Myasthenia gravis in children

Introduction to pediatric myasthenia gravis Myastheniagravis (MG) is a chronic disease of neurotransmitter dysfunction. It has been clarified that the onset of myasthenia gravis is caused by autoimmunity of the postsynaptic acetylcholine (Ach) receptor, an autoimmune disease that transmits dysfunction between nerve-muscle junctions (synapses). The acetylcholine receptor (AchR) on the postsynaptic membrane at the neuromuscular junction of the striated muscle is also involved in other parts of the body and tissues. It is characterized by low musculoskeletal muscle strength, fatigue, and short-term contraction of the muscles. The force is rapidly reduced, the symptoms are relieved after rest, and it is effective for cholinesterase drug treatment. Pediatric myasthenia gravis includes three syndromes: neonatal MG, congenital MG, MG in children, among which neonatal and pediatric MG is an acquired autoimmune disease with neuromuscular junction transmission disorder, 90% adult nicotinic type Acetylcholine receptor antibody (nAChRab) is positive, and pediatric cases are mostly negative for nAChRab. basic knowledge The proportion of illness: the incidence rate is about 0.001% - 0.003% Susceptible people: children Mode of infection: non-infectious Complications: myasthenia gravis crisis

Pediatric myasthenia gravis

(1) Causes of the disease

In the 1970s, the nicotinic acetylcholine receptor (nAChR) was successfully obtained from an electric fish discharge organ and successfully produced a model of experimental MG, as well as the application of radiolabeled venom alpha-neurotoxin radioimmunoassay. The pathogenesis of MG has made breakthrough progress.

1. Myasthenia gravis is an autoimmune disease of the striated muscle synaptic membrane nAChR

Neuromuscular junctions are combined with sarcolemmal receptors by receiving excitatory transmitters such as acetylcholine (ACh) and nicotine, resulting in ion channel opening, Na influx, sarcolemmal depolarization, endplate potential, and myofilament. This causes muscle contraction. nChR is known to be an antigen that is highly specific for the autoimmune response of MG. The nAChR is located in the postsynaptic membrane of the neuromuscular junction. Experiments have shown that thymic epithelial cells in MG patients contain myofibrils and a common antigen (nAChR) with skeletal muscle. The antigen sensitizes T cells and produces an anti-nAChR antibody (nAChRab). The antibody produces a cross-immune immune response to skeletal muscle nAchR, which blocks the receptor; accelerates the degradation of AChR, and damages the sarcolemma by activating complement. Electron microscopy revealed post-synaptic membrane IgG and C3 deposition. Ultrastructural examination of motor endplates by horseradish-labeled snake venom neurotoxin showed that MG pathological damage was characterized by a decrease in the surface area of skeletal muscle postsynaptic membrane folds and a decrease in nAChR activity, resulting in muscle weakness.

2. Myasthenia gravis is a T cell-dependent autoimmune disease

A large number of studies on humoral immunity have shown that nAchR is impaired as a target for MG and is mediated by nAChRab; whereas nAChRab is T cell dependent for nAChR immune response. T cells play a key role in the autoimmune response of MG. The production of nAChRab must be involved in the involvement of nAChR-specific CD4 T cells. nAChR-specific CD4 T cells first recognize the nAChR-specific site through their receptor (TCR), and then provide the NAchR major immunogenic region-specific antibody to B cells by T helper cells (Th), which promotes B cell secretion. Sick nAChRab. Th cells regulate the secretion of nAChRab by secreting cytokines.

3. Genetic and viral infections

It is well known that myasthenia gravis is an abnormal autoimmune response, but the cause of autoimmunity has not been fully understood. It is currently believed that the pathogenesis of MG is related to human leukemia antigen (HLA), and its correlation is related to race and region, and there are gender differences. HLA class II antigens (including D, DP, DQ, DR and other gene products) play an important role in the process of autoimmune. DQ is more sensitive to autoimmune diseases than the DR allele. PCR-RFLP technique was used to detect the significant correlation between non-thymoma MG and HLA-DQA1*0301 gene in China. In addition, DQB1*0303 and DPDL*1910 genes were found to be significantly correlated, indicating that the pathogenesis of MG is related to polygenic inheritance.

In addition to genetics, the pathogenesis of MG also includes external environmental influences, such as the disease is often induced or aggravated by viral infection.

