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Myasthenia gravis (meye-uhss-THEEN-ee-uh GRAV uhss) (MG) is an autoimmune disease that weakens the muscles. The name comes from Greek and Latin words meaning "grave muscle weakness." But most cases of MG are not as "grave" as the name implies. In fact, most people with MG can expect to live normal lives.
When you have MG, your muscles weaken with activity. Muscle strength returns with rest. MG usually affects the muscles that control:
The muscles that control breathing and neck movements also may be affected.
With MG, normal communication between the nerve and muscle is stopped at the place where nerve endings connect with the muscles they control — the nerve-muscle junction. Normally, the nerve endings release a substance called acetylcholine (uh-SET-uhl-KOH-LEEN), which binds to the muscle tissue at the nerve-muscle junction, causing the muscle to contract (move). In someone with MG, the body's own immune system makes antibodies that block the binding of acetylcholine to the muscle.
The thymus gland, part of the immune system, is abnormal in most MG cases. Some people with MG have benign tumors of the thymus gland called thymomas. Doctors do not fully understand the relationship between the thymus gland and MG.
Estimates of the number of people affected by MG vary, ranging from 5 to 14 people per 100,000. It occurs in all ethnic groups and both sexes. It most commonly occurs in:
MG can occur at any age. Children sometimes develop it as well.
MG is not passed down through the family. You can't "catch it" from someone who has it. The disease rarely occurs in more than one member of the same family. If a woman with MG becomes pregnant, sometimes the baby gets antibodies from the mother and has MG symptoms for a few weeks or months after birth. This is called neonatal myasthenia. The symptoms can be treated and the baby does not have permanent MG.
A group of rare disorders called congenital myasthenic syndromes (CMS) can produce symptoms similar to MG. Unlike MG, these disorders are not autoimmune disorders but are caused by defective genes. Because of these genes, the nerve-muscle junctions in the body cannot work properly. CMS usually starts at or near birth. But it can start in childhood or even adulthood.
MG can affect any muscle, but the muscles that control eye and eyelid movement, facial expression, and swallowing are most often affected. In some people, the first symptom is weakness of the eye muscles. In others, having a hard time swallowing, talking, and breathing can be the first signs. Different people have different levels of muscle weakness. Symptoms may include:
The onset of the disorder may be sudden. And the symptoms often are not immediately recognized as MG.
Some drugs can trigger or worsen MG symptoms.
MG is hard to diagnose because weakness is a common symptom of many disorders.
Your doctor will ask you about your symptoms, take a medical history, and perform a physical exam. If your doctor thinks you may have MG, she or he may run some tests:
It is important for you to see a neurologist who is an expert in diagnosing MG. Diagnosis can take a long time (sometimes even years), so try to be patient with your doctor.
There are several therapies that can help strengthen the muscles of someone with MG. Most people with MG have good results from treatment. In some people, MG may go into remission for a while and muscle weakness may go away completely. In rare cases, people go into remission or improve without treatment.
Treatment for MG may include:
Other therapies sometimes used to treat MG when weakness is very acute include:
Your doctor will decide which treatment is best for you depending on the severity of the weakness, which muscles are affected, and your age and other medical problems. With treatment, many people with MG can expect to lead normal lives.
A myasthenic crisis occurs when weakness affects the muscles that control breathing. This can create a medical emergency requiring either a respirator to help the person breathe or measures to prevent a person from taking too much air into their lungs. Weak respiratory muscles, infection, fever, or a bad reaction to medication can also trigger a crisis. The treatments described above — in particular, intravenous immune globulin and plasma exchange — can reverse the severe weakness of a myasthenic crisis.
To help ease fatigue:
The National Institute of Neurological Disorders and Stroke, within the National Institutes of Health, conducts and supports research on MG. Research findings have led to more timely and accurate diagnoses. New and enhanced therapies have improved management of the disorder.
Despite these advances, there is still much to learn. The ultimate goal of MG research is to increase understanding of the disorder. Researchers are seeking to learn what causes the autoimmune response in MG and to better define the relationship between the thymus gland and MG.
For more information about myasthenia gravis, call womenshealth.gov at 800-994-9662 (TDD: 888-220-5446) or contact the following organizations:
Myasthenia gravis fact sheet was reviewed by:
Audrey S. Penn, M.D.
Senior Advisor to the Director
National Institute of Neurological Disorders and Stroke
National Institutes of Health
Henry J. Kaminski, M.D.
Chair, Department of Neurology & Psychiatry
Saint Louis University School of Medicine
Content last updated: July 16, 2012.