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Key Features

Essentials of Diagnosis

  • Chronic low backache in young adults, generally worst in the morning

  • Progressive limitation of back motion and of chest expansion

  • Transient (50%) or persistent (25%) peripheral arthritis

  • Anterior uveitis in 20–25%

  • Diagnostic radiographic changes in sacroiliac joints

  • Negative serologic tests for rheumatoid factor and anti-CCP antibodies

  • HLA-B27 testing is most helpful when there is an intermediate probability of disease

General Considerations

  • Chronic inflammatory disease of the joints of the axial skeleton, manifested clinically by pain and progressive stiffening of the spine

Demographics

  • The age at onset is usually in the late teens or early 20s

  • The incidence is greater in males than in females

Clinical Findings

Symptoms and Signs

  • Gradual onset with intermittent bouts of back pain that may radiate into the buttocks

  • Pain and stiffness improve with activity, in contrast to back pain due to mechanical causes and degenerative disease, which improves with rest and worsens with activity

  • Symptoms progress in a cephalad direction

  • Motion becomes limited, with the normal lumbar curve flattened and the thoracic curvature exaggerated

  • Chest expansion is often limited as a consequence of costovertebral joint involvement

  • In advanced cases, the entire spine becomes fused, allowing no motion in any direction

  • Transient acute arthritis of the peripheral joints occurs in about 50% of cases, and permanent changes—most commonly the hips, shoulders, and knees—are seen in about 25%

  • Anterior uveitis in up to 25% of cases

  • Constitutional symptoms similar to those of rheumatoid arthritis are absent in most patients

Differential Diagnosis

  • Rheumatoid arthritis

    • Predominantly affects multiple, small, peripheral joints of the hands and feet

    • Usually spares the sacroiliac joints with little effect on the rest of the spine except for C1–C2

  • Ankylosing hyperostosis (diffuse idiopathic skeletal hyperostosis [DISH], Forestier disease)

    • Exuberant enthesophytes formation

    • Enthesophytes are thicker and more anterior than the syndesmophytes of ankylosing spondylitis

    • Sacroiliac joints are not affected

  • Reactive arthritis (formerly Reiter syndrome)

  • Psoriatic arthritis

  • Inflammatory bowel disease

  • Osteitis condensans ilii

  • Hyperparathyroidism

  • Whipple disease

  • Synovitis-acne-pustulosis-hyperostosis-osteitis (SAPHO) syndrome

  • Sciatica

  • Lumbar disk herniation, spinal stenosis, or facet joint degenerative arthritis

Diagnosis

Laboratory Tests

  • The erythrocyte sedimentation rate is elevated in 85% of cases

  • Serologic tests for rheumatoid factor and anti-CCP antibodies are characteristically negative

  • HLA-B27 is found in 90% of white patients and 50% of black patients with ankylosing spondylitis

    • Because this antigen occurs in 8% of the healthy white population (and 2% of healthy blacks), it is not a specific diagnostic test

Imaging Studies

  • The earliest radiographic changes of sclerosis and erosion are usually in the sacroiliac joints (early on may be detectable only by MRI)

  • Inflammation where the annulus fibrosus attaches to the vertebral bodies initially causes sclerosis ("the ...

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