Chronic inflammatory disease of the axial skeleton that leads to partial or even complete fusion and rigidity of the spine

Aetiology

• Genetic predisposition - HLA B27 (90%)
  • Often has a strong family history
• Three times more common in men than women
• Typical age of onset is 20-40 years

Pathophysiology

Clinical features

Articular symptoms

• Inflammatory spinal and back pain
  • Gradual onset of dull pain that progresses slowly
  • Early morning stiffness > 30 mins which gets better with activity
• Peripheral arthritis (knee, shoulders, hips) - rare

Signs

• Lumbar spine
  • Patients display restricted movements in almost all cases of ankylosing spondylitis
  • Schobers test: used to measure lumbar spine flexion
    • Involves measuring 5cm below the posterior superior iliac crests and 10cm above, whilst the patient is upright, then asking them to bend forwards and remeasuring the distance
    • In normal situations it should extend beyond 20cm
• Thoracic spine
  • Dorsal kyphosis can develop as the disease progresses
  • There is reduced chest expansion in some cases (defined as <5 cm)
• Cervical spine
  • Movements at the C-spine can be globally reduced, with the neck forced into a flexed position by dorsal kyphosis
  • Patient should be asked to stand with their back to the wall – the occiput-to-wall distance should be measured as a readout of fixed neck flexion (normal = 0)
• Tenderness of the sacroiliac joints
• Inflammatory enthesitis e.g. of the Achilles tendon, iliac crests - painful on palpation
• Late AS - loss of lumbar kyphosis with pronounced cervical lordosis ('question mark' posture)

Extra articular features

• Anterior uveitis (20–30%)