Focal myositis. Description of a case and review of the literature.

The authors describe a rare form of pseudotumor of the muscle tissue of an inflammatory nature with an unknown etiology that occurred in a boy aged 13 years, characterized by the occurrence of rapidly-developing swelling, no pain symptoms, with degeneration of the myofibers, evident eosinophilia and lymphomonoplasmacellular infiltrate. Surgical excision of the lesion is the treatment of choice.