What Is a Muscle Disorder?

Muscular disorders usually refer to skeletal muscle disorders. Skeletal muscle is the main organ that performs body movements and is an important organ for energy metabolism in the body. There are more than 600 muscles in the human body, and their weight accounts for about 40% of the adult's weight. Skeletal muscle is composed of thousands of longitudinally arranged muscle fibers. The muscle fibers (muscle cells) are multinucleated cells, the outer envelope is the serosa (muscle membrane, that is, the muscle cell membrane), and the outer layer is the basement membrane. Nuclei are arranged longitudinally below the myometrium and can number in the thousands. The length of muscle fiber is several millimeters to several centimeters, and the diameter is 10-100gm. The muscle fibers contain sarcoplasm, which contains myofibrils and longitudinal tubes arranged longitudinally, as well as organelles such as mitochondria, ribosomes, and lysosomes. Myofibrils are composed of many thick and thin muscle filaments arranged longitudinally and containing contractile and regulatory proteins. The thick muscle filaments contain myosin and the thin muscle filaments contain actin. Both proteins are contractile proteins. Although muscle fibers appear as independent units anatomically and physiologically, the disease may invade only a part of them, and depending on the characteristics and severity of the disease course, the remaining parts may also have dysfunction or atrophy, degeneration or regeneration. Although the structure is the same, not all muscles are equally susceptible to disease. In fact, it is impossible for a certain disease to invade all muscles of the body. Substantial lesions of some muscles, such as various muscular dystrophies and myositis, can directly damage myofibrils; depolarization blockage due to decreased endplate potential can be seen in periodic paralysis. Myopathy caused by a variety of reasons can manifest muscle weakness.

Muscle disease

Primary non-inflammatory diseases at the skeletal muscle or neuromuscular junction, referred to as myopathy. Mainly manifested as muscle contraction loss or disappearance and muscle atrophy. Congenital or acquired, no neurological disease, but the main symptoms of myopathy and muscle weakness caused by damage to the nervous system are not easy to distinguish, it is often necessary to identify with neuropathy. The etiology includes genetic defects, metabolic disorders, and immune damage. Broadly defined myopathy includes primary and secondary diseases, as well as inflammation.

Introduction to Muscle Diseases

Classification of myopathy

The classification of myopathy is very uneven. The World Collaborative Group on Neuromuscular Diseases met in Vienna in 1965 to prepare an international unified classification of neuromuscular diseases. Walton and others considered from two aspects of neurogenic myopathy and myogenic myopathy, and proposed that neuromuscular disease should include diseases of the spinal cord horn cells, nerve roots, peripheral nerves, neuromuscular junctions and the muscle itself. The classification scheme was adopted at the Montreal International Conference in 1967. It was announced by the World Federation of Neurology (WFN) in 1968 and updated in 1981. In September 1986, the first academic symposium on myopathy and peripheral neuropathy in China was held in Jilin. Chen Qingtang, Guo Yuzhang, Luo Yi and others drafted a draft classification of muscle and peripheral neuropathy in China, dividing myopathy into myogenic diseases and neurons- Two major categories of abnormal muscle transmission were published in the Chinese Journal of Neuropsychiatry in 1987.

Walton's classification is more comprehensive, but there are too many duplicate entries and it is not convenient for clinical application. The classification method in China is relatively simple, and the main types are included, which is also convenient for clinical application.

Muscle disease manifestation

Weak muscle disease

Most commonly, there are only a few myopathy, such as congenital myotonic McCard's disease and lipid storage disease, and some cases lack this symptom. In the early stages of the disease, weakness occurs in long-lasting, slow movements such as slow running. In the future, some actions in daily life (such as walking, sitting up, etc.) will also be difficult to complete. Muscle function is completely lost in the later stages of the disease. The symptoms of the affected muscles are also different. For example, weak pharyngeal and tongue muscles can cause difficulty in swallowing and tongue extension; weak scapular muscles cause difficulty in dressing, washing the face, and combing the hair; Difficulty in holding chopsticks and writing; weak muscles in the lower limbs and weak pelvic girdle muscles make it difficult to walk, climb stairs, and stand up while squatting. ^[1]

The distribution of muscle weakness, the rate of progression, the persistence or onset of symptoms, and the presence or absence of remissions are of great value in the diagnosis and differential diagnosis of myopathy. Proximal muscle weakness is more common in myopathy. Distal muscle weakness is more common in neurogenic diseases. Weakness of muscle strength quickly reaches a peak in a short period of time, more common in polymyositis, and often recurrence of remission. The slow and continuous progression is mostly progressive muscular dystrophy or other degenerative diseases. Paroxysmal weakness is seen in periodic paralysis.

