What are the Spondyloarthropathies?
- The seronegative spondyloarthropathies (SpA) are a group of chronic autoimmune inflammatory joint diseases
- Seronegative implies no association with rheumatoid factor
- Predominantly affects the axial skeleton (spine and sacroiliac joints)
- Often accompanied by a peripheral arthritis
Spondyloarthropathy
- Ankylosing Spondylitis (AS) is the prototype of the SpA. We will use AS throughout this presentation as our archetype which includes:
- Psoriatic arthritis
- Reactive arthritis
- Arthritis associated with inflammatory bowel disease
- Undifferentiated SpA
Spondyloarthropathy
- Onset generally occurs in young adulthood
- Often insidious onset with periods of relapse and remittance
- In many cases it is a progressive disease with increased limitation of spinal mobility
- Often presents with inflammatory back pain, enthesitis, peripheral joint synovitis, uveitis
- Inflammatory Back Pain has several definitions with variable sensitivity and specificity and include the Calin, Berlin and ASAS criteria. The Calin criteria include insidious onset, morning symptoms, duration of > 3 months ,age of onset < 45yrs and symptoms relieved with exercise.
- Enthesitis is inflammation at ligament and tendon attachment to bone. Achilles enthesitis is the most common peripheral enthesitis.
- Peripheral joint synovitis may present before or after axial presentation. Usually oligoarthritis, asymmetrical with lower limb dominance (hips, knees, ankles, MTPJ commonest)
- Anterior uveitis occurs in up to 1/3 patients, presents with pain, redness and photophobia. Usually unilateral and may be recurrent.
- With Ankylosing Spondylitis as the model for SpA, the time from initial symptom presentation to final diagnosis can be up to 9 years (symptoms often relapse and remit, may be low grade, often thought to be related to muscular strain injuries/degenerative disease by patients/clinicians all of which contribute to a significant delay in diagnosis)
- Delay in diagnosis has negative implications for the patient's well-being
- Treatment with anti-TNF agents is most effective earlier in the course of the disease before structural changes occur.
Demographic AS
- Ankylosing spondylitis (AS) is more common in men (2:1)
- Men develop chronic radiographic findings earlier than women
- Majority of patients present in middle age although disease often commences in late teens and twenties
- 75% present between 20-45 years of age
- 20% before the age of 20
- 5% after 45 years of age
Prevalence
- Varies between ethnic populations (Highest in European ancestry, 1.4%)
- Overall prevalence in the United States of SpA is as high as 1.3%
- 0.2% - 0.5% for ankylosing spondylitis
- 0.05% for psoriatic arthritis
- 0.065% for enteropathic peripheral arthritis
- 0.05% - 0.25% for enteropathic axial arthritis
Predispositions
- Closely linked with HLA-B27 status: constitutes 40% of total disease risk for SpA
- 5% of HLA-B27 positive individuals will develop AS
- 95% of patients with AS are HLA-B27 positive
- 60-70% with psoriatic arthritis or inflammatory back disease are HLA-B27 positive
- HLA-B27 status predisposes greater risk to certain populations
- Up to 75 variants of HLA-B27 described, some of which demonstrate a greater predisposition to AS
- 12% risk of developing AS in HLA-B27 positive primary relatives of patient with AS
- Theorized that HLA-B27 positive patients with SpA have interacted with an environmental factor/s, likely infectious, causing an inflammatory response at the cartilage-bone interface
- Other genetic predispositions include ERAP1, endoplasmic reticulum aminopeptidase 1, interlukin 1 and 23.