Snapshot A 21-year-old man presents with severe morning back pain over the past three months. His pain improves as the day progreses and with excercise. Physical exam shows a stooped posture and diminished anterior flexion of the lumbar spine. Radiography of the lumbar spine shows bilateral sclerotic changes in the sacroiliac area. Laboratory testing shows that the patient is HLA-B27 positive. Introduction Clinical definition chronic inflammatory disorder that primarily affects the sacroiliac joint and spine Epidemiology demographics more common in men peak onset age is 15-35 years of age risk factors HLA-B27 gene presence Etiology unknown but may involve both genetic (e.g., HLA B-27 positivity) and environmental factors Pathogenesis unclear but involves inflammation, bone erosion, and spur formation can result in spinal fusion and costovertebral and costosternalankylosis involves the entheses connective tissue between bone and a tendon or ligament Associated conditions psoriasis inflammatory bowel disease anterior uveitis aortic regurgitation Prognosis may lead to chronic pain and stiffness Presentation Symptoms back pain worse in the morning and lasts approximately 30 minutes improves with activity stiffness of the spine with anterior uveitis photophobia watering and redness of the eye Physical exam may have stooped posture positive Schober test demonstrates limited spine flexibility decreased chest wall expansion Presentation Radiography indication gold standard for evaluating and supporting the diagnosis of ankylosing spondylitis findings "bamboo spine" Studies Labs HLA-B27 positivity seen in > 90% of patients Differential Mechanical low back pain Enteropathic arthritis Reactive arthritis Psoriatic arthritis Treatment Conservative patient education and exercise indication mainstay of treatment Medical nonsteroidal antiinflammatory drugs (NSAIDs) indication considered first-line treatment for managing pain and stiffness tumor necrosis factor (TNF) inhibitors indication typically used in patients who do not respond to conservative and NSAID treatment medications adalimumab etanercept Complications Low bone density Spine fracture leading to injury of the spinal cord Restrictive lung disease