Undifferentiated spondyloarthritis

Undifferentiated spondyloarthritis (uSpA), also known as undifferentiated arthritis, is a non-specific mono- or polyarthropathy that lacks the clinical, serological and radiological features that would allow specific diagnosis. It often turns out to be an early presentation of a more well-known form of arthritis.

Epidemiology

The prevalence of uSpA is estimated at ~1% .

Clinical presentation

Back pain, enthesitis, peripheral arthritis are common, as well as extra-skeletal manifestations such as dactylitis and fatigue .

Pathology

Depends on the underlying cause. Most cases reveal themselves to be either:

• rheumatoid arthritis
• seronegative spondyloarthropathy
  • ankylosing spondylitis
  • psoriatic arthritis
• degenerative joint disease

Markers

• HLA B27 positive in ~75% (range 70-84%)

Markers

Only 50% of presentations have abnormal levels of acute-phase reactants (CRP, ESR) and only 10% are positive for rheumatoid factor despite many eventually declaring themselves as rheumatoid arthritis .

Treatment and prognosis

A specific diagnosis is usually reached within three months:

• rheumatoid arthritis (30%)
• ankylosing spondylitis: uSpA often considered an early manifestation
• psoriatic arthritis
• degenerative joint disease
• a small number will remain "undifferentiated"
• ~45% will recover without a more specific diagnosis