Ankylosing Spondylitis (AS)

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management | References

Definition

Ankylosing Spondylitis (AS) is a chronic inflammatory disorder primarily affecting the axial skeleton, particularly the sacroiliac joints and spine. It leads to pain, stiffness, and progressive fusion of the vertebrae, resulting in reduced mobility and, in severe cases, a stooped posture.

Aetiology

The exact cause of AS is unknown, but it is believed to result from a combination of genetic and environmental factors. Key contributors include:

• Genetic predisposition, particularly the presence of the HLA-B27 gene, which is found in over 90% of people with AS
• Environmental triggers, such as infections, that may play a role in initiating the immune response
• Immune system dysregulation, leading to chronic inflammation of the joints and entheses (the sites where tendons and ligaments attach to bone)

Pathophysiology

The pathophysiology of AS involves:

• Chronic inflammation of the sacroiliac joints and spine, leading to pain and stiffness
• Enthesitis, or inflammation of the entheses, which contributes to the symptoms of pain and stiffness
• New bone formation, which can lead to the fusion of vertebrae (ankylosis) and reduced spinal mobility
• Progressive fusion of the vertebrae, leading to a rigid spine and, in severe cases, a characteristic stooped posture
• Extra-articular manifestations, including uveitis, cardiovascular disease, and pulmonary involvement

Risk Factors

• Male gender, as AS is more common in men
• Age of onset typically between 20 and 40 years
• Positive family history of AS or other spondyloarthropathies
• Presence of the HLA-B27 gene
• Chronic gastrointestinal infections, which may increase the risk of developing AS

Signs and Symptoms

The signs and symptoms of AS include:

• Chronic back pain and stiffness, particularly in the lower back and buttocks, often worse in the morning or after periods of inactivity
• Improvement of symptoms with exercise and worsening with rest
• Limited spinal mobility, leading to difficulty bending or turning the body
• Fatigue, which is common and can be severe
• Peripheral arthritis, particularly affecting the hips, shoulders, and knees
• Enthesitis, causing pain at the sites of tendon and ligament attachment to bone, such as the Achilles tendon
• Extra-articular manifestations, including uveitis (eye inflammation), psoriasis, and inflammatory bowel disease

Investigations

Specific investigations to diagnose AS include:

• Blood tests: Raised inflammatory markers such as erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP). HLA-B27 testing may be performed to assess genetic predisposition.
• Imaging studies: X-rays of the sacroiliac joints and spine to detect characteristic changes such as sacroiliitis, syndesmophytes, and vertebral fusion.
• MRI: Magnetic resonance imaging is more sensitive than X-rays in detecting early inflammatory changes in the sacroiliac joints and spine.
• Clinical assessment: Evaluation of spinal mobility using measures such as the Schober's test and chest expansion.

Management

Primary Care Management

• Referral to rheumatology: Early referral is crucial for the initiation of disease-modifying treatment.
• NSAIDs: Nonsteroidal anti-inflammatory drugs (e.g., ibuprofen, naproxen) are the first-line treatment for pain relief and inflammation control.
• Physical therapy: Regular exercise, including stretching and strengthening exercises, is essential to maintain spinal mobility and posture.
• Education and support: Providing patients with information about AS, its course, and the importance of regular exercise and adherence to treatment.

Specialist Management

• DMARDs: Disease-modifying antirheumatic drugs such as sulfasalazine may be used for peripheral joint involvement, although they are generally less effective for axial symptoms.
• Biologic therapy: TNF inhibitors (e.g., etanercept, infliximab) or interleukin-17 (IL-17) inhibitors (e.g., secukinumab) are effective in reducing inflammation and slowing disease progression in patients with active AS who do not respond to NSAIDs.
• Management of extra-articular manifestations: Specialist care may be required for associated conditions such as uveitis, inflammatory bowel disease, or cardiovascular disease.
• Surgical intervention: In severe cases, corrective surgery may be considered for spinal deformities or joint replacements for damaged peripheral joints.
• Regular monitoring: Ongoing assessment of disease activity, treatment side effects, and overall health, including periodic imaging and blood tests.

References

1. NHS (2024) Ankylosing Spondylitis. Available at: https://www.nhs.uk/conditions/ankylosing-spondylitis/ (Accessed: 24 June 2024).
2. National Institute for Health and Care Excellence (2024) Ankylosing Spondylitis and Axial Spondyloarthritis. Available at: https://cks.nice.org.uk/topics/ankylosing-spondylitis/ (Accessed: 24 June 2024).
3. British Medical Journal (2024) Ankylosing Spondylitis: Clinical Features, Diagnosis, and Management. Available at: https://www.bmj.com/content/350/bmj.h3050 (Accessed: 24 June 2024).
4. American College of Rheumatology (2024) Ankylosing Spondylitis. Available at: https://www.rheumatology.org/I-Am-A/Patient-Caregiver/Diseases-Conditions/Ankylosing-Spondylitis (Accessed: 24 June 2024).

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