The thymus is the immune center. Whether it is thymus lymphocytes (especially T cells) or epithelial cells (especially muscle-like cells containing nAchR-specific antigens), they are immunely attacked, breaking immune tolerance and causing autoimmune responses against nAchR, thus MG onset.

(two) pathogenesis

Pathogenesis

Myasthenia gravis is an autoimmune disease involving the acetylcholine receptor (AChR) of the postsynaptic membrane at the neuro-muscle junction, and is a data suggesting that the serum acetylcholine receptor antibody (AChRAb) drops in the child. The degree is obviously related to the clinical condition. When the newborn case is born, the level of acetylcholine receptor antibody in the body is higher, and the condition is also heavier. As the antibody titer decreases, the condition begins to decrease, and the plasma exchange method is used to treat the severe disease. In the process of muscle weakness, as the level of antibodies in the blood decreases, the condition also improves. The study also proves that the acetylcholine receptor antibody acts through the acetylcholine receptor on the postsynaptic membrane at the neuro-muscle junction. Acetylcholine The receptor antibody competes with acetylcholine (ACh) for the binding site (AChR), which inhibits the binding of ACh to the receptor through spatial interference and interference, or directly destroys AChR through antibody-mediated cytotoxicity; Complement, destroying the postsynaptic membrane, reducing the number of effective receptors or impairing receptor function, making nerve impulses unable to pass, resulting in Muscle fatigue and other symptoms of poor workability.

2. Pathological changes

Muscle morphology is generally normal, serious disease can have disuse muscle atrophy, and some authors believe that half of patients with myasthenia gravis, especially those with longer course of disease, may have denervated muscular atrophy, pathological features and anterior horn cell lesions Muscle lesions are similar, 70% to 80% of patients with thymus abnormalities, mostly manifested as lymphatic thymic hyperplasia, although in patients with myasthenia gravis, 10% with thymoma, but in children, this lesion is extremely rare Half of the cases of autopsy combined with myocardial abnormalities, 87% of patients with myasthenia gravis were positive for serum acetylcholine receptor antibody (AchRAb). Repeated injection of IgG extracted from the patient's blood can cause electrophysiological changes in myasthenia gravis. Most authors believe that this The disease may be due to the presence of certain factors (such as viral infections), an immune response to Ach R in the thymus, followed by a cross-immunoreaction to the neuromuscular junction Ach R.

Juvenile myasthenia gravis is similar to adult type. It is immune damage to endplate Ach R protein due to humoral and cellular factors. Neonatal myasthenia gravis is related to maternal IgG transfer to the fetus through the placenta. Studies have shown that muscle weakness is severe. The degree and type are closely related to the AchRAb titer.

Pediatric myasthenia gravis prevention

The cause of this disease has not been fully elucidated and may be related to the impact of viral infection and should be actively prevented.

Pediatric myasthenia complication Complications myasthenia gravis crisis

Because the muscle weakness patients are unable to maintain their basic life due to breathing and difficulty swallowing, the vital signs are called muscle weakness, and the incidence rate is about 9.8%~26.7% of the total muscle weakness.

According to the causes of myasthenia gravis, it can be divided into three types: myasthenia gravis, cholinergic crisis and ruminant crisis.

1. Myasthenia gravis crisis: caused by disease development and anti-cholinesterase drug deficiency, clinical manifestations of swallowing, coughing, respiratory distress, difficulty and even stop the serious condition, physical examination showed dilated pupils, sweating, bloating The bowel sounds are normal and the symptoms of the neostigmine are improved after injection.

2. Cholinergic crisis: about 1.0% to 6.0% of the number of dangerous cases, due to the anti-cholinesterase excess, in addition to the common features of muscle weakness, the patient's pupil shrinks, sweating, muscles Beating, bowel sounds hyperthyroidism, intramuscular injection of neostigmine symptoms and other symptoms.

3. Ruminant crisis: It is caused by infection, poisoning and electrolyte imbalance. It can be temporarily relieved after the application of anti-cholinesterase drugs, and then it is aggravated.

Myasthenia gravis may be associated with other diseases, such as thymoma, followed by hyperthyroidism, a small number may be associated with rheumatoid arthritis, lupus erythematosus and autologous hemolytic anemia.

