Myotonic dystrophy Curschmann-Steinert is a hereditary slowly progressive disease based on a defect of myotonin—protein kinase, which leads to the development of myotonia in combination with dystrophic changes in muscle tissue. The disease is manifested by myotonic spasms, atrophic changes in the muscles of the neck, face and distal extremities, decreased intelligence, arrhythmias and endocrine pathology. The diagnosis of dystrophic myotonia is based on clinical data, the results of genealogical analysis and DNA research. Treatment is symptomatic, directed against the symptoms of myotonia (phenytoin, procainamide, quinine, diuretics) and muscular dystrophy (anabolic steroids, ATP).
ICD 10
G71.1 Myotonic disorders
General information
Myotonic dystrophy Curschmann-Steinert is a hereditary disease and is transmitted from parents to children in an autosomal dominant type. The classical form of this disease develops mainly in the age period from 10 to 20 years. In rarer cases, Rossolimo-Steinert-Kurschmann congenital dystrophic myotonia occurs, the clinical symptoms of which appear immediately after birth.
Morphologically, with myotonic dystrophy Curschmann-Steinert, there is a combination of hypertrophic changes in some muscle fibers with atrophy of others, replacement of part of the muscle fibers with adipose and connective tissue. Examination of muscle tissue samples under an electron microscope shows the destruction of myofibrils and a change in the size of mitochondria.
Causes
Recent studies of the genetic set of patients with dystrophic myotonia have shown that the basis of the disease is a defect in the DMPK gene located on chromosome 19 and responsible for the synthesis of myotonin protein kinase. In patients with dystrophic myotonia, a significant increase in trinucleotide CTG repeats in the main part of the DMPK gene is detected. At the same time, the form and severity of myotonia depends on the number of repetitions.
Normally, the number of trinucleotide repeats varies from 5 to 37. An increase in repetitions to 50-80 leads to the appearance of a mild form of myotonic dystrophy Curschmann-Steinert. If the number of trinucleotide repeats is in the range from 100 to 500, a late form of the disease develops. Congenital forms of dystrophic myotonia occur with an increase in the number of CTG repeats from 500 to 2000. Studies have shown that an increase in trinucleotide repeats occurs mainly in female gametes during meiosis. In this regard, when the disease is transmitted from the mother, the child has a more severe form of myotonia or its congenital variant.
Symptoms
In the classical version, myotonic dystrophy Curschmann-Steinert begins to manifest after the first 5 years of life and can manifest up to the age of 35. But the most common clinical manifestations of the disease occur in the age range from 10 to 20 years. They are a combination of typical symptoms of myotonia with signs of myopathy, damage to the cardiovascular system and central nervous system, endocrine disorders and cataract.
Of the myotonic manifestations, myotonic dystrophy Curschmann-Steinert is characterized by myotonic spasms, most pronounced in the masticatory muscles and flexor muscles of the hand. Mechanical reactions of the myotonic type are also observed, detected when struck with a neurological hammer. A distinctive feature of myotonic dystrophy Curschmann-Steinert is the presence of atrophic changes in various muscle groups. At the same time, the course of the disease is characterized by a gradual extinction of the symptoms of myotonia against the background of progressive muscular dystrophy.
Most often, myotonic dystrophy Curschmann-Steinert affects the muscles of the distal extremities, facial muscles, sternocleidomastoid and temporal muscles. The defeat of the facial muscles is manifested by a characteristic mask-like sad expression of the face of patients with dystrophic myotonia. Atrophic changes in the muscles of the pharynx and larynx lead to the development of myopathic paresis of the larynx with impaired voice and difficulty swallowing. Myopathic changes may occur in the respiratory muscles. Along with myotonic spasms, they lead to deterioration of pulmonary ventilation, the appearance of sleep apnea attacks, the appearance of stagnant or aspiration pneumonia.
Disorders of the cardiovascular system are observed in about half of cases of dystrophic myotonia. These include arrhythmias associated with impaired conduction and hypertrophy of the left ventricle. The most common blockade of the legs of the Gis bundle. Of the signs of central nervous system damage, hypersomnia and a decrease in intellectual abilities, reaching a mild degree of debility, are most often observed.
Endocrine disorders in myotonic dystrophy Curschmann-Steinert affect mainly the sexual sphere. In men, they are manifested by a decrease in libido, cryptorchidism, impotence, hypogonadism, in women — hirsutism, menstrual disorders (oligomenorrhea, dysmenorrhea) and early menopause. A typical change in the structure of the hair in combination with alopecia. Men have hair loss on the temples and forehead, women have diffuse or focal baldness.
The first signs of the congenital form of myotonic dystrophy Curschmann-Steinert may appear even during intrauterine development. As a rule, they are expressed in a significant decrease in fetal motor activity, which is diagnosed by an obstetrician-gynecologist according to obstetric ultrasound in the third trimester of pregnancy.
After the birth of a child, the symptoms of myopathy prevail. There is diffuse hypotension of the muscles, more pronounced in the facial, masticatory and oculomotor muscles, as well as in the muscle groups of the distal extremities. Feeding difficulties and respiratory disorders are characteristic. Myotonic symptoms begin to manifest somewhat later. Congenital dystrophic myotonia is accompanied by a delay in motor development and oligophrenia. Typically, the rapid progression of symptoms of the disease, often leading to death in early childhood.
Diagnostics
A typical combination of myotonia with signs of dystrophic changes in muscle tissue, mental retardation, disorders of the cardiovascular and endocrine systems allows a neurologist to assume myotonic dystrophy Curschmann-Steinert. The diagnosis is confirmed by the results of genealogical analysis, indicating an autosomal dominant type of inheritance of the disease, and DNA analysis data. Additionally, electromyography, electroneurography, studies of sex hormones, ECG are performed. Geneticists, cardiologists, endocrinologists, gynecologists, andrologists can additionally be involved in the diagnosis of patients with myotonic dystrophy Curschmann-Steinert.
When diagnosing dystrophic myotonia, it is necessary to differentiate it from other types of myotonia. Thus, the presence of muscular atrophy makes it possible to distinguish myotonic dystrophy Curschmann-Steinert from Thomsen myotonia, for which muscular hypertrophy is typical. From Becker’s myotonia, the disease is distinguished by an early lesion of the facial muscles and a dominant type of inheritance. In addition, a differential diagnosis of myotonic dystrophy Curschmann-Steinert with myopathies, ALS and Charcot-Marie-Toute amyotrophy should be carried out.
Treatment
Radical therapy of myotonic dystrophy Curschmann-Steinert does not yet exist. Patients with this disease are shown a diet with a reduced potassium content. They should also avoid hypothermia, which provokes myotonic spasms. The reduction of myotonic manifestations is facilitated by the intake of quinine, procainamide, phenytoin in combination with acetazolamide. Anabolic steroids (nandrolone decanoate, methylandrostenediol, methandrostenol), small doses of ATP, B vitamins are shown.