Ankylosing Spondylitis def., causes, pathology, clinical picture

This article is to discuss Ankylosing Spondylitis (AS) regarding its medical definition, Aetiology (Causes and incidence), Pathogenesis and clinical picture (symptoms and signs).
Investigations, Differential diagnosis and treatment are discussed later .
It is an inflammatory arthropathy starting in the sacroiliac and spinal joints with tendency to ankylosis of the axial skeleton.

Causes and incidence of Ankylosing Spondylitis 

• The prevalence is about 0.2% of the general population.
• Age of onset: 15 - 40 years.
• Sex:  male : female  = 3 : 1
• HLA - B27 association (95% of patients have HLA-827).
• High incidence of prostatic infection by klebsiella
So, there may be an association between this disease and klebsiella infection .

pathology of Ankylosing Spondylitis

1- Vertebrae become square shaped due to erosion of their corners.
2- Periosteal reaction with new bone formation around vertebrae (bony bridging) = Syndesmophytes (osteophytes) spread up and down from vertebral body with fusion ==> bamboo spin
3- Calcification of anterior longitudinal ligament.
4- Extra-articular lesions:
   - Aortic valve (Aortitis) ===>  fibrosis at valve base ==> Aortic incompetence
   - Lung? upper lobe fibrosis.
   - Iritis in 25% of patients.
- Amyloidosis of kidney ==> nephrotic syndrome.

Clinical picture 

• The onset is usually insidious over months or years with recurring episodes of low back pain and stiffness sometimes radiating to buttocks or thighs, improved with movement.
1- Vertebral column .
    • Limited lumber movement.
    • Chest pain aggravated by breathing results from affection of costovertebral joints.
    • Neck pain.
    • Atlanto - axial sublaxation.
2- Enthesopathy
     • Inflammation at the site of ligamentous insertion. e.g. Achilles tendenitis.
3- Peripheral joint
       •  Asymmetrical arthritis.
       • Shoulder and hi joint are usuall affected.

 Sacroiliits lead to low back ache. it is tested by pushing the sacrum forward.

4- Extra-articular manifestations
• Amyloidosis kidney.
• Aortic incompetence, cardiac conduction defects, pericarditis.
• Apical lung fibrosis.
• Prolonged fever.
• Uveitis.

How can you differentiate between mechanical and inflammatory back ache e.g AS?

1- Character of pain.
Inflammatory : +++ at night, it is improved by movement.
Mechanical    : +++ with movement and improved with rest.
2- Laboratory findings.
- ESR, CRP +++ in inflammatory back ache.
Schober test

Ankylosing spondylitis differential diagnosis, investigations,prognosis, treatment

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