Congenital myopathy is a congenital disease caused by genetically determined disorders in the structure of muscle tissue. Disease is manifested by diffuse muscle weakness and a decrease in muscle tone, the severity of which varies significantly depending on the type of myopathy. In severe cases, congenital myopathy can lead to the death of a child from respiratory failure. Pathology is diagnosed mainly based on the results of morphological examination of samples obtained during muscle biopsy; electromyography, ergometry and the study of muscle tone are only of auxiliary importance. Congenital myopathy may require measures to combat respiratory disorders, provide probe nutrition, correct existing orthopedic deformities, etc.
G71.2 Congenital myopathies
The term “congenital myopathy” is used in neurology in relation to a whole group of fairly rare hereditary diseases that have a similar clinical picture and are differentiated only by specific morphological changes in the structure of muscle tissue. The most common types include: central core disease, non-medial myopathy, myotubular myopathy, myopathy with multiple rods and congenital disproportion of muscle fiber types.
Disease is a genetically determined disease. Depending on the type of myopathy, the anomaly can be localized in different chromosome loci and inherited dominantly, recessively or linked to the X chromosome. The presence of an abnormal gene leads to a violation of the synthesis of a protein that is part of the structure of muscle tissue. As a result, the structure of muscle fibers changes, which negatively affects their contractility and leads to generalized muscle weakness. Usually congenital myopathy manifests itself in early childhood. Its symptoms persist throughout the patient’s life. In most cases, congenital myopathy is characterized by a benign course with little or no progression.
The classification was based on 2 signs: the presence of information about the localization of a gene anomaly and data on which protein of muscle tissue is defective. In accordance with this, congenital myopathy with a known mutant gene and a certain defective protein is distinguished (non-myopathy, central core disease, myotubular myopathy), congenital myopathy with an unspecified defective protein but an established mutant gene (desmin-related and actin-dependent myopathy) and congenital myopathy, for which both the gene and the defective protein remain unknown (congenital disproportion of fiber types, centronuclear myopathy, myopathy with multiple rods).
Congenital myopathy in the first months of a child’s life is characterized by the presence of the “sluggish child” syndrome: a diffuse decrease in muscle tone, mild muscle weakness, poor musculature development and weakened sucking. As the child develops, muscle weakness becomes more noticeable. It is manifested by the inability to get up from the floor, climb on a chair, difficulty walking and other actions that other children of the same age perform without problems. Muscle weakness in congenital myopathy can be expressed to varying degrees. Usually, its significant progression is not observed. In severe cases, the child can not get back on his feet and is forced to move around on a gurney all his life. But the skills that were acquired by him are no longer lost.
The greatest danger is associated with weakness of the respiratory muscles. With moderate muscle weakness, there is a gradual development of respiratory failure, frequent bronchopulmonary diseases (bronchitis, focal pneumonia, congestive pneumonia, etc.). Pronounced weakness of the respiratory muscles can lead to the rapid development of respiratory failure and the death of a child in infancy.
In some cases, congenital myopathy is combined with dysmorphic features (high palate, elongated and narrow face shape) and skeletal abnormalities (kyphosis, scoliosis, clubfoot, shoemaker’s chest, congenital hip dislocation).
Characteristics of certain types
The disease of the central core is inherited autosomally dominant, there are also some sporadic cases of the disease. Congenital myopathy of this type is manifested by a delay in motor development during the first year of life, less often found in adult patients, often accompanied by weakness of facial muscles. Characterized by a small growth of patients and a fragile figure, the presence of skeletal deformities. Patients with this type have an increased risk of malignant hyperthermia. Muscle fibers with single or multiple zones of aseptic necrosis are detected in the biopsy of muscle tissue.
Nonmaline congenital myopathy includes actinopathy, nebulopathy, tropomyosinopathy and troponopathy. Its inheritance occurs more often according to the autosomal dominant principle, but recessive inheritance and sporadic cases of morbidity also occur. The classic form of nemaline congenital myopathy is characterized by the syndrome of a sluggish child. The severe form manifests itself even in the prenatal period in the form of fetal akinesia, and at the birth of a child — severe motor disorders, facial muscle weakness and respiratory failure. A mild form of this type is diagnosed after a period of early childhood, sometimes in adolescence, and proceeds without weakness of the facial muscles. There is also a specific form of non-medial congenital myopathy, in which the development of ophthalmoplegia, cardiomyopathy, rigid spine syndrome is possible. Morphological examination reveals the presence of characteristic rod- or thread-like bodies in the muscles.
Myotubular congenital myopathy is more often inherited as autosomal, in which muscle weakness is mild and can be observed in both girls and boys. X-linked myotubular congenital myopathy affects only males and is characterized by a more severe course with weakness of facial muscles, disorder of swallowing and respiratory function. In the biopsy of muscle tissue, the lesion of type I fibers prevails. The central location of the myocyte nuclei is noted, which corresponds to the muscle tissue of the embryo at 8-10 weeks of pregnancy. In this regard, most researchers consider myotubular myopathy as a result of underdevelopment of muscle tissue.
Myopathy with multiple rods is more often observed as an autosomal recessive disease, although a dominant type of inheritance is also possible. Typical muscle weakness in the proximal parts, which is observed in infancy. Much less often, the disease debuts at an older age. In such cases, generalized muscle weakness is noted. In a muscle biopsy, cells with the absence of mitochondria, destruction of sacromeres and hypotrophy of muscle fibers are determined.
Congenital disproportion of muscle fiber types is manifested by generalized muscle weakness, including facial, muscle hypotension, skeletal abnormalities. The type of inheritance of this congenital myopathy has not yet been established. In the muscle biopsy, an increase in the number and small size of type I fibers is observed against the background of hypertrophy or normal size of type II fibers.
In mild cases, only a targeted examination with a study of muscle strength and tone allows the neurologist to suspect the presence in the child. A thorough examination of the muscles with strength testing (ergometry), standard and stimulation electromyography, myotonometry or electrotonometry allows us to obtain additional data in favor of the diagnosis of “congenital myopathy”. To exclude generalized inflammatory myopathy (dermatomyositis, polymyositis) and diffuse myositis allows the absence of pain syndrome, seals and inflammatory swelling of the muscles.
Finally, congenital myopathy can be diagnosed only after the results of morphological examination of muscle tissue obtained by muscle biopsy. Only this examination makes it possible to determine changes specific to each type of myopathy and establish an accurate diagnosis. However, even a biopsy does not always allow to reliably verify the type of congenital myopathy.
Unfortunately, today there are no sufficiently effective methods of treatment and congenital myopathy retains its manifestations throughout the patient’s life. Possible therapies are aimed at maintaining the highest possible level of viability of the patient. If congenital myopathy is accompanied by a significant decrease in muscle strength, in the first months of life, medical measures consist in combating respiratory insufficiency, providing nutrition through a gastric tube, and relieving bronchopulmonary complications. Massage, hydrotherapy and physiotherapy procedures have a beneficial effect on the condition of patients at any age. At an older age, orthopedic correction of existing disorders and social adaptation of patients may be required.