Polymyositis and dermatomyositis are quite rare rheumatic diseases. For Polymyositis, phlogistic changes in muscles are characteristic, and for dermatomyositis also the inflammatory skin is one of the main signs. The appearance on the skin of heliotrope rashes is the most specific characteristic. The muscles of the patient are damaged symmetrically, the organism feels weak, painful, which further leads to emaciation of the central proximal muscles of the upper extremity girdle. Untimely medical care may lead to the damage to the internal organs of a patient.
The reason of the disease is supposed to be an autoimmune response to muscle tissue of persons who are genetically predisposed. Possible starting factors are malignant neoplasms and virus myositis. There is a research of the detection in muscle cells of structures similar to picornaviruses; also, viruses may induce similar diseases in animals. The association of malignant neoplasms with dermatomyositis suppose that neoplasm growth can also be a trigger mechanism for the development of the disease as a result of triggering autoimmune reactions to the common tumor and muscle antigens. Deposits of IgM, IgG and the third complement component are detected in the walls of the blood vessels of skeletal muscles.
The beginning of polymyositis can be acute or subacute. Acute viral infection sometimes precedes or is the starting factor of manifestation of the disease, the most frequent signs of which are a weakness of center proximal muscles or skin rashes. Painful sensations are less expressed than weakness. Perhaps the development of polyarthralgia, the phenomenon of Raynaud, dysphagia, infringement of the lungs, common symptoms (fever, a decrease in body weight, weakness).