Muscle Tissue
Content:
- Diagnostics
- Muscular System
- Atrophies
- Neuromuscular disorders
- Botulism
- Tetanus
- Muscular dystrophy
Muscle is a soft tissue of animals. Muscle cells contain protein filaments that slide past one another, producing a contraction that changes both the length and the shape of the cell. Muscles function to produce force and cause motion. They are primarily responsible for maintenance of and changes in posture, locomotion of the organism itself, as well as movement of internal organs, such as the contraction of the heart and movement of food through the digestive system via peristalsis.
Muscle tissues are derived from the mesodermal layer of embryonic germ cells. They are classified as skeletal, cardiac, or smooth muscles. Cardiac and smooth muscle contraction occurs without conscious thought and is necessary for survival. Voluntary contraction of the skeletal muscles is used to move the body and can be finely controlled. Examples are movements of the eye, or gross movements like the quadriceps muscle of the thigh.
Muscles are predominantly powered by the oxidation of fats and carbohydrates, but anaerobic[disambiguation needed] chemical reactions are also used, particularly by fast twitch fibers. These chemical reactions produce adenosine triphosphate (ATP) molecules which are used to power the movement of the myosin heads.
Muscle tissues are derived from the mesodermal layer of embryonic germ cells. They are classified as skeletal, cardiac, or smooth muscles. Cardiac and smooth muscle contraction occurs without conscious thought and is necessary for survival. Voluntary contraction of the skeletal muscles is used to move the body and can be finely controlled. Examples are movements of the eye, or gross movements like the quadriceps muscle of the thigh.
Muscles are predominantly powered by the oxidation of fats and carbohydrates, but anaerobic[disambiguation needed] chemical reactions are also used, particularly by fast twitch fibers. These chemical reactions produce adenosine triphosphate (ATP) molecules which are used to power the movement of the myosin heads.
Muscular System
There are three distinct types of muscles: skeletal muscles, cardiac or heart muscles, and smooth (non-striated) muscles. Muscles provide strength, balance, posture, movement and heat for the body to keep warm.
Upon stimulation by an action potential, skeletal muscles perform a coordinated contraction by shortening each sarcomere. The best proposed model for understanding contraction is the sliding filament model of muscle contraction. Actin and myosin fibers overlap in a contractile motion towards each other. Myosin filaments have club-shaped heads that project toward the actin filaments.
Larger structures along the myosin filament called myosin heads are used to provide attachment points on binding sites for the actin filaments. The myosin heads move in a coordinated style, they swivel toward the center of the sarcomere, detach and then reattach to the nearest active site of the actin filament. This is called a rachet type drive system. This process consumes large amounts of adenosine triphosphate (ATP).
Energy for this comes from ATP, the energy source of the cell. ATP binds to the cross bridges between myosin heads and actin filaments. The release of energy powers the swiveling of the myosin head. Muscles store little ATP and so must continuously recycle the discharged adenosine diphosphate molecule (ADP) into ATP rapidly. Muscle tissue also contains a stored supply of a fast acting recharge chemical, creatine phosphate which can assist initially producing the rapid regeneration of ADP into ATP.
Calcium ions are required for each cycle of the sarcomere. Calcium is released from the sarcoplasmic reticulum into the sarcomere when a muscle is stimulated to contract. This calcium uncovers the actin binding sites. When the muscle no longer needs to contract, the calcium ions are pumped from the sarcomere and back into storage in the sarcoplasmic reticulum.
Upon stimulation by an action potential, skeletal muscles perform a coordinated contraction by shortening each sarcomere. The best proposed model for understanding contraction is the sliding filament model of muscle contraction. Actin and myosin fibers overlap in a contractile motion towards each other. Myosin filaments have club-shaped heads that project toward the actin filaments.
Larger structures along the myosin filament called myosin heads are used to provide attachment points on binding sites for the actin filaments. The myosin heads move in a coordinated style, they swivel toward the center of the sarcomere, detach and then reattach to the nearest active site of the actin filament. This is called a rachet type drive system. This process consumes large amounts of adenosine triphosphate (ATP).
