Inflammatory myopathy is an inflammatory process that occurs mainly in skeletal muscles and leads to their degenerative changes. Disease is characterized by muscle weakness, muscle pain, a sharp decrease in the volume of active movements, the development of contractures, compaction and swelling of muscles. Of the diagnostic methods, the most informative is the determination of the level of CPK and myoglobin, electromyography and muscle biopsy. Treatment is carried out with high doses of glucocorticosteroids followed by maintenance therapy. However, corticosteroid-resistant forms of the disease are quite common.
G72.4 M60 M33
Inflammatory myopathies are a whole group of diseases, which includes both systemic damage to muscle tissue and local inflammatory processes in individual muscles. Systemic inflammatory myopathy is represented by dermatomyositis, polymyositis, eosinophilic myositis, myositis with inclusions, rheumatic polymyalgia and myopathies in systemic diseases. An example of local inflammatory myopathy may be myositis of the ocular muscles, pseudothrombophlebitis of the lower leg muscles, etc. In addition, inflammatory myopathy can be observed in some infectious diseases.
The age of patients most susceptible to morbidity varies depending on the type of inflammatory myopathy. Thus, polymyositis usually occurs in people over 30 years of age. Dermatomyositis is observed both in adults and in childhood. And myositis with inclusions is more common after 40 years and is the most common form of inflammatory myopathy in old age.
In some cases, disease is directly related to the infectious process. The agents that cause infectious and inflammatory muscle damage can be viruses (rubella, influenza, HIV infection, enteroviruses, etc.), bacteria (more often streptococcal infections), parasitic infestations (cysticercosis, toxoplasmosis, trichinosis). In this case, the disease is classified as infectious inflammatory myopathy.
In cases where there is no direct link between myopathy and infection, they speak of idiopathic myopathy. It includes: myositis with inclusions, polymyositis, dermatomyositis, myopathies in systemic diseases (systemic lupus erythematosus, scleroderma, Sjogren’s syndrome, systemic vasculitis, rheumatoid arthritis). The most common opinion in both neurology and rheumatology is that idiopathic inflammatory myopathy has an autoimmune mechanism of development. However, the antigen that triggers the underlying autoimmune reaction has not yet been isolated. In some cases, inflammatory myopathy has a family character, indicating its genetic origin.
Inflammatory myopathy is clinically manifested by muscle pain, progressive muscle weakness and stiffness in the affected parts of the extremities. Pain syndrome (myalgia) occurs not only during the period of motor activity, but also when probing muscles, and sometimes in a state of complete rest. Muscle weakness, as a rule, begins to manifest itself by difficulty in holding objects in your hands. As it progresses, it becomes impossible for the patient to raise an arm or leg, sit down, stand up. Inflammatory myopathy of a widespread nature often leads to a significant reduction in the volume of active movements that the patient can perform, and sometimes to complete immobility.
Pathology occurs with swelling and compaction of the affected muscles. As a result of inflammation, atrophic changes occur in them, myofibrosis develops — the replacement of muscle fibers with connective tissue, calcification is possible. The resulting muscle contractures lead to joint stiffness. Often inflammatory myopathy has a long-term remitting course. In some cases, more often in children, there is a complete recovery after an acute attack of inflammatory myopathy.
The most severe inflammatory myopathy occurs when the laryngeal and respiratory muscles are involved in the inflammatory process, which leads to the development of myopathic laryngeal paresis and respiratory failure. The weakness of the respiratory muscles leads to a decrease in pulmonary ventilation and the occurrence of congestive pneumonia. Weakness of the pharyngeal muscles is the cause of dysphagia (swallowing disorders), in which food may enter the respiratory tract and the occurrence of aspiration pneumonia. If inflammatory myopathy spreads to the oculomotor muscles, then strabismus and drooping of the upper eyelid occur. The defeat of facial muscles leads to a mask-like facial expression. Systemic inflammatory myopathy, for example, dermatomyositis and polymyositis, may be accompanied by damage to the heart muscle with the clinic of myocarditis, cardiomyopathy and heart failure.
