RESUMEN
The most common idiopathic inflammatory myopathies in children include juvenile dermatomyositis, juvenile polymyositis, and myositis associated with another autoimmune disease (overlap myositis). Idiopathic inflammatory myopathies manifest different characteristics affecting children. Only a few investigations of childhood idiopathic inflammatory myopathies were reported, involving 27 patients. In addition, clinical findings, serum muscular enzyme levels, results of electromyography studies, muscle biopsy features, and treatment responses were studied. Seventeen female and 10 male were classified as exhibiting juvenile dermatomyositis (n = 19), juvenile polymyositis (n = 6), or overlap myositis (n = 2). Overlap myositis was associated with systemic sclerosis and systemic erythematous lupus. The mean age at onset was 6.1 years for juvenile dermatomyositis, 4.9 years for juvenile polymyositis, and 8.5 years for overlap myositis. The most common signs included proximal weakness and myalgia. The serum creatine kinase level was increased in 48.2% of patients. An electromyography study revealed myopathic features in 85% of patients. Muscle biopsies led to observations of inflammatory infiltrates with preferential perivascular involvement in the juvenile dermatomyositis group, and endomysial involvement in the juvenile polymyositis group. Fiber atrophy was predominantly perifascicular in the juvenile dermatomyositis group. Treatment with prednisone improved the findings in 81.5% of children.