Energy for this comes from ATP, the energy source of the cell. ATP binds to the cross bridges between myosin heads and actin filaments. The release of energy powers the swiveling of the myosin head. Muscles store little ATP and so must continuously recycle the discharged adenosine diphosphate molecule (ADP) into ATP rapidly. Muscle tissue also contains a stored supply of a fast acting recharge chemical, creatine phosphate which can assist initially producing the rapid regeneration of ADP into ATP.
Calcium ions are required for each cycle of the sarcomere. Calcium is released from the sarcoplasmic reticulum into the sarcomere when a muscle is stimulated to contract. This calcium uncovers the actin binding sites. When the muscle no longer needs to contract, the calcium ions are pumped from the sarcomere and back into storage in the sarcoplasmic reticulum.
Atrophies
Muscle atrophy, or disuse atrophy, is defined as a decrease in the mass of the muscle; it can be a partial or complete wasting away of muscle. When a muscle atrophies, this leads to muscle weakness, since the ability to exert force is related to mass. Muscle atrophy results from a co-morbidity of several common diseases, including cancer, AIDS, congestive heart failure, COPD (chronic obstructive pulmonary disease), renal failure, and severe burns; patients who have "cachexia" in these disease settings have a poor prognosis. Moreover, starvation eventually leads to muscle atrophy. Disuse of the muscles will also lead to atrophy.
There are many diseases and conditions which cause a decrease in muscle mass, known as atrophy, including: Dejerine Sottas syndrome (HSMN Type III), inactivity, as seen when a cast is put on a limb, or upon extended bedrest (which can occur during a prolonged illness); cachexia - which is a syndrome that is a co-morbidity of cancer and Congestive Heart Failure; Chronic Obstructive Pulmonary Disease; burns, liver failure, etc. Other syndromes or conditions which can induce skeletal muscle atrophy are liver disease, and starvation.
Muscular atrophy decreases quality of life as the sufferer becomes unable to perform certain tasks or worsen the risks of accidents while performing those (like walking). Muscular atrophy increases the risks of falling in conditions such as IBM (inclusion body myositis). Muscular atrophy affects a major number of elderly.
During aging, there is a gradual decrease in the ability to maintain skeletal muscle function and mass. This condition is called "sarcopenia". The exact cause of sarcopenia is unknown, but it may be due to a combination of the gradual failure in the "satellite cells" which help to regenerate skeletal muscle fibers, and a decrease in sensitivity to or the availability of critical secreted growth factors which are necessary to maintain muscle mass and satellite cell survival.
In addition to the simple loss of muscle mass (atrophy), or the age-related decrease in muscle function (sarcopenia), there are other diseases which may be caused by structural defects in the muscle (muscular dystrophy), or by inflammatory reactions in the body directed against muscle (the myopathies).
In addition to the simple loss of muscle mass (atrophy), or the age-related decrease in muscle function (sarcopenia), there are other diseases which may be caused by structural defects in the muscle (muscular dystrophy), or by inflammatory reactions in the body directed against muscle (the myopathies).
Neuromuscular disorders
Neuromuscular disorders affect the nerves that control your voluntary muscles. Voluntary muscles are the ones you can control, like in your arms and legs. Your nerve cells, also called neurons, send the messages that control these muscles. When the neurons become unhealthy or die, communication between your nervous system and muscles breaks down. As a result, your muscles weaken and waste away. The weakness can lead to twitching, cramps, aches and pains, and joint and movement problems. Sometimes it also affects heart function and your ability to breathe.
Examples of neuromuscular disorders include
Amyotrophic lateral sclerosis
Multiple sclerosis
Muscular dystrophy
Myasthenia gravis
Spinal muscular atrophy
Many neuromuscular diseases are genetic, which means they run in families or there is a mutation in your genes. Sometimes, an immune system disorder can cause them. Most of them have no cure. The goal of treatment is to improve symptoms, increase mobility and lengthen life.
