JDM is a connective tissue disease that is characterized by inflammation of the muscles and the skin. Corticosteroids, such as prednisolone and methylprednisolone, can be administered to help control symptoms of the disease, but absorption patterns of these medications in oral and IV forms are unknown. This study will assess absorption of oral prednisolone and IV methylprednisolone, measure levels of two disease activity indicators (von Willebrand factor and neopterin), and correlate these values in children with JDM.

Patients will participate in this study twice within a period of up to a year, once when the patient's disease is active, and again 6 to 12 months later when the disease is less active. Each of the two study periods will last two nights and two days. Patients will be admitted to the hospital the first night, and a small IV port will be inserted in the patient's arm the first morning to allow for multiple blood draws without additional needle sticks.

Patients will receive oral prednisolone the first morning and IV methylprednisolone the second morning. Baseline blood draws will be performed prior to administration of drug, with 13 additional draws over a 6 hour period following drug administration. Following the final blood draw on the second day, the IV port will be removed from the patient's arm and the patient will be discharged from the hospital.

Blood drawn from patients will be assessed for absorption of the drugs and levels of von Willebrand factor and neopterin. Patients will undergo the same sequence of events sometime between 6 to 12 months after the first hospitalization, after their vasculitis is judged to be less active.