What Are Muscular System Diseases?

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Muscular system diseases affect an important structure of the human body—the muscle. Muscles produce the force needed to move and function. Diseases and disorders resulting from direct abnormalities of the muscles are considered primary muscle diseases.

Muscle diseases that cannot be traced back to the muscles are usually secondary to another condition, which may have triggered or caused the muscle disease. Because both types affect the muscles (and sometimes the nerves), both may eventually result in muscle wasting and paralysis, involving loss of motor function in one or more muscles.

Muscle disease
Patrik Giardino/Getty Images.

About the Muscular System

Every single 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—for example, those that control posture and contract blood vessels.

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

  • Skeletal muscle: These muscles are connected to the bones and supported by tendons—flexible, but tough cords of tissue. As muscle contracts, it will pull on the tendons, moving bone. Bones are also connected to other bones by ligaments, which are similar to tendons and help to hold the skeleton together. 
  • Smooth muscle: This is a type of muscle that is smooth and responsible for muscle actions that are involuntary and out of your control. Smooth muscle exists in places such as your stomach, intestines, and blood vessels. These muscles perform all the tasks your body needs to function. 
  • Cardiac muscle: Cardiac muscle is a type of muscle marked with slanted dark and light branches made up of stretched-out fibers. Cardiac muscle is found in the heart and responsible for coordinated and involuntary contractions that allow the heart to pump blood efficiently. The heart is the only muscle in the body that continuously contracts.

Each muscle type serves a specific purpose. For example, you walk because of your skeletal muscles. You digest food because of smooth muscle, and your heart beats because of cardiac muscle. Additionally, the different muscle types work together. For example, when you run, you use your skeletal muscles, cardiac muscle because the heart is pumping, and smooth muscles as you breathe heavier.

Types of Muscular System Diseases

Muscle diseases are any disease that affects the human muscle system. A muscle disease will be either primary or secondary. 

Primary Muscle Diseases

Common primary diseases of the muscular system include inflammatory myopathies, such as polymyositis and dermatomyositis, muscular dystrophy, myasthenia gravis, amyotrophic lateral sclerosis, rhabdomyolysis, and cardiomyopathy, among others.

Here is what you need to know about these conditions, including causes, when to see a doctor, diagnosis, treatment, and prevention. 

  • Polymyositis (PM): This a rare type of inflammatory myopathy (also called myosotis), a group of muscle diseases that cause inflammation of muscle and their associated tissues, including blood vessels. According to The Myositis Foundation, the condition is mostly seen in people over age 20, many of which are women. PM is marked by muscle inflammation and weakness. A person with this condition may experience falls and problems getting up falls, chronic dry cough, and/or dysphagia (difficulty swallowing). PM has no known cause and there is no cure for the condition. Fortunately, the condition is treatable. 
  • Dermatomyositis (DM): DM is a rare inflammatory muscle disease affecting people of any age or sex, although it's more often seen in women. Common symptoms of DM include a distinctive rash, muscle weakness, and inflamed and painful muscles. Much like other inflammatory myopathies, the cause unknown, and while there is no cure, the condition can be managed with medications and other therapies.   
  • Muscular dystrophy (MD): MD is a group of inherited muscle diseases. These conditions all cause muscle loss and weakness. Some appear in infancy or childhood, and others may not appear until middle age or even later. Symptoms are specific to the type of MD and vary based on the muscle groups and people they affect. All forms grow worse with time, and most people lose their ability to walk. There is no cure for MD, but symptoms can be treated, and complications can be prevented. Treatments include medications, physical therapy, speech therapy, orthopedic devices, and surgery. Some people with MD are lucky enough to have mild symptoms that progress slowly, where others are less fortunate and have disease symptoms that are severe and disabling. 
  • Myasthenia gravis (MG): MG is a neuromuscular disease that causes weakness of the skeletal muscles, resulting from impaired communication between nerve cells and muscles. Because the impairment reduces crucial muscle contractions, muscle weakness eventually occurs. According to the Myasthenia Gravis Foundation of America, MG is the most common chronic autoimmune neuromuscular disorder, affecting 20 in 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 with the condition, as some people will have only mild symptoms, while others may become disabled. Early and appropriate treatment can limit the disease’s progression.
  • Amyotrophic lateral sclerosis (ALS): ALS, also called Lou Gehrig’s disease, is a group of rare neurological diseases affecting the nerve cells in the brain and spinal cord. ALS affects the muscles responsible for voluntary muscle movement. Most cases are diagnosed in people ages 40 to 70, and it is estimated at least 16,000 Americans have the condition, according to the ALS Foundation. There is no cure for ALS and symptoms will get worse with time. Treatment can help control symptoms, prevent complications, and make it easier to live with the condition. However, typical life expectancy is only a few years after receiving the diagnosis. Treatments include medication, speech therapy, and physical therapy. In more severe cases, ALS may require nutritional and breathing support. 
  • Rhabdomyolysis: Rhabdomyolysis is a muscle disease that causes the breakdown of skeletal muscle. This breakdown causes myoglobin release in the bloodstream—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, and 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: Cardiomyopathy­—also called heart muscle disease—is a type of progressive disease affecting cardiac muscle. It causes the heart to become abnormally enlarged, thickened, and/or stiff, making it harder for the heart muscle to pump blood efficiently. Eventually, this may lead to heart failure and buildup of blood into the lungs and other parts of the body. Cardiomyopathy can also cause abnormal heart rhythms and heart valve problems