Symptoms of myasthenia gravis in children Common symptoms Myasthenia gravis crisis Repeated infection Facial muscle weakness Capilla ptosis valgus ptosis Drooping diarrhea Infant feeding difficulties Newborn licking milk weakness and reduction

Pediatric myasthenia gravis is generally divided into 3 types:

1. neonatal transient myasthenia gravis (transient neonatal myasthenia gravis)

It is a transient muscle weakness in a newborn born to a mother with myasthenia gravis. It is only found in the newborn born to the mother with MG. The incidence is 1/7 of the newborn born to the mother. The child is born. Muscle weakness occurred within a few hours to 3 days, all of which showed ciliary muscle paralysis, showing low crying, sucking, swallowing and breathing difficulties, facial muscle weakness, active exercise can be reduced, half of the infants with systemic muscle tension is low, hug reflection And deep reflexes are weakened or disappeared, usually no extraocular muscle paralysis. The symptoms are not related to the time of mother's illness and treatment during pregnancy. It is easy to be relieved by cholinesterase inhibitors, but most cases are not symptomatic. Remission, the duration is generally no more than 5 weeks, usually after half a month, the condition can be alleviated, the blood nAchR-Ab can be increased in children, and severe cases can also die from respiratory failure.

2. Congenital myasthenia syndrome (congnital myasthenia syndrome)

It refers to myasthenia gravis caused by infants born to non-myasthenia gravis mothers. This disease is related to autosomal inheritance. The siblings also often suffer from this disease. In most cases, fetal movement is weak. After birth, it is symmetrical, persistent, and incomplete extraocular muscles. Inability and ptosis are characteristic, there is no nAchR-Ab in serum, the course of disease is generally longer, a small number of children can relieve themselves, the main manifestations in the neonatal period are low crying, feeding difficulties, the symptoms of this type of initial onset is lighter. Diagnosis is often difficult, and a few cases can be naturally relieved, but most often last long, the symptoms are not heavy and the response to cholinesterase inhibitors is poor.

3. Juvenile myasthenia gravis in juvenile

It is the most common type of myasthenia gravis in children. The age of onset is 2 to 20 years old, most of them occur before the age of 10, and the female: male is 2 to 6:1. The onset can be occult. Can also be acute onset, often induced by acute febrile illness, can be found in the serum nAchR-Ab, most of the foreign cases after the age of 10, mainly systemic, and domestic data and Hong Kong and Japan reported more In early childhood (2 to 3 years old), the eye muscle type is the most common type, which is the most common type of children's MG.

(1) Clinical features: The onset of the disease is insidious, and there are also emergent eruptions. The first to be affected is the muscles innervated by the brain. The most common one is the ptosis of the upper jaw. A few of them are the muscle weakness of the ball or the weakness of the trunk muscles. Symptoms, symptoms and signs of muscle weakness are mild to light, can be changeable, can be in a state of incomplete paralysis in the later stage, increased after muscle weakness, relieved after rest, generally no muscle atrophy, no muscle bundle vibration, tendon reflex Normal or weakened, no sensory disturbance, individual cases with acute fulminant muscle weakness, more common in children 2 to 10 years old, no history of muscle weakness, respiratory failure as the first performance, acute bulbar palsy within 24h, Attention should be paid to the identification of polio and fulminant cranial nerve type Guillain-Barré syndrome.

Extraocular muscles are most often involved, often early symptoms, can also be confined to the eye muscles, blinking weakness, ptosis is mostly bilateral, but also unilateral, eye movement is limited when the extraocular muscles are weak, often accompanied by strabismus And double vision, or even the eyeball is fixed, the intraocular muscle is generally unaffected, and the pupil reflex is normal, called the myasthenia gravis.

When the muscles of the ball are involved, the facial muscles, the tongue muscles, the masticatory muscles and the throat muscles are also susceptible, the soft diaphragm muscles are weak, the pronunciation is nasal, and the tone is low or vocal after a short conversation, often manifested as difficulty in swallowing and pronunciation, drinking water coughing, chewing. Powerless, tongue movement is not free, no muscle bundles vibrate, facial expression is dull, frontal lines and nasolabial folds become shallow, mouth angle droops, neck weakness, etc., or sudden death due to acute respiratory insufficiency.

The neck muscles, trunk, and limbs are fatigued when fatigue is weak. In severe cases, the respiratory muscles are involved, especially in the proximal end of the limbs. The performance is difficult to lift, the head is difficult to hold, the chest is tight, the face is short, the face is tired, the walking is difficult, and the walking is difficult. Some only show weakness in both lower limbs, sputum reflexes, no sensory disturbances, called systemic myasthenia gravis.

