What Are Muscular System Diseases?

A muscle disease is any disease that affects the human muscle system. Primary muscle diseases result from abnormalities of the muscles themselves. Secondary muscle diseases are caused by another condition that may have triggered or caused the muscle disease.

Primary muscular system diseases include:

  • Polymyositis
  • Dermatomyositis 
  • Muscular dystrophy
  • Myasthenia gravis
  • Amyotrophic lateral sclerosis (ALS)
  • Rhabdomyolysis
  • Cardiomyopathy
  • Sarcopenia

Both primary and secondary muscular system diseases affect the muscles and sometimes the nerves that supply them. Because of this, these diseases may eventually result in muscle wasting, or loss of muscle mass. This may involve loss of strength and function in one or more muscles. Sometimes paralysis may occur.

This article discusses primary and secondary muscular system diseases. It also explains the symptoms, causes, diagnosis, and treatment of muscle diseases.

Muscle disease
Patrik Giardino / Getty Images.

About the Muscular System

Every movement you make—talking, walking, sitting, standing, and even blinking—is controlled by your muscles.

You even have muscles that you are not aware of. Examples include the muscles that control your posture and contract blood vessels.

There are over 600 muscles in the human body. There are also three recognized muscle types. Each of the three types has its own specific functions. 

  • Skeletal muscle: These muscles are connected to bones by tendons. Tendons are flexible but tough cords of tissue. Your bones move when skeletal muscles contract and pull on the tendons. Bones are also connected to other bones by ligaments. These are similar to tendons and help to hold the skeleton together. Myopathies are diseases that affect the skeletal muscles.
  • Smooth muscle: This type of muscle is responsible for muscle actions that are involuntary, or out of your control. Smooth muscle exists in places like your stomach, intestines, and blood vessels. These muscles perform tasks your body needs to function. 
  • Cardiac muscle: Cardiac muscle is a type of muscle marked with slanted dark and light branches. These branches are made up of stretched-out fibers. Cardiac muscle is found in the heart and is responsible for coordinated involuntary contractions. This is what lets the heart pump blood efficiently. The heart is the only muscle in the body that continuously contracts.


Each muscle type serves a specific purpose. You walk because of skeletal muscles. You digest food because of smooth muscles. Your heart beats because of cardiac muscle.

Different muscle types work together. When you run, you use your skeletal muscles to move your limbs. Your cardiac muscle makes your heart beat, and your smooth muscles help you breathe.


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This video has been medically reviewed by Oluseun Olufade, MD

Primary Muscle Diseases

Primary muscle diseases are caused by abnormalities of the muscles. A muscle disease is considered primary if it occurs on its own, not because of any other associated diseases.


Myositis is an inflammation of muscles and their associated tissues, including blood vessels. Polymyositis (PM) is a rare type of myositis. PM is mostly seen in people over age 20, more often in females.

PM is marked by muscle inflammation and weakness. A person with this condition may experience falls and problems getting up from falls. Other symptoms include chronic dry cough and/or difficulty swallowing.

PM has no known cause, and there is no cure for the condition. Fortunately, the condition is treatable. 


Dermatomyositis (DM) is a rare inflammatory muscle disease. It can affect people of any age or sex, though it's more often seen in women.

Common symptoms of DM include:

  • A distinctive rash
  • Muscle weakness
  • Inflamed, painful muscles

Like other inflammatory myopathies, the cause is unknown. There is no cure, but the condition can be managed with medications and other therapies.   

Muscular Dystrophy

Muscular dystrophy (MD) is a group of inherited myopathies. These conditions all cause muscle loss and weakness.

Some types of MD appear in infancy or childhood. Others may not appear until middle age or even later.

Symptoms are specific to the type of MD. They can vary based on the muscle groups and people they affect.

All forms of MD grow worse with time. Most people lose their ability to walk. There is no cure for MD, but symptoms can be treated. Treatment can also prevent complications.

Treatments include:

Some people with MD have mild symptoms that progress slowly. Others have symptoms that are severe and disabling. 

Myasthenia Gravis

Myasthenia gravis (MG) is an autoimmune neuromuscular disease. Neuromuscular diseases are caused by problems with how the nerves and muscles work together.

