How to diagnose and manage ankylosing spondylitis?

How to Examine Ankylosing Spondylitis

Diagnostic Criteria

Diagnosis of ankylosing spondylitis requires meeting the modified New York criteria: radiological evidence of sacroiliitis plus at least one clinical criterion. 1

Clinical Criteria (need ≥1 of the following):

• Low back pain and stiffness for >3 months that improves with exercise but is not relieved by rest 2, 1
• Limitation of motion of the lumbar spine in both sagittal and frontal planes 2
• Limitation of chest expansion relative to normal values correlated for age and sex 2

Radiological Criterion:

• Sacroiliitis on plain radiographs (bilateral grade ≥2 or unilateral grade 3-4) 1
• For early disease without radiographic changes, MRI can detect active sacroiliitis before structural damage appears, allowing diagnosis of non-radiographic axial spondyloarthritis 3, 4

Clinical Assessment Parameters

The ASAS core set for daily practice should guide your examination and includes the following domains: 2

History Components:

• Pain assessment using visual analog scale (VAS) for spine pain at night and during the day due to AS 2
• Duration and intensity of morning stiffness (record both duration up to 120 minutes and VAS intensity) 2
• Overall level of fatigue/tiredness in past week 2
• Pain/swelling in peripheral joints other than neck, back, or hips 2
• Discomfort from areas tender to touch or pressure 2
• Patient's global assessment of disease activity (VAS, past week) 2

Physical Examination:

• Spinal mobility measurements:

  • Modified Schober test (lumbar flexion) 2
  • Chest expansion 2
  • Occiput-to-wall distance 2
  • Lateral lumbar flexion 2
  • Cervical rotation 5
  • Tragus-to-wall distance 5
  • Intermalleolar distance 5

• Peripheral joint assessment: 44-joint count for swollen joints 2

• Enthesitis scoring using validated instruments (Maastricht, Berlin, or San Francisco scoring systems) 2

Functional Assessment:

• Bath Ankylosing Spondylitis Functional Index (BASFI) or Dougados functional index 2
• Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) - calculate score from 6 VAS questions (0-10 scale) covering fatigue, spinal pain, peripheral joint pain, enthesitis, and morning stiffness 2
• Bath Ankylosing Spondylitis Metrology Index (BASMI) 5

Laboratory Tests:

• Acute phase reactants: ESR or CRP 2
• HLA-B27 testing (90-95% of AS patients are positive, though only 1% of HLA-B27+ individuals develop AS) 6

Imaging:

• Plain radiographs of sacroiliac joints and spine for established disease 1
• MRI of sacroiliac joints and spine for early disease detection when radiographs are normal 3, 4
• Radiographic monitoring generally not needed more often than every 2 years unless rapid progression is suspected 7

Disease Activity Assessment

Active disease is defined as: 2

• Disease activity for >4 weeks AND
• BASDAI >4 (on 0-10 scale) 2
• Expert clinical opinion (based on history, examination, acute phase reactants, and/or imaging showing rapid progression or continuing inflammation) 2

Common Pitfalls to Avoid

• Do not rely solely on imaging without clinical correlation - overreliance on imaging findings without symptoms leads to unnecessary interventions 7, 1
• Do not miss early disease - inflammatory back pain in patients aged 20-40 with morning stiffness improving with exercise should prompt consideration of AS, even with normal radiographs 6, 3
• Do not forget to assess extra-articular manifestations including uveitis, inflammatory bowel disease, and psoriasis 8
• Do not overlook cardiovascular risk and osteoporosis screening in established disease 8
• Suspect AS in patients with chronic lower back pain - up to 5% of primary care patients with chronic lower back pain have inflammatory disease 6