Juvenile dermatomyositis (JDM) and juvenile polymyositis (JPM) are rare autoimmune myopathies affecting children. JDM is characterized primarily as a capillary vasculopathy, whereas JPM involves direct T cell invasion of muscle fibers similar to that seen in adult polymyositis [1,2]. (See "Clinical manifestations of dermatomyositis and polymyositis in adults".)
JDM is the more common of the two disorders accounting for approximately 85 percent of idiopathic inflammatory myopathies of childhood. JPM accounts for only 3 to 6 percent of cases.
The diagnosis of JDM and JPM will be reviewed here. The pathogenesis, clinical manifestations, and treatment of these disorders are discussed elsewhere. (See "Pathogenesis and clinical manifestations of juvenile dermatomyositis and polymyositis" and "Treatment and prognosis of juvenile dermatomyositis and polymyositis".)
CLASSIFICATION AND DIAGNOSTIC CRITERIA
In 1975, Bohan and Peter proposed a classification schema and diagnostic criteria for the various forms of myositis including juvenile dermatomyositis (JDM) . Their diagnostic criteria for JDM included all of the following findings :
●Symmetrical weakness of the proximal muscles.