Myotonic Dystrophy

Introduction to myotonic dystrophy Myotonic dystrophy was first described by Delege (1890). Muscle tonic manifests a significant delay in the relaxation of skeletal muscle after contraction, resulting in significant muscle stiffness, and characteristic continuous high-frequency potential discharge in EMG. The disease can occur at any age, but more common after puberty, more men than women. The main symptoms are muscle weakness, muscle atrophy and myotonia. Atrophy and weakness manifest as inflexibility of the limbs, atrophy of the forearm and hand muscles, and sagging of the lower limbs and cross-threshold gait. Atrophy can also develop to the facial muscles, masseter muscles, diaphragm muscles and sternocleidomastoid muscles, so the patient's face is long and thin, the humerus is raised, with an axe-like face, and the neck is thin and slightly flexed. Myotonia can be treated with a stable system of membrane system, which can promote sodium pump activity, reduce sodium ion concentration in the membrane, increase resting potential, and improve muscle rigidity. Such as quinine sulfate, 300-400mg, 3 times / d. Procainamide 0.5-1 g, 4 times / d. Metoin 0.1g, 3 times / d. Benzoin may be preferred for myotonic dystrophy because other drugs have an adverse effect on cardiac conduction. basic knowledge The proportion of illness: 0.001% Susceptible people: no specific population Mode of infection: non-infectious Complications: Acne

Causes of myotonic dystrophy

Myotonic dystrophy type 1 is an autosomal dominant genetic disease with multiple activities involved. The gene defect is located on the chromosome 19q13.2-19q13.3 gene trinucleotide (CTG) repeat amplification, this amplification The trinucleotide repeats form the basis of diagnostic tests. The protein encoded by this gene is called myotonic protein kinase. The gene penetrance rate is 100%. The global prevalence rate is 3-5/100,000, and the incidence rate is about 1/8000 live infants. It is the most common muscular dystrophy in adults, with no obvious geographical or ethnic differences. The pathogenesis of myotonia is unclear and is considered to be a wide range of membrane abnormalities, including skeletal sarcolemma, erythrocyte membrane, lens membrane and vascular membrane. At least in some cases, myofibroblastic abnormalities appear to be associated with decreased chloride ion conductivity across the transfibrillar membrane. In addition to showing multiple groups of muscle atrophy and myotonia, there are many activities such as lens, skin, heart, endocrine and reproductive activities. The genetic pattern of tonic muscular dystrophy type 2 is different. A group of related tonic lesions proximal myotonic myopathy is usually dominant and sporadic, independent of the atrophic myotonic kinase (DMPK) gene, which is located on the 3q21.3 chromosome.

Myotonic dystrophy prevention

The family of patients should make detailed genealogical analysis and serum CPK determination and genetic analysis, find carriers early, and do a good job in marriage, genetics and eugenics. For women who are diagnosed as carriers, amniocente should be examined at the end of pregnancy, and whether the fetus is abnormal by PCR. This work can not only achieve intrauterine diagnosis, but also timely treatment and prevention of the purpose of the disease.

Myotonic dystrophy complications Complications

In the advanced stage, the limbs are contracted and the activity is completely impossible. Often due to a pulmonary infection, hemorrhoids are equal to the death before the age of 20. IQ often has varying degrees of decline. More than half of the patients may have heart damage and abnormal ECG. Early manifestation of cardiac hypertrophy, generally asymptomatic except palpitations.

Symptoms of myotonic dystrophy Symptoms Common symptoms Dysphagia Muscle atrophy Myocardial dystrophy Muscle muscle weakness Benign pseudo-hypertrophic large muscle...

The disease can occur at any age, but more common after puberty, more men than women. The main symptoms are muscle weakness, muscle atrophy and myotonia. Atrophy and weakness manifest as inflexibility of the limbs, atrophy of the forearm and hand muscles, and sagging of the lower limbs and cross-threshold gait. Atrophy can also develop to the facial muscles, masseter muscles, diaphragm muscles and sternocleidomastoid muscles, so the patient's face is long and thin, the humerus is raised, with an axe-like face, and the neck is thin and slightly flexed. Some patients may have speech and difficulty swallowing. The distribution of myotonia is not as extensive as congenital muscle rigidity.

Most limited to upper limb muscles and tongue muscles. There is no significant relationship between muscle atrophy and muscle rigidity. Most patients have cataracts, sweating, alopecia, decreased basal metabolic rate, decreased lung capacity, weight loss, irregular menstruation, impotence, decreased libido and infertility. There may be gastrointestinal smooth muscle dysfunction, and some patients have mental retardation and even dementia.

