[Dermatomyositis]

Dermatomyositis (DM) is a systemic inflammatory disease involving skin, muscles and other organs. Immunologically mediated inflammation of small vessels leads to vascular damage, especially of the muscular tissue. Typically DM presents clinically with DM-type local or generalized rash and proximal muscular weakness. Laboratory signs of muscular damage (elevated serum CK, myoglobinuria) may be initially absent. Magnetic resonance tomography frequently shows edema of the involved muscles, while electromyography shows a myopathic pattern with spontaneous activity. Muscle biopsy from involved muscle with histological, immunohistological, histochemical and possibly electron-microscopic examination confirms the diagnosis of inflammatory muscle disease and furthermore of DM-specific muscular findings. Typical findings include the deposition of 5b-9 complement components (membrane attack complex) at the capillaries, perifascicular inflammatory infiltrates composed predominantly of CD4+ T-lymphocytes, B-lymphocytes and plasmacytoid dendritic cells, endothelial swelling and damage, loss of capillaries with perifascicular atrophy and tubuloreticular endothelial inclusions on electron-microscopic examination. Detection of myositis-specific autoantibodies is especially helpful in the diagnosis of early and atypical cases with features of overlapping disease.