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For further information, see CMDT Part 22-31: Axial Spondyloarthritis (Ankylosing Spondylitis)

KEY FEATURES

Essentials of Diagnosis

  • Chronic low backache and stiffness in young adults (onset age < 45 years), 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%

  • May be radiographic (ankylosing spondylitis) or non-radiographic

  • 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 SpA is a chronic inflammatory disease of the joints of the axial skeleton, manifested clinically by pain and progressive fusion of the spine

  • Axial SpA can be

    • Radiographic, with diagnostic changes of sacroiliac joints or spine visible on plain radiograph; radiographic axial SpA is also called ankylosing spondylitis

    • Nonradiographic, in which axial inflammation (sacroiliitis) is only visualized by MRI

  • The radiographic/nonradiographic classification more likely represents a spectrum of disease rather than distinct conditions

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

  • Worse in the morning and associated with stiffness that lasts hours

  • Pain and stiffness improve with activity, in contrast to back pain due to mechanical causes, 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

  • 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%

  • Enthesopathy, a hallmark of the spondyloarthropathies, can manifest as

    • Swelling of the Achilles tendon at its insertion

    • Plantar fasciitis or

    • Dactylitis

  • Anterior uveitis in up to 25% of cases

Differential Diagnosis

  • Rheumatoid arthritis

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

    • Usually spares the sacroiliac joints and only affects the cervical component of the spine

  • Spondyloarthropathy associated with inflammatory bowel disease (IBD) causes bilateral sacroiliitis that is indistinguishable from ankylosing spondylitis

  • Sacroiliitis associated with reactive arthritis and psoriasis is often asymmetric or even unilateral

  • 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

  • Osteitis condensans ilii

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

DIAGNOSIS

Laboratory ...

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