Muscle disease muscle fatigue

Muscle weakness occurs after repeated exercise, and symptoms decrease after rest, so symptoms are milder in the morning and worsen after exercise. During the examination, the patient can repeat the action multiple times (such as opening and closing eyes, clenching and releasing fists, etc.), or continuously eliciting tendon reflexes to observe whether the amplitude of muscle movement is getting smaller and smaller. Muscle fatigue is common in myasthenia gravis, myasthenic syndrome, and polymyositis.

Muscle disorders myalgia and tenderness

It is characteristic of inflammatory myopathy and metabolic myopathy. Diseases related to myalgia are roughly divided into four types: inflammation of muscle fibers, such as polymyositis and dermatomyositis, about half of which have symptoms of myalgia, which appear continuously and can worsen during exercise. The disintegration and destruction of muscle fibers are found in McCard's disease, other metabolic diseases and myotonic diseases. Vascular pain, such as thrombo-occlusive vasculitis, spinal stenosis caused by ischemia of the cauda equina. Unexplained myalgia.

Muscle disorders muscle atrophy

Muscle volume decreases. Generally, it is not difficult to determine, but it is not easy to find when infants and young children have more subcutaneous fat. Touch and judge by hand during inspection. Subcutaneous fat atrophy is often mistaken for muscle atrophy, but fat atrophy is mostly distributed in hips, waists, abdomen, shoulders, and local fat-rich areas, showing patchy or annular atrophy, which is inconsistent with the direction of muscle travel.

Muscle atrophy can occur in myopathy and other diseases, and its causes and distribution characteristics are:

Central nervous system disease. Cerebral parietal lobe lesions, congenital motor area hypoplasia, deep tumors in the cerebral hemisphere, inflammation, and cerebrovascular disease can cause muscle atrophy on the opposite side of the lesion. Muscle atrophy that occurs during parietal lobe lesions often affects the hand and arm muscles. The skin of the hands is delicate, with or without hemiplegia, and may be accompanied by varying degrees of sensory disturbances and finger position disturbances, known as lateral muscle atrophy.

Anterior horn cells of the spinal cord and brain stem motor neuron lesions. Muscle atrophy is distributed in the early stages according to nerve segments, unilateral or bilateral, and distal muscle atrophy is obvious, accompanied by muscle bundle tremor. The cranial nerve motor nucleus is involved, and the inner muscles are atrophied.

peripheral neuropathy. Muscle atrophy is distributed by nerve root, segment or neural stem, consistent with the innervation range.

Neuromuscular junction disease. Muscle atrophy is rare. If muscle atrophy occurs, there is no regular pattern. If myasthenia gravis occurs and muscle atrophy occurs, it is mostly in the forearm, the proximal part of the upper limb, the facial muscle, and the chewing muscle.

Myogenic disease. Polysymmetrically distributed near the extremities. In some myogenic diseases such as periodic paralysis and polymyositis, the degree of muscle weakness is not consistent with muscle atrophy.

Disused muscle atrophy. Plaster fixation, osteoarthropathy, and prolonged bed rest can cause disused muscle atrophy, which is distributed near the diseased joint. Once the cause is resolved, muscle volume can be restored after exercise.

Muscle disorders muscle hypertrophy

Excessive muscle exercise, exercise, and fatty connective tissue hyperplasia can cause muscle hypertrophy. The former is called working hypertrophy or true hypertrophy, and the latter is called pseudohypertrophy. True hypertrophy is seen in athletes, bodybuilders or manual workers. The sequelae of polio can manifest as muscle atrophy on one side and excessive relative movement and hypertrophy on the other. Pseudohypertrophy is seen in muscular dystrophy.