Symptoms and signs

1. Myotonic dystrophy type 1 (MDI)

Symptoms usually appear at 30 or 40 years of age, although they can occur early in childhood. More men than women, and the symptoms are heavier. The main symptoms are muscle weakness, muscle atrophy and muscle rigidity, the first two symptoms are more prominent. Muscle weakness is seen in the whole body skeletal muscle, forearm muscle and hand muscle weakness with muscle atrophy and muscle rigidity, foot drop and cross-threshold gait, difficulty walking and falling; some patients have dysarthria and difficulty swallowing. Muscular atrophy often involves the facial muscles, masseter muscles, diaphragm muscles and sternocleidomastoid muscles. The patient's face is long and thin, and the humerus is raised, showing an axe-like face, and the neck is long and thin. Myotonia often occurs several years or at the same time before muscle atrophy, and the distribution is not as extensive as congenital muscle rigidity, limited to upper limb muscles, facial muscles and tongue muscles. Examination can prove the existence of muscle rigidity. If the patient can not release the hand immediately after the fist is kept, it can be relaxed after repeated several times. After closing the eye, the eye can not be blinked immediately, and the mouth can not be opened when chewing. The muscles that use the hammer to smash the muscles continue to contract, and the local muscles are formed. It is more common in the forearm and hand extensors. It lasts for a few seconds and then returns to its original state. This sign is of great value in diagnosing this disease.

2, tonic muscular dystrophy type 2 (MD2)

Occasionally, the clinical manifestations of patients were similar to those of myotonic dystrophy, but there was no repetitive amplification of myotonic protein kinase gene. The clinical features are similar to those of MD1, with significant muscle weakness, muscle weakness, and muscle atrophy in the distal muscles, facial muscles, and sternocleidomastoid muscles, with muscle rigidity, cataracts, alopecia, testicular atrophy, diabetes, cardiac abnormalities, and intelligence. Abnormal, etc.

3, proximal myotonic myopathy

The manifestations of myotonia, proximal muscle weakness and cataract, the course of disease is not as serious as MD1, and variants of severe muscle involvement and hearing loss have also been reported.

4, many patients with cataract, retinal degeneration, eyelids, eyelid ptosis, sweating, weight loss, heart block, arrhythmia and basal metabolic rate decline, about half of the men with low intelligence, common testicular atrophy, but fertility is rare Decline, so the disease can spread in the family. Vitreous blush is an early characteristic feature. The disease progresses slowly. Some patients lose their ability to work at the age of 40 due to muscle atrophy and heart, lung and other complications. They often die from secondary infection and heart failure; the condition of mild cases can be stable for a long time.

Examination of myotonic dystrophy

1. EMG shows typical myotonic discharge. The affected muscles appear continuous high frequency and strong direct wave attenuation. The EMG speaker emits a sound similar to a dive bomber or chain saw; 67% of patients have shorter exercise time limits, 48% have Multiphase waves. Electrocardiogram often reveals conduction block and arrhythmia

2, serum CK and LDH and other muscle enzyme titers or mild increase.

3. Muscle biopsy showed mild non-specific myogenic damage.

4, the gene detection is specific, the patient chromosome 19q13.3 site DMPK gene CTG trinucleotide sequence abnormal amplification more than 100 (normal human 5-40), the number of repetition is related to the severity of the symptoms.

Diagnosis and differentiation of myotonic dystrophy

1, diagnosis

According to the characteristic muscle weakness, muscle atrophy and myotonia symptoms of young and middle-aged onset, it mainly involves the distal muscles, the head and face muscles and the sternocleidomastoid muscles of the extremities; the physical examination shows that the muscles are straight, the muscles are slammed, and the typical muscles are strong and straight. Electromyography, as well as DNA analysis, abnormal CTG repeat amplification.

2, differential diagnosis

Clinical needs and other types of muscle tonic identification

(1) Congenital myotonia: Thomsen (1876) describes four generations of his own and his family, also known as Thomsen's disease. Usually an autosomal dominant genetic disease associated with a 7q35 chromosome mutation. Usually, there is generalized muscle rigidity from birth, without muscle weakness and muscle atrophy, but it progresses to early childhood symptoms and tends to be stable in adulthood. Myotonic manifestations are similar to tonic muscular dystrophy. Cold and static muscle stiffness can be aggravated and activity can be alleviated. Muscle fake hypertrophy is a prominent sign. The muscle hypertrophy of the whole body looks like an athlete. The muscles of the sniper muscle are locally depressed or globular. Sometimes mental symptoms such as irritability, depression, solitude, depression and obsessiveness can occur. The electromyogram is a typical myotonic potential. A late-onset autosomal recessive genotype (Becker's disease) with distal mild muscle weakness and muscle atrophy, also localized to the 7q35 chromosome.

(2) Congenital accessory muscle rigidity: young onset, muscle rigidity is light, no muscle atrophy, muscle hypertrophy is not obvious.

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