Axial Spondyloarthritis (Ankylosing Spondylitis)

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

• Axial spondyloarthritis is a general term for inflammatory arthritides that affect the spine and the sacroiliac joints

• Ankylosing spondylitis, the prototypic radiographic axial spondyloarthritis, is a chronic inflammatory disease of the joints of the axial skeleton, manifested clinically by pain and progressive fusion 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

• 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 White persons and 2% of healthy Black persons, this is not a specific diagnostic ...