Myopathy are a group of diseases based on various disorders in the metabolism and structure of muscle tissue, leading to a decrease in the strength of the affected muscles and restriction of motor activity. Typical features of myopathy are: progressive muscle weakness, the development of muscle atrophy, a decrease in tendon reflexes and muscle tone. Electrophysiological studies, biochemical blood and urine tests, the results of molecular genetic and histochemical analysis of samples obtained by muscle biopsy help to establish the diagnosis of myopathy. Treatment involves the complex administration of metabolic drugs in courses 3 times a year.
General information
Myopathy belong to the group of neuromuscular diseases. They are characterized by a dystrophic lesion of muscle tissue (mainly skeletal muscles) with selective atrophy of individual fibers (myofibrils) with complete functional preservation of the animal nervous system. They are characterized by a chronic steadily progressive course. As a rule, the manifestation of clinical manifestations of myopathy occurs in childhood and adolescence. Most of the cases of the disease are genetic pathology — these are the so-called primary myopathy. Less common are myopathy of acquired genesis — secondary or symptomatic.
Causes
Primary myopathy are based on genetically determined disorders in the functioning of mitochondria and ion channels of myofibrils, in the synthesis of muscle proteins or enzymes that regulate the metabolism of muscle tissue. Inheritance of a defective gene can occur recessive, dominant and linked to the X chromosome. At the same time, external factors often act as triggers that trigger the development of the disease. Such “triggering” factors can be a variety of infections (chronic tonsillitis, frequent acute respiratory infections, bacterial pneumonia, salmonellosis, pyelonephritis, etc.), alimentary dystrophy, severe injuries (pelvic bone fracture, polytrauma, TBI, etc.), physical overstrain, intoxication.
Acquired myopathy can develop against the background of endocrine disorders (hyperparathyroidism, Itsenko-Cushing’s disease, hyperaldosteronism), chronic intoxication (substance abuse, drug addiction, alcoholism, occupational hazards), malabsorption and vitamin deficiency, severe chronic diseases (CRF, chronic liver failure, heart failure, COPD), tumor processes.
Pathogenesis
The presence of genetically determined or acquired defects of metabolites involved in metabolism and the construction of muscle fibers leads to the emergence and progression of degenerative changes of the latter. Atrophy of myofibrils develops, their replacement with adipose and connective tissue occurs. Muscles lose their ability to contract, which causes muscle weakness and limitation of the ability to perform active movements.
Recent studies have revealed in patients with various forms of myopathy disorders of the functioning of both the central (at the diencephalic level) and peripheral parts of the autonomic nervous system, which play an important role in the pathogenesis of the disease. This can explain the predominant lesion of the proximal parts of the extremities, which are typical for myopathies, having a richer vegetative innervation.
Classification
Specialists in the field of neurology have developed several classifications of myopathy. The etiopathogenetic principle of separation, according to which hereditary, inflammatory, metabolic, membrane, paraneoplastic and toxic myopathies are distinguished, has gained the greatest popularity among clinicians. Among hereditary myopathies, 3 types are most common: the juvenile/juvenile form of Erb, the pseudohypertrophic form of Duchene and the shoulder-scapular-facial form. Less common are scapuloperoneal, oculopharyngeal, distal, and other forms. A separate group includes congenital myopathies: central core disease, non-medial and myotubular myopathy, disproportion of types of myofibrils.
Inflammatory myopathy are classified as infectious – arising from infectious and inflammatory lesions of muscle tissue in various infectious processes: bacterial (streptococcal infection), viral (enteroviruses, influenza, rubella, HIV), parasitic (trichinosis, toxoplasmosis) and idiopathic — dermatomyositis, myositis with inclusions, polymyositis, myopathy with collagenoses.
Metabolic myopathy are divided into disorders associated with lipid metabolism in muscles (acetyl-CoA dehydrogenase deficiency, carnitine deficiency), glycogen metabolism (Andersen disease, Pompe disease, type III glycogenosis, McArdle’s disease, phosphorylase b kinase deficiency, phosphoglyceromutase deficiency), purine metabolism (MADA enzyme deficiency) and mitochondrial myopathies (deficiency of reductase, ATP, cytochrome b, b1).
Symptoms
Most myopathies have a gradual onset with the appearance of a slight muscle weakness in the extremities, fatigue from walking and other physical exertion occurring more quickly. For several years, there is an increase in weakness, muscle atrophy appears and progresses, deformities of the limbs occur. Due to significant muscle weakness, patients hardly get up from the floor and walk up stairs, cannot jump and run. In order to get up from the chair, they have to use special techniques. The patient’s appearance is characteristic: wing-like shoulder blades, drooping shoulders, protruding abdomen and reinforced lumbar lordosis. There is a “duck walk” — the patient moves, swinging to the sides.
Pathological changes in myopathies occur symmetrically in the muscles of the limbs and trunk. As a rule, muscle atrophy is observed in the proximal parts of the arms and legs. In this regard, the muscles of the distal extremities may look hypertrophied. Such myopathic pseudohypertrophy is most noticeable in the muscles of the lower legs. Along with the increase in muscle weakness, there is a gradual extinction of tendon reflexes and a progressive decrease in muscle tone, i.e. peripheral flaccid paralysis develops and worsens. Over time, the result of a sharp restriction of active movements are joint contractures.
Myopathies can be accompanied by damage to the facial muscles, which is manifested by the inability to pull out the lips with a tube, whistle, frown or smile. The defeat of the circular muscle of the mouth leads to the appearance of dysarthria associated with difficulty in pronouncing vowel sounds.
