Seronegative spondyloarthritides, also known as spondyloarthropathies (SpA), are a group of musculoskeletal syndromes linked by common clinical features and immunopathologic mechanisms. The subtypes of spondyloarthritis are usually distinguished on the basis of history and clinical findings.
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 (ASAS) proposed a new classification system in order to recognize early disease . They propose using the term spondyloarthritis to refer to all spondyloarthropathies, with the following distinctions:
- axial spondyloarthritis: predominantly axial symptoms (i.e. chronic back pain)
- preradiographic/non-radiographic: no changes on radiographs (but may have MRI changes)
- radiographic: sacroiliitis on radiographs
- peripheral spondyloarthritis: only peripheral manifestations (e.g. peripheral arthritis, dactylitis)
Extra-axial involvement such as uveitis, calcaneal enthesitis, or peripheral arthritis occurs in all five subtypes, albeit with different frequencies.
These arthritides are typically negative to rheumatoid factor (RF) and involve the axial skeleton. However, a small proportion of patients may have serum RF detected. Most patients test positive for the protein product of the HLAB27 gene.
Five subgroups of spondyloarthritis are distinguished:
- ankylosing spondylitis: ~90% HLAB27 positive
- psoriatic arthritis: ~60% HLAB27 positive
- reactive arthritis (Reiter syndrome): ~85% HLAB27 positive
- enteropathic arthritis (i.e. extraintestinal manifestation of IBD)
- undifferentiated spondyloarthritis
Imaging does not play a major role in differentiating between the subtypes as imaging features are similar, especially in early disease. Exceptions to this rule are:
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 .