Expression of HLA class I antigens in skeletal muscle is a diagnostic marker in juvenile dermatomyositis.

HLA class I gene products are immunocytochemically detectable in the skeletal muscle of many patients with inflammatory conditions. We report three cases of juvenile dermatomyositis with minimal histologic abnormalities and no inflammation in the muscle biopsies. All three showed strong expression of HLA class I antigens on muscle fibers. Analysis of HLA class I expression is thus a useful marker for the diagnosis of inflammatory muscle disease, even in the absence of histologic changes.