The disease mainly involves skeletal muscle, but also may have myocardial damage, but there is no obvious complaint, and the literature reports that 25% to 50% of MG patients have myocardial damage, myasthenia gravis with other diseases, such as thymoma, followed by thyroid function Hyperthyroidism, and a few associated rheumatoid arthritis, polymyositis, lupus erythematosus, autologous hemolytic anemia.

Half of the patients experienced more than one remission period in the early stage of the disease. The trauma, systemic infection, electrolyte imbalance, endocrine disorders and overwork can aggravate the symptoms.

(2) MG classification: To indicate the location, extent and duration of MG muscle weakness, the Ossernen improvement method is generally divided into the following types:

Type I (eye muscle type): The lesion is only affected by extraocular muscles, which is more common in the clinic and more common in children.

Type II (systemic type): Type IIA shows eye, facial and limb muscle weakness; Type IIB is weak and has throat muscle weakness, also known as medullary paralysis.

Type III (burst type): Sudden general weakness, extremely prone to muscle weakness.

Type IV (migration type): The course of the disease is repeated for more than 2 years, often developed from type I or type II.

Type V (muscle atrophy): A small number of patients have muscle atrophy.

The course of the disease is prolonged, during which it can be alleviated, relapsed, or worsened, cold, diarrhea, agitation, fatigue, menstruation, childbirth or surgery often exacerbate the condition, and even appear dangerous, life-threatening.

(3) MG crisis: refers to the sudden increase of muscle weakness, especially the respiratory muscles (including the diaphragm, intercostal muscles) and the throat muscles are severely weak, leading to difficulty in breathing, mostly induced on a heavy basis, infection is the most dangerous Common predisposing factors, accompanied by thymoma are prone to crisis, and the crisis can be divided into three types:

1 myasthenia gravis crisis: due to the increase of muscle weakness in the disease itself, cholinesterase inhibitors are often under-dosed, increase the dose or intravenous injection of Tengxilong (based on phenol chloride), muscle strength is improved, often by Cold-induced, can also occur in the application of neuro-muscular blockade agents (such as streptomycin), high-dose corticosteroids, thymus radiation therapy or surgery.

2 Cholinergic crisis: due to excessive cholinesterase inhibitor, ACh is free from hydrolysis, and excessive accumulation of synapses, showing cholinergic toxicity: muscle weakness, fasciculation (nicotine-like reaction, Endplate membrane excessive depolarization); pupil diminution (less than 2mm in diameter under natural light), sweating, increased saliva (toxin-like reaction): headache, nervousness (central nervous response), injection of Tengxilong (by phenol) The symptoms of incompetence of ammonium chloride are not improved, but worse.

3 ruminant crisis: temporary failure of cholinesterase inhibitors, increased doses to no avail, pediatrics did not report this crisis.

Pediatric myasthenia gravis

1. Acetylcholine receptor antibody determination

In children with systemic myasthenia gravis, 90% of cases have elevated anti-acetylcholine receptor antibody levels in the blood, more than 10nmol/L; the eye muscle type antibody level is low, the concentration is 0-10nmol/L, often in the early stage of the disease Negative, and early antibody levels and no significant relationship between the disease, myasthenia gravis symptoms, if the blood in this antibody is not high, then mostly simple eye type, generally do not require surgery; if high, it may be systemic early, the more The better the efficacy of early thymectomy, the determination of acetylcholine receptor antibody for the diagnosis of myasthenia gravis, the choice of treatment methods, and the monitoring of immunosuppressive drugs.

2. Anti-striated muscle antibody test (antistriomuscular antibody determination)

More than 90% of children with myasthenia gravis with thymoma can detect anti-striated muscle antibodies, but in children with myasthenia gravis, thymic tumors are rarely seen.

3. Muscle biopsy

For patients with difficult diagnosis, muscle biopsy can be performed. If the post-synaptic membrane folds are reduced at the neuromuscular junction, the number of nAChRs on the synapse can be confirmed.

4. Teng Xi Long or Xin Si Ming test

Tensionon (tensilon) is an analogue of bromine neostigmine, intramuscular or intravenous Tengxilong (0.5-1mg for newborns, 2-5mg for children under 34kg, 5mg for 34kg or more) for 1min, patients often appear obvious The curative effect disappeared after 5 minutes, and the symptoms of myasthenia gravis were positive as initial, and the symptoms of the patients were significantly improved within 15 minutes after intramuscular injection of methyl sulphate (0.5-1.5 mg or 0.03-0.04 mg/kg). The improvement was most pronounced at 30 min, and the effect gradually disappeared after 45 min.

