Abnormal muscle MRI in a patient with systemic juvenile arthritis.

Although myositis has been described in children with systemic-onset juvenile arthritis (JA), its documentation by MRI has not been reported. We describe a 13-year-old boy with systemic-onset JA, severe myalgia, and elevated muscle enzymes, but normal muscle strength, who had an MRI consistent with myositis. Magnetic resonance imaging can identify the specific location of myositis, allowing more precise definition of a potential complication of systemic JA.