Juvenile dermatomyositis.

Myositis in childhood is characterized by elevated serum levels of muscle-derived enzymes, proximal symmetrical muscle weakness, abnormal EMG findings, and a muscle biopsy, which frequently documents an inflammatory process. In the pediatric age group, JDMS, which has characteristic cutaneous involvement in addition to myositis, is much more common than PM and is more common among female patients. With the use of steroids, mortality has been reduced from 33 per cent to 7 per cent. The development of calcifications can be the most debilitating consequence of JDMS. It is our premise that JDMS is a distinct disease entity and that the increase in HLA-B8 and DR3 in JDMS suggests that genetic background may predispose to disease development. There are conflicting data concerning immunologic abnormalities in JDMS, but there appears to be impairment of natural killing and evidence of complement activation. Results of tests for ANA frequently are positive in JDMS, but Jo-1 antibody, found in some adults with PM, has not been found in JDMS. Most newly diagnosed JDMS patients have antibodies to coxsackie B that may be related to the pathogenesis of this disease. Specific pathologic findings of endothelial cells containing reticulotubular inclusions are associated with small vessel occlusion, subsequent obliteration, and increased factor VIII levels in clinically active disease. In addition to physical therapy, steroids are used most frequently, but other immunosuppressive agents and plasmapheresis have been tried in severely ill children. Rigorous evaluation of the efficacy of these modalities is needed.