The Tengxilong test has a rapid response and less toxic side effects, but the drug source is more difficult.

Neostigmine test 0.03 ~ 0.04mg / kg (0.1 ~ 0.15mg per newborn) intramuscular injection, compare the muscle strength of each affected muscle group half an hour before and after injection, the muscle strength is significantly improved, help the diagnosis of MG M-cholinergic adverse reactions (dilated pupils, bradycardia, drooling, hyperhidrosis, abdominal pain, diarrhea, vomiting) against neostigmine may be administered intramuscularly with atropine at the same time or for a longer period of time. Side effects such as intestinal colic appear, but the source of medicine is sufficient, and should be reasonably selected according to the specific situation.

5. Electromyography

Repeated electrical stimulation common muscle action potential gradually changed from normal to abnormal, amplitude and frequency gradually decreased, nerve repetition frequency stimulation experiment and single fiber EMG examination, respectively, with 2 ~ 3Hz low frequency super current to stimulate the surface, sacral and ulnar nerve trunk And record the corresponding muscles, namely the orbicularis muscle, deltoid muscle and small finger muscles of the composite muscle action potential, such as the fourth wave amplitude after stimulation is more than 10% attenuation than the first wave is positive, the eye muscle type MG positive rate is low, single Fiber electromyography is the most sensitive and accurate electrophysiological test. It is used to measure the interval between the muscle fibers of the same innervation, but the nerve conduction velocity is normal. The initial induction electrical stimulation can cause muscle contraction. When the affected muscles are repeatedly stimulated, the muscle contraction gradually weakens and eventually disappears. After the muscle injection of Tengxiong, the abnormal electrical reaction can be reversed.

6. Thymography examination

Chest X-ray or CT examination can help to find out whether there is a thymic tumor or thymic hypertrophy.

Diagnosis and diagnosis of pediatric myasthenia gravis

diagnosis

The diagnosis of typical cases is not difficult. The diagnosis of atypical patients is mainly based on laboratory and auxiliary examination.

1. Determine if myasthenia gravis

Mainly based on medical history, the typical clinical features are fatigue after skeletal muscle activity, the most common eye involvement, can be relieved by rest or with cholinesterase inhibitors, and can be further confirmed by one of the following tests.

(1) Fatigue test (Jolly test): Let the patient continue the movement (or contraction) of the affected muscle group, such as closing the eyelids, gazing upwards, continuing to inhale, chewing or flat-lifting on both sides of the arms, often continuing After dozens of seconds, eyelid eversion is rapid, diplopia is obvious, chewing is weak or both arms are drooping, and these reactions are muscle fatigue.

(2) Anticholinergic esterase experiment: Intravenous injection of neostigmine methyl sulphate or Tengxilong experiment can be performed if the fatigue test is not improved.

(3) nerve repetition frequency stimulation test and single fiber electromyography examination.

(4) Detection of serum nAChRab: This test is an important reference for MG diagnosis. If the positive person is helpful for diagnosis, the negative person cannot exclude MG, eye muscle type, and the child MG case nAChRab is more negative.

(5) Muscle biopsy: MG can be diagnosed.

2. Defining whether to merge thymoma

Adult cases are about 75% thymic hyperplasia, 15% MG with thymoma; pediatric cases 8.4% with thymic hyperplasia, 2.2% MG with thymoma, tumor often located in the anterior superior mediastinum, in addition to showing muscle weakness, generally no symptoms of mass lesions and Signs, easy to miss diagnosis, thymoma is more common in male patients after 40 years old, muscle weakness is more serious, cholinesterase inhibitors are not effective, prone to crisis, lateral or orthotopic chest X-ray can be found abnormal Mediastinal CT scan can directly display the tumor location, size, shape, and relationship with adjacent organs. Immunological examination: CAEab (also known as thymoma-related antibody) is of great value to MG patients with thymoma. The positive rate of MG with thymoma CAEab Up to 80% to 90%, the diagnosis still needs to be combined with clinical and CT mediastinal scan, comprehensive analysis.

3. Identify whether there are other comorbidities

MG as a "sister disease" in autoimmune diseases, may be associated with the following inclusions: such as hyperthyroidism, rheumatoid arthritis, systemic lupus erythematosus, hemolytic anemia, polymyositis or multiple sclerosis, With the history, symptoms and signs of related diseases, the corresponding immunochemical tests can be found abnormal.

