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Myasthenia gravis

Medically reviewed by Last updated on Feb 18, 2024.

What is myasthenia gravis?

Harvard Health Publishing

Myasthenia gravis is a chronic (long-lasting) and rare disease that affects the way muscles respond to signals from nerves, leading to muscle weakness. The disease can occur at any age, but it mainly affects women between ages 20 and 40. After age 50, men are more likely to get the disease.

Normal muscle movement relies on chemical signals from the nerves. Nerve signals cause the nerve endings to release a chemical called acetylcholine into the small space between the nerve and the muscle. This chemical binds to special acetylcholine receptors on the muscle cells and causes the muscle to contract.

Myasthenia gravis is an autoimmune disease, which means the body's defense mechanism, the immune system, begins to attack the body's own tissues instead of foreign invaders, such as viruses. In myasthenia gravis, the immune system attacks the acetylcholine receptors with specific antibodies. Some of the receptors are destroyed or blocked, which means that the chemical message cannot be received. Therefore, muscles do not contract properly and become weak. It has been estimated that up to 80% of a person's acetylcholine receptors can be damaged due to this disease.

Normally, the amount of acetylcholine available to be released to muscle cells diminishes with repeated, prolonged or strenuous activity. In a person with myasthenia gravis, that normal decrease combined with fewer working receptors causes increasing weakness, or myasthenic fatigue. Muscles that may seem normal at first become weak with continued use. This is why a person with myasthenia gravis will feel strongest immediately after waking up or resting and weakest at the end of the day when muscles have been in continual use.

Myasthenia gravis typically strikes muscles in the face first. Muscles that control the eyelids and eye movements usually are affected early in the disease. Later, facial weakness can make smiling, chewing, swallowing and talking difficult.

In most people, the disease eventually spreads to other areas and can affect the muscles of the arms and legs. Sometimes, the disease affects the muscles that control breathing. In some situations, such as during a respiratory infection, this weakness becomes severe. The person may need a breathing tube and a ventilator. It's known as a myasthenic crisis.

No one knows what causes the body to attack its own cells. The thymus, a gland located in the chest just above the heart, is involved in immunity early in life. The thymus gland is thought to be the site of abnormal antibody production in myasthenia gravis, although its precise role is not yet understood. The thymus is abnormal in about 80% of people with myasthenia gravis; enlargement is the most common abnormality but about 10% to 15% of people with the disease have a benign (noncancerous) tumor of the thymus.

Although myasthenia gravis is not believed to be inherited or contagious, babies born to mothers who have myasthenia gravis have an increased risk of having the disease at birth. This probably is because the baby acquires the antibodies that attack the body's cells from the mother during gestation. Usually, the baby's symptoms go away within a few weeks after birth.

Symptoms of myasthenia gravis

The primary symptoms of myasthenia gravis are that muscles are weak and tire quickly. These symptoms can take many forms, and the symptoms may be more or less severe for different people. Symptoms may include some or all of the following:

Sudden, severe weakness (myasthenic crisis) may develop without warning, sometimes triggered by an infection or other stress, causing breathing and swallowing problems. Ocular myasthenia gravis is limited to the eye while generalized myasthenia gravis may affect muscles throughout the body.

Diagnosing myasthenia gravis

Your doctor will ask detailed questions about your symptoms and will examine you. He or she will test your muscle strength and reflexes, eyelid strength and eye movements.  If you are experiencing drooping eyelids as part of your weakness, your doctor may apply a bag of ice to your eyelids to see if the drooping improves (because weakness tends to improve with direct cooling of the weak muscles).  If the results suggest myasthenia gravis, some specific tests may be done to confirm the diagnosis. These include:

In addition, magnetic resonance imaging (MRI) scans or computed tomography (CT) scans may be done to look for abnormalities of the thymus. Pulmonary function tests, which measure breathing strength, also may be recommended, because they can alert doctors to any potential breathing problems. Additional testing, including blood tests or other imaging tests, often is suggested to exclude other possible explanations for a person's symptoms.

Treatment options

The following list of medications are related to or used in the treatment of this condition.

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Expected duration of myasthenia gravis

Myasthenia gravis is a chronic (long-lasting) disease that usually worsens slowly over time. Although symptoms may fluctuate in severity over the years, the disease rarely goes away on its own. It is likely to return even after periods when the disease has not been active.

Preventing myasthenia gravis

Because the cause of myasthenia gravis is unknown, there is no way to prevent it. However, once the disease has developed, there may be ways to prevent episodes of worsening symptoms or flare-ups:

Treating myasthenia gravis

There are many possible treatments for myasthenia gravis. You and your doctor should work together to determine the best treatment for you.

When to call a professional

See your doctor if you experience any unexplained muscle weakness or fatigue.

If you have been diagnosed with myasthenia gravis, it is critically important to be prepared to seek help in case of a myasthenic crisis. If the muscles that control your breathing are affected, call your doctor if you develop a respiratory infection or even a small breathing difficulty. Seek immediate help if you have significant difficulty with breathing or swallowing.


Myasthenia gravis is a chronic disease, although there may be periods of remission, when symptoms disappear. Current treatments, however, can allow most people with myasthenia gravis to live normal or near-normal lives. People with ocular myasthenia gravis (without progression over several years) have a better prognosis than those with generalized disease.

Other autoimmune disorders, such as systemic lupus erythematosus (SLE or lupus) or rheumatoid arthritis, may be associated with myasthenia gravis and may develop either before or after the weakness is noticed.

Additional info

National Institute of Neurological Disorders and Stroke

Myasthenia Gravis Foundation of America

Learn more about Myasthenia gravis

Treatment options

Care guides

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.