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Ankylosing Spondylitis

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Overview

Ankylosing spondylitis (AS) is a chronic seronegative spondyloarthritis (arthritis affecting the spine) primarily affecting the axial skeleton (sacroiliitis and spondylitis).

It is diagnosed using a combination of clinical features of inflammatory back pain and enthesitis, or arthritis with radiological findings.

Epidemiology

  • AS is twice as common in men than in women
  • AS most commonly begins between 20-30 years of age

Risk Factors

  • HLA-B27 presence
  • Family history of AS
  • Male sex

Presentation

Suspect AS in a patient aged 20-30 with an insidious onset of lower back pain. Features include:

  • Inflammatory joint pain:
    • Pain and stiffness improve with movement and are worse with rest
    • Prolonged morning stiffness (usually >1 hour)
    • There may be pain at night that wakes the patient up
  • Enthesitis – Achilles tendonitis, tibial tuberosity enthesitis, plantar fasciitis
  • Dactylitis – swelling of a digit
  • Peripheral arthritis – there may be involvement of lower limb joints
  • Fatigue
  • Extra-articular features and complications:

Signs on examination

  • Loss of lumbar lordosis
  • Schober’s test positive
    • The examiner marks the L5 spinous process and marks 10cm above and 5cm below this point. The examiner then asks the patient to bend forward as far as possible and measures the distance between the two points. A distance of <20cm is positive.
  • Dyspnoea
    • May be due to spinal kyphosis leading to lung expansion limitation
  • Kyphosis
  • Tenderness at the sacroiliac joint

Differential Diagnoses

Osteoarthritis (OA)

  • Arthritis is non-inflammatory (relieves with rest, worse on exertion)
  • Usually seen in older patients (>45 years)

Psoriatic arthritis (PsA)

  • There may be a history of psoriasis
  • Dactylitis is more commonly seen in PsA
  • There may be associated nail changes (e.g. nail pitting or onycholysis)
  • Sacroiliitis may be unilateral

Reactive arthritis

  • There is usually a history of a recent sexually-transmitted infection or gastroenteritis
  • There may be additional features including conjunctivitis and urethritis

Enteropathic arthritis

Diagnosis

Some investigations include:

  • Pelvic x-ray:
    • Shows sacroiliitis
    • Vertebral bodies may become squared
    • Syndesmophytes (bony-bridges) may form between adjacent vertebrae
    • In late disease, there may be a complete fusion of the vertebral column – bamboo spine
  • Chest x-ray:
    • This may show apical fibrosis
    • If spirometry is performed this shows a restrictive defect
  • MRI – performed if the x-ray does not show signs:
    • May show early signs of inflammation (e.g. bone marrow oedema)

AS is diagnosed using a combination of clinical features of inflammatory back pain and enthesitis, or arthritis with radiological findings.

Management

Overview

All patients should be encouraged to exercise regularly.

  • Adults with pain with or without stiffness
    • 1st line: NSAIDs + physiotherapy
  • Adults with pain with or without stiffness unresponsive to 2 different NSAIDs
    • 1st line: TNF-inhibitors + physiotherapy and continue NSAID
      • Adalimumab
      • Etanercept
      • Infliximab
      • Golimumab

Patient Advice

  • Patients should keep active and perform regular stretches
  • Patients should use NSAIDs when they have inflammatory back pain symptoms
  • Patients should be aware of iritis and when to seek help

Complications

  • Spinal fusion due to new bone formation
  • Spinal fractures
  • Hip joint involvement
  • Anterior uveitis
  • Osteoporosis
  • Aortic regurgitation
  • Congestive heart failure
  • Restrictive pulmonary fibrosis
  • Neurological defects due to vertebral fracture, dislocation, or cauda equina syndrome
  • Adverse effects from treatment:
    • NSAIDs – gastritis/ulcers/renal impairment
    • DMARDs – infection/immunosuppression/malignancy
  • Decreased quality of life

Prognosis

  • Damage is progressive and irreversible
  • Prognosis depends on the presence of extraspinal manifestations, age at diagnosis, and choice of treatment
  • Increased risk of spinal fracture later in life

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