Myopathy – Causes, Signs and symptoms

Myopathy

Also called: Inheritable Myopathy, Acquired Myopathy

Summary

Myopathy is a broad term used to describe conditions affecting the skeletal muscles that leads to muscle weakness and deterioration.

Skeletal muscles are attached to bones and joints throughout the body and are used in movement. While many medical conditions may lead to muscle weakness, myopathies begin with muscle disorder or disease.

Movement is achieved through a complex process that can be disrupted by genetic mutations, an overactive immune system, or the use of certain medications or illicit drugs. Muscular dystrophy is one of the most common groups of myopathies that cause muscles to gradually deteriorate throughout the body. Inflammatory myopathies are considered autoimmune disorders in which the immune system attacks muscle cells or supporting tissues.

Myopathies are characterized by muscle weakness that can range from muscle fatigue to an impaired ability to move. Additional symptoms may also occur, depending on the type of myopathy involved.

To diagnose myopathy, a physician may examine muscle performance in a number of ways. A physical examination and neurological examination are likely, as are other tests that may be used to confirm a diagnosis of myopathy. These additional tests may include blood tests, urine tests, muscle biopsy, electromyography (EMG) and MRI (magnetic resonance imaging). Some of these tests may need to be repeated over time to compare results.

In most cases, there is no cure for myopathy. Treatment concentrates on alleviating a patient’s symptoms. This may include the use of certain medications, physical therapy, occupational therapy and braces. Psychological counseling may also be recommended. In many cases, myopathy cannot be prevented. For inheritable types of myopathies, genetic counseling may be advised for people with a family history of the disease. Drug-induced myopathies may stop when patients discontinue use of the drug causing the myopathy.

About myopathy

A myopathy is a disorder or disease of the skeletal muscles that may cause muscle weakness and deterioration. Many types of myopathy worsen over time, with weakness becoming more severe and affecting a larger area of the body. In some cases, muscle weakness may become so severe that a patient loses the ability to move certain parts of the body.

Unlike the muscles of the heart and lungs, the skeletal muscles are largely under a person’s conscious control. The exception are skeletal muscles that control reflex movements (e.g., knee jerk), which are not consciously controlled.

The process that enables skeletal muscles to function is complex. Impairment at any point during this process may lead to myopathy. Movement begins with neurons (nerve cells) that release chemicals called neurotransmitters, which send messages to the muscles. The neurotransmitters bind to receptors located on muscle fibers and start a cascade of chemicals. This causes muscle fibers to contract, resulting in a specific type of movement (e.g., the bending of a joint).

Each muscle fiber is signaled by neurotransmitters separately and the strength of the total contraction depends on how many fibers respond. Almost immediately, chemicals in the space around muscle fibers weaken the neurotransmitters, allowing the reaction to end and the muscle fibers to relax. In situations requiring long-term contractions, some fibers will relax while others contract to maintain prolonged muscle action.

Myopathy can affect various areas of the body. Most often, muscle weakness develops in proximal, symmetric or localized patterns. Proximal muscle weakness appears closest to the core of the body (e.g., muscles of the neck, shoulders and hips). Symmetric muscle weakness affects the same muscles on both the right and left sides of the body. Localized muscle weakness occurs only in specific areas of the body, although it may spread as the disease progresses. Some myopathies may also occur in distal patterns, away from the center of the body, with muscle weakness appearing in the hands, wrists, feet and ankles.

Conditions other than myopathies may also cause muscle weakness. This may include anemia (low red blood cell count), heart disease, depression and a variety of diseases that are neuromuscular (involving disorder of nerves and muscles) in nature. These are not considered myopathies because muscle dysfunction alone is not the underlying problem.

Types and differences of myopathy

There are many different types of myopathies. All involve muscle dysfunction that can cause muscle weakness and deterioration. Myopathies can be inherited or acquired. They may appear at birth or later in life.

Myopathies are generally categorized into groups, according to certain characteristics. There may be other ways of grouping myopathies, but the four main groups are described here. 

One group of myopathies, muscular dystrophy (MD), includes a collection of disorders that cause muscle weakness and deterioration. Symptoms may also include impaired reflexes, movement and breathing. There are many types of MD that may differ in the typical age when symptoms begin, which muscle groups are affected, and how the disease progresses. MD occurs as the result of genetic mutations that block the body from producing proteins needed to build and maintain muscle. As muscle becomes damaged during normal use, it cannot be repaired through the typical body processes. The most common MD types are Duchenne muscular dystrophy and Becker muscular dystrophy. According to the Centers for Disease Control and Prevention, 400 to 600 boys are born with these types of MD each year.

Inflammatory myopathies are muscle diseases characterized by an intense immune system reaction in the muscle and surrounding tissue. They are considered autoimmune disorders. Because the immune system is occupied with attacking body cells, patients may be at greater risk of infection from bacteria, viruses and other organisms. This group of myopathies includes:

  • Polymyositis. An uncommon disease that causes continued and progressive weakness of the body core, especially in the shoulders and hips. Muscle weakness tends to be symmetrical. It may also cause difficulty swallowing, joint or muscle tenderness and fatigue. The age of onset can vary greatly. Most cases begin between the ages of 40 and 60, although other age groups may be affected. Polymyositis rarely occurs in patients under 18.

