This subset was previously referred to as either juvenile ankylosing spon-dylitis or type II pauciarticular arthritis. It is a spondyloarthropathy usually manifesting as a predominantly lower limb arthritis and enthesitis (inflammation of the insertions of tendon, ligament, or joint capsule into bone). It is the only form of JIA to show a male preponderance (19), usually occurring in the early teens.
There is a reduced incidence of sacroiliitis, with 23.4% of enthesis-related JIA showing radiological changes at diagnosis, compared to 100% of patients with adult ankylosing spondylitis as demanded by New York classification criteria. However, there is also likely to be significant overlap of enthesitis-related JIA with adult undifferentiated spondyloarthropathy where radiological sacroiliitis is not a cardinal diagnostic feature.
If enthesitis is absent, then the diagnosis can still be made if arthritis and two other spondyloarthropathy-related features are present as described by the ILAR criteria for enthesitis-related arthritis (Table 3) (8).
As seen in adults with spondyloarthropathies, acute painful anterior uveitis is a prominent extra-articular feature, usually occurring as an acute unilateral anterior uveitis with a high frequency of recurrence, sometimes in the contralateral eye. Anterior uveitis in these cases is likely to be extremely painful and therefore not liable to go undetected, in contrast to the uveitis associated with oligo-arthritis JIA.
Table 3 ILAR (International League Against Rheumatism) Criteria for Enthesitis-Related JIA
Arthritis and enthesitis or Arthritis and at least one of the following: Sacroiliac joint tenderness Inflammatory spinal pain HLA-B27
Positive family history of at least one of the following: Anterior uveitis
Spondyloarthropathy confirmed by a rheumatologist Inflammatory bowel diseases
In juvenile enthesitis-related arthritis there is a higher rate of peripheral arthritis and enthesitis at presentation when compared to adult onset ankylosing spondylitis (19), and more enthesitis when compared to other subtypes of JIA (Table 4) (21). The rate of patients being HLA-B27 positive are similar in enthesis-related JIA and ankylosing spondylitis.
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