Ankylosing Spondylitis

Chronic inflammatory disorder primarily affecting the axial skeleton, but with significant involvement of the appendicular skeleton  affected joints tend to fibrosis and ankylosis. Cause unknown, but genetic factors play a role - strongly associated with HLA-B27 histocompatibility antigen. Affects up to 1% of population.

Greek: ankylos (“bent”) and spondylos (“bent”)

Infective agent may initiate immune response. Klebsiella areogenes has been implicated  gives rise to cross reacting antibodies that bond to HLA-B27 positive cells  pathology. Primary pathologic site is the entheses.

Clinical features:
Usually insidious onset of intermittent hip, buttock or back pain – associated with decreased mobility – insidious onset often leads to delay in diagnosis. Usually worse in morning and in middle of night – usually 15-35 years (there is a well recognised juvenile onset ankylosing spondylitis). The stiffness improves with movement and exercise. M:F = 3-5:1. More severe outcome if age of onset is earlier. In females, first symptoms can often occur during pregnancy. 25% have iritis; 4% develop cardiovascular disease; some have breathing difficulties due to limited chest expansion. 50% have peripheral arthritis at some stage during disease. X-ray of sacroiliac joint  erosions, sclerosis, joint space narrowing – later get sclerosis and ankylosis. Can also get C1-C2 subluxations.

Extra-articular involvement:
Aortic valve regurgitation; breathing difficulties from restriction of rib cage; iritis; cauda equina syndrome; prostatitis (in men); secondary amyloidosis

Course is highly variable – characterised by exacerbations and remissions. Less then 20% now go on to significant disability. Life expectancy appears not to be reduced.

Disease activity can be measured with the Bath ankylosing spondylitis function index (BASFI), Dougados function index (DFI), Stoke ankylosing spondylitis spine score (SASSS).

Involvement of foot:
• foot is affected less frequently than in psoriatic spondyloarthropathy and Reiter’s syndrome
• Arthritis is bilateral – can by symmetric or asymmetric – usually MPJ’s and first tarsometatarsal joint. X-rays  soft tissue swelling, joint space narrowing, erosions – also get adjacent bone proliferation.
• up to 30% are considered to get plantar heel pain and/or achilles tendonitis
• X-ray of calcaneus – plantar proliferation (from enthesopathy) and posterosuperior erosions (from bursitis). Erosive changes are generally found in early stages and the sclerotic proliferative changes are more typical late in the disease
• A ‘tarsal index’ has been developed to determine the extent of the involvement of the tarsal bones . 65% of subjects in this study had involvement of the tarsal bones.
• Enthesopathy – at attachments of plantar fascia, achilles tendon and peroneus brevis.
• Synovitis of metatarsophalangeal joints
• Lateral deviation of lessor digits (less severe than rheumatoid arthritis)
• Bony ankylosis of small joints can occur
• Gait analysis has shown reduced stride length, decreased flexion at knee and hip in those that are asymptomatic compared to healthy controls
• may seek Podiatric consultation due to difficulty in reaching feet due to spinal problems
• a chronic increase in the volume of the tarsus or swelling on the dorsum on the foot can occur in juvenile onset ankylosing spondylitis and the pain may resemble tendonitis. Histological analysis of one case demonstrated deposition of acid mucopolysaccharides in the synovial sheath . The patient responded to synovectomy of the tendon sheath.

Management:
• In most cases, AS is relatively mild with reasonable prognosis
• Aim of management is pain relief and prevention of deformity  importance of early diagnosis
• Patient education (sleep on form mattress; exercises; avoid smoking; patient support groups)
• NSAID’s (usually very effective for spinal pain); sulfasalazine appears to be an effective second line drug. Methotrexate if sulfasalazine is ineffective.
• Physiotherapy  postural exercises, joint mobility; activity and range of motion exercises to prevent spinal rigidity (swimming helpful); breathing exercises
• Surgery in advanced cases for deformity (hip replacement; vertebral osteotomy)

http://onlinelibrary.wiley.com/doi/10.1002/acr.22708/full

External Links:
Podiatry Arena threads on Ankylosing Spondylitis

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