The clinic of some myopathies includes damage to the respiratory muscles, leading to the occurrence of congestive pneumonia and the development of respiratory failure. There may be pathological changes in the heart muscle with the occurrence of cardiomyopathy and heart failure, the muscles of the pharynx and larynx with the development of dysphagia and myopathic paresis of the larynx.
Features of individual forms
Juvenile Erb myopathy is inherited autosomal recessive. Pathological processes begin to manifest themselves at the age of 20-30 years. First of all, they cover the muscles of the pelvic girdle and hips, then quickly spread to other muscle groups. The involvement of facial muscles is not typical. The onset of myopathy at a younger age leads to early immobility of patients. With the development of the disease in older age, its course is less severe: patients retain the ability to move for a long time.
Duchene’s pseudohypertrophic myopathy is inherited recessively linked to gender. Only boys get sick. As a rule, it manifests during the first 3 years of life, less often – in the period from 5 to 10 years. Typically, it begins with atrophic changes in the pelvic girdle and proximal leg muscles, accompanied by pseudohypertrophy of the calf muscles. Contractures and curvature of the spine occur early (kyphosis, scoliosis, hyperlordosis). Oligophrenia may be observed. The disease occurs with damage to the respiratory muscles and heart (cardiomyopathy is noted in 90% of patients with Duchenne myopathy), which is the cause of early death.
Shoulder-scapular-facial myopathy of Landuzi – Dejerin has autosomal dominant inheritance. Manifests in 10-20 years with the defeat of facial muscles. Gradually, weakness and atrophy cover the muscles of the upper arms, shoulders and chest. The pelvic girdle muscles usually do not suffer. It is characterized by a slow flow with long-term preservation of working capacity, without reducing life expectancy.
Scapuloperoneal myopathy is an autosomal dominant disease. Its peculiarity is the development of atrophy in the muscles of the distal legs and proximal arms, as well as the presence of mild sensory disturbances of the distal parts of both the lower and upper extremities.
Oculopharyngeal myopathy is characterized by a combination of oculomotor muscle damage with weakness of the muscles of the tongue and pharynx. Usually manifests bilateral ptosis, then swallowing disorders are added. The peculiarity of this myopathy is its late onset — in the 4th-6th decade of life.
Distal late myopathy is inherited autosomally dominant. It is characterized by the development of weakness and atrophy in the distal parts of the limbs: first in the feet and hands, and then in the shins and forearms. The slow flow is characteristic.
The clinical manifestations of various forms of congenital, hereditary and metabolic myopathies are described in independent reviews.
Diagnostics
Electrophysiological examination methods: electroneurography (ENG) and electromyography (EMG) help the neurologist to diagnose myopathy. They make it possible to exclude damage to the peripheral motor neuron and, thus, differentiate myopathy from infectious myelopathy, cerebrospinal circulation disorders, myelitis and spinal cord tumors. EMG data indicate changes in muscle potentials characteristic of myopathies – a decrease in their amplitude and a reduction in duration. The presence of a large number of short peaks indicates a progressive process.
Biochemical blood test in myopathy shows an increase in the content of aldolase, CK, ALT, AST, LDH, and other enzymes. In the biochemical analysis of urine, an increase in creatinine concentration is indicative. Muscle biopsy is of paramount importance in determining the form of myopathy. Morphological examination of muscle tissue samples reveals the presence of randomly scattered atrophied myofibrils among practically preserved and hypertrophied muscle fibers, as well as the replacement of areas of muscle tissue with connective or fatty tissue. The final diagnosis is possible only after comparing the results of histochemical, immunobiochemical and molecular genetic studies.
In order to diagnose heart muscle lesions, a cardiologist’s consultation, ECG, ultrasound of the heart may be prescribed to a patient with myopathy; if pneumonia is suspected, a pulmonologist’s consultation and lung x-ray may be prescribed.
Treatment
Currently, the pathogenetic treatment of myopathies is in the state of scientific experiments in the field of genetic engineering. In clinical practice, symptomatic therapy is used, consisting mainly in improving the metabolism of muscle tissue. For this purpose, vitamins E, B1, B6, B12, ATP, neostigmine, amino acids (glutamic acid, hydrolysate from pig brain), anticholinesterase drugs (ambenonium, galantamine), anabolic steroids (nandrolone decanoate, methandienone), potassium and calcium preparations, thiamine pyrophosphate are used. Combinations of several drugs are prescribed for a course of 1-1.5 months. 3 times a year.
Medical treatment of myopathies is supplemented with physiotherapy (electrophoresis with neostigmine, ionophoresis with calcium, ultrasound), light massage and physical therapy. Physical therapy can be carried out in the pool. The set of exercises should be selected in such a way as to avoid overloading the weakened muscles. In some cases, patients need to consult an orthopedist and the selection of orthopedic correction tools (corsets, shoes).
The basis of treatment of acquired forms of myopathy is the therapy of the underlying disease: correction of endocrine disorders, elimination of toxic effects and detoxification of the body, elimination of the infectious process, transfer of chronic disease to the stage of stable remission, etc.
Prognosis and prevention
Hereditary myopathies, manifested in early childhood, are the most unfavorable in prognostic terms. Otherwise, the prognosis depends on the form of myopathy, involvement of the cardiac and respiratory muscles in the process. The prognosis of secondary myopathies is more favorable if the underlying disease is successfully treated.
Prevention of primary myopathies is a thorough collection of family history and mandatory counseling from a geneticist of couples planning pregnancy. Prevention of secondary myopathies is the exclusion of toxic effects on the body, timely treatment of infectious and endocrine diseases, correction of metabolic disorders.
