類風濕性關節炎
Arthritis involving 5 or more joints in the first 6 months, with a positive Rheumatoid factor on at least 2 occasions, tested 3 months apart. In this subtype of arthritis both small and large joints are typically involved, usually in a symmetric pattern. The Anti-nuclear antibody may also be positive in up to 75% of patients. This subtype of arthritis behaves in a very similar fashion to the equivalent adult disease Rheumatoid arthritis. It affects mostly adolescent girls and is typically more aggressive than other forms of JIA in terms of joint damage and the development of erosions in surrounding bone. The clinical presentation is similar to that of Rheumatoid arthritis with a symmetric polyarthritis typically involving the PIP and MCP joints. Children may develop rheumatoid nodules and similar complications to adult disease, including joint erosions.