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What causes juvenile dermatomyositis?
Last reviewed: 19.10.2021
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The causes of juvenile dermatomyositis are unknown. According to modern ideas, juvenile dermatomyositis is a multifactorial disease that develops as a result of antigenic stimulation of an autoimmune response according to the type of molecular mimicry under the influence of environmental factors, in all probability, in genetically predisposed individuals.
At present, the greatest importance as an etiological factor is given to infectious agents. Epidemiological studies often indicate infectious diseases for 3 months preceding the debut of juvenile dermatomyositis. It is suggested that the autoimmune response develops according to the mechanism of molecular mimicry due to the similarity of infectious antigens and autoantigens of the macroorganism. Etiologically significant infectious agents in juvenile dermatomyositis: influenza viruses, parainfluenza, hepatitis B, picornaviruses (Coxsackie B), parvovirus, protozoa (Toxoplasmagondii). Among the bacterial pathogens emphasize the role of Borrelia burgdorferi and beta-hemolytic streptococcus group A.
Other putative etiological factors in juvenile dermatomyositis: some vaccines (against typhus, cholera, hepatitis B virus, measles, rubella and mumps), insolation and medicinal substances (D-penicillamine, growth hormone).
In favor of hereditary predisposition, cases of family dermatomyositis. An important proof of the hereditary predisposition to the disease is a high (in comparison with the population) frequency of occurrence of certain immunogenetic markers, in particular leukocyte antigens of the main complex of human histocompatibility - HLA BS and DR3.
Pathogenesis of juvenile dermatomyositis
It has now been proven that the key link in the pathogenesis of dermatomyositis in both children and adults is microangiopathy with the involvement of endotomy capillaries. At the heart of the vascular wall is the deposition of deposits consisting of antibodies to an unknown antigen in endothelial cells and activated components of the complement system C5b-9 in the form of a so-called membrane-attack complex (MAC). The deposition of these complexes induces necrosis of the endothelium, leading to loss of capillaries, ischemia and destruction of muscle fibers. MAC deposition was detected at the earliest stages of the disease, before the changes in muscles. This process regulates cytokines produced by immunocompetent and endothelial cells, in turn, causing activation of T-lymphocytes, macrophages and secondary destruction of myofibrils.