Rheumatology · Spondyloarthropathies
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Ankylosing spondylitis is strongly associated with the HLA-B27 allele.
Patients typically present with inflammatory back pain that improves with exercise and worsens with rest.
Physical examination reveals limited spinal mobility, specifically a positive Schober test.
Radiographic imaging of the pelvis demonstrates bilateral sacroiliitis as the hallmark finding.
Advanced disease progression leads to the classic bamboo spine appearance on lateral radiographs due to syndesmophyte formation.
The most common extra-articular manifestation is anterior uveitis, which presents with unilateral eye pain, photophobia, and blurred vision.
First-line pharmacologic therapy for symptomatic management is NSAIDs.
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A 26-year-old male presents with a 6-month history of chronic low back pain and morning stiffness that lasts for 2 hours and improves after he goes for a run. He reports that his symptoms are worse at night, often waking him from sleep. On physical exam, he has decreased lumbar flexion and a positive Schober test. He also mentions a recent episode of redness and pain in his right eye that resolved with topical steroids.
What is the most likely diagnosis?
Ankylosing Spondylitis
The patient's presentation of inflammatory back pain, morning stiffness, and history of anterior uveitis is classic for ankylosing spondylitis, though confirmation requires imaging demonstrating sacroiliitis.
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High yield triage
Etiology / Epidemiology
Chronic inflammatory arthropathy primarily affecting young males (20s-30s) with strong HLA-B27 association.
Clinical Manifestations
Insidious onset of morning stiffness that improves with exercise; Bamboo spine on imaging.
Diagnosis
MRI is the gold standard for early detection; Schober test < 5cm indicates restricted lumbar flexion.
Treatment
NSAIDs are first-line; TNF-alpha inhibitors or IL-17 inhibitors (equally recommended as first biologic) if refractory; monoclonal antibody TNF inhibitors are preferred over etanercept when recurrent uveitis or IBD is present.
Prognosis
Risk of restrictive lung disease and uveitis; monitor for fracture of the rigid, fused spine (especially cervical) and aortic regurgitation.
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Epidemiology & Etiology
Strong genetic predisposition linked to the HLA-B27 allele. Typically presents in males aged 15–30. It is a systemic inflammatory condition classified under the seronegative spondyloarthropathies; in current ACR/ASAS nomenclature it is termed radiographic axial spondyloarthritis, the radiographic subtype of axial spondyloarthritis (axSpA), alongside non-radiographic axSpA.
Pertinent Anatomy
Primarily affects the axial skeleton, specifically the sacroiliac joints and the vertebral column. Enthesitis at the insertion of tendons and ligaments is the hallmark anatomical site of inflammation.
Pathophysiology
Chronic inflammation leads to the formation of syndesmophytes and eventual bony fusion of the spine. The process involves an immune-mediated attack on the entheses, followed by reactive bone formation and ossification of the annulus fibrosus.
Clinical Manifestations
Patients report inflammatory back pain that is worse at night and improves with activity. Physical exam reveals limited spinal mobility and a positive Schober test. Acute anterior uveitis is the most common extra-articular manifestation, presenting with unilateral eye pain and photophobia.
Diagnosis
In adults, sacroiliac joint radiographs remain the preferred initial diagnostic test, followed by MRI of the sacroiliac joints, which identifies early sacroiliitis before radiographic changes appear. Radiographs show the classic bamboo spine and squaring of the vertebral bodies. ESR and CRP are typically elevated, while RF and ANA are negative.
Treatment
Initial management requires NSAIDs (e.g., indomethacin) to reduce pain and inflammation. If patients fail two different NSAIDs, initiate either a TNF-alpha inhibitor (e.g., adalimumab) or an IL-17 inhibitor (e.g., secukinumab), which are equally recommended as first biologic therapy; JAK inhibitors are recommended but not as first-line. Live vaccines are contraindicated while on biologic therapy.
Prognosis
Long-term complications include vertebral fractures and restrictive lung disease due to limited chest wall expansion. Patients require regular ophthalmologic screening for uveitis and monitoring for spinal stability.
Differential Diagnosis
Mechanical back pain: improves with rest, worsens with activity
Reactive arthritis: follows infection, associated with urethritis/conjunctivitis
Psoriatic arthritis: associated with dactylitis and skin plaques
Diffuse idiopathic skeletal hyperostosis: lacks sacroiliitis, involves thoracic spine
Fibromyalgia: generalized pain, lacks inflammatory markers or radiographic changes