Seronegative spondyloarthritis

Seronegative spondyloarthritides, also known as spondyloarthropathies or spondyloarthritis, are a group of musculoskeletal syndromes linked by common clinical features and common immunopathologic mechanisms. The subtypes of spondyloarthritis are usually distinguished on the basis of the patient’s history and clinical findings.

Terminology

The diagnostic criteria for spondyloarthritides have evolved in step with the changing understanding of the disease process. In particular, there is growing recognition that early forms of disease precede the typical changes on plain radiography.

In 2009, the Assessment of SpondyloArthritis International Society (ASIS) proposed a new classification system in order to recognize early disease ^4,5. They propose using the term spondyloarthritis (SpA) to refer to all spondyloarthropathies, with the following distinctions:

• axial SpA - predominantly axial symptoms (i.e. chronic back pain)
  • preradiographic / non-radiographic - no changes by imaging (radiograph oron radiographs (but may have MRI changes)
  • radiographic SpA - sacroiliitis by imagingon radiographs
• peripheral SpA - only peripheral manifestations (e.g. peripheral arthritis, dactylitis)

Clinical presentation

Extra-axial involvement such as uveitis, calcaneal enthesitis or peripheral arthritis occurs in all five subtypes, albeit with different frequencies.

Pathology

As such these arthritides are negative to rheumatoid factor and involve the axial skeleton. Most patients test positive to the HLAB27 gene.

Five subgroups of spondyloarthritis are distinguished:

• ankylosing spondylitis: ~ 90% HLAB27 positive
• psoriatic arthritis: ~ 60% HLAB27 positive ¹
• reactive arthritis (Reiter syndrome): ~ 85% HLAB27 positive
• enteropathic arthritis (i.e. extra-intestinal manifestation of IBD)
• undifferentiated spondyloarthritis

Radiographic features

Imaging does not play a major role in differentiating between the subtypes as imaging features are comparable, especially in early disease. Exceptions to this rule are:

1. Undifferentiated spondyloarthritis, diagnosed in cases with no definite radiologic signs of sacroiliitis.
2. Psoriatic arthritis, known to produce parasyndesmophytes, a form of bony outgrowth distinct from syndesmophytes.

Also, spondylitis with bone marrow edema of the entire vertebra occurs more frequently in psoriatic arthritis.

Treatment and prognosis

All forms of spondyloarthritis may ultimately develop into ankylosing spondylitis in patients with longstanding disease ³.