Muscle disorders muscle involuntary movement

A movement of muscles, muscle groups, or parts of a muscle that is not governed by will. It is found in many diseases and also in myopathy. Muscle fibrillation and muscle bundle tremor are more common in secondary muscle atrophy caused by degeneration of lower motor neurons. Beam tremor is also seen in normal people when they are fatigued, cold, and in patients with neuropathy. Muscle fiber twitch is a continuous, slow, spontaneous movement of muscle fibers, undulating along the longitudinal axis of the muscle. The muscle map appears as a single potential repetitive issuance, or a high frequency issuance of continuous potential. Can be seen in neuromuscular rigidity, hyperthyroidism myopathy, etc. (see Involuntary movement).

Muscle disorders involuntary movements caused by muscle contraction or stimulation

Including: muscle rigidity. After the muscles contract randomly, they cannot relax immediately or muscle depression and muscle mounds appear. High frequency discharges appear on the electromyogram, the frequency and amplitude of which gradually decrease and then gradually decrease. Found in myotonic syndrome.

Painful spasms after exercise. Refers to muscle spasm contraction after exercise, hard to touch, with severe pain, lasting from minutes to hours. Electromyography appears as electrical rest. Symptoms are reduced after continuous exercise, as seen in McCard's disease, phosphofructokinase deficiency, and muscle lipid storage disease.

Exercise-induced tonic muscle spasm is also found in stiff-man syndrome, neuromuscular rigidity, and tetanus.

Muscle disorders

Is one of the characteristics of myopathy, often accompanied by muscle atrophy. However, lower motor neuron disease and cerebellar disease also show low muscle tone, so the diagnosis of low muscle tone is of little value. However, some myopathies in infants such as congenital muscle relaxation, infantile muscular atrophy (Weldnich-Huffman's disease), glycogen storage disease and other manifestations of muscle tone are significantly low, the so-called " Soft baby "syndrome.

Muscle disease Low tendon reflex

Myopathy is often manifested by low tendon reflexes. Late tendon reflexes may disappear.

EMG changes in myopathy

Including the following:

The average duration of the motor unit is shortened. The peak wave portion of the normal motor unit potential is formed by the depolarization of the nearest muscle fiber under the needle pole, and the slow wave portion of the initial and final low amplitude is depolarized by the muscle fiber 0.5 to 1 mm away from the needle electrode. produce. When muscle disease occurs, muscle fiber necrosis, degeneration, atrophy, the number of muscle fibers with normal functions decreases, and the number of muscle fibers that can be excited 0.5 to 1 mm away from the needle electrode also decreases. The slow-wave component voltage they generate is extremely low, so the motor unit potential has lost Beginning and end, so the time limit is shortened. In addition, due to the uneven distribution of muscle fibers in the exercise unit, the density of the edge portion is the lowest. When the surrounding muscle fiber degenerates and necroses, the surrounding portion of the exercise unit is lost, the range is reduced, and the ultimate area of exercise is narrowed. In this way, when the muscle fibers in the exercise unit are depolarized to form a motor unit potential, the dispersion in time course is also small, so a short-term potential occurs. In myopathy, the time limit of motor potential can be shortened by 20 to 60%.

The average amplitude of motor units decreases. Due to muscle disease, muscle fibrosis is necrotic and the number decreases, causing the average amplitude of motor unit potentials to decrease. However, in some patients, the range may be normal or increased.

The increase of polyphasic potential is also an important indication of myopathy. The most valuable is the short-term, low-amplitude polyphase potential, called myopathy potential. The mechanism of polyphasic potential generation is nerve collateral budding, and due to the decrease in the number of muscle fibers, the potentials generated by the remaining muscle fibers are dispersed in time course.

When there is an interference phase or a pathological interference phase during muscle contraction, although the number of muscle fibers is reduced and dysfunction during muscle disease, the number of motor units is still in the normal range. Even in the case of severe weakness, the generated potential can still be integrated into the interference phase. Moreover, due to the weak muscle strength, the distribution frequency of the exercise unit is increased compensatingly, and the interference phase wave pattern is more dense than normal. In addition, due to the increase of polyphase potential, the peaks of the composed interference phase are slim and the middle part is dense. Pathological interference phase. Its voltage decreases, mostly less than 2.0mV, and some less than 0.5mV.

