The spondyloarthritides (SpAs) (also termed spondyloarthropathies) are a group of disorders with a predilection for inflammatory arthritis of the axial skeleton (sacroiliac joints and spine) and peripheral joints. SpAs include ankylosing spondylitis, psoriatic arthritis, reactive arthritis, juvenile-onset spondyloarthritis, arthritis associated with inflammatory bowel disease (enteropathic arthritis), arthritis associated with anterior uveitis, and undifferentiated spondyloarthritides. SpAs are characterized by inflammation of bones (osteitis), joints (arthritis), and peri-articular tissues, particularly entheses (enthesitis: inflammation of the sites where tendons or ligaments attach to the bone), as well as a number of extra-articular manifestations (such as psoriasis, anterior uveitis, and inflammatory bowel disease).
Spondyloarthritides can be broadly classified into:
1) Axial SpAs, which primarily affect the axial skeleton, typically the sacroiliac (SI) joints but often involving the spine itself.
2) Peripheral SpAs, which primarily manifest as peripheral arthritis (large and small joints), enthesitis, and dactylitis.
Of note, there is no single diagnostic feature for the SpA group as a whole or for any of the disease subsets. Diagnosis is therefore dependent on the assessment of symptoms and signs, laboratory investigations, and imaging studies, such as radiographs and magnetic resonance imaging (MRI). In patients with SpA serum IgM rheumatoid factor is negative (hence the name “seronegative spondyloarthropathies”) and HLA-B27 is frequently positive.
The term “nonradiographic axial spondyloarthritis” (nrAxSpA) refers to patients with clinical features of axial SpA but without adequate evidence of sacroiliitis on radiographs. Such patients would usually have positive findings on MRI.
Recent developments in the understanding of these diseases and introduction of new advanced therapies (biologic agents, Janus kinase inhibitors) underscore the need for specialist expertise in the diagnosis and management of SpAs.