Myasthenia gravis (my-us-THEE-nee-uh GRAY-vis) causes muscles under your voluntary control to feel weak and get tired quickly. This happens when the communication between nerves and muscles breaks down.
There's no cure for myasthenia gravis. Treatment can help with symptoms. These symptoms can include weakness of arm or leg muscles, double vision, drooping eyelids, and problems with speaking, chewing, swallowing and breathing.
This disease can affect people of any age, but it's more common in women younger than 40 and in men older than 60.
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Muscle weakness caused by myasthenia gravis gets worse when the affected muscle is used. Because symptoms usually get better with rest, muscle weakness can come and go. However, the symptoms tend to progress over time. They usually reach their worst within a few years after the disease begins.
Myasthenia gravis may affect any of the muscles that you can control. Certain muscle groups are more commonly affected than others.
In more than half the people who develop myasthenia gravis, their first symptoms affect the eyes. Symptoms include:
- Drooping of one or both eyelids, called ptosis.
- Double vision, called diplopia, which may be horizontal or vertical, and improves or resolves when one eye is closed.
Face and throat muscles
In about 15% of people with myasthenia gravis, the first symptoms involve face and throat muscles. These symptoms can:
- Make speaking difficult. Your speech might sound soft or nasal, depending on which muscles are affected.
- Cause problems with swallowing. You might choke easily, making it difficult to eat, drink or take pills. Sometimes, liquids you're trying to swallow come out your nose.
- Affect chewing. The muscles used for chewing might tire halfway through a meal. This is especially true if you've been eating something hard to chew, such as steak.
- Change facial expressions. For example, your smile might look like a snarl.
Neck and limb muscles
Myasthenia gravis also can cause weakness in the neck, arms and legs. Weakness in the legs can affect how you walk. Weak neck muscles make it hard to hold up the head.
When to see a doctor
Talk to your health care provider if you have problems:
- Using your arms or hands.
- Holding up your head.
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Chemicals messengers, called neurotransmitters, fit precisely into receptor sites on your muscle cells. In myasthenia gravis, certain receptor sites are blocked or destroyed, causing muscle weakness.
Your nerves communicate with your muscles by releasing chemicals, called neurotransmitters, that fit into places on the muscle cells, called receptor sites, at the nerve-muscle junction.
In myasthenia gravis, the immune system makes antibodies that block or destroy many of your muscles' receptor sites for a neurotransmitter called acetylcholine (as-uh-teel-KOH-leen). With fewer receptor sites available, your muscles receive fewer nerve signals. This causes weakness.
Antibodies also can block a protein called muscle-specific receptor tyrosine kinase (TIE-roh-seen KIE-nays), sometimes referred to as MuSK. This protein helps form the nerve-muscle junction. Antibodies against this protein can lead to myasthenia gravis.
Antibodies against another protein, called lipoprotein-related protein 4 (LRP4), can play a part in this condition. Research studies have found other antibodies and the number of antibodies involved will likely grow over time.
Some people have myasthenia gravis that isn't caused by antibodies blocking acetylcholine, MuSK or LRP4. This type of myasthenia gravis is called seronegative myasthenia gravis, also known as antibody-negative myasthenia gravis. In general, researchers believe that this type of myasthenia gravis still comes from a problem with autoimmunity, but the antibodies involved just can't be found yet.
The thymus gland, a part of your immune system situated in the upper chest beneath the breastbone, may trigger or maintain the production of antibodies that result in the muscle weakness.
The thymus gland is a part of your immune system. This gland is located in the upper chest beneath the breastbone. Researchers believe that the thymus gland makes or helps produce the antibodies that block acetylcholine.
The thymus gland is large in babies and small in healthy adults. In some adults with myasthenia gravis, however, the thymus gland is larger than usual. Some people with myasthenia gravis also have tumors of the thymus gland, called thymomas. Usually, thymomas aren't cancerous, also known as malignant. But thymomas can become cancerous.
Rarely, mothers with myasthenia gravis have children who are born with myasthenia gravis. This is called neonatal myasthenia gravis. If treated immediately, children usually recover within two months after birth.
Some children are born with a rare, hereditary form of myasthenia gravis, called congenital myasthenic syndrome.
Factors that can make myasthenia gravis worse include:
- Illness or infection.
- Some medicines — such as beta blockers, quinidine gluconate, quinidine sulfate, quinine (Qualaquin), phenytoin (Dilantin), certain anesthetics and some antibiotics.
- Menstrual periods.
Complications of myasthenia gravis are treatable, but some can be life-threatening.
Myasthenic crisis is a life-threatening condition. It happens when the muscles that control breathing become too weak to work. Emergency treatment and mechanical assistance with breathing are needed. Medicines and therapies that filter the blood help people to breathe on their own.
Thymus gland tumors
Some people with myasthenia gravis have a tumor in the thymus gland. The thymus is a gland under the breastbone that is part of the immune system. Most of these tumors, called thymomas, aren't cancerous.
People with myasthenia gravis are more likely to have the following conditions:
- Underactive or overactive thyroid. The thyroid gland in the neck secretes hormones that regulate the metabolism. If the thyroid is underactive, you might have problems dealing with cold, weight gain and other issues. An overactive thyroid can cause problems dealing with heat, weight loss and other issues.
- Autoimmune conditions. People with myasthenia gravis might be more likely to have autoimmune conditions, such as rheumatoid arthritis or lupus.