PReS-FINAL-1014: Role of MHC class I overexpression on muscle biopsy of patients with juvenile dermatomyositis

Juvenile Dermatomyositis (JDM) is the most common idiopathic inflammatory myopathy in childhood, a systemic vasculopathy that usually affects skin and skeletal muscle but also can affect gastrointestinal tract and other organs. Diagnosis is based on Bohan and Peter's criteria and the goals of treatment include control of skin and muscle symptoms and prevention of disease complications. Stepwise aggressive treatment decreases JDM activity and improves long-term outcome. Muscle involvement in JDM can be assessed by electromyography (EMG), magnetic resonance imaging (MRI) and/or muscle biopsy. Muscle biopsy assesses the presence of lymphocytic inflammatory infiltrate, perifascicular atrophy, muscle fibers necrosis and it allows studying the overexpression of major histocompatibility complex (MHC) class I in the sarcolemma and sarcoplasm of the muscle cell. In healthy muscles, there is no MHC class I expression but in inflammatory myopathies there is a distinctive and generalized overexpression, not limited to the affected areas, it appears before the inflammatory infiltrate occurs and it is not modified by immunosuppressive treatment.