Myotonic myopathy


Introduction to myotonic myopathy

Myotonic myyomyopathy refers to the skeletal muscle that is not easy to relax immediately after contraction or physical stimulation. The muscle excitability increases during electrical stimulation and mechanical stimulation. The skeletal muscle relaxes after repeated contraction or repeated electrical stimulation, and the symptoms disappear. In a cold environment, the tonicity is aggravated, and the electromyogram examination presents a group of muscle diseases characterized by continuous high-frequency discharge phenomena. Myotonic myopathy is divided into myotonic dystrophy, congenital myotonia and congenital accessory myotonia according to clinical manifestations and etiology. The clinical symptoms are diverse and involve multiple systems, including muscle, heart, lens, endocrine gland, and central nervous system. The age of onset and the onset of the disease are mostly concealed after the age of 30. Men are more likely than women, and progress is slow. Muscle rigidity occurs several years or at the same time before muscle atrophy. The severity of the disease varies greatly, some patients may have no symptoms, and only abnormalities are found when the body is examined. Treatment problems for myotonia include drug treatment to relieve symptoms, avoid certain medications, prevent aggravation of myotonia, and treat different types depending on the type of disease.

basic knowledge

The proportion of sickness: 0.01% - 0.02%

Susceptible people: more than 30 years old

Mode of infection: non-infectious

Complications: Diabetes Infertility Elderly heart block


Causes of myotonic myopathy

Myotonic dystrophy (30%):

The myogenic dystrophy type I (DM1) causative gene is atrophic myotonic kinase (DMPK) located on the long arm of chromosome 19 (19q13.3), encoding 582 amino acids. Abnormal amplification of a trinucleotide tandem repeat (CTG) exists in the 3'-end untranslated region of the gene. The DM2 pathogenic gene is ZNF9 located in 3q21, which is a DM2 caused by abnormal extension of the tetranucleotide string (CCTG) in intron 1. DM is currently considered to be an RNA-mediated disease, and selective splicing abnormalities are the cause of multiple systemic damage in the clinic.

Congenital muscle rigidity (25%):

Congenital myotonia is caused by a mutation in the chloride channel (CLCN1) gene located on chromosome 7q35. The skeletal muscle voltage-gated chloride channel protein encoded by this gene is a transmembrane protein that plays an important role in the transport of chloride ions inside and outside the skeletal muscle cell membrane. When the CLCN1 gene point mutation causes the amino acid substitution of the main hydrophobic region of the chloride channel protein, the permeability of the chloride ion is lowered to induce muscle rigidity.

Congenital accessory muscle rigidity (25%):

Congenital accessory muscle rigidity is autosomal dominant, and the disease-causing gene is located at 17q35, encoding skeletal muscle-gated sodium channel protein. The mutation of the gene causes dysfunction of the sodium channel protein, mainly due to abnormal inactivation, sodium ions continuously enter the cell, the sarcolemma continues to depolarize, and muscle rigidity occurs.


Myotonic myopathy prevention

Myotonic dystrophy varies widely among individuals. The earlier the onset, the worse the prognosis, and those who have symptoms often die of heart disease between the ages of 45 and 50. Those with mild symptoms can approach normal life years. Congenital myotonia and accessory muscle rigidity have a good prognosis and longevity.


Myotonic myopathy complications Complications, diabetes infertility, heart block in the elderly

Multiple neurological symptoms can occur. In addition to muscle involvement, other diseases such as the endocrine system, including thyroid function, islet function, reproductive function, and hypothalamic function. Therefore, hypothyroidism caused by subcutaneous edema, diabetes and testicular atrophy, women cause infertility, habitual abortion and menstrual irregularities. In addition, myocardial involvement can cause heart conduction to be blocked.