  • Dermatomyositis. Similar to polymyositis, except that a skin rash also develops, sometimes before muscle weakness is experienced. This rash may be patchy and blue/purple in color. It results from the immune system attacking blood vessels in the skin. The degradation of blood vessels in muscle leads to muscle weakness. In most cases, symptoms first occur during two different periods: between the ages of 5 and 15, and between 40 and 70. The childhood form may also include symptoms of calcium deposits under the skin, stomach ulcers and infections. Dermatomyositis is more common in women than in men.

  • Inclusion body myositis (IBM). This type is similar to and may be confused with polymyositis. IBM involves the formation of empty spaces, known as vacuoles, in muscle tissue. IBM usually develops after age 50 and symptoms gradually become more severe over a period of months to years. Symptoms may include falling and tripping, weakness in the hands, shrinking of the forearms and difficulty swallowing. This type of inflammatory myopathy is more common in men than in women.

Congenital myopathies are a group of muscle diseases that are present at birth. They are often hereditary conditions, although they may also be due to nonhereditary factors, such as a spontaneous genetic defect. Unlike many other types of myopathy, the congenital types are usually not progressive. There are several forms, including:

  • Central core disease. Muscle weakness occurs more frequently in the legs than arms and may affect a child’s motor development (e.g., delayed ability to walk, difficulty climbing stairs). This type of congenital myopathy is associated with malignant hyperthermia, a life-threatening condition that causes fever and muscle contractions when the patient is under general anesthesia.

  • Nemaline myopathy. Disease characterized by mutations of filament proteins, which are vital components of muscle tissue involved in muscle contraction. Symptoms include generalized weakness (especially in the face, head and lungs), loss of muscle tone, skeletal abnormalities, delays in walking and respiratory difficulties. The most severe form of nemaline myopathy causes death in newborns with the disease. Other forms are less severe and may cause delays in typical motor development milestones in children. In rare cases, symptoms of increasing weakness in proximal skeletal muscles (those closest to the body’s core) may not occur until adulthood.

  • Centronuclear myopathy (also known as myotubular myopathy). This type of congenital myopathy causes severe weakness (e.g., loss of muscle tone, paralysis) in newborns that is fatal in many cases. It is most likely to occur in males. Sometimes symptoms do not appear until late infancy. When this occurs, it can cause delays in a child’s motor development and may be associated with skeletal deformities (e.g., scoliosis). In some cases, symptoms may not appear until adolescence or young adulthood. Unlike many other congenital myopathies, centronuclear myopathy may be progressive with symptoms that become increasingly severe over time.  

Drug-induced myopathies are those caused by the use of medications or illicit drugs. In some cases, severe weakness may occur. Medications that may cause muscle damage include immunosuppressants (e.g., corticosteroids) and those used to treat high cholesterol, gout, HIV/AIDS and malaria. Other drugs that may cause myopathy include syrup of ipecac, alcohol, cocaine, amphetamines and heroin.

Mitochondrial myopathies are a group of neuromuscular diseases that may involve both nerve and muscle damage. Thus, although myopathy is in its name, disorder or dysfunction of the muscles alone may not be the primary problem in these diseases.

Risk factors and causes of myopathy

The cause of myopathy depends on the type of myopathy involved.

In many cases, myopathy results from an inherited or spontaneous genetic mutation. This is the case for muscular dystrophy (MD) and congenital myopathies.  

Inflammatory myopathies are believed to be autoimmune disorders in which the immune system attacks muscle or its supportive tissues, such as blood vessels. The origin of autoimmune disorders is unknown, but some studies indicate there may be a genetic link that increases susceptibility to the diseases. In addition, it is believed that viral infections may trigger the autoimmune reaction in some cases.

Drug-induced myopathies are caused by the use of certain medications (e.g., corticosteroids) as well as the use of legal or illegal drugs (e.g., alcohol, cocaine). Ingestion of toxins may also cause this type of myopathy. Medications may include those prescribed for high cholesterol, rheumatoid arthritis, malaria and psychoses. In many cases, the myopathy stops when patients discontinue use of the drug. Extended use of syrup of ipecac to induce vomiting (e.g., as may occur in people with eating disorders) can cause muscle damage and result in myopathy.

Risk factors for developing myopathy may vary, depending on myopathy type. Some examples include age, gender, family history of myopathy and the presence of other autoimmune diseases

Signs and symptoms of myopathy

The most common symptom of myopathy is muscle weakness. This weakness can vary in a number of ways, including:

  • Intensity of muscle weakness (e.g., from muscle fatigue to hindered movement)

  • Location where weakness first occurs

  • Whether weakness progresses to other parts of the body or becomes more severe

  • Response of muscles following periods of rest

In some cases, muscle weakness may be accompanied by other muscle-related symptoms such as cramps. For more type-specific descriptions of symptoms, see Types and Differences of Myopathy.

