Muscle pathology in juvenile dermatomyositis.

OBJECTIVE To study muscle biopsies, using histochemistry, on ten children with infantile dermatomyositis. DESIGN Series of ten patients (of whom eight patients had received treatment and two had not) were submitted to muscle biopsy in order to diagnose possible inflammatory myopathy or to detect recurrences. PLACE OF DEVELOPMENT OF THE STUDY: Public Health Service of São Paulo State. PARTICIPANTS Children with clinical features of inflammatory myopathy. INTERVENTION Biopsies were performed on the vastus lateralis using local anesthetic. Histochemistry was performed according to standardized methods. RESULTS Architectural changes of the muscle fibers, necrosis of variable intensity and accentuated evidence of regeneration were observed in patients who had not received treatment (2 cases) and in one case where muscular weakness persisted in spite of corticosteroid therapy. Necrosis and regeneration were minimal or absent in cases treated for one year or more (4 cases). In 3 cases with clinical and laboratorial recurrences, muscle necrosis and architectural changes were detected. CONCLUSIONS It was concluded that muscle biopsy could aid in diagnosing infantile dermatomyositis as well as in detecting recurrences even in cases without clinical activity of the disease.