Symptoms of myotonic myopathy common symptoms myocardium muscle weakness muscle atrophy muscle pain acute atrial fibrillation muscle hypertrophy limb stiffness conduction block lens opacity

Myotonic dystrophy

The clinical symptoms of DM are diverse and involve multiple systems, including muscle, heart, lens, endocrine gland, and central nervous system. The age of onset and the onset of the disease are mostly concealed after the age of 30. Men are more likely than women, and progress is slow. Muscle rigidity occurs several years or at the same time before muscle atrophy. The severity of the disease varies greatly, some patients may have no symptoms, and only abnormalities are found when the body is examined.

1. Muscle: The clinical symptoms of DM1 patients are mainly muscle weakness, muscle atrophy, and muscle rigidity. The distal muscle weakness of the limb is significantly earlier than the proximal end, and the extensor muscle is heavier than the flexor. In the early stage of the disease, tibialis anterior muscle weakness and foot drop may occur. There are also facial muscle weakness in the early stage, but it is difficult to be detected by patients. The weakness of the cervical muscles and the slight flexion of the neck are also early signs of the disease, which is manifested by the difficulty of lifting the patient's head from the pillow. Atrophy first affects the distal muscles of the extremities, especially the flexors, which can cause the hands to lose function. The distal muscle atrophy of the limb is significantly earlier than the proximal end of the limb. There may be diaphragmatic muscles, masticatory muscle atrophy, prominent humerus, and long and thin face. It is a typical "axe-like face". The sternocleidomastoid muscle atrophy causes the neck to be slender and the head is tilted forward, showing a "goose neck". Symptoms of myotonia are muscles that do not relax properly after contraction, which can affect the facial muscles and tongue muscles, causing difficulty in speaking, chewing, and swallowing. Sniping the tongue muscle, the muscles of the big fish can appear muscle or muscle depression.

2. Heart: Symptoms of heart involvement include conduction block, atrial flutter, and atrial fibrillation. William et al. evaluated ECG for 406 adult DM1 patients to determine whether ECG predicts sudden cardiac death. The criteria for severe ECG abnormalities are non-sinus rhythm, PR interval 240m, QRS wave 120m or 2 degrees/3 degree room. Ventricular block. It was found that patients with DM1 had a high risk of arrhythmia and sudden death. Patients with severe ECG abnormalities and atrial arrhythmias can predict a risk of sudden death.

3. Lens: The edema of the posterior capsule of the lens is predominant. The detection of cataracts in slit lamps contributes to early diagnosis.

4. Endocrine glands: DM1 patients have been found to have multiple endocrine abnormalities, mainly insulin resistance, but rarely found symptoms of obvious diabetes, men have forehead alopecia, testicular atrophy and decreased reproductive capacity. 34 patients with diabetes-free DM1 were measured for serum leptin (fat hormone) concentration (physiologically, serum leptin levels were positively correlated with body mass index BMI and negatively correlated with testosterone levels), and DM1 patients were found to have increased BMI, insulin. Resistance, serum leptin concentration increased, but DM1 patients have no other symptoms of metabolic syndrome such as glucose intolerance, high blood pressure and so on. High levels of leptin in male DM1 patients may be caused by hypogonadism and decreased serum testosterone levels. In this study, it was found that only male DM1 patients had significantly elevated serum leptin levels, while female DM1 patients had a slightly elevated level.

5. Central nervous system related symptoms: There is a correlation between DM1 cognitive impairment and CTG repeat length. The examined DM1 patients performed functions, computational power, attention, speed, visual space function, and facial expression recognition ability scores below the standard value. The greater the number of CTG repeat amplifications, the lower the test score associated with the above capabilities. Therefore, in clinical work, patients with DM1 should be assessed for cognitive deficits, and the extent of cognitive deficits in DM1 can be predicted by measuring the number of CTG repeat amplifications. A neuropsychological assessment of 200 patients with DM1 found that 60% of patients had symptoms of fatigue, 30% had symptoms of Excessive Daytime Sleepiness, and patients with daytime sleepiness were more likely to fatigue and fatigue. It is easier to sleep during the day. Data statistics The incidence of fatigue symptoms is twice as high as that of daytime sleepiness. However, some patients may feel that their sleepiness is a weak personality and lack of initiative. They are not willing to describe their subjective feelings as sleepiness or sleepiness. Instead, describe it as fatigue. Therefore, the actual incidence of fatigue symptoms may be lower.

