Ankylosing spondylitis - Seronegative arthritides (spondyloarthropathies)

Seronegative arthritides (spondyloarthropathies)

Ankylosing spondylitis

Definition

Ankylosing spondylitis is a chronic inflammatory arthritis predominantly affecting the axial skeleton, causing pain and progressive stiffness.

Prevalence

0.2% of the population.

Age

Usual onset at 16–40 years.

Sex

5M : 1F, overt disease.

Aetiology

HLA B27 is present in over 90% of Caucasians with ankylosing spondylitis. Environmental factors are implicated due to discordance in identical twins. Suggested agents include bacterial infection (such as Klebsiella).

Pathophysiology

There is an inflammatory reaction at the site of ligament to bone attachment (enthesopathy), which then progresses to ligamentous ossification. Microscopically, there is oedema and inflammation, especially in the adjacent bone marrow. Synovitis of the spine and large joints may occur, and there is both synovitis and enthesopathy at the sacroiliac joints. The outer layer of the intervertebral disc becomes calcified and forms a bony bridge between vertebral bodies (syndesmophytes). As these extend up the spine, calcification causes rigidity and a typical ‘bamboo’ appearance on X-ray.

Clinical features

Patients develop a gradual onset of episodic low-back pain and morning stiffness. There is a loss of normal lumbar lordosis due to muscle spasm and sacroiliac joint tenderness. Movement of the spine is restricted in all planes and a limitation of chest expansion may occur. Late in the disease there is a severe kyphosis (see Fig. 8.2) with marked limitation of movement or complete rigidity of the spine. Acute anterior uveitis, aortic regurgitation and apical lung fibrosis are known extra-articular features.

Complications

Spinal fractures may occur with minimal trauma due to localised osteoporosis (secondary to immobility and inflammation). Atlantoaxial subluxation and cauda equina syndrome may occur.

Investigations

Inflammatory markers (particularly CRP) are often elevated in active phases of the disease, although may be normal even with severe disease.

X-rays may be normal in early stages.

i.            Early signs on bilateral AP views of sacroiliac joints are of sclerosis and erosions in the sacroiliac joints,

ii.            Lateral views of lumbar spine show erosions of edges of vertebral bodies, squaring of the vertebrae, syndesmophyte formation and ‘bamboo’ spine.

Management

Major objectives are to relieve the pain and stiffness.

Patients should be encouraged to remain active, avoid prolonged bed rest and avoid lumbar supports. Physiotherapy involvement is important.

Pain and morning stiffness are treated with non-steroidal antiinflammatory drugs.

Large joint involvement may also respond to drugs such as sulphasalazine. Anti-TNF-α antibodies have been shown to be effective in severe disease.

Surgery may be indicated for disease in large joints (including arthroplasty). A lumbar or cervical spinal osteotomy may be helpful in patients with severe curvature.

Prognosis

There is a wide range of severity: In over 85% there is minimal disability, 50% of patient’s children will inherit HLA B27 and of these, 33% will develop the condition.