Trial of Early Aggressive Drug Therapy in Juvenile Idiopathic Arthritis

JIA is a type of arthritis with no definite cause and an onset prior to 16 years of age. JIA causes joint destruction, pain, and permanent disability. There are multiple types of JIA; collectively, they represent one of the most common chronic diseases in children and the most prevalent pediatric rheumatic illness. Poly-JIA, one type of JIA, affects at least five joints in the body within the first 6 months of disease. Long-term remission of poly-JIA is uncommon, and most children must remain on multiple combinations of medications for many years. The usual treatment for poly-JIA is based upon the gradual addition of medications that might be more effective in treating this disease. There is a need to find uniformly effective treatments for children with poly-JIA. Based on previous adult arthritis studies, there appears to be an early window of opportunity in the disease progression during which aggressive therapy has a profound beneficial long-term effect. The purpose of this study is to compare the effectiveness of two aggressive drug regimens in treating children with poly-JIA. Specifically, the study will determine whether aggressive therapy started in the first 6 months of disease onset can result in inactive disease and clinical remission while on these medications. All participants will receive weekly methotrexate shots while in the study. In addition, participants will be randomly assigned to one of two groups: * Group 1 participants will receive placebo etanercept shots for up to 12 months and daily placebo prednisolone liquid for 4 months. * Group 2 participants will receive etanercept shots for up to 12 months and daily prednisolone liquid for 4 months. The study will last up to 12 months and include two parts. Part A will last 1 to 6 months, depending on response to assigned treatments. If participants are still experiencing active arthritis at 6 months, they will be offered open-label treatment with etanercept and prednisolone. If participants experience inactive disease any time prior to 6 months, they will enter Part B of the study. During Part B, which will last up to 6 months, participants will remain on the same treatment regimen that they were provided in Part A. If participants experience inactive disease followed by a flare of disease any time during the study, they will stop participating. During the study, there will be 11 study visits for all participants. Study visits will include a physical exam, including joint evaluations; blood and urine collection; and questionnaires regarding function, quality of life, medication compliance, other medications used, infections, and adverse symptoms. Blood will be collected for translational studies.