6. The clinical manifestations of DM2 patients are basically similar to those of DM1, except that muscle weakness and muscle atrophy are mainly proximal, often accompanied by myalgia, and there is no report of congenital onset.

Congenital muscle rigidity

1. The onset age Most patients start from infancy or childhood, and also have symptoms in adolescence. Myotonia and muscle hypertrophy gradually progress and tend to be stable in adulthood.

2. Muscle rigidity, general skeletal muscle, general muscle rigidity. The patient's limbs are stiff and clumsy. After the rest, the first exercise is heavier. If you sit for a long time, you can't stand immediately. You can't start after standing still. You can't relax after shaking hands, but the symptoms are relieved after repeated exercise. The muscles of the face, jaw, tongue, pharynx, and upper extremities are more pronounced than the lower extremities, and the above symptoms are aggravated in a cold environment. Sniper muscles can be seen in the muscle ball. Respiratory and urinary sphincter involvement can cause difficulty breathing and urinating.

3. Muscle hypertrophy The general skeletal muscle is hypertrophic and resembles an athlete. Muscle strength is basically normal, no muscle atrophy, normal feeling, and sputum reflex exists.

4. Other patients may have psychiatric symptoms such as irritability, depression, solitude, depression and obsessive attitudes. The heart is not tired, the patient can generally maintain the ability to work, and the life is not limited.

Congenital accessory muscle rigidity

1. Congenital accessory muscle rigidity manifests as muscle rigidity and paroxysmal weakness. Muscle tonic symptoms affect the face, masked face or stiffness, in the case of cold, wind, cold rain, the eye can not open in a few seconds, the newborn can not wipe the face with a cold towel, when working in a cold environment The fingers are stiff and unable to move.

2. Muscle strength lasts for a few minutes and can last for hours.

3. Myalgia, muscle atrophy, and muscle hypertrophy are rare.

4. No sniper muscle rigidity.


Examination of myotonic myopathy

Myotonic dystrophy

1. Serum CK and LDH and other enzymes are normal or slightly elevated.

2. EMG typical muscle tonic discharge is important for diagnosis. The affected muscles appear to be continuously attenuated by high-frequency strong waves, and the EMG speaker emits a similar sound like a bomber.

3. Muscle biopsy, typical type II muscle fiber hypertrophy, type I muscle fiber atrophy, with a large number of nuclear internal migration, visible muscle mass and ring muscle fibers, as well as muscle fiber necrosis and regeneration.

4. Gene detection The abnormality of the CTG repeat sequence of the 3'-untranslated region of the myotonic kinase gene of chromosome 19q13.3 in patients with chromosome 19q13.3 was more than 40 replicates (normally 5 to 40), which can be confirmed.

5. Brain MRI: MRI studies in the brain of DM1 patients showed a decrease in brain volume, enlarged ventricles, impaired focal white matter, and cortical atrophy. The corpus callosum and pituitary gland were smaller in DM1 patients than in normal subjects, while the parietal cortex volume was not significantly reduced. Fifteen DM1 patients underwent exercise testing, and the right thumb repeatedly touched the remaining four fingers in sequence, while using fMRI to study the patient's brain activity. It was found that the activity of the inferior lobular lobe, basal ganglia, thalamus and ipsilateral anterior region, and supplemental motor area in the bilateral sensorimotor area of DM1 patients was enhanced compared with normal subjects. Analysis of the relationship between disease and age found that DM1 patients with age, their bilateral sensorimotor and contralateral dysfunctional movement activities were greater than the normal control group. The brain of DM1 patients may compensate for the ultrastructural and neurochemical changes that occur during aging of the patient through changes such as recombination and redistribution of the functional zone.

