Myasthenia Gravis

Myasthenia gravis is an autoimmune disorder that causes muscle weakness. An autoimmune disorder is one in which the body produces antibodies against its own tissues.

What is going on in the body?

For unknown reasons, myasthenia gravis causes a person's immune system to produce antibodies that attack the muscles in his or her body. The antibodies destroy the part of the muscle that receives signals from the nerves. When a muscle is used a great deal, it may not work properly. After a period of rest, the muscle generally improves.

What are the causes and risks of the disease?

No one knows why a person with myasthenia gravis produces antibodies that attack the muscles. This disorder occurs more often in women than in men. It usually starts in women during their childbearing years. In men, the disease most often starts in middle age. Rarely, a child may be born with myasthenia gravis from a genetic defect.

New research findings suggest that autoimmune disorders may be set off by a transfer of cells between the fetus and the mother during pregnancy. The study involved women with scleroderma, an autoimmune disorder that affects the skin. These women have more fetal cells in their blood even decades after a pregnancy than women who don't have scleroderma. While further research is needed to confirm these findings, the study does offer an explanation for the much higher incidence of autoimmune disorders in women than in men.

Symptoms can be worsened by a number of factors, such as:

What are the signs and symptoms of the disease?

Myasthenia gravis causes muscle weakness that is worsened by use and improved with rest. For this reason, a person may have few or no symptoms right after awakening or resting. As the person goes about his or her daily activities, the symptoms may become obvious.

Eye muscle involvement may cause drooping eyelids and double vision. The person may have a masklike expression if the facial nerves are affected. Head control, chewing, swallowing, and speech may also be affected by muscle weakness.

Approximately 15% to 20% of people who have myasthenia gravis have muscle weakness in the arms and hands. Weakness in the leg muscles is less common. Increasing weakness of the muscles in the chest may lead to difficulty breathing. Respiratory distress, which is an emergency, can occur.

How is the disease diagnosed?

Diagnosis of myasthenia gravis begins with a medical history and physical exam. The healthcare provider may ask the person to perform repetitive movements of a muscle. The provider looks for signs of muscle weakness with use. A blood test known as antibody titer can often detect the antibodies that attack the muscles

A Tensilon test can be done to diagnose myasthenia gravis. A medicine called Tensilon is given to the person intravenously, or into a vein. If the person has myasthenia gravis, the Tensilon will temporarily strengthen the person's muscles.

Electromyography, or EMG, can be done to measure the way the muscles respond to electrical stimulation. When myasthenia is present, the muscles have an abnormal response to the stimulation.

What can be done to prevent the disease?

There are no known ways to prevent myasthenia gravis.

What are the long-term effects of the disease?

The symptoms of myasthenia gravis often worsen over the first 5 to 7 years of the disease. After this time, the disease is usually not progressive. Symptoms may worsen and improve as muscles are used and then rested throughout the day.

In some cases, myasthenia gravis may get better or worse over time. About 20% of the people with myasthenia gravis have a natural remission, or improvement, of the disease that lasts a year or more. With good treatment, people with myasthenia gravis have a normal life expectancy.

What are the risks to others?

Myasthenia gravis is not contagious and poses no risk to others.

What are the treatments for the disease?

There is no cure for myasthenia gravis. Lifestyle changes may improve the symptoms. The following measures may be helpful:

Treatment of myasthenia gravis often involves medicines, such as the following:

Surgery to remove the thymus gland gets rid of the risk of tumors and often improves symptoms. Fifteen percent of the people with myasthenia gravis have a tumor of the thymus gland. This surgery may be recommended in a person who is otherwise healthy.

Plasmapheresis is sometimes used. This technique allows removal of some of the person's plasma and plasma components. The remaining cells are reinfused. This produces a temporary reduction in circulating antibodies. This process can cause remarkable improvement in some people, but does not cure the disease.

What are the side effects of the treatments?

Many of the medicines used to treat myasthenia gravis can cause allergic reactions, stomach upset, diarrhea, and nervousness. Medicines used to suppress the immune system can increase the person's risk of infections. Surgery has a risk of bleeding, infection, and allergic reaction to anesthesia.

What happens after treatment for the disease?

If the person improves, he or she can resume normal daily activities. If the muscles involved in breathing are severely weakened, the individual may need a ventilator to help with breathing. Protection against choking or falls might be needed. Some people require intense treatment for long periods of time.

A number of medicines aggravate myasthenia gravis. People are advised to consult with their healthcare provider before taking any new medicines. The person's dentist should be told that the person has myasthenia gravis, and that local anesthetic medicine such as novacaine might cause problems.

How is the disease monitored?

Any new or worsening symptoms should be reported to the healthcare provider.

Author:Adam Brochert, MD
Date Written:
Editor:Ballenberg, Sally, BS
Edit Date:09/30/01
Reviewer:Eileen McLaughlin, RN, BSN
Date Reviewed:09/11/01

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