Botulism
Examples of neuromuscular disorders include
Amyotrophic lateral sclerosis
Multiple sclerosis
Muscular dystrophy
Myasthenia gravis
Spinal muscular atrophy
Many neuromuscular diseases are genetic, which means they run in families or there is a mutation in your genes. Sometimes, an immune system disorder can cause them. Most of them have no cure. The goal of treatment is to improve symptoms, increase mobility and lengthen life.
Botulism
Botulism is a rare but serious illness caused by a bacterium called Clostridium botulinum, which occurs in soil. It produces a toxin that affects your nerves. There are three kinds of botulism. Foodborne botulism comes from eating foods contaminated with the toxin. Wounds infected with toxin-producing bacteria result in wound botulism. Infant botulism is caused by consuming the spores of the bacteria, usually from honey. All three forms can be deadly and are medical emergencies.
Symptoms include double vision, blurred vision, drooping eyelids, slurred speech, difficulty swallowing, dry mouth and muscle weakness. Treatment may include antitoxins, intensive medical care or surgery of infected wounds.
Symptoms include double vision, blurred vision, drooping eyelids, slurred speech, difficulty swallowing, dry mouth and muscle weakness. Treatment may include antitoxins, intensive medical care or surgery of infected wounds.
Botulism can be caused by foods that were canned or preserved at home. Maybe you've had fruits or vegetables that someone picked from the garden in the summer and jarred so they could be eaten during the winter months. These foods need to be cooked at very high temperatures to kill the germs.
If not, bacteria called Clostridium botulinum could cause botulism in the people who eat the food. You can't always see, smell, or taste these bacteria, but they release a poison, also called a toxin. This toxin travels through the blood to attach to the nerves that control muscles. From several hours to a week after eating contaminated food, the person may get sick.
Many botulism cases occur in infants, and experts think that's because their digestive systems can't protect them from germs the way an older kid's or an adult's digestive system can.
Infant botulism can happen if a baby younger than 1 year eats honey, so it's important that babies don't eat honey until they're older.
Tetanus
Infectious agent
Clostridium tetani, the tetanus bacillus, is a spore-forming, anaerobic, gram-positive bacterium. Clinical disease is caused by a potent neurotoxin produced by the vegetative state of the bacterium growing in contaminated wounds.
Clostridium tetani, the tetanus bacillus, is a spore-forming, anaerobic, gram-positive bacterium. Clinical disease is caused by a potent neurotoxin produced by the vegetative state of the bacterium growing in contaminated wounds.
Mode of transmission
C. tetani spores are ubiquitous in the environment and can be introduced into the body through nonintact skin, usually via injuries from contaminated objects. Lesions that are considered “tetanus prone” are wounds contaminated with dirt, feces, or saliva; punctures; burns; crush injuries; or injuries with necrotic tissue. However, tetanus has also been associated with apparently clean superficial wounds, surgical procedures, insect bites, dental infections, compound fractures, chronic sores and infections, and intravenous drug use. In 10% of reported cases in the United States, no antecedent wound was identified. Tetanus is not transmitted from person to person.
C. tetani spores are ubiquitous in the environment and can be introduced into the body through nonintact skin, usually via injuries from contaminated objects. Lesions that are considered “tetanus prone” are wounds contaminated with dirt, feces, or saliva; punctures; burns; crush injuries; or injuries with necrotic tissue. However, tetanus has also been associated with apparently clean superficial wounds, surgical procedures, insect bites, dental infections, compound fractures, chronic sores and infections, and intravenous drug use. In 10% of reported cases in the United States, no antecedent wound was identified. Tetanus is not transmitted from person to person.
Epidemiology
Tetanus occurs everywhere in the world, almost exclusively in people who are inadequately immunized. Travel does not increase risk of disease. In the United States, tetanus occurs rarely in people who have completed the primary series and received appropriate boosters. In 2006, an estimated 290,000 people worldwide died of tetanus, most of them in Asia, Africa, and South America.
