Juvenile dermatomyositis (JDMS): new clues to diagnosis and pathogenesis.

The localization of focal inflammatory myopathy (IM) is aided by MRI, which facilitates diagnostic testing (muscle biopsy or EMG). Antibodies to antigens involved in protein synthesis are specific for IM and characterize distinct subsets of adult IM, but are rare in pediatric IM. In definite juvenile dermatomyositis, serological indicators of disease activity include neopterin and von Willebrand factor antigen, markers of macrophage activation, and endothelial cell damage, respectively; nailfold capillarioscopy documents small blood vessel involvement. Monitoring the percentage of circulating B cells may indicate the response to therapy.