In people with MG, the immune system mistakenly attacks the receptors that make it possible for nerve cells and muscles to communicate. This interferes with nerve signals to the muscles, causing muscle weakness.

MG is the most common chronic autoimmune neuromuscular disorder. It affects 20 out of every 100,000 people.

The primary symptom of MG is weakness in the voluntary skeletal muscles. There is no cure for MG, but treatment can control the activity of the immune system.

The outlook for MG is different for each person. Some people will have only mild symptoms. Others may become disabled. Early treatment can limit the disease’s progression.

Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is also called Lou Gehrig’s disease. This group of rare neurological diseases affects the nerve cells in the brain and spinal cord.

ALS affects the muscles responsible for voluntary movement. Most cases are diagnosed in people ages 40 to 70.

According to some estimates, at least 16,000 Americans have this condition. There is no cure for ALS, and symptoms get worse with time.

Treatment can help control symptoms and prevent complications. Typical life expectancy, though, is only a few years after diagnosis.

Treatments for ALS include:

  • Medication
  • Speech therapy
  • Physical therapy

In severe cases, patients may need nutritional and breathing support.


Rhabdomyolysis is a disease that causes the breakdown of skeletal muscle. This breakdown causes myoglobin to release in the bloodstream.

Myoglobin is a protein that stores oxygen in the muscles. Too much myoglobin in the blood can lead to kidney damage.

Causes of rhabdomyolysis include:

  • Trauma
  • Infection and inflammation
  • Medications
  • Toxins
  • Genetic and metabolic disorders

Treatment depends on the severity of symptoms and the presence of complications. Kidney damage from rhabdomyolysis may not be reversible.


Cardiomyopathy­, also called heart muscle disease, is a disease that affects cardiac muscle.

In cardiomyopathy, the heart becomes abnormally enlarged, thickened, and/or stiff. This makes it harder for the heart muscle to pump blood efficiently.

Eventually, this may lead to heart failure. Blood and fluids may back up into the lungs and other parts of the body. Cardiomyopathy can also cause abnormal heart rhythms and heart valve problems. 


Sarcopenia, also called geriatric muscle disease, is common in older adults. Other types of muscle diseases are less common in older adults. Sarcopenia risk in older adults ages 65 to 70 is around 14%. This risk is 53% in those over age 80.

Sarcopenia causes loss of muscle mass and strength. Risk factors include:

  • Poor nutrition
  • Chronic disease
  • Reduced hormone levels

For some people, muscle weakness appears suddenly. For others, it comes on slowly over many years.

Sarcopenia can be diagnosed in a number of ways, including:

  • Physical exam
  • Medical history
  • Blood tests to look for inflammation, genetic disease, low hormone levels, or low vitamin D levels
  • Imaging, such as magnetic resonance imaging (MRI)
  • Electrical activity testing
  • Muscle biopsy

Physical therapy, an improved diet, and medications can improve the condition.


Older adults become more susceptible to sarcopenia as they age. Poor nutrition, chronic disease, and reduced hormone levels are thought to contribute to this risk.

Secondary Muscle Diseases

Sometimes, muscle diseases appear as a result of other more serious health conditions. They may appear with many different diseases, including:

  • Infectious diseases
  • Endocrine disorders, or diseases of the glands
  • Metabolic disorders, such as diabetes
  • Immunological conditions such as HIV/AIDS
  • Vascular diseases, conditions of the blood vessels

Primary muscle diseases that can also be secondary to another health condition include:

  • Rhabdomyolysis
  • Myopathy
  • Myositis
  • Myasthenia gravis
  • Sarcopenia

Some secondary muscle diseases may even affect the respiratory muscles.

Secondary muscle diseases are diagnosed the same way as primary conditions. Treatment involves managing the underlying cause and treating the secondary condition. 

Muscular System Disease Symptoms

One of the first signs of muscle problems is muscle weakness. This means the muscle lacks strength and cannot do its job. Many different diseases can cause muscles to become weak.

Muscle pain that improves with home therapies is usually nothing to worry about. Pain from severe injuries or a serious illness that affects the whole body often requires medical care.

Seek immediate medical attention if you have any of the following symptoms:

  • Muscle pain with breathing issues
  • Dizziness
  • Muscle weakness
  • High fever
  • Stiff neck

People with muscle disease may also experience muscle spasms, cramping, or twitching.

