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 seen with PAIR (Psoriasis, Ankylosing spondylitis, Inflammatory bowel disease, Reactive arthritis) 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 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 Imaging Radiography indication gold standard for evaluating and supporting the diagnosis of ankylosing spondylitis findings "bamboo spine" sacroiliac joint best initial test CT will show bony changes but not active inflammation CT is most sensitive test to diagnose cervical fractures in patients with AS MRI will detect inflammation, making it the best modality for early detection of AS in young patients obtain with cervical fractures to look for epidural hemorrhage 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 due to inflammation and osteoporosis/osteopenia can predispose the patient to vertebral fractures Spine fracture leading to injury of the spinal cord Restrictive lung disease Prognosis May lead to chronic pain and stiffness