This is classified as an arthritis involving five or more joints during the first six months of disease associated with a rheumatoid factor positive test on at least two occasions at least three months apart. This subtype is generally considered to be the juvenile form of erosive adult rheumatoid arthritis (RA) although erosions are often late due to the greater amount of cartilage the younger the patient. The peak age of onset is in mid to late adolescence although it can develop in much younger children. As in adult RA, there is a female predominance. Rheumatoid nodules and classical vasculitis are seen only in this group, in which all extra-articular manifestations found in adult RA may occur, including ocular, cardiac and pulmonary involvement. There are no major differences known between juvenile- and adult-onset arthritis pathological processes. There are however differences in outcome related to effects of joint inflammation occurring in a growing skeleton and the psychosocial impact of having arthritis in childhood.
The genetic associations of both juvenile and adult rheumatoid factor positive arthritis are strongly linked to the "shared epitope" HLA-DRB1 01401/ 01404 (24). Interestingly in adult RA, this association is stronger with a younger onset of adult onset disease (25).
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