Secondary Muscle Diseases

Some muscle diseases can appear secondary to other more serious health conditions. These may appear alongside many different diseases, including infectious diseases, endocrine disorders, metabolic disorders, immunological conditions, and vascular diseases.

Muscle diseases that may be secondary to another health condition include rhabdomyolysis, myopathy, myositis, and myasthenia gravis. 

Secondary conditions may affect one single muscle, a group of muscles, or an entire system of muscles. The severity of affected muscles may be permanent or temporary. A person may experience mild symptoms or severe ones.

Some secondary muscle diseases may even affect the respiratory muscles. Diagnosis for a secondary muscle disease is made in the same way it would be made for a primary condition. Treatment involves managing the underlying cause and treating the secondary condition. 

Geriatric Muscle Disease—Sarcopenia 

Sarcopenia is a muscle disease common in older adults, while other types of muscle diseases are less common in older adults. This muscle disease can be primary or secondary. Sarcopenia causes muscle mass loss and muscle strength loss. One 2014 report in the journal Clinical Cases Mineral Bone Metabolism notes sarcopenia risk in older adults ages 65 to 70 is around 14% and up to 53% in those over age 80.

Risk factors may include poor nutrition, chronic disease, and reduced hormone levels. Muscle weakness may appear suddenly, or it may come on slowly over many years. Sarcopenia is diagnosed with a physical exam, medical history, blood work to look for inflammation, genetic disease, or low hormone or vitamin D levels, and with imaging. Electrical activity testing or a muscle biopsy may also be done. Physical therapy, an improved diet, and medications can improve the condition.

Muscular System Disease Symptoms

Muscle weakness is one of the first signs of a problem with your muscles. This means there is a lack of strength in the affected muscle and it cannot do its job. Many different diseases can cause muscles to become weak.

Muscle pain that improves with home therapies can be managed at home and poses little concern. However, muscle pain from severe injuries or a serious systemic illness (a disease affecting the entire body) often requires medical care. You should get immediate medical attention if you have muscle pain with breathing issues, dizziness, muscle weakness, high fever, and/or a stiff neck

In addition to muscle pain and weakness, a person with a muscle disease may 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
  • Problems with swallowing—dysphagia
  • Breathing troubles, especially dyspnea (shortness of breath)

If you are experiencing muscle weakness, get in touch with your doctor to determine the cause of symptoms. Anyone who experiences sudden, severe muscle weakness should seek urgent medical attention.


There are many different causes of muscle diseases. Genetics is one cause, which means the condition may be inherited or the result of a new genetic mutation in the individual affected. Some muscle diseases are autoimmune diseases, which results when a person’s immune system malfunctions and 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

Regardless of the cause, most muscle diseases are incurable. However, treatment can manage a person’s symptoms and pain, help with maintaining mobility and improve quality of life. 


Electromyography (EMG) is the most commonly used tool to diagnose muscle diseases. An EMG can look for neuromuscular abnormalities by measuring electrical activity in the muscles. It can diagnose a number of problems, including muscle disorders, nerve and motor problems, and degenerative diseases.

An EMG test involves using a thin needle called an electrode inserted into the skin and into muscle tissue. Once the needle is in place, you are asked to contract or relax muscles. The electrode will detect electrical activity and show results on a nearby monitor called an oscilloscope. A nerve conduction velocity test may be done with an EMG in order to determine whether 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 to determine whether muscle weakness or other muscle problems exist. 

Additional testing that may be done includes: 

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


Most diseases of the muscular system are incurable, but they can be treated and managed. The goals of treatment for muscle diseases may include treating symptoms, delaying disease progression, and improving quality of life. 

Treatment may include drug therapy. A class of drugs known as immunosuppressants—drugs inhibit or prevent the overactivity of the immune system—can treat some muscle and nerve diseases, and conditions that affect both the nerves and muscles. Corticosteroids and other medications may be given for reducing muscle spasms and cramping.

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

A Word From Verywell 

The outlook with most muscle diseases can be positive. In many cases, treatment can effectively manage most symptoms, including muscle pain and weakness. Your long-term outlook will depend on your condition and the effect it has on your muscle function. Talk to your doctor to learn more about your condition, helpful treatments, and your outlook.

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Article Sources
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