There are THREE main types of juvenile arthritis, also known as juvenile idiopathic arthritis. They're all caused by a hyperactive immune system that attacks the healthy joint lining instead of battling invading microbes. The inflammation sparked by this attack eventually spreads to the cartilage and the bones, causing damage. FIFTY percent of children with juvenile arthritis have the oligoarticular type. The word means "few joints"-so named because during the first 6 months of the disease it only occurs in at MOST four -usually large - joints-often the knees, ankles and wrists. Eye inflammation is a common secondary symptom. Oligoarticular arthritis occurs most often in girls between one and four years old. If oligoarthritis is not promptly and effectively treated, a child may develop limb length discrepancy, because of a shortening of the affected limb or an inability to extend it fully. Oligoarthritis is the one form of childhood arthritis that GOES AWAY as a child grows up. But that doesn't happen 100 percent of the time. For a subset of kids, researchers cannot explain why the disease spreads, affecting more of the joints, and persists into adulthood. Children with POLYarticular juvenile arthritis may have a more difficult time recovering from the disease. They're unlikely to grow out of it, and some of them may develop FULL-BLOWN rheumatoid arthritis earlier than normal. Meaning "many joints", polyarticular juvenile arthritis starts in MORE than four areas-commonly the knees, ankles or wrists, but it can ALSO hit the hands, feet, neck and jaw joints. Girls get polyarthritis more often than boys. It arises most often in TWO age groups - kids between 18 months and eight years, and teenagers who are going through puberty. SYSTEMIC juvenile arthritis, also known as Still's disease, crops up in boys and girls equally. Affecting 10 to 20 percent of children with juvenile arthritis, systemic arthritis begins with DAILY fevers 103 degrees or higher, as well as a salmon-colored rash. Interestingly, the fever and the rash will break at least once a day. At least one joint will be swollen and painful, although this symptom might not appear until months after the fevers start... and may not improve after the fevers STOP. The disease sometimes even inflames the INTERNAL organs. For the small subset of kids who develop systemic juvenile arthritis in many joints, there is a chance that it will persist into adulthood. But for many, if not most kids, this form of arthritis does fade as they grow up. If you think your child has arthritis, make a doctor's appointment right away. The earlier this potentially damaging disease is treated, the better the chances for recovery or to minimize joint damage.Watch other videos in this series to learn more about joint issues.