Childhood polymyositis/dermatomyositis.

Children with PM/DM differ in many respects from adults with PM/DM. The most characteristic and distinctive feature is the presence of a widespread vasculopathy. Although the pathogenesis is unknown, roles for both humoral and cell-mediated immunity have been proposed. Most intriguing is the evidence for a viral agent that is capable of precipitating an ongoing, immunologically mediated reaction damaging muscles and endothelial cells. Much remains to be discovered, however, regarding the pathogenesis of this disease.