Other symptoms of muscle diseases include: 

  • Muscle wasting or muscle loss
  • Problems with movement and balance
  • Numbness, tingling, or painful sensations
  • Double vision
  • Droopy eyelids
  • Dysphagia, problems with swallowing
  • Breathing troubles, especially dyspnea, which is a shortness of breath

Causes of Muscle Diseases

There are many different causes of muscle diseases. Some muscle diseases are genetic. Genetic conditions may be inherited, or they may be the result of a new genetic mutation in the affected person.

Some muscle diseases are autoimmune diseases, which occur when the immune system attacks its own healthy muscle tissues.

Sometimes, the cause of the muscle disease is unknown. 

Additional causes of muscle diseases include: 

  • Overuse or injury of muscles
  • Some cancers
  • Infections
  • Nerve diseases
  • Medications

Diagnosis of Muscle Diseases

Muscle diseases are often diagnosed with electromyography (EMG). An EMG measures electrical activity in the muscles. This can help identify neuromuscular abnormalities.

EMG can diagnose a number of problems, including:

  • Muscle disorders
  • Nerve and motor problems
  • Degenerative diseases (diseases that get worse over time)

During an EMG test, a thin needle called an electrode is inserted into the skin and into muscle tissue. Once the needle is in place, the patient is asked to contract or relax muscles. The electrode detects electrical activity.

A nerve conduction velocity test may be done with an EMG. This test measures the speed of the electrical impulses moving through your nerves. This can help determine if the cause of symptoms is muscle disease or a nerve disorder.

If your doctor suspects you have a muscle disease, a muscle strength exam may be done. This helps determine if there is muscle weakness or other muscle problems. 

Additional testing may include: 

  • Blood tests for measuring antibodies and muscle enzymes, which may be specific to one disorder or many
  • Muscle biopsy, where a small sample of muscle tissue is taken and sent for testing
  • Magnetic resonance imaging (MRI) to show areas of abnormal muscle

Treatment of Muscle Diseases

Most diseases of the muscular system are incurable. The good news is they can often be treated and managed.

Treatment goals may include relieving symptoms, delaying disease progression, and improving quality of life. 

Treatment may include drug therapy. This may include immunosuppressants, drugs that reduce or prevent the overactivity of the immune system. These drugs may be used to treat some muscle and nerve diseases. They may also be used for conditions that affect both the nerves and muscles.

Corticosteroids and other medications may be given to reduce muscle spasms and cramping.

Your healthcare provider may also recommend physical and occupational therapy to manage symptoms and, if needed, surgery to correct muscle damage.


Diseases of the muscles can occur on their own or due to other conditions. There are many different types of muscle diseases, including conditions that cause inflammation of the muscles and neuromuscular conditions. 

People with muscle diseases may experience muscle weakness, problems with moving and balance, and other symptoms like numbness, droopy eyelids, and problems swallowing or breathing.

Muscle diseases have many causes, including genetics and autoimmune conditions. Sometimes, the cause is not known. 

Muscle diseases are often diagnosed with a test that measures electrical activity in the muscles. These disorders are usually incurable, but many of them can be managed.

13 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  3. The Myositis Foundation. Polymyositis.

  4. The Myositis Foundation. Dermatomyositis.

  5. Centers for Disease Control and Prevention. What is muscular dystrophy?

  6. Myasthenia Gravis Foundation of America, Inc. MG facts.

  7. The ALS Foundation. What is ALS?

  8. Medline Plus. Rhabdomyolysis.

  9. American Heart Association. What is cardiomyopathy in adults?

  10. Santilli V, Bernetti A, Mangone M, et al. Clinical definition of sarcopenia. Clin Cases Miner Bone Metab. 2014;11(3):177–180. doi:10.11138/ccmbm/2014.11.3.177

  11. Finsterer J, Löscher WN, Wanschitz J2, et al. Secondary myopathy due to systemic diseases. Acta Neurol Scand. 2016;134(6):388-402. doi:10.1111/ane.12576 

  12. The IQVIA Institute for Human Data Science. Understanding neuromuscular disease care.

  13. Brigham and Women’s Hospital. Electromyography.

By Lana Barhum
Lana Barhum has been a freelance medical writer since 2009. She shares advice on living well with chronic disease.