Snapshot A 21-year-old man presents to his physician's clinic with lower back pain. He reports the pain is accompanied by stiffness, is worse in the morning, and improves with exercise. He denies any radiation of pain or bowel and bladder incontinence. On physical exam, there is decreased anterior flexion of the lumbar spine. Laboratory testing is positive for HLA-B27. A plain radiograph of the spine is shown. Introduction Clinical definition login to view 1 more bullet Epidemiology login to view 5 more bullets Etiology login to view 1 more bullet Pathogenesis login to view 4 more bullets Associated conditions login to view 4 more bullets Prognosis login to view 1 more bullet Presentation Symptoms login to view 7 more bullets Physical exam login to view 4 more bullets Imaging Radiography login to view 4 more bullets Studies Labs login to view 2 more bullets Differential Mechanical low back pain Enteropathic arthritis Reactive arthritis Psoriatic arthritis Treatment Conservative login to view 3 more bullets Medical login to view 9 more bullets Complications Low bone density Spine fracture leading to injury of the spinal cord Restrictive lung disease