inheriting human lymphocyte antigen B27 (HLA-B27). However, the prevalence in B27-positive relatives of patients with AS is up to 30%. Men are three times more likely to be affected.