Ankylosing spondylitis

Ankylosing spondylitis:


Ankylosing spondylitis (AS) is characterised by a chronic
inflammatory arthritis predominantly affecting the sacroiliac
joints and spine, which can progress to bony fusion
of the spine. It has a peak onset in the second and third
decades, with a male:female ratio of about 3:1. In Europe,
more than 90% of those affected are HLA-B27-positive.
The overall prevalence is less than 0.5% in most communities.
Over 75% of patients are able to remain in employment
and enjoy a good quality of life. Even if severe
ankylosis develops, functional limitation may not be
marked as long as the spine is fused in an erect posture.
AS is thought to result from exposure to a common
environmental pathogen in genetically susceptible individuals,
although no specific trigger has been identified.
Chronic prostatitis is more common than expected
but appears to be non-infective in origin. Increased faecal
carriage of Klebsiella aerogenes occurs in patients with
established AS and may relate to exacerbation of both
joint and eye disease.

Clinical features
The onset is usually insidious, with recurring episodes
of low back pain and marked stiffness. Radiation of pain
to the buttocks or posterior thighs may be misdiagnosed
as sciatica. Unlike mechanical back pain, symptoms
extend over many segments and are axial and symmetrical
in distribution. Symptoms are most marked in the
early morning and after inactivity, and are relieved by
movement. Although the lumbosacral area is usually
the first and worst affected region, some patients present
with mainly thoracic or neck symptoms. The disease
tends to ascend the spine slowly and eventually, after
several years, the whole spine may be affected. As the
spine becomes progressively ankylosed, spinal rigidity
and secondary osteoporosis predispose to spinal
fracture.
Spinal cord compression is rare.

Early physical signs include failure to obliterate the
lumbar lordosis on forward flexion, restriction of movements
of the lumbar spine in all directions, and possible
pain on sacroiliac stressing. As the disease progresses,
stiffness increases throughout the spine, and chest expansion
frequently becomes restricted. Spinal fusion varies
in its extent and in most cases does not cause a gross
flexion deformity, but a few develop marked kyphosis of
the dorsal and cervical spine that may interfere with forward
vision. This may prove incapacitating, especially
when associated with fixed flexion contractures of hips
or knees. Pleuritic chest pain aggravated by breathing
is common and results from costovertebral joint involvement
involvement.
Plantar fasciitis, Achilles tendinitis and tenderness
over bony prominences such as the iliac crest and greater
trochanter are common, reflecting inflammation at the
sites of tendon insertions (enthesitis).
Peripheral arthritis
Up to 40% of patients have peripheral arthritis. This is
usually asymmetrical at first, mainly affecting hips,
knees, ankles or shoulders. Involvement of a peripheral
joint, most commonly ankle, knee or elbow, may precede
the development of spinal symptoms in around 10% of
cases. In a further 10%, symptoms begin in childhood as
one variety of pauciarticular juvenile idiopathic arthritis.
Extra-articular disease
Fatigue is often a major complaint and may result from
both chronic interruption of sleep due to pain, as well as
chronic systemic inflammation. Acute anterior uveitis is
the most common extra-articular feature. Occasionally,
this precedes joint disease. Other extra-articular features
are rare.

Extra-articular features of ankylosing spondylitis:
• Anterior uveitis (25%) and conjunctivitis (20%)
• Prostatitis (80% men): usually asymptomatic
• Cardiovascular disease
Aortic incompetence
Mitral incompetence
Cardiac conduction defects
Pericarditis
• Amyloidosis
• Atypical upper lobe pulmonary fibrosis

Investigations
X-ray changes are characteristic but may take years
to develop. Sacroiliitis is often the first abnormality,
beginning in the lower synovial parts of the joints with
irregularity and loss of cortical margins, widening of
the joint space and subsequently sclerosis, narrowing
and fusion. MRI is more sensitive for detection of
early sacroiliitis, but is seldom required. Lateral thoracolumbar
spine X-rays may show anterior ‘squaring’
of vertebrae due to erosion and sclerosis of the
anterior corners and periostitis of the waist. Bridging
syndesmophytes are fine and symmetrical, and follow
the outermost fibres of the annulus.
Ossification of the anterior longitudinal ligament and
facet joint fusion may also be visible. The combination
of these features may result in the typical ‘bamboo’
spine. Erosive changes may be seen in the
symphysis pubis, the ischial tuberosities and peripheral
joints. Osteoporosis and atlanto-axial dislocation
can occur as late features.
The ESR and CRP are usually raised in active disease.
RF and other autoantibodies are usually negative.
Testing for HLA-B27 can be a helpful investigation for
pauciarticular juvenile idiopathic arthritis but is unhelpful
in adults with spinal symptoms.

Management
The aims are to relieve pain and stiffness, maintain
a maximal range of skeletal mobility and avoid the
development
of deformities. Education and appropriate
physical activity are the cornerstones of management.
Early in the disease, patients should be taught to perform
daily back extension exercises, including a morning
‘warm-up’ routine, and to punctuate prolonged
periods of inactivity with regular breaks. Swimming is
ideal exercise. Poor posture must be avoided.
NSAIDs and analgesics are often effective in relieving
symptoms but do not alter the course of the disease.
A long-acting NSAID at night is helpful for marked
morning stiffness. Peripheral arthritis can be treated
with methotrexate or sulfasalazine, but these drugs have
no effect on axial disease. Anti-TNF therapy should be
considered for disease inadequately controlled by these
measures since it often has a significant impact on axial
symptoms.
Local corticosteroid injections can be useful for persistent
plantar fasciitis, other enthesopathies and peripheral
arthritis. Oral corticosteroids may be required for acute
uveitis but do not help spinal disease. Severe hip, knee
or shoulder restriction may require surgery. Total hip
arthroplasty has largely removed the need for difficult
spinal surgery in those with advanced deformity.