Muscular weakness

Introduction Muscular muscle weakness refers to the transmission of obstacles between the neuromuscular junctions and the lesions of the muscle fibers themselves, that is, the muscle weakness caused by the lesions of the presynaptic membrane, the synaptic sulcus, the postsynaptic membrane, and the muscle fibers themselves. For example, the postsynaptic membrane choline receptor is damaged in the myasthenia gravis neuromuscular junction; in organophosphorus poisoning, the activity of cholinesterase is affected, and the action of choline acetate is prolonged to affect the excitability of muscle cells. Periodic paralysis is due to changes in membrane potential. Myotonic myopathy is instability of membrane potential; muscle phosphorylase deficiency and carnitine brown phase acid transferase deficiency are due to muscle energy supply disorders; muscular dystrophy and polymyositis are both muscle fibers themselves The lesion. Botulism and hypermagnesemia affect calcium ions into the nerve endings, and amino-based drugs block the release of choline acetate, which affect the presynaptic nerve impulses; the American arrow toxin and the choline acetate receptors A combination of choline acetate and choline acetate receptors can cause muscle weakness.

Cause

Causes:

1. Transmission disorders between neuromuscular junctions: myasthenia gravis, the cause of myasthenia gravis syndrome, such as lung cancer and other malignant tumors or other autoimmune diseases such as lupus erythematosus.

2, the muscle fiber itself causes muscle weakness, polymyositis, muscular dystrophy and so on.

3, other: abnormal membrane potential such as periodic paralysis, myotonic myopathy, botulism and hypermagnesemia. The activity of cholinesterase is affected by the combination of amino-based drugs, American arrowhead toxin and choline acetate receptors, and organophosphorus poisoning. Abnormal energy metabolism such as muscle phosphorylase deficiency and carnitine brown acid transferase deficiency.

Mechanism :

After thymus lesions in patients with myasthenia gravis, an antithymocyte antibody is induced, which cross-reacts with the choline receptor of the striated muscle synaptic membrane, ie, choline acetate receptor antibody, when choline acetate is affected When the body antibody binds to the choline acetate receptor, the choline acetate receptor is blocked, and the receptor antibody complex can dissolve the receptor with the participation of complement. The killer T cells and lymphokines can also destroy the receptor and make the striated muscle. The number of acetate choline receptors in the postsynaptic membrane is reduced and the function is decreased. Under normal circumstances, when nerve impulses reach the nerve endings, many vesicles can simultaneously release large amounts of acetylcholine; however, only a portion of them bind to the phenolic choline receptor on the endplate membrane to produce an effective endplate potential. Most are hydrolyzed by choline acetate or retaken by nerves. Therefore, when nerve impulses are continuously dispensed, although the vesicles near the presynaptic membrane are insufficiently supplemented, the release amount of choline acetate is gradually reduced, but still maintains effective muscle contraction. The disease is reduced by the receptors in the endplate, thereby reducing the chance of binding of choline acetate to the receptor, causing a large amount of choline acetate to be hydrolyzed by choline acetate and lost in the synaptic cleft. At the beginning of nerve impulses, although the receptors in the endplates are reduced, effective muscle contraction can still be produced because the release of a large amount of choline acetate from the nerve endings is not significantly reduced. When nerve impulses are continuously dispensed, more and more muscle fibers cannot produce effective endplate potential due to the decrease in the release of choline acetate, resulting in abnormalities in the clinically affected striated muscles, which are prone to fatigue, increased during activities, and relieved after rest.

The cause of myasthenia gravis syndrome is an autoimmune disease caused by malignant tumors, especially oat cell type lung cancer. The pathogenesis is that the surface of the tumor cells has the same antigen as the presynaptic calcium channel binding protein, and the anti-tumor antibody cross-reacts with the presynaptic calcium channel binding protein, thereby affecting the release of presynaptic choline acetate, lacking sufficient amount. Choline acetate binds to the choline acetate receptor, which reduces the generation of action potentials and causes abnormal fatigue of skeletal muscle. That is to say, when the muscle strength is weakened at rest, the abnormal fatigue phenomenon of the muscle weakness is improved after the activity, and the action potential increase phenomenon can be diagnosed when the nerve high-frequency repeated electrical stimulation test is performed.

