How is Ankylosing Spondylitis (AS) diagnosed and treated?

Ankylosing Spondylitis: Diagnosis and Treatment

Diagnosis

Diagnose AS using the modified New York criteria: radiographic evidence of sacroiliitis (bilateral grade 2 or unilateral grade 3-4) plus at least one clinical criterion. 1

Clinical Criteria for Diagnosis

• Inflammatory back pain lasting >3 months with onset before age 45, characterized by: 2
  • Morning stiffness >30 minutes
  • Improvement with exercise but not rest
  • Insidious onset
  • Alternating buttock pain
• Limitation of lumbar spine motion in sagittal and frontal planes 2
• Limitation of chest expansion relative to age/sex-matched normal values 2

Early Detection Strategy

For chronic back pain >3 months with onset before age 45, use inflammatory back pain plus HLA-B27 testing as screening parameters. 2

• Inflammatory back pain alone increases post-test probability to 14% for axial spondyloarthritis 2
• MRI can detect sacroiliac joint inflammation years before radiographic changes appear 2
• Consider the diagnosis even without radiographic sacroiliitis (pre-radiographic or non-radiographic axial spondyloarthritis) 2

Disease Monitoring

Monitor using the ASAS core set including: 2

• BASDAI (Bath Ankylosing Spondylitis Disease Activity Index) score
• Physical function (BASFI)
• Spinal mobility measurements (chest expansion, modified Schober, occiput-to-wall distance)
• Inflammatory markers (ESR, CRP)
• Patient global assessment

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Treatment Algorithm

Step 1: Non-Pharmacological Foundation (Initiate Immediately)

All patients require patient education and regular exercise as cornerstone treatment. 2, 1

• Supervised physical therapy (individual or group, land or water-based) is superior to home exercises alone 2, 1
• Group therapy shows better patient global assessment outcomes than individual therapy 1

Step 2: First-Line Pharmacological Treatment

NSAIDs are first-line drug treatment for pain and stiffness. 2, 1

• 75% of AS patients show good/very good response to full-dose NSAIDs within 48 hours (versus 15% with mechanical back pain) 2
• Continuous long-term NSAID treatment is preferred for persistently active symptomatic disease 2
• For patients with increased GI risk: use selective COX-2 inhibitor OR non-selective NSAID plus gastroprotective agent (PPI or H2-blocker at double doses) 2, 1
• Cardiovascular and renal risks must be assessed before prescribing 2

Common Pitfall: Inadequate NSAID trial—must try at least 2 different NSAIDs at maximum tolerated dose for at least 3 months each before declaring treatment failure 2, 1

Step 3: Adjunctive Therapies

If NSAIDs are insufficient, contraindicated, or poorly tolerated: 2, 1

• Analgesics (paracetamol, opioids) for residual pain control 2
• Local corticosteroid injections for peripheral arthritis or enthesitis 2, 1
• Avoid systemic corticosteroids for axial disease—no evidence of efficacy 2, 1

Step 4: Disease-Modifying Treatment

Traditional DMARDs (sulfasalazine, methotrexate) have NO efficacy for axial disease. 2

• Sulfasalazine may be considered ONLY for peripheral arthritis 2
• There is no evidence supporting obligatory DMARD use before anti-TNF therapy in axial disease 2

Step 5: Anti-TNF Therapy (Biologic Treatment)

Initiate anti-TNF treatment when persistently high disease activity (BASDAI >4) persists despite conventional treatments. 2, 1

Eligibility Criteria for Anti-TNF Therapy 2

• Active disease >4 weeks with BASDAI >4
• Failed adequate trials of at least 2 NSAIDs (3 months each at maximal recommended/tolerated dose)
• For peripheral arthritis: failed at least one local corticosteroid injection if appropriate
• For persistent peripheral arthritis: failed sulfasalazine trial (4 months at standard target dose)

Anti-TNF Agent Selection

Both etanercept and infliximab/adalimumab (monoclonal antibodies) are effective for AS, but efficacy differs for extra-articular manifestations. 3, 4

• Etanercept (50 mg weekly subcutaneously) is FDA-approved for reducing signs and symptoms in active AS 3
• Monoclonal antibodies (infliximab, adalimumab) are preferred over etanercept for patients with inflammatory bowel disease or recurrent uveitis 4
• Etanercept has limited efficacy for uveitis and very little effect on inflammatory bowel disease 4
• 72% of patients with disease duration <10 years achieve ≥50% improvement with anti-TNF therapy 2

Response Assessment

• Evaluate response between 6-12 weeks 2
• Responder criteria: 50% relative change in BASDAI OR absolute change of 20mm (0-100 scale) 2
• Continue therapy if response criteria met and expert opinion favors continuation 2

Step 6: Surgical Intervention

Total hip arthroplasty should be considered for refractory pain/disability with radiographic structural damage, independent of age. 2

• Spinal corrective osteotomy and stabilization may benefit selected patients 2

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Critical Pitfalls to Avoid

1. Delaying diagnosis: Average 5-7 year delay between first symptoms and diagnosis is unacceptable given effective treatments 2
2. Overreliance on radiographs: MRI detects inflammation years before radiographic changes 2
3. Using systemic corticosteroids for axial disease: No evidence of benefit 2, 1
4. Prescribing DMARDs for axial disease: Sulfasalazine and methotrexate are ineffective for axial manifestations 2
5. Inadequate NSAID trials: Must try 2 different NSAIDs for 3 months each at maximum dose before declaring failure 2, 1
6. Not considering anti-TNF therapy early enough: Patients with disease duration <10 years respond better 2
7. Choosing etanercept for patients with IBD or recurrent uveitis: Monoclonal antibodies are superior for these extra-articular manifestations 4