A reservoir of tetanus bacteria exists in the intestines of horses and other animals, including humans, in which the organism is a harmless normal inhabitant. Soil or fomites contaminated with animal and human feces propagate transmission. Worldwide, the disease is more common in agricultural regions and in areas where contact with soil or animal excreta is more likely and immunization is inadequate. In developing countries, tetanus in neonates born to unvaccinated mothers (neonatal tetanus) is the most common form of the disease.
There is no increased risk to travelers who are adequately vaccinated. With or without travel, inadequately vaccinated people are at risk when they are injured by a contaminated object, use injection drugs, or require surgery or dental care in unhygienic conditions. In addition, there may be an increased risk of neonatal tetanus for infants of inadequately vaccinated mothers who deliver outside the United States, if the birth occurs in an unhygienic environment.
Tetanus occurs everywhere in the world, almost exclusively in people who are inadequately immunized. Travel does not increase risk of disease. In the United States, tetanus occurs rarely in people who have completed the primary series and received appropriate boosters. In 2006, an estimated 290,000 people worldwide died of tetanus, most of them in Asia, Africa, and South America.
A reservoir of tetanus bacteria exists in the intestines of horses and other animals, including humans, in which the organism is a harmless normal inhabitant. Soil or fomites contaminated with animal and human feces propagate transmission. Worldwide, the disease is more common in agricultural regions and in areas where contact with soil or animal excreta is more likely and immunization is inadequate. In developing countries, tetanus in neonates born to unvaccinated mothers (neonatal tetanus) is the most common form of the disease.
There is no increased risk to travelers who are adequately vaccinated. With or without travel, inadequately vaccinated people are at risk when they are injured by a contaminated object, use injection drugs, or require surgery or dental care in unhygienic conditions. In addition, there may be an increased risk of neonatal tetanus for infants of inadequately vaccinated mothers who deliver outside the United States, if the birth occurs in an unhygienic environment.
Clinical presentation
Acute manifestations of tetanus are characterized by muscle rigidity and painful spasms, often starting in the muscles of the jaw and neck. Severe tetanus can lead to respiratory failure and death. The incubation period is usually 3–21 days (average 10 days), although it may range from 1 day to several months, depending on the character, extent, and location of the wound. Most cases occur within 14 days. In general, shorter incubation periods are associated with more heavily contaminated wounds, more severe disease, and a worse prognosis.
Generalized Tetanus
Generalized tetanus is the most common form, accounting for more than 80% of cases. Neonatal tetanus usually occurs because of umbilical stump infections. The most common initial sign is trismus (spasm of the muscles of mastication or “lockjaw”). Trismus may be followed by painful spasms in other muscle groups in the neck, trunk, and extremities and by generalized, tonic, seizurelike activity or frank convulsions in severe cases. Generalized tetanus can be accompanied by autonomic nervous system abnormalities, as well as a variety of complications related to severe spasm and prolonged hospitalization. The clinical course of generalized tetanus is variable and depends on the degree of prior immunity, the amount of toxin present, and the age and general health of the patient. Even with modern intensive care, generalized tetanus is associated with death rates of 10%–20%.
Localized Tetanus
Localized tetanus is an unusual form of the disease consisting of muscle spasms in a confined area close to the site of the injury. Although localized tetanus often occurs in people with partial immunity and is usually mild, progression to generalized tetanus can occur.
Generalized tetanus is the most common form, accounting for more than 80% of cases. Neonatal tetanus usually occurs because of umbilical stump infections. The most common initial sign is trismus (spasm of the muscles of mastication or “lockjaw”). Trismus may be followed by painful spasms in other muscle groups in the neck, trunk, and extremities and by generalized, tonic, seizurelike activity or frank convulsions in severe cases. Generalized tetanus can be accompanied by autonomic nervous system abnormalities, as well as a variety of complications related to severe spasm and prolonged hospitalization. The clinical course of generalized tetanus is variable and depends on the degree of prior immunity, the amount of toxin present, and the age and general health of the patient. Even with modern intensive care, generalized tetanus is associated with death rates of 10%–20%.
