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Myasthenia gravis is an autoimmune disorder that causes muscle weakness and fatigue. 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 frequently, it may cease to work properly. After a period of rest, the muscle generally improves.

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 and in extreme cases, to respiratory distress, a medical emergency.

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, usually starting during the 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.

• certain medicines, such as those used to treat muscle spasms, seizures, or infection
• excessive cold or heat
• fever
• hypothyroidism or hyperthyroidism, which cause abnormal levels of thyroid hormone
• infections, such as colds, flu, or a tooth abscess
• insufficient potassium in the diet
• pregnancy
• stress

What can be done to prevent the disease?

There are no known ways to prevent myasthenia gravis.

How is the disease diagnosed?

Diagnosis of myasthenia gravis begins with a medical history and physical exam. The healthcare professional may ask the person to perform repetitive movements of a muscle, watching for signs of muscle weakness with use. In addition, a blood test known as an 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 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 appropriate 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:

• Avoid contact with people who have contagious infections.
• Dress appropriately in very cold or very hot environments.
• Eat a balanced diet high in potassium.
• Follow the healthcare professional's recommendations for flu shots and pneumonia vaccines.
• Get plenty of sleep.
• Learn to manage stress.
• Pace activities throughout the day to avoid fatigue.
• Rest the affected muscles often throughout the day.
• Seek effective treatment of underlying conditions, such as hypothyroidism.
• Use good oral hygiene and get regular dental care.

Medicines used to treat myasthenia gravis include:

• anticholinesterases, such as neostigmine (i.e., Prostigmin) and pyridostigmine (i.e., Mestinon), which help nerves send impulses to the muscles
• ephedrine sulfate, which can be given with other medicines to increase muscle strength
• immunosuppressive medicines, such as prednisone, azathioprine (i.e., Azasan, Imuran), cyclosporine, and cyclophosphamide (i.e., Cytoxan), which suppress the body's immune attack on the muscles
• intravenous human immune globulin, or IVIG, which works for a short period of time by flooding the body with antibodies from many donors

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. In this technique, some of the person's plasma and plasma components are separated from the blood cells, which are given back to the person through another tube. This produces a temporary reduction in circulating antibodies, resulting in a remarkable improvement in some people, but not in a cure for 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 can be complicated by bleeding, infection, or an allergic reaction to anesthetic.

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. Because a number of medicines aggravate myasthenia gravis, a person should take any new medication only after consultation with the professional taking care of his or her condition. The person's dentist should be told that the person has myasthenia gravis, because the local anesthetics used by dentists may have unusual effects in persons with this condition.

How is the disease monitored?

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