The exact etiology and pathogenesis of polymyositis are not yet clear. It is generally considered to be an autoimmune disease, which may be an immune disease caused by factors such as viral infection, manifested as interstitial inflammation of the muscle and degeneration of muscle fibers. Some patients under the electron microscope showed that the presence of viral particles was quite obvious in the activation of human cells and killer cells. Lymphocyte infiltration was observed around the muscle fibers, and anti-myosin antibodies and anti-nuclear antibodies were present in the serum of some patients. Some patients have other autoimmune diseases. It manifests as muscle weakness and muscle atrophy of the affected muscles.

The underlying cause of muscular dystrophy is genetic defects that may lead to difficulties in the production of dystrophin (anti-dystrophin). When the muscle fiber lacks dystrophin, the muscle cell membrane is dysfunctional, a large amount of free calcium, a high concentration of extracellular fluid enters the muscle fiber, and the immune substance enters the muscle cell to cause intramuscular cells, causing the myofibril to break and necrosis.

The causes of hypokalemic periodic paralysis and high potassium periodic paralysis are autosomal dominant inheritance. The excitability of nerves and muscles is closely related to the difference between membrane potential and threshold potential. The membrane potential is the equilibrium potential of potassium. At rest, the intracellular potassium concentration is significantly higher than the extracellular potassium concentration, and the membrane potential is related to the intracellular and extracellular potassium concentration ratio. When the extracellular potassium concentration decreases, the amplitude of the membrane potential increases; the difference between the membrane potential and the threshold potential increases, the cell membrane is in an excessively polarized state, and the stress of the cell decreases. Conversely, when extracellular potassium is present, the membrane potential decreases, the difference between the membrane potential and the threshold potential decreases, and the cell excitability should increase. However, when the membrane potential is less than the threshold potential, the repolarization is affected, and the excitability of the cells is also lowered. When the body eats sugary food, rest after exercise, stress, application of insulin and adrenaline drugs, potassium is quickly introduced into the cells to form hypokalemic periodic paralysis; after hunger, exercise and other factors , resulting in extracellular high potassium, the formation of high potassium periodic paralysis. Frequent seizures, there may be round or elliptical vesicles in the muscle fibers, and may be accompanied by focal necrosis in the late stage, the nucleus is displaced, and the muscle fibers vary in size.

an examination

Related inspection

Neostigmine test electromyogram

First, medical history

For muscle weakness, you should pay attention when asking for medical history:

1. General situation: The age of the patient, the condition at the time of onset, is acute or chronic, is gradually progressing, or is developing rapidly, with or without anger, anxiety, fatigue, infection, over-satisfaction, overwork, excessive drinking, hunger Wait. Note that muscle weakness is persistent, intermittent, with or without fluctuations. Relationship with activities, etc.

2, past history: should pay attention to: history of infection: whether you have had epidemics plus polio. History of poisoning: history of exposure or poisoning of heavy metals such as carbon dioxide, carbon disulfide, organic fluorine, organic phosphorus, organic chlorine, botulism, high blood magnesium, aminophonic drugs, and arrow toxin. Whether there is a malignant tumor or a history of tumors with unclear nature, a history of immune diseases. Family history: Special genetic diseases, such as muscular dystrophy, often have a distinct family history. In addition, should ask whether there is a close relative marriage in the immediate family.

Second, physical examination:

1, muscle volume and appearance: pay attention to the presence or absence of muscle atrophy and hypertrophy, if any, determine its distribution and range, and compare the bilateral symmetrical parts; observe the presence or absence of muscle bundle vibration.

2, muscle strength: the patient in turn in the joints to be examined, and against the resistance of the inspector's resistance to flexion and extension movement, to observe whether the muscle strength is normal, with or without pathological fatigue, should pay attention to the location and extent of muscle weakness, local lesions must be Each muscle involved is examined separately. The patient's feet were square, the lower limbs of the muscle weakness were in the abduction and external rotation, and the toes of the affected side were more external rotation. Fatigue test, so that the patient can make the affected muscles continue to contract, such as continuous upper eye, observe whether the eyelids are drooping; the two arms are continuously lifted to observe whether the upper limbs are abnormal and easy to fatigue; the lower limbs can make the lower jaw stand up and test to see if there is any Symptoms of fatigue, positive.