Localized Tetanus
Localized tetanus is an unusual form of the disease consisting of muscle spasms in a confined area close to the site of the injury. Although localized tetanus often occurs in people with partial immunity and is usually mild, progression to generalized tetanus can occur.
Cephalic Tetanus
The rarest form, cephalic tetanus, is associated with lesions of the head or face and has been described in association with ear infections (otitis media). The incubation period is short, usually 1–2 days. Unlike generalized and localized tetanus, cephalic tetanus results in flaccid cranial nerve palsies rather than spasm. Trismus may also be present. Like localized tetanus, cephalic tetanus can progress to the generalized form.
The rarest form, cephalic tetanus, is associated with lesions of the head or face and has been described in association with ear infections (otitis media). The incubation period is short, usually 1–2 days. Unlike generalized and localized tetanus, cephalic tetanus results in flaccid cranial nerve palsies rather than spasm. Trismus may also be present. Like localized tetanus, cephalic tetanus can progress to the generalized form.
Diagnosis
The diagnosis is made clinically, since tetanus is a clinical syndrome without confirmatory laboratory tests. The disease is characterized by painful muscular contractions, primarily of the masseter and neck muscles, secondarily of trunk muscles. A common first sign suggestive of tetanus in older children and adults is abdominal rigidity, although rigidity is sometimes confined to the region of injury. Generalized spasms occur, frequently induced by sensory stimuli; typical features of the tetanic spasm are the position of opisthotonos and the facial expression known as “risus sardonicus.” History of an injury or apparent portal of entry may be lacking. The organism is rarely recovered from the site of infection, and usually there is no detectable antibody response.
The diagnosis is made clinically, since tetanus is a clinical syndrome without confirmatory laboratory tests. The disease is characterized by painful muscular contractions, primarily of the masseter and neck muscles, secondarily of trunk muscles. A common first sign suggestive of tetanus in older children and adults is abdominal rigidity, although rigidity is sometimes confined to the region of injury. Generalized spasms occur, frequently induced by sensory stimuli; typical features of the tetanic spasm are the position of opisthotonos and the facial expression known as “risus sardonicus.” History of an injury or apparent portal of entry may be lacking. The organism is rarely recovered from the site of infection, and usually there is no detectable antibody response.
Treatment
Tetanus is a medical emergency requiring hospitalization, immediate treatment with human tetanus immune globulin (TIG) (or equine antitoxin if human immune globulin is not available), a tetanus toxoid booster, agents to control muscle spasm, and aggressive wound care and antibiotics as indicated. TIG is administered intramuscularly in doses of 3,000–6,000 IU. If immunoglobulin is not available, tetanus antitoxin (equine origin) in a single large dose should be given intravenously, after testing for hypersensitivity.
Metronidazole is the most appropriate antibiotic. It is associated with the shortest recovery time and lowest case-fatality ratio. It should be given for 7–14 days in large doses, which also allows for a reduction in the amount of muscle relaxants and sedatives required. The wound should be debrided widely and excised if possible. Wide debridement of the umbilical stump in neonates is not indicated.
Depending on the severity of disease, mechanical ventilation and agents to control autonomic nervous system instability may be required. An adequate airway should be maintained, and sedation should be used as indicated; muscle relaxant drugs, together with tracheostomy or nasotracheal intubation and mechanically assisted respiration, may be lifesaving. Active immunization should be initiated concurrently with treatment.
Tetanus is a medical emergency requiring hospitalization, immediate treatment with human tetanus immune globulin (TIG) (or equine antitoxin if human immune globulin is not available), a tetanus toxoid booster, agents to control muscle spasm, and aggressive wound care and antibiotics as indicated. TIG is administered intramuscularly in doses of 3,000–6,000 IU. If immunoglobulin is not available, tetanus antitoxin (equine origin) in a single large dose should be given intravenously, after testing for hypersensitivity.