4. Diagnosis of myasthenia gravis

Myasthenia gravis crisis refers to the severe dyspnea state and the high muscle weakness state caused by respiratory muscle weakness caused by aggravation of myasthenia gravis or a treatment error, which can be roughly divided into three cases.

(1) Myasthenia gravis crisis: due to aggravation of myasthenia gravis itself, neuromuscular junction conduction disorder, respiratory difficulties caused by severe respiratory muscle weakness, accounting for 95% of myasthenia gravis crisis, myasthenia gravis crisis case There are often repeated infections, traumatic or irregular medication history.

(2) Cholinergic crisis: due to the excessive use of cholinesterase inhibitors, the post-synaptic membrane is continuously depolarized, the repolarization process is blocked, and the cholinergic block at the neuro-muscle junction is blocked. Respiratory muscle weakness.

(3) ruminant crisis: also known as non-reactive crisis, is completely non-responsive to cholinesterase inhibitors, occasionally visible in the myasthenia gravis crisis, accounting for about 1%, the mechanism is unknown.

Differential diagnosis

Diagnosis of myasthenia gravis should be differentiated from other diseases. Eye muscle type should be differentiated from congenital upper eyelid drooping and neurogenic upper eyelid drooping; spherical type, systemic type should be associated with polymyositis, acute multiple radiculitis, brain stem Identification of encephalitis.

1. Identification of myasthenia gravis

Diagnosis of myasthenia gravis patients can occur in two kinds of crisis, namely muscle weakness and cholinergic crisis. The clinical manifestations of the two crisis are very similar, both have severe muscle weakness and respiratory failure, the former often have infections. Trauma, mental attack or irregular medical history; the latter may be accompanied by hypercholesterergic hyperfunction, such as pale, sweating, diarrhea, muscle twitching, dilated pupils, wet skin, etc., when it is difficult to identify Tengxilong test If the symptoms are improved after medication, it is a muscle weakness crisis, and vice versa is considered a cholinergic crisis.

2. MG acute muscle weakness should be differentiated from other acute sputum diseases

include:

(1) Periodic paralysis: often at night, when waking up, it is found that the limbs are weak, the blood potassium is low at the time of onset, and the U wave appears on the electrocardiogram. Each episode lasts for several days, and potassium supplementation is effective.

(2) acute inflammatory demyelinating multiple radiculopathy: fever or diarrhea at the beginning of the disease, in addition to limb spasm, there are nerve root traction pain, cerebrospinal fluid protein-cell separation phenomenon.

(3) myelitis: three major symptoms and signs of fever and spinal cord damage (including upper motor neuron type fistula, transastal sensory disturbance and dysuria).

3. Chronic muscle weakness needs to be identified with the following diseases

include:

(1) oculomotor nerve paralysis: in addition to the ptosis of the palsy side, it can also be seen that the pupil dilated, eyeball up, down and adduction movement restricted, seen in neuritis or intracranial aneurysm.

(2) polymyositis: proximal limb muscle weakness, muscle pain, increased muscle enzymes, inflammatory cell infiltration in muscle biopsy.

(3) muscular dystrophy: slow progressive limb weakness, muscle atrophy, pterygopalatine in children, pseudohypertrophy of the gastrocnemius, elevated blood muscle enzymes, family history.

(4) Mitochondrial myopathy: The skeletal muscle is extremely intolerant to fatigue, the symptoms are complex and diverse, the blood lactic acid is elevated, the red body fibers are visible in the muscle biopsy, and the abnormal mitochondria are shown by electron microscopy.

(5) glycogen storage disease: especially in type II patients, acid maltase deficiency caused by limb muscle weakness, respiratory muscle paralysis may occur, easy to be misdiagnosed, muscle biopsy PAS staining can be seen glycogen accumulation, a family history.

(6) Cancerous muscle weakness: mainly seen in elderly patients with small cell lung cancer, limb weakness, post-activity relief, high-frequency repeated electrical stimulation of neuromuscular electrograms showed increased myoelectric potential.

(7) Motor neuron disease: In the early stage, only the tongue and limb muscles are weak, the signs are not obvious, and the identification is not easy. If muscle atrophy occurs, muscle fibrillation or pyramidal bundle sign is not difficult to identify.

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