Ankylosing spondylitis

🦴 Ankylosing Spondylitis (AS) is a chronic, progressive inflammatory disease of the axial skeleton. It causes loss of lumbar lordosis, ↑ thoracic kyphosis, and sacroiliitis, with systemic extra-articular features. 💡 Classic: young man with back pain + morning stiffness that improves with exercise but not rest! 🏃‍♂️

ℹ️ About

• Part of the seronegative spondyloarthritides (RF negative, HLA-B27 linked).
• Onset: age 15–40, male:female ≈ 4:1.
• Inflammatory back pain starts in sacroiliac joints → ascends spine.
• Associated with enthesitis, peripheral arthritis, and systemic features.

⚙️ Pathology

• Chronic enthesitis (inflammation where ligaments/tendons attach to bone).
• New bone formation → syndesmophytes → gradual spinal fusion (bamboo spine on X-ray).
• Loss of lumbar lordosis, ↑ thoracic kyphosis, fixed flexion deformity.
• Costovertebral joint involvement → ↓ chest expansion.

🧬 Aetiology

• Strong genetic link: HLA-B27 present in >90% of patients.
• Environmental/infective triggers suggested (e.g. Klebsiella pneumoniae molecular mimicry).

📊 HLA-B27 Association

• Caucasian general population: ~8% carry HLA-B27.
• Ankylosing spondylitis: 90%.
• Reactive arthritis (Reiter’s): 70%.
• Enteropathic arthritis: 50%.
• Psoriatic arthritis: 20%.

Modified Schober Test

👨‍⚕️ Clinical – Spinal

• Young male, insidious onset chronic low back pain + morning stiffness >1h.
• Symptoms improve with exercise, not with rest.
• Loss of lumbar lordosis, ↑ thoracic kyphosis → “question-mark posture ❓”.
• Alternating buttock pain (sacroiliitis).
• Spinal rigidity → risk of fractures, cauda equina, cord compression.

🌍 Clinical – Extra-articular

• 👁️ Acute anterior uveitis (red, painful eye, photophobia, blurred vision).
• ❤️ Aortic regurgitation, aortitis, AV block.
• 🫁 Apical pulmonary fibrosis → restrictive lung disease.
• 🦵 Peripheral arthritis (hips, shoulders); enthesitis (Achilles, plantar fascia).
• 🧪 Rare: secondary AA amyloidosis.

📝 Aide-Mémoire – “9 A’s”

• Ankylosis (spinal fusion)
• Anterior uveitis
• Amyloidosis
• Aortic regurgitation / Aortitis
• AV block
• Apical pulmonary fibrosis
• Achilles tendonitis
• Anderson lesion (spinal fracture)
• Anti-TNF therapy (treatment)

📏 Clinical Tests of Spinal Mobility

• Modified Schober Test: lumbar flexion ↑ >3 cm normally.
• Lateral flexion: fingertip–floor distance ↓ >10 cm.
• Chest expansion: normally >3 cm at 4th intercostal space.
• Occiput–wall distance: normally 0 cm.
• Chin–sternum distance: should touch sternum.
• Cervical rotation: >50° normally.
• Intermalleolar distance: reduced if hip involvement.

🔎 Investigations

• Inflammatory markers: ESR, CRP often ↑.
• HLA-B27: supportive but not diagnostic.
• X-ray pelvis: bilateral sacroiliitis, squaring of vertebrae, syndesmophytes → “bamboo spine”.
• MRI sacroiliac joints: detects early inflammation before X-ray changes.

💊 Management

• 🏃 Physiotherapy + exercise: cornerstone of management.
• 💊 NSAIDs (naproxen, indomethacin) first-line for pain/stiffness.
• 🧴 Biologics: anti-TNF (etanercept, adalimumab) or IL-17 inhibitor (secukinumab) if refractory.
• 💊 DMARDs (e.g. sulfasalazine, methotrexate): helpful for peripheral arthritis, not axial disease.
• 🦴 Bisphosphonates if osteoporosis risk.
• 👁️ Treat uveitis promptly with steroids (ophthalmology input).
• 💉 Surgery: joint replacement if severe hip involvement.

📚 Teaching Pearls

💡 Key exam clue = young man + inflammatory back pain that improves with activity. 🔍 Always check for extra-articular features (esp. uveitis, cardiac). ⚠️ Complication to remember = spinal fractures + cauda equina. 🏥 Long-term monitoring: bone density, echo (aortic regurg), chest imaging, ophthalmology.