Metronidazole is the most appropriate antibiotic. It is associated with the shortest recovery time and lowest case-fatality ratio. It should be given for 7–14 days in large doses, which also allows for a reduction in the amount of muscle relaxants and sedatives required. The wound should be debrided widely and excised if possible. Wide debridement of the umbilical stump in neonates is not indicated.
Depending on the severity of disease, mechanical ventilation and agents to control autonomic nervous system instability may be required. An adequate airway should be maintained, and sedation should be used as indicated; muscle relaxant drugs, together with tracheostomy or nasotracheal intubation and mechanically assisted respiration, may be lifesaving. Active immunization should be initiated concurrently with treatment.
Muscular dystrophy
Muscular dystrophy (MD) is a genetic disorder that weakens the muscles that help the body move. People with MD have incorrect or missing information in their genes, which prevents them from making the proteins they need for healthy muscles. Because MD is genetic, people are born with the problem — it's not contagious and you can't catch it from someone who has it.
MD weakens muscles over time, so children, teens, and adults who have the disease can gradually lose the ability to do the things most people take for granted, like walking or sitting up. Someone with MD might start having muscle problems as a baby or their symptoms might start later. Some people even develop MD as adults.
Several major forms of muscular dystrophy can affect teens, each of which weakens different muscle groups in various ways:
Duchenne (pronounced: due-shen) muscular dystrophy (DMD), the most common type of the disease, is caused by a problem with the gene that makes a protein called dystrophin. This protein helps muscle cells keep their shape and strength. Without it, muscles break down and a person gradually becomes weaker. DMD affects boys. Symptoms usually start between ages 2 and 6. By age 10 or 12, kids with DMD often need to use a wheelchair. The heart may also be affected, and people with DMD need to be followed closely by a lung and heart specialist. They can also develop scoliosis (curvature of the spine) and tightness in their joints. Over time, even the muscles that control breathing get weaker, and a person might need a ventilator to breathe.
Becker muscular dystrophy (BMD), like DMD, affects boys. The disease is very similar to DMD, but its symptoms may start later and can be less severe. With BMD, symptoms like muscle breakdown and weakness sometimes don't begin until age 10 or even in adulthood. People with BMD can also have breathing, heart, bone, muscle, and joint problems. Many people with BMD can live long, active lives without using a wheelchair.
Emery-Dreifuss (pronounced: em-uh-ree dry-fuss) muscular dystrophy (EDMD) typically starts causing symptoms in late childhood to early teens and sometimes as late as age 25. EDMD is another form of muscular dystrophy that affects mostly boys. It involves muscles in the shoulders, upper arms, and shins, and it often causes joint problems (joints can become tighter in people with EDMD). The heart muscle may also be affected.
Limb-girdle muscular dystrophy (LGMD) affects boys and girls equally, weakening muscles in the shoulders and upper arms and around the hips and thighs. LGMD can begin as early as childhood or as late as mid-adulthood, and it often progresses slowly. Over time, a wheelchair might be necessary to get around. There are many different types of LGMD, each with its own specific features.
Facioscapulohumeral (pronounced: fa-she-o-skap-you-lo-hyoo-meh-rul) muscular dystrophy (FSHD) can affect both guys and girls, and it usually begins during the teens or early adulthood. FSHD affects muscles in the face and shoulders and sometimes causes weakness in the lower legs. People with this type of MD might have trouble raising their arms, whistling, or tightly closing their eyes. How much a person with this form of muscular dystrophy is affected by the condition varies from person to person. It can be quite mild in some people.
Myotonic (pronounced: my-uh-tah-nick) dystrophy (MMD) is a form of muscular dystrophy in which the muscles have difficulty relaxing. In teens, it can cause a number of problems, including muscle weakness and wasting (where the muscles shrink over time), cataracts, and heart problems.
