Anklylosing Spondylitis

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%)
  • More common in males (~4:1)
  • Typical age of onset is 20-40 years

Pathophysiology

notion image

Clinical presentation

Articular symptoms

  • Spinal and neck pain
    • Gradual onset of dull pain that progresses slowly
  • Morning stiffness > 30 mins that improves with activity
  • Peripheral arthritis (knee, shoulders, hips) - rare
  • Late AS - loss of lumbar kyphosis with pronounced cervical lordosis ('question mark' posture)

Signs

  • 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
  • Reduced chest expansion
  • Occiput-to-wall (normal = 0)
  • Inflammatory enthesitis e.g. of the Achilles tendon, iliac crests - painful on palpation

Extra articular features

  • Anterior uveitis
  • Cardiovascular involvement (aortic valve/root - aortic regurg)
  • Pulmonary involvement (upper lobe fibrosis)
  • Asymptomatic enteric mucosal inflammation
  • Neurological involvement (rarely A-A sublaxation)
  • Amyloidosis

Investigations

Bloods

  • Raised inflammatory markers
  • HLA B27

Imaging

  • X-ray
    • Bone density (normal early disease, reduced in later disease)
    • May show sclerosis and fusion of the sacroiliac joints
    • Bony spurs from the vertebral bodies (syndesmophytes) can bridge the intervertebral disc resulting in fusion, producing a 'bamboo spine'
    • Skinny corners
    • Common for X-rays to be normal at the time of presentation
  • MRI - can detect sacroiliitis (active inflammation) and earlier changes such as bone marrow oedema and enthesitis of the spinal ligaments

ASAS classification criteria for axial spondylarthritis (SpA)

  • In patients with ≳ 3 months back pain and age of onset <45 years
  • Sacrolitis on imaging and ≳1 SpA feature OR HLA-B27 positive and ≳ 2 other SpA features (e.g. inflammatory back pain, arthritis, enthesitis, dactilitis, raised CRP)

Management

Non-pharmacological

  • Physiotherapy, occupational therapy, orthotics, chiropodist

Pharmacological

  • NSAIDs - first line
  • Symptomatic - corticosteriods/joint injections, topical steriod eyedrops
  • DMARDs e.g. methotrexate, sulfasalazine, leflunomide
  • Anti-TNF in severe disease unresponsive to NSAIDs and methotrexate
  • Consider other biologics if still unresponsive e.g. secukinumab (anti-IL17)

Surgery

  • Mainly reserved for hip and knee arthritis, kyphoplasty is controversial and carries considerable risk