An update on juvenile dermatomyositis.

Juvenile dermatomyositis (JDMS) is a systemic vasculopathy characterized primarily by inflammation of skin and muscle. JDMS is identified in more than three per million persons per year, using established diagnostic criteria. Although originally thought to be a relatively homogeneous disease, new data confirm that heterogeneity in JDMS may be found at several levels and that each variant may be associated with a different disease course. Unlike adults with dermatomyositis, of whom more than 50% have a specific myositis-associated antibody (MSA), a much smaller number of children appear to test positive for a known MSA (about 10%), despite the evidence that more than 60% of children with JDMS test positive for antinuclear antibodies. In children, the most common MSA is directed against Mi-2, not toward one of the tRNA synthetases, such as tRNA histidine, as is found in 20% to 30% of adults with myositis. About 50% of children with JDMS have circulating evidence of endothelial cell damage (increased vWF:Ag), whereas others have different indicators of disease activity, such as elevated neopterin (> 60%) or increased circulating B cells with peripheral lymphopenia (> 80%). Newer modes of assessment of functional ability may help evaluate response to therapy. Finally, physicians with newly diagnosed (< 6 months) JDMS patients are urged to call the new National Institutes of Health Rare Disease Registry for New Onset Dermatomyositis (312-880-3333) to enroll their patients and for more information on the onset of this disease.