The maximum amplitude decrease of the motor unit potential is based on the maximum amplitude of the motor unit potential measured by the multi-core needle electrode. Therefore, this kind of electrode is less affected by the position of the needle pole. In myogenic diseases, the maximum amplitude of motor unit potential can be reduced by 30%. Generally speaking, the largest decrease in motor unit potential of hereditary diseases is more significant than that of acquired myopathy (such as polymyositis and dermatomyositis). It may be due to acquired myopathy with peripheral nerve buds and increased local muscle fibers.

Prolongation of insertion activity and spontaneous generation of myogenic myopathy can occur in various forms of insertion activity. Ankylosing discharge of myotonic myopathy is an important diagnostic indicator. Progressive muscular dystrophy and myotonic discharge of polymyositis represent an increase in excitability of the myometrium.

Spontaneous potentials such as fibrillation potentials and normal phase potentials are very common in myopathy and generally occur early in the disease. It is presumed that when the muscle is diseased, the muscle fibers are focally necrotic, and some muscle fibers are separated from the ultimate, resulting in temporary denervation. More scholars believe that the reason is that the reduced potassium ion concentration in the diseased muscle cells reduces the resting membrane potential and increases the cell excitability, which causes spontaneous muscle fiber activity. In the chronic and late stages, the number of fibrillation potentials decreases, and when the muscle fibers are significantly fibrotic, the fibrillation potentials disappear.

Types of myopathy

Myasthenia gravis, progressive muscular dystrophy, and periodic paralysis are more common. Other myopathy is rare.

Myasthenia gravis is an autoimmune disease characterized by transmission dysfunction at the neuromuscular junction of skeletal muscle. The affected skeletal muscles are easily fatigued and muscle weakness occurs.

Dermatomyositis is a rare connective tissue disease, which is mainly manifested by weakness in the proximal muscles of the extremities and characteristic skin damage.

Progressive muscular dystrophy A group of primary muscle degenerative diseases, which are manifested by aggravating symmetrical muscle weakness and muscle atrophy, are genetic diseases.

Myotonic disorders are a rare group of hereditary diseases. The typical manifestation is muscle rigidity, that is, tonic contraction after the voluntary movement starts or muscle stimulation. It takes a few seconds to ten seconds to relax. As a result, the limbs become stiff and the movement is ineffective. For example, when shaking hands with a person, the hand cannot be released immediately. Including atrophic or dystrophic muscular rigidity (Stanna's disease, with muscular rigidity, but muscle weakness and muscle atrophy are more prominent), congenital muscular rigidity (Thomson's disease, infantile onset, with muscle hypertrophy), congenital Paramuscular rigidity (Oillenberg's disease, onset in childhood, manifested by muscle rigidity and paroxysmal weakness, muscle rigidity is obvious in the facial muscles), etc. No special treatment. Quinine, procainamide, and corticotropin alleviate symptoms.

Congenital myopathy such as bacillus myopathy, central axonopathy, and myotube-type myopathy (both showing muscle weakness, low muscle tone, and rods, central axial emptiness, and myotubes in the muscle fibers); congenital myofibers Imbalanced types; multiple axonosis; fingerprint body myopathy, etc.

There are many types of metabolic myopathy, such as glycogen storage disease type , type can show muscle weakness, low muscle tone. Type and can show muscle spasm after exercise. Lipid storage myopathy is a group of autosomal recessive diseases, including carnitine deficiency syndrome (representing low intramuscular carnitine content, progressive muscle weakness, and paroxysmal liver dysfunction), carnitine palmitate transferase Deficiency (recurrent myalgia, myoglobinuria), etc. Myoglobinuria manifests as paroxysmal muscle weakness, swelling and pain, brownish red urine, and various causes (glycogen storage disease V, type , carnitine palmitate transferase deficiency, poison, muscle contusion, etc.).

Infectious myopathy such as viral and parasitic infections can cause myositis, such as toxoplasma and trichinellosis. Epidemic chest pain is caused by type B Cooksaki virus, which is more common in children and adolescents and manifests as chest, back, and shoulder muscle pain.

Others such as hyperthyroidism, myxedema, Cushing's disease, and malignant tumors can also be accompanied by myopathy.