Ankylosing Spondylitis

Definition of ankylosing spondylitis (AS)

An inflammatory disease of the spine affecting young (usually) HLA-B27 positive adults.
- HLA-B27 is present in about 8% of normal population, but up to 90% of patients with ankylosing spondylitis
- Possible environmental trigger in these patients: potentially gut micro-flora or mechanical (as yet uncertain)
Males are affected more than women (3:1)
“Rule of twos” – ank spond occurs in:
- 2% of the general population
- 2% of HLA-B27 positive people
- 20% of HLA-B27 positive people with an affected family member

Episodic inflammation of the sacroiliac joints in late teens/early 20s
Morning low back pain and stiffness
- Improves on exercise
- May radiate into both buttocks
Extra-spinal features
- Other joint pain
  - Hips (in about 1/3 of patients)
  - Shoulder girdle, costochondral joints
  - Peripheral joint involvement in about 25%, usually oligo-articular, large joint & asymmetric
- Inflammation of the Achilles tendon insertion (enthesitis)
- Uveitis
- Aortitis & aortic insufficiency
- Apical fibrosis

Mobility
- Reduced flexion in the lumbar spine
  - Modified Shober’s test: distance between the midpoint of the posterior superior iliac spines and a point 10cm vertically above when standing erect, following maximal forward flexion of the spine (normal > 15cm)
- Increased extension at cervical spine
  - Increased occiput to wall distance: patient stands facing away from wall with heels touching wall. Occiput may not be able to touch wall in ankylosing spondylitis
- Reduced rotation at lumber, thoracic and cervical spine
Other
- Reduced chest expansion often present (restrictive pattern on lung function tests)
- Listen for fine crepitations in upper lung zones
NB. The Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) is used to assess burden of active disease

Bloods
- CRP and ESR usually raised
- HLA testing is rarely indicated. Many HLA-B27 positive don’t get AS, and some people without it do.
  - Prevalence 2-8% (30% in eskimos!)

Imaging
- Plain X-rays
  - Loss of definition, then sclerosis, of sacroiliac joints
    - Bilateral sacroiliac erosion on X-Ray is the most suggestive feature of AS, more than HLA-B27 positivity
  - Sclerosis of intervertebral joints and the insertions of intervertebral ligaments
  - Late changes
    - Sacroiliac joints fus
    - Intervertebral discs, facet joints and syndesmophytes all fuse
      - This is ‘bamboo spine’ or tramline appearance
- MRI spine

Conservative
- Morning exercises to preserve flexibility
Medical
- NSAIDs during exacerbations
- Local steroid injections for peripheral arthritis
- DMARDs (e.g. methotrexate and sulphasalazine)
  - May help with peripheral arthritis but not particularly effective for spinal disease
  - See here for monitoring of DMARDS
- TNF-alpha blocker drugs are effective in severe disease

Most patients do well with exercise and analgesia
80% are employed
Hip disease is more disabling than other components
Indicators of poor prognosis:
- High ESR
- Poor response to NSAIDs
NB the rigid AS spine requires very little force to fracture – have a high index of suspicion