muscle disease
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What is a muscle disease?
Muscle disease refers to any disease or disorder that impacts the human muscle system. Primary muscle diseases stem from direct abnormalities of the muscles. Diseases that are symptoms of nervous system disorders aren't primary muscle diseases because nerves and muscles work as a functional unit; thus, disease in either system results in muscle atrophy and paralysis.
Muscle weakness and wasting can indicate muscle disease and can be assessed through physical exams, blood tests, and muscle biopsies. Common symptoms include muscular atrophy, pain, cramps, and muscle enlargement.
Muscular dystrophies are hereditary disorders characterized by progressive muscular atrophy and weakness. Myositis refers to muscle tissue inflammation, which may result from bacterial, viral, or parasitic infections, or from unknown origins.
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How do muscle diseases affect the body?
Muscle diseases, also known as primary muscle diseases, directly affect the muscles, leading to several indications, including muscular atrophy (wasting) and weakness. The degree of weakness is proportional to the amount of wasting in nerve or muscle involvement. Myasthenia gravis is characterized by persistent weakness that gets worse with exercise.
Pain can also occur due to defects in blood circulation, injury, or inflammation, though it is rare, except as a result of abnormal posture or fatigue in muscular dystrophy, which is a hereditary disease characterized by progressive wasting of the muscles.
Other effects include muscle enlargement (muscular hypertrophy), tetany (intermittent muscle spasms), fasciculation (twitching), and glycogen storage diseases (enzyme defects prevent the release of energy by the normal breakdown of glycogen in muscles).
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What are some common types of muscle diseases?
Muscle diseases, also known as myopathies, are conditions that directly affect muscle fibers. These diseases lead to muscular degeneration and weakness and can be caused by genetic or nongenetic factors.
Common types of muscle diseases:
* Muscular Dystrophy This is a group of hereditary conditions characterized by progressive weakness and degeneration of skeletal muscles. The most common type is Duchenne muscular dystrophy, which involves the progressive destruction of muscle tissue.
* Myositis This refers to the inflammation and infection of muscle tissue, which can be caused by bacteria, viruses, or parasites, or can be of unknown origin. Examples include bacterial myositis, viral myositis, and trichinosis.
* Myasthenia Gravis This is the most common disease of the neuromuscular junction, where nerve impulses trigger muscle contraction. It leads to muscle weakness and fatigue, particularly in the eye muscles.
* Glycogen-Storage Diseases These are rare hereditary diseases where enzyme defects prevent the normal breakdown of glycogen in muscles, leading to abnormal glycogen storage and muscle weakness.
* Other Myopathies These can result from genetic defects in enzymes necessary for metabolism or external factors like alcohol or steroid hormones.6 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What are the symptoms of muscle diseases?
Muscle diseases show a range of symptoms, including muscle atrophy and weakness, which are the most common indicators. The degree of weakness usually corresponds to the amount of wasting in the muscle. Myasthenia gravis is characterized by persistent weakness that gets worse with exercise.
Other symptoms include:
* Muscle pain, which can result from defects in blood circulation, injury, or inflammation
* Cramps, which can occur due to motor or sensory neuron disease or certain biochemical disorders
* Muscular hypertrophy, or muscle enlargement, which occurs naturally in athletes but can also be found in muscular dystrophy
* Tetany, which is intermittent spasms or involuntary muscle contractions caused by low calcium levels in the blood and increased alkalinity of blood and tissues
* Fasciculation, or twitching of muscle fibers, which may indicate motor nerve cell disease in the spinal cord
* Fatigue, or the failure of the muscle to sustain force in a prolonged contraction
* Glycogen storage diseases, which can cause muscle weakness due to the abnormal storage of glycogen in the muscles
* Bacterial myositis, or inflammation of muscle tissues as the result of a bacterial infection, is commonly localized and occurs after an injury
* Viral myositis, an example of which is pleurodynia, is caused by the Coxsackie virus
* Autoimmune diseases of the muscle, grouped together under the term polymyositis, are frequently associated with inflammation of the skin2 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How do doctors diagnose muscle diseases?
Doctors use several methods to diagnose muscle diseases, including physical and laboratory assessments.
To assess muscle strength, doctors evaluate if a patient can resist the physician's efforts when they push or pull. They also observe the patient performing movements against gravity, such as walking. A myometer can quantify muscle weakness by measuring force.
Other diagnostic tools include:
* Electromyography (EMG) This test measures the electrical activity in muscles to differentiate between muscle and peripheral nerve diseases.
* Blood tests These can reveal muscle inflammation or damage.
* Muscle biopsy A sample of muscle tissue is analyzed for abnormalities.
* Genetic testing This can detect mutations that cause muscular dystrophy.4 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What treatments are available for muscle diseases?
There is currently no cure for muscular dystrophy, but treatments are available to help relieve symptoms and slow the disease's progression.
Available treatments:
* Medications Corticosteroids can help to slow the progression of the disease. Givinostat may enhance muscle regeneration and lower inflammation and fibrosis in muscle tissue in Duchenne muscular dystrophy.
* Physical Therapy Exercises, splints, and braces can help relieve some symptoms.
* Surgery Corrective surgery may help relieve some of the symptoms.