Diagnosis methods for myopathy

To diagnose myopathy, a physician typically performs a physical examination that may include several tests of the patient’s muscle strength. This may help determine whether muscle weakness is due to myopathy or another cause, such as anemia (low red blood cell count), depression, heart disease or neuromuscular disorders. The examination will also check for specific signs of different types of myopathy. For the example, the presence of skin rashes in addition to muscle weakness may indicate a type of inflammatory myopathy.

A physician may review the patient’s medical history, possibly asking questions about the occurrence of muscle diseases in the family and what current medications the patient takes. In addition, patients should describe their symptoms, including where and when they began as well as their duration.

A neurological examination may also be performed. This may include tests to identify muscle weakness patterns (e.g., symmetric, proximal, distal), which may help identify the type of myopathy involved.

While myopathy may be suspected based on the patient’s initial evaluation, additional tests are often necessary to confirm a physician’s diagnosis. In some cases, the tests may need to be performed repeatedly, before and after certain types of exercise.

Tests that may be used to help diagnose myopathy include:

  • Nerve conduction velocity (NCV) studies and electromyography (EMG). These two tests measure how well signals travel through nerves to muscles. An NCV may help identify whether nerve problems are causing a patient’s muscle weakness. An EMG examines the muscle at rest and when stimulated.

  • Blood tests and urine tests. In these tests, samples are analyzed for indicators of muscle breakdown, the presence of autoimmune disorder or to rule out other causes of a patient’s symptoms.

  • Muscle biopsy. Removal of a tiny section of muscle tissue allows it to be studied under a microscope. This examination may help determine which type of myopathy is involved.

  • MRI (magnetic resonance imaging). Radio waves and magnets are used to create three-dimensional images of muscles and other tissues. The images can help physicians identify areas of muscle deterioration and may help distinguish one type of myopathy from another.

  • Genetic testing. Samples taken from a swab of a patient’s cheek or saliva (or blood samples drawn from a vein) may be used to identify genetic mutations that may indicate a certain type of myopathy (e.g., muscular dystrophy).  

If the results of these tests are inconclusive, a physician may recommend that a patient also consult a neurologist or rheumatologist (specialist in musculoskeletal disorders, such as arthritis). 

Certain types of myopathies (e.g., centronuclear myopathy, a type of congenital myopathy) may be diagnosed before birth using specialized prenatal tests.

Treatment and prevention of myopathy

There is no cure for most types of myopathies. Instead, treatment usually focuses on alleviating a patient’s symptoms. Possible treatments may include:

  • Corticosteroids and other immunosuppressants. Medications to reduce inflammation related to myopathies caused by autoimmune disorders. Long-term use of corticosteroids may lead to severe side effects, including loss of bone density (osteoporosis), weight gain, cataracts, mood swings and high blood pressure. These medications are often effective in relieving symptoms associated with inflammatory myopathies. However, corticosteroids are also known to be a cause of drug-induced myopathy. Patients should consult their physician about whether corticosteroids are appropriate for them.

  • Physical therapy. Instruction and assistance in performing certain exercises may help patients maintain and improve muscle strength and flexibility. In some cases, as the disease progresses, the patient may require training with assistive devices to maintain mobility.

  • Occupational therapy. Focuses on maintaining and improving fine motor control, such as in the hands and fingers. This differs from physical therapy, which tends to focus on general muscle strength.

  • Braces. Support devices, especially for the feet and ankles, can help patients maintain mobility after myopathy reduces the strength of leg muscles.

  • Counseling. Individual and group counseling may help patients and loved ones better understand the disease, its progression and lifestyle changes that may occur.

People with dermatomyositis (a type of inflammatory myopathy) may experience sensitivity to light and are typically advised to avoid sun exposure and use a broad spectrum sunscreen.

In many cases of drug-induced myopathies, the myopathy stops when patients discontinue use of the drug or medication causing the myopathy. Some forms of myopathy, such as inclusion body myositis(IBM), have not responded to any treatment to date.

In most cases, myopathy cannot be prevented. In some cases, adults with a family history of the disease may choose to undergo genetic counseling. The results of certain tests (e.g., DNA tests) may indicate the risk of transmitting an inheritable myopathy to a child.

Questions for your doctor regarding myopathy

Preparing questions in advance can help patients have more meaningful discussions with healthcare professionals regarding their condition. Patients may wish to ask their doctor the following questions related to myopathy:

  1. Do you think my muscle weakness is a sign of myopathy? Why or why not?
  2. What type of myopathy do you suspect I have?
  3. What tests will you need to perform to confirm your diagnosis? How do I prepare for these tests?
  4. What caused my myopathy?
  5. Could my symptoms be caused by conditions other than myopathy?
  6. Is my condition hereditary?
  7. Are my symptoms likely to get worse over time? How will this affect me?
  8. What treatment do you recommend for me? What are its risks and benefits?
  9. For how long will I need to be treated?
  10. Can my condition recur, even after treatment?
  11. Would you recommend a physical, occupational or psychological therapist for me?
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