Myasthenia Gravis

What Is Myasthenia Gravis?
Myasthenia gravis (MG) is a neuromuscular disorder that causes muscle weakness. It affects muscles that a
person can usually control consciously. Muscles most commonly affected are those controlling the eyelids,
eye movement, and breathing and swallowing, as well as the facial and shoulder muscles. The weakness
tends to temporarily worsen with activity and improve with rest. MG is an autoimmune disorder. This means
the body’s immune system mistakenly attacks the connection between the nerve and muscle. In MG, the
muscle cells have problems responding to the nerve impulses that normally signal them to contract, and
this results in weakness.

The disease usually does not reduce life expectancy. Most people with MG manage their symptoms and
lead active lives. MG affects people of all ages and ethnic groups. Women are most often affected in
their 20s and 30s. Men usually develop MG in late middle age.

What Causes Myasthenia Gravis?
MG is caused by a problem with nerve impulses getting to muscles. Normally when impulses travel
down the nerve, the nerve endings release a protein called acetylcholine. Acetylcholine is like a key that fits
into the acetylcholine receptor, which is like a lock.

With the proper fit, the door is opened and a signal is sent to the muscle to do its job. Antibodies are
proteins produced by the body in response to harmful substances. In MG, the body mistakenly makes
antibodies to the acetylcholine receptor. Acetylcholine receptor antibodies fit into the receptor and cause it
to be destroyed so the door does not open and no signal is received by the muscle. This leads to
muscle weakness.

It is thought that the thymus gland may instruct the immune system to produce the antibodies. The
thymus gland is in the chest. In some people with MG, the thymus becomes enlarged. In others, tumors
of the thymus may develop.

In rare cases, children develop MG symptoms due to a genetic defect. In these children, acetylcholine
antibodies cannot be detected in the blood.

Women with MG who are planning pregnancies should talk to their physicians. Temporary MG
occurs in about 15 percent of infants born to women with MG due to transfer of antibodies across the
placenta. The condition lasts for only a few weeks, but it needs to be recognized. These infants often
need to be treated in an intensive care unit until the weakness is gone.

What Are the Symptoms?
The symptoms of MG vary from one person to the next. For some, only the muscles that control eye movements
and the eyelids are affected. In others, the muscles that control swallowing and speech are affected. Some muscles
are weaker than others. In some people, breathing can be affected. This is due to weakness of the throat or diaphragm muscles. In a few cases, weakness can cause respiratory failure that requires emergency medical support. In contrast to many other diseases producing weakness, the legs are less commonly involved in MG.

How Is Myasthenia Gravis Diagnosed?
Many disorders can cause weakness. The diagnosis of MG should be made by a neurologist. The evaluation may include:

What Are the Treatment Options?
MG does not yet have a cure, but effective treatments are available. It can take time to find the right combination
of treatments for each person. In up to 20 percent of people symptoms may improve or disappear for up to
a year or more. Occasionally the disease may disappear permanently, although this is rare. No one knows why
these remissions occur.

Treatments include:

• Drugs to suppress the immune system and decrease the autoantibodies
  
• Drugs that slow the breakdown of acetylcholine and prolong its action at the nerve-muscle connection.
  

Surgery: The thymus gland should be removed if the thymus is enlarged on imaging as it could indicate a
tumor. It is still not clear whether removal of a thymus that appears normal on imaging is a useful treatment.

Plasma exchange: In plasma exchange, abnormal antibodies are removed from the blood. Then red blood cells are returned in artificial plasma. Antibody removal in this way produces temporary improvement in the majority of patients but also requires some form of immune suppression so that the antibodies do not rebound.

Intravenous immunoglobulin (IVIG): Treatment involves administering purified antibodies. These
temporarily modify the immune system and provide the body with normal antibodies from donated blood.
Living with Myasthenia Gravis
With treatment, the outlook for most people with MG is bright. You can have a full, productive life.
Learning to manage the symptoms of MG can make it easier. MG support groups can be a source of help, comfort, and information. Counseling can help in coping with the emotional aspects of MG.
People with MG need to plan their activities to conserve their energy:

• Schedule regular rest periods during the day
  
• Delegate tasks to other family members
  
• Learn to manage and reduce your stress
  
• If your swallowing is affected, plan meals at times when your muscle strength is greater