Can you have Ankylosing Spondylitis (AS) in your ankle and how is it diagnosed, particularly with X-rays or other imaging modalities?

Ankylosing Spondylitis in the Ankle: Diagnosis and Imaging

Yes, ankylosing spondylitis (AS) can affect the ankle, though it is uncommon compared to its typical involvement of the sacroiliac joints and spine. 1 Peripheral joint involvement, including the ankle, occurs in approximately 30-50% of patients with axial spondyloarthritis. 2

Ankle Involvement in Ankylosing Spondylitis

• Ankle involvement is less common than involvement of the sacroiliac joints and spine
• In juvenile ankylosing spondylitis, peripheral joint involvement (including ankles) is more frequent and can precede back symptoms by many years 3
• In rare cases, AS can lead to complete fusion of the ankle joint, hindfoot, and midfoot (termed "boot sign") 1
• Peripheral manifestations such as arthritis and enthesitis (including in the ankle) have been reported more frequently in Latin America than in Europe or USA 4

Diagnostic Approach for AS with Ankle Symptoms

Clinical Assessment

• Look for inflammatory characteristics:
  • Pain that improves with activity but not with rest
  • Morning stiffness lasting more than 30 minutes
  • Pain at night/early morning
  • Age of onset before 45 years
  • Symptoms lasting more than 3 months 4
• Check for extra-articular manifestations:
  • Uveitis
  • Psoriasis
  • Inflammatory bowel disease 5

Laboratory Testing

• HLA-B27 testing (positive in 74-89% of AS patients) 4
• Inflammatory markers (ESR, CRP) - though normal levels don't rule out AS (sensitivity only 50%) 4

Imaging for Diagnosis

First-line Imaging

• Radiographs (X-rays) are recommended as the first imaging modality 2
  • Look for erosions, sclerosis, joint space narrowing, and ankylosis
  • Limitations: Low sensitivity for early disease; findings may lag behind clinical symptoms by 7+ years 2

Second-line Imaging

• MRI is the preferred second-line imaging when radiographs are negative or equivocal 2

  • Should include:
    • T1 sequences
    • Fat-suppressed fluid-sensitive sequences (T2-weighted fat-suppressed or STIR images) 2, 4
  • Bone marrow edema on MRI is the hallmark of active inflammation 4
  • Can detect inflammatory changes before radiographic damage 6
  • No need for contrast in most cases, though gadolinium can help differentiate synovitis from fluid 2

• CT may be helpful when:

  • MRI is contraindicated
  • Radiographs show equivocal findings
  • Better for detecting subtle erosions and reparative changes 2
  • Allows better assessment of complex joint anatomy 2
  • Limitation: Lacks sensitivity for direct inflammatory changes of early disease 2

Diagnostic Pitfalls to Avoid

• Over-reliance on radiographs alone can delay diagnosis 4
• Normal inflammatory markers don't rule out AS 4
• Focusing only on axial symptoms and missing peripheral manifestations 4
• Referring to inappropriate specialists (pain management instead of rheumatology) 4
• Delay in diagnosis is common (average 7-10 years from symptom onset) 4

Management Considerations

• Refer to a rheumatologist for diagnosis, treatment, and ongoing management 4
• NSAIDs are first-line treatment 4
• For persistent symptoms, TNF inhibitors are recommended as first biologic therapy 4
• Regular assessment of disease activity using validated tools (ASDAS-CRP, BASDAI) 4
• Physical therapy and exercise are important components of treatment 2

Remember that ankle involvement in AS, while less common than axial involvement, can be a significant source of disability and should be properly evaluated and managed to improve quality of life and prevent long-term joint damage.