Congenital muscular dystrophy (CMD) is the term for all types of MD that show signs in babies and young children, although the MD isn't always diagnosed right away. Like other forms of MD, CMD involves muscle weakness and poor muscle tone. Occurring in both girls and boys, it can have different symptoms. It varies in how severely it affects people and how quickly or slowly it worsens. In rare cases, CMD can cause learning or intellectual disabilities.
The life expectancy (in other words, how long a person may live) for many of these forms of muscular dystrophy depends on the degree to which a person's muscles are weakened as well as how much the heart and lungs are affected.
MD weakens muscles over time, so children, teens, and adults who have the disease can gradually lose the ability to do the things most people take for granted, like walking or sitting up. Someone with MD might start having muscle problems as a baby or their symptoms might start later. Some people even develop MD as adults.
Several major forms of muscular dystrophy can affect teens, each of which weakens different muscle groups in various ways:
Duchenne (pronounced: due-shen) muscular dystrophy (DMD), the most common type of the disease, is caused by a problem with the gene that makes a protein called dystrophin. This protein helps muscle cells keep their shape and strength. Without it, muscles break down and a person gradually becomes weaker. DMD affects boys. Symptoms usually start between ages 2 and 6. By age 10 or 12, kids with DMD often need to use a wheelchair. The heart may also be affected, and people with DMD need to be followed closely by a lung and heart specialist. They can also develop scoliosis (curvature of the spine) and tightness in their joints. Over time, even the muscles that control breathing get weaker, and a person might need a ventilator to breathe.
Becker muscular dystrophy (BMD), like DMD, affects boys. The disease is very similar to DMD, but its symptoms may start later and can be less severe. With BMD, symptoms like muscle breakdown and weakness sometimes don't begin until age 10 or even in adulthood. People with BMD can also have breathing, heart, bone, muscle, and joint problems. Many people with BMD can live long, active lives without using a wheelchair.
Emery-Dreifuss (pronounced: em-uh-ree dry-fuss) muscular dystrophy (EDMD) typically starts causing symptoms in late childhood to early teens and sometimes as late as age 25. EDMD is another form of muscular dystrophy that affects mostly boys. It involves muscles in the shoulders, upper arms, and shins, and it often causes joint problems (joints can become tighter in people with EDMD). The heart muscle may also be affected.
Limb-girdle muscular dystrophy (LGMD) affects boys and girls equally, weakening muscles in the shoulders and upper arms and around the hips and thighs. LGMD can begin as early as childhood or as late as mid-adulthood, and it often progresses slowly. Over time, a wheelchair might be necessary to get around. There are many different types of LGMD, each with its own specific features.
Facioscapulohumeral (pronounced: fa-she-o-skap-you-lo-hyoo-meh-rul) muscular dystrophy (FSHD) can affect both guys and girls, and it usually begins during the teens or early adulthood. FSHD affects muscles in the face and shoulders and sometimes causes weakness in the lower legs. People with this type of MD might have trouble raising their arms, whistling, or tightly closing their eyes. How much a person with this form of muscular dystrophy is affected by the condition varies from person to person. It can be quite mild in some people.
Myotonic (pronounced: my-uh-tah-nick) dystrophy (MMD) is a form of muscular dystrophy in which the muscles have difficulty relaxing. In teens, it can cause a number of problems, including muscle weakness and wasting (where the muscles shrink over time), cataracts, and heart problems.
Congenital muscular dystrophy (CMD) is the term for all types of MD that show signs in babies and young children, although the MD isn't always diagnosed right away. Like other forms of MD, CMD involves muscle weakness and poor muscle tone. Occurring in both girls and boys, it can have different symptoms. It varies in how severely it affects people and how quickly or slowly it worsens. In rare cases, CMD can cause learning or intellectual disabilities.
The life expectancy (in other words, how long a person may live) for many of these forms of muscular dystrophy depends on the degree to which a person's muscles are weakened as well as how much the heart and lungs are affected.
