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.