📋 Key Information Summary
- Spondyloarthritis (SpA) encompasses a group of inflammatory rheumatic diseases with shared genetic (HLA-B27) and clinical features.
- Classification is split into axial SpA (including ankylosing spondylitis) and peripheral SpA.
- Diagnosis is clinical, supported by imaging (X-ray/MRI sacroiliac joints) and HLA-B27 testing per ASAS classification criteria.
- First-line pharmacotherapy for axial disease is regular NSAIDs (e.g., naproxen 500 mg BD); monitor renal/GI risk.
- TNF inhibitors (e.g., adalimumab) or IL-17 inhibitors (e.g., secukinumab) are PBS Authority Required for severe active axial SpA after NSAID failure.
- Peripheral arthritis may respond to DMARDs (sulfasalazine, methotrexate); evidence is limited.
- HLA-B27 testing is most useful in patients with intermediate pre-test probability of axial SpA; not a standalone diagnostic.
- MRI is more sensitive than X-ray for early sacroiliitis (bone marrow oedema).
- Enthesitis and dactylitis are hallmark clinical features; assess with clinical exam (e.g., Leeds Enthesitis Index).
- Non-pharmacological management is essential: physiotherapy, exercise, smoking cessation.
- Aboriginal and Torres Strait Islander peoples have higher HLA-B27 prevalence and SpA burden; ensure culturally safe care and access to specialist services.
Introduction & Australian Epidemiology
Spondyloarthritis (SpA) is a group of interrelated chronic inflammatory rheumatic diseases. In Australia, prevalence of axial SpA is estimated at 0.5–1.0%. Disease typically presents in young adults (20–40 years), with a male predominance for radiographic axial SpA (ankylosing spondylitis).
Diagnostic delay: Average time from symptom onset to diagnosis in Australia is 5–7 years, leading to avoidable structural damage and disability.
Axial Spondyloarthritis
Axial SpA primarily affects the spine and sacroiliac joints. It is subdivided into:
- Radiographic axial SpA (ankylosing spondylitis): Definite sacroiliitis on X-ray (≥Grade 2 bilateral or ≥Grade 3 unilateral).
- Non-radiographic axial SpA: Inflammatory back pain + sacroiliitis on MRI or HLA-B27 positivity, but without definitive X-ray changes.
Clinical Features
- Inflammatory back pain: age of onset <45 years, insidious onset, improves with exercise, not relieved by rest, night pain (second half of night).
- Reduced spinal mobility (Schober's test, lateral flexion).
- Alternating buttock pain.
Peripheral Spondyloarthritis
Peripheral SpA presents with one or more of:
- Peripheral arthritis: Typically oligoarticular, asymmetric, lower limb predominant.
- Enthesitis: Inflammation at tendon/ligament insertion (e.g., Achilles, plantar fascia).
- Dactylitis: "Sausage digit" (diffuse swelling of a finger or toe).
This may occur in isolation or with concurrent axial disease. Subtypes include psoriatic arthritis, reactive arthritis, and arthritis associated with inflammatory bowel disease.
HLA-B27 Testing
HLA-B27 is a genetic marker strongly associated with SpA, but not diagnostic.
| Aspect | Details |
|---|---|
| Prevalence in Australia | 8–10% general population; ~90% of ankylosing spondylitis patients. |
| MBS Item | MBS item 71151 (HLA typing, one locus). |
| When to test | Suspected axial SpA with intermediate pre-test probability (e.g., chronic back pain + ≥1 SpA feature). |
| Interpretation | Positive result increases likelihood; negative result makes axial SpA less likely (especially if pre-test probability low). |
Sacroiliitis (Imaging & ASAS Criteria)
ASAS Classification Criteria for Axial SpA
In patients with back pain ≥3 months and age of onset <45 years:
- Sacroiliitis on imaging* PLUS ≥1 SpA feature, OR
- HLA-B27 positivity PLUS ≥2 other SpA features.
*Imaging: X-ray (radiographic sacroiliitis) or MRI (active inflammation: bone marrow oedema).
Imaging Modalities
✔ MBS Available
Plain radiograph (AP pelvis)
Detects chronic structural changes (sclerosis, erosions, ankylosis). MBS item 59502.
✔ MBS Available
MRI sacroiliac joints (STIR sequence)
Gold standard for early inflammatory sacroiliitis (bone marrow oedema). MBS item 63053.
TNF & IL-17 Inhibitors
Indicated for severe active axial SpA (radiographic or non-radiographic) with inadequate response to ≥2 NSAIDs over 4 weeks total.
Authority Required (PBS): Prescribing requires PBS Authority approval. Must be initiated/supervised by a rheumatologist. Patient must meet specific clinical and prior therapy criteria.
Adalimumab
Humira® · TNF inhibitor
Adult dose
40 mg SC every 14 days
PBS status
✔ PBS Authority Required
Secukinumab
Cosentyx® · IL-17A inhibitor
Adult dose
150 mg SC every 4 weeks (after loading)
PBS status
✔ PBS Authority Required
Key Considerations
- Screening: Mandatory for latent TB (IGRA/TST) and hepatitis B/C before initiation.
- Live vaccines contraindicated during therapy.
- Choice: TNF-i are first-line biologics. IL-17i are an alternative first-line or second-line if TNF-i fail/contraindicated.
Enthesitis & Dactylitis
These are hallmark clinical features of SpA.
Assessment
- Enthesitis: Tenderness at specific sites (e.g., lateral epicondyle, Achilles insertion, plantar fascia). Validated index: Leeds Enthesitis Index (LEI).
- Dactylitis: Diffuse swelling of entire digit ("sausage digit").
Management
- Local corticosteroid injection for severe focal enthesitis/dactylitis.
- Systemic therapy (NSAIDs, biologics) for widespread or refractory disease.
- IL-17 inhibitors (e.g., secukinumab) show particular efficacy for enthesitis.
Aboriginal and Torres Strait Islander Health
Aboriginal and Torres Strait Islander Health Considerations
📚 References
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