JRA is a chronic inflammatory arthritis in children. It occurs in 50-100 per 100,000 children in the United States. JRA is a general term for the most common types of arthritis in children. It is divided into several categories: - Systemic JRA: This form, which occurs in about 10% of cases, involves joint pain and swelling as well as fevers and rash. It is similar to adult Still's disease. The cause of this form of JRA is unknown.
- Polyarticular JRA: This form occurs in about 40% of cases and involves multiple joints that are painful and swollen. The cause of this form of JRA is unknown. Some children may have a positive rheumatoid factor and the condition may evolve into rheumatoid arthritis.
- Pauciarticular JRA: This form occurs in about 50% of cases and involves only a few joints. Some of these children, in particular boys, will be HLA-B27 positive. Families with HLA-B27 are at increased risk for this arthritis.
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