In polyarticular disease, five or more joints are affected. The small joints, such as those in the hands and feet, are most commonly involved, but the disease may also affect large joints. Polyarticular JRA often is symmetrical, that is, it affects the same joint on both sides of the body. These children often have a more severe form of the disease, which doctors consider to be the same as adult rheumatoid arthritis. Besides joint swelling, the systemic form of JRA is characterized by fever and a light pink rash, and may also affect internal organs such as the heart, liver, spleen, and lymph nodes.
Doctors sometimes call it Still's disease.
A small percentage of these children develop arthritis in many joints and can have severe arthritis that continues into adulthood. The main difference between juvenile and adult rheumatoid arthritis is that many people with JRA outgrow the illness, while adults usually have lifelong symptoms. Studies estimate that by adulthood, JRA symptoms disappear in more than half of all affected children. Additionally, unlike rheumatoid arthritis in an adult, JRA may affect bone development as well as the child's growth. About 70 to 80 percent of all adults with rheumatoid arthritis are positive for RF, but fewer than half of all children with rheumatoid arthritis are RF positive.