This subtype is classified as a polyarthritis affecting five or more joints during the first six months of disease in the absence of a consistently raised rheumatoid factor. Onset is most frequently in girls below the age of seven. There is a much lower risk and severity of erosive changes on X ray and extra-articular manifestations than in rheumatoid factor positive JIA and prognosis is less severe. There is an association to chronic asymptomatic anterior uveitis, but with a lower incidence than in the oligo-arthritis JIA subset, but there is a similar association with ANA positivity.
In adults with rheumatoid arthritis, there is a subgroup of 25% of patients who are rheumatoid factor negative. In this adult seronegative subgroup, erosive joint damage and extra-articular manifestations are less common than in rheumatoid factor positive disease. The occult anterior uveitis and ANA positivity associations seen in juveniles are not, however, seen in adult disease.
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