* Other Therapies Heat, massage, and electrical currents, along with psychological counseling, can supplement basic treatments.5 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
muscle disease, any of the diseases and disorders that affect the human muscle system. Diseases and disorders that result from direct abnormalities of the muscles are called primary muscle diseases; those that can be traced as symptoms or manifestations of disorders of the nervous system or other systems are not properly classified as primary muscle diseases. Because muscles and nerves (neurons) supplying muscle operate as a functional unit, disease of both systems results in muscular atrophy (wasting) and paralysis.
Indications of muscle disease
Muscular atrophy and weakness are among the most common indications of muscle disease (see below Muscle weakness). Though the degree of weakness is not necessarily proportional to the amount of wasting, it usually is so if there is specific involvement of nerve or muscle. Persistent weakness exacerbated by exercise is the primary characteristic of myasthenia gravis.
Pain may be present in muscle disease because of defects in blood circulation, injury, or inflammation of the muscle. Pain is rare, except as a result of abnormal posture or fatigue in muscular dystrophy—a hereditary disease characterized by progressive wasting of the muscles. Cramps may occur with disease of the motor or sensory neurons, with certain biochemical disorders (e.g., hypocalcemia, a condition in which the blood level of calcium is abnormally low), when the muscle tissues are affected by some form of poisoning, with disease of the blood vessels, and with exercise, particularly when cold.
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Muscle enlargement (muscular hypertrophy) occurs naturally in athletes. Hypertrophy not associated with exercise occurs in an unusual form of muscular dystrophy known as myotonia congenita, which combines increased muscle size with strength and stiffness. Pseudohypertrophy, muscular enlargement through deposition of fat rather than muscle fibre, occurs in other forms of muscular dystrophy, particularly the Duchenne type.
Tetany is the occurrence of intermittent spasms, or involuntary contractions, of muscles, particularly in the arms and legs and in the larynx, or voice box; it results from low levels of calcium in the blood and from alkalosis, an increased alkalinity of the blood and tissues. Tetanus, also called lockjaw, is a state of continued muscle spasm, particularly of the jaw muscles, caused by toxins produced by the bacillus Clostridium tetani.
The twitching of muscle fibres controlled by a single motor nerve cell, called fasciculation, may occur in a healthy person, but it usually indicates that the muscular atrophy is due to disease of motor nerve cells in the spinal cord. Fasciculation is seen most clearly in muscles close to the surface of the skin.
Glycogen is a storage form of carbohydrate, and its breakdown is a source of energy. Muscle weakness is found in a rare group of hereditary diseases, the glycogen-storage diseases, in which various enzyme defects prevent the release of energy by the normal breakdown of glycogen in muscles. As a result, abnormal amounts of glycogen are stored in the muscles and other organs. The best-known glycogen-storage disease affecting muscles is McArdle disease, in which the muscles are unable to degrade glycogen to lactic acid on exertion because of the absence of the enzyme phosphorylase. Abnormal accumulations of glycogen are distributed within muscle cells. Symptoms of the condition include pain, stiffness, and weakness in the muscles on exertion. McArdle disease usually begins in childhood. No specific treatment is available, and persons affected are usually required to restrict exertion to tolerable limits. The condition does not appear to become steadily worse, but serious complications may occur when the muscle protein myoglobin is excreted in the urine. Other glycogen-storage diseases result from deficiency of the enzymes phosphofructokinase or acid maltase. With acid maltase deficiency, both heart and voluntary muscles are affected, and death usually occurs within a year of birth.
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Muscle weakness
Signs and symptoms
Weakness is a failure of the muscle to develop an expected force. Weakness may affect all muscles or only a few, and the pattern of muscle weakness is an indication of the type of muscle disease. Often associated with muscle weakness is the wasting of affected muscle groups. A muscle may not be fully activated in weakness because of a less than maximal voluntary effort; a disease of the brain, spinal cord, or peripheral nerves that interferes with proper electrical stimulation of the muscle fibres; or a defect in the muscle itself. Only when all causes have been considered can weakness be attributed to failure of the contractile machinery (i.e., the anatomy) of the muscle cell.
The effect of weakness in a particular muscle group depends on the normal functional role of the muscle and the degree to which force fails to develop. A weakness in muscles that are near the ends of the limbs usually results in a tendency to drop things if the upper limb is affected or in “foot drop” if the lower limbs are affected. The overall disability is not as great as weakness of more proximal (closer to the body) muscles controlling the pelvic or shoulder girdles, which hold large components of the total body mass against the force of gravity. Weakness of the proximal muscles that control the shoulder blade (scapula), for example, results in “winging” (i.e., when the sharp inner border protrudes backward) as the arms are held outstretched. If the weakness is severe, the arms cannot be raised at all.
Assessment
Muscle disease may be detected by assessing whether the muscle groups can withhold or overcome the efforts of the physician to pull or push or by observing the individual carrying out isolated voluntary movements against gravity or more complex and integrated activities, such as walking. The weakness of individual muscles or groups of muscles can be quantified by using a myometer, which measures force based on a hydraulic or electronic principle. Recordings of contraction force over a period of time are valuable in determining whether the weakness is improving or worsening.
The assessment of muscle weakness (and wasting) is directed toward discovering evidence of muscle inflammation or damage. These changes are discerned by blood tests or by measuring alterations of the electrical properties of contracting muscles. Another investigative tool is the muscle biopsy, which provides muscle specimens for pathological diagnosis and biochemical analysis. Muscle biopsies can be taken with a needle or during a surgical procedure.