Congenital muscle rigidity

The electromyography showed a myotonic potential, and the speaker made a bomber dive or frog sound. Muscle biopsy showed muscle fiber hypertrophy and nuclear center displacement may not be obvious. The serum muscle enzyme is normal and the electrocardiogram is normal.

Congenital accessory muscle rigidity

1. Blood CK is elevated

2. The electromyogram muscle has fibrillation-like electrical activity when it is cold, and the motor unit is normal.

3. There is no characteristic change in muscle pathology, but it can be seen that the central nucleus increases, the muscle fiber size is different, and occasionally the formation of muscle fiber vacuoles.

4. Induction test: The forearm or hand is bathed in ice water for 15-20 minutes, and the muscle strength and relaxation time of the isometric contraction of the flexor digitorum muscle are measured. The contraction muscle strength of the patient is decreased by 10-50% or more, and the relaxation time is prolonged by 0.5- 50mS. It is also possible to measure the magnitude of the evoked potential and observe the decrease in amplitude.


Diagnosis and differentiation of myotonic myopathy

Myotonic dystrophy


According to the autosomal dominant inheritance history, the middle-aged onset is slow. The clinical manifestations are generalized skeletal muscle rigidity, weakness and atrophy. At the same time, it has multiple systemic manifestations such as cataract, baldness, endocrine and metabolic changes. The electromyogram showed a typical myotonic discharge. The CTG repeat sequence of the 3'-untranslated region of the DMPK gene was abnormally amplified more than 37 times. The muscle biopsy was myogenic damage and the serum CK level was normal or slightly elevated. Generally not difficult.

Differential diagnosis

Clinically, it is mainly identified with other types of muscle rigidity.

1. Congenital myotonia: The main difference between myotonic dystrophy and myotonic dystrophy is muscle rigidity and muscle hypertrophy, which looks like athletes but weakened muscles, no muscle atrophy and endocrine changes.

2. Congenital paramyotonia congenital (paramyotonia congenital): prominent feature is that after the birth of the face, hands, upper limbs, muscles in the distal part of the muscles after cold or muscle hypertonic Incapable, such as cold water after washing your face, the eyes open slowly, in a warm environment, the symptoms quickly disappear, and the sniper muscles are strong. Autosomal dominant inheritance, the pathogenic gene is located at 17q23. The patient has a normal life.

3. Hyperkalemia type periodic sputum: flaccid paralysis with muscle rigidity before the age of 10 years, elevated blood potassium level, increased T wave of electrocardiogram, and point mutation detection of -subunit gene of chromosome 17q13 diagnosis.

4. Neuromyyotonia: Also known as Isaacs syndrome, childhood and adolescent concealed onset, slowly progressing, clinical features of persistent muscle twitching and sweating, persistent or intermittent paralysis of the wrist and ankle.

Congenital muscle rigidity

According to the positive family history, the clinical manifestations of generalized musculoskeletal muscle rigidity and muscle hypertrophy in infancy or childhood onset can be diagnosed by combining electromyography, muscle biopsy and serum muscle enzyme test.

Congenital accessory muscle rigidity


According to the family history of autosomal dominant inheritance, exercise, cold induced muscle stiffness, weak muscle strength, electromyography has muscle tonic activity, and elevated serum CK can make a diagnosis.

Differential diagnosis

1. Congenital muscle rigidity: Congenital myotonia is an autosomal dominant genetic disease, which is characterized by difficulty in muscle relaxation after exercise. Although the cold factor can aggravate the symptoms, it is not as obvious as congenital accessory muscle rigidity, lacking facial and neck muscle rigidity. Distribution characteristics. Looks like an athlete but weak muscles.

2. High potassium periodic paralysis: high potassium periodic paralysis has paroxysmal limb muscle stiffness, weak, may have clinical or electrical muscle rigidity, but lacks facial muscle characteristics. Rest after intense activity, muscle starvation, potassium, cold, alcohol abuse, excessive carbohydrates, stress induced, such as sustained mild exercise, intake of carbohydrates can reduce or eliminate seizures. Temperature dependence is not as significant as PC.

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