Polymyositis is manifested by a muscle syndrome typical of inflammatory myopathy, which captures the muscles of the proximal extremities, primarily the shoulder and pelvic girdle. In most cases, there is also damage to internal organs: gastrointestinal tract (diarrhea, constipation, intestinal obstruction, gastric ulcer with perforation or gastrointestinal bleeding), heart and blood vessels (arterial hypotension, arrhythmia, cardiomyopathy, etc.), lungs (focal or lobar pneumonia). In 15% of cases, this inflammatory myopathy is accompanied by articular syndrome in the form of arthritis of the joints of the hand, less often — other joints of the extremities.
Dermatomyositis has a clinical picture similar to polymyositis. A distinctive feature is the presence of skin manifestations: erythematous spots, areas of hypo- and hyperpigmentation, foci of hyperkeratosis. It is possible to damage the mucous membranes with the development of stomatitis, gingivitis, conjunctivitis.
Myositis with inclusions is characterized by an early lesion of the musculature of the distal parts of the hands: the flexors of the fingers and the muscles of the forearm. In the legs, inflammatory myopathy spreads to both distal and proximal muscle groups. The defeat of the extensors of the foot and quadriceps is typical.
In addition to neurologists, rheumatologists, cardiologists, pulmonologists, dermatologists, immunologists and other specialists can be involved in the diagnosis of inflammatory myopathy. Unfortunately, today inflammatory myopathy does not have clear diagnostic criteria. Of particular importance is the detection in the biochemical analysis of blood of an increase in the level of creatine phosphokinase (CPK), as well as lactate dehydrogenase and aldolase, which indicates damage to muscle tissue. Often inflammatory myopathy is accompanied by an increase in myoglobin. However, the level of these indicators does not correlate with the severity of clinical manifestations. For this reason, the only reliable criterion for the progression of myopathy can only be the results of a study of muscle strength (ergometry) in dynamics. It should also be noted that the increase in CPK and myoglobin is not observed in all types of inflammatory myopathy. For example, with myositis with inclusions, the level of CK and myoglobin is often within the normal range.
Electromyography data are of great diagnostic importance. With dermatomyositis and polymyositis, there is a decrease in the duration and amplitude of the potentials of motor units, increased electrical excitability. In myositis with inclusions, along with low-amplitude and short-term potentials typical of myopathy, high-amplitude and long-term potentials characterizing neurogenic damage are noted.
A muscle biopsy allows you to clarify the nature of muscle damage and determine its prevalence. Morphological examination of the biopsy reveals the presence of inflammatory infiltrates, atrophic changes and necrosis of muscle fibers, their replacement by connective tissue.
The generally accepted method of treatment of inflammatory myopathy is glucocorticosteroid therapy. The daily dose of prednisone is 80-100 mg. When the clinical effect of treatment is achieved in the form of an increase in muscle strength, a gradual reduction in the daily dose to a maintenance level of 15 mg / day is performed. In severe cases, inflammatory myopathy is treated with pulse therapy with methylprednisolone. The difficulty of using long-term treatment with glucocorticoids consists in their side effects, because of which such therapy is contraindicated in patients with peptic ulcer and gastric ulcer, arterial hypertension, osteoporosis, cataract and glaucoma. The absence of an increase in muscle strength within 3 months from the start of treatment with corticosteroids indicates the steroid resistance of inflammatory myopathy.
Alternative drugs in the treatment of inflammatory myopathy are cytostatics (azathioprine, methotrexate, cyclosporine, cyclophosphamide). They are used instead of corticosteroids in the presence of steroid resistance or in combination with them to reduce the dose of glucocorticosteroids in order to avoid their side effects.
Since systemic inflammatory myopathy usually has an autoimmune character, plasmapheresis is often used in its treatment, which allows reducing the amount of CEC in the blood.