Overview of ankylosing spondylitis
The term ‘spondyloarthritis’ (SpA) comprises AS, reactive arthritis, arthritis/spondylitis associated with psoriasis, and arthritis/spondylitis associated with inflammatory bowel disease (IBD). There is considerable overlap between the single subsets (Figure 2.1). The main link between each is the association with the human leukocyte antigen (HLA)–B27, the same pattern of peripheral joint involvement with an asymmetrical, often pauciarticular, arthritis, predominantly of the lower limbs, and the possible occurrence of sacroiliitis, spondylitis, enthesitis, dactylitis and uveitis. All SpA subsets can evolve into AS, especially in those patients who are positive for HLA–B27. The SpA subsets can also be split into patients with predominantly axial and predominantly peripheral SpA (Figure 2.2), with an overlap between the two parts in about 20–40% of cases. Through use of such a classification the presence or absence of evidence for a preceding gastrointestinal or urogenital infection, psoriasis or IBD is recorded but does not result in a different classification. The term ‘predominant axial SpA’ covers patients with classic AS and those with non–radiographic axial SpA . The latter group of patients would not have radiographic sacroiliitis according to the modified New York criteria, but would normally have evidence of active inflammation as shown by magnetic resonance imaging (MRI) or other means (discussed in more detail in Chapter 5).
KeywordsInflammatory Bowel Disease Human Leukocyte Antigen Reactive Arthritis Radiographic Sacroiliitis European Spondyloarthropathy Study Group
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