3, muscle tension: should allow patients to relax as much as possible, in a warm environment and comfortable position. It can be judged by touching the hardness of the muscle and the resistance that is felt when the patient's limb is flexibly flexed. When the muscle tone is reduced, the muscles are slack. When the muscle tension is increased, the muscle firmness increases.

4, gait:

(1) Swing gait: due to the weakness of the pelvic muscles and the psoas muscles, the lower limbs and the pelvic muscles are atrophy. When standing, the lordosis of the spine is used to maintain the balance of the center of gravity of the body. When walking, the pelvis cannot be fixed due to the muscle weakness. The duck line is also called duck step. Found in progressive muscular dystrophy.

(2) gluteal muscle paralysis gait: one side of the gluteus medius lesion, the trunk bends to the affected side while walking, and swings left and right. Found in gluteus medius lesions, polymyositis, progressive malnutrition, etc.

(3) Congenital myotonia: The skeletal muscle is strong and straight when exerting force, so when walking or running, if you want to stop at that time, the muscle tension can not be relaxed immediately, causing a fall.

Third, auxiliary inspection:

Choose the appropriate examination based on the distribution, nature, time and age of the muscle weakness.

1, neostigmine test: Xinsi Ming 0.5-1mg, intramuscular injection, observed changes in muscle weakness after half an hour, such as the positive improvement of muscle weakness before injection of drugs is positive. Suitable for patients with myasthenia gravis.

2, wind power examination: for myasthenia gravis, myasthenia gravis syndrome, polymyositis, muscular dystrophy, periodic paralysis, myotonic myopathy.

3, serum anti-acetic acid choline antibody and autoantibody determination: for myasthenia gravis, myasthenia gravis syndrome, polymyositis, myotonic myopathy.

4, serum muscle enzyme series determination: such as serum creatine phosphokinase, lactate dehydrogenase, transaminase, aldolase and so on. Suitable for multiple myositis, muscular dystrophy, myotonic myopathy.

5, muscle biopsy: for myasthenia gravis, myasthenia gravis syndrome, polymyositis, muscular dystrophy, periodic paralysis, myotonic myopathy.

6, blood potassium: for periodic paralysis and so on.

7, ECG: for periodic paralysis and so on.

Differential diagnosis

The diagnosis should be differentiated from the following symptoms:

1. Segmental dystonia: characterized by segmental distribution, such as cranial-neck dystonia, upper or lower limbs with or without the central axis, dystonia of the head and neck, lower limbs with or without trunk dystonia, Trunk-neck (does not affect the head and face) dystonia. Segmental dystonia is a type of dystonia syndrome.

2. Laryngeal muscle weakness: vocal cord closure insufficiency refers to a disease in which the laryngeal muscles are unable to cause hypokinetic glottic dyskinesia when vocalization, and is also a laryngeal muscle weakness and vocal fatigue.

3. Symmetrical muscle weakness: Progressive muscular dystrophy is a group of primary muscle degeneration diseases, which are characterized by aggravation of symmetrical muscle weakness, muscle atrophy, and hereditary diseases.

4. Myasthenia gravis is an autoimmune disease of nerve to muscle transmission disorder. It is a chronic disease that transmits disorders at the neuromuscular junction. Acetylcholine receptor (AChR) antibody is the main autoantibody that causes its pathogenesis. It mainly produces Ach receptor antibodies that bind to the Ach receptor, causing neuromuscular junction block, leading to the eye. Muscle, swallowing muscles, respiratory muscles, and skeletal muscle weakness in the limbs, that is, the nerves that govern muscle contraction cannot transmit the signal command to the muscles under the influence of various etiologies, so that the muscles lose their contractile function, clinically There are eyelid drooping, diplopia, strabismus, expression muscles and masticatory muscle weakness, manifested as apathy, can not be suffocated, etc., medullary muscle weakness, language disadvantage, lack of tongue, eating difficulties, eating cough, And limb muscle weakness.

5. Extraocular muscle movement weakness: due to various factors caused by extraocular muscle dyskinesia, muscle weakness, common in botulism, pediatric myasthenia gravis, progressive muscular dystrophy.

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