05 April 2010

What is Myasthenia Gravis (MG)?

Myasthenia Gravis comes from the Greek and Latin words meaning "grave muscular weakness." The most common form of MG is a chronic autoimmune neuromuscular disorder that is characterized by fluctuating weakness of the voluntary muscle groups. The prevalence of MG in the United States is estimated to be about 20/100,000 population. However, MG is probably under diagnosed and the prevalence may be higher. Myasthenia Gravis occurs in all races, both genders, and at any age. MG is not thought to be directly inherited nor is it contagious. It does occasionally occur in more than one member of the same family.

The voluntary muscles of the entire body are controlled by nerve impulses that arise in the brain. These nerve impulses travel down the nerves to the place where the nerves meet the muscle fibers. Nerve fibers do not actually connect with muscle fibers. There is a space between the nerve ending and muscle fiber; this space is called the neuromuscular junction.

When the nerve impulse originating in the brain arrives at the nerve ending, it releases a chemical called acetylcholine. Acetylcholine travels across the space to the muscle fiber side of the neuromuscular junction where it attaches to many receptor sites. The muscle contracts when enough of the receptor sites have been activated by the acetylcholine. In MG, there is as much as an 80% reduction in the number of these receptor sites. The reduction in the number of receptor sites is caused by an antibody that destroys or blocks the receptor site.

Antibodies are proteins that play an important role in the immune system. They are normally directed at foreign proteins called antigens that attack the body. Such foreign proteins include bacteria and viruses. Antibodies help the body to protect itself from these foreign proteins. For reasons not well understood, the immune system of the person with MG makes antibodies against the receptor sites of the neuromuscular junction. Abnormal antibodies can be measured in the blood of many people with MG. The antibodies destroy the receptor sites more rapidly than the body can replace them. Muscle weakness occurs when acetylcholine cannot activate enough receptor sites at the neuromuscular junction.

Common symptoms can include:

  • A drooping eyelid
  • Blurred or double vision
  • Slurred speech
  • Difficulty chewing and swallowing
  • Weakness in the arms and legs
  • Chronic muscle fatigue
  • Difficulty breathing

Myasthenia Gravis: Frequently Asked Questions

What is myasthenia gravis and what are common symptoms?
I think I have MG. What do I do?
How does the doctor test for MG?
How is MG treated?
Are there medications a patient with MG should not take?
Why aren’t my medications working?
Will my MG go away?
Is it safe to switch to generic Mestinon® (pyridostigmine)?
Can people with MG receive the flu shot?
How did I get MG?
Is MG hereditary?
Is MG contagious?
General Facts
How many people have MG?
At what age do most patients get MG?
Will my children get MG?
Will I be able to have children?
Will I be able to continue working?
Can you refer me to a specialist in myasthenia gravis?
Where can I get information to show my doctor?
Where can I get more information on MG?
Where can I get the Practical Guide or Survival Guide?
Where can I get more information on research?
Do you have a newsletter?
Chapters/Support Groups
Do you have a chapter in my area?
Do you have a support group in my area?
How do I make a donation to MGFA?
Financial Assistance/Scholarships/Research Fellowships
Where can I get more information about Social Security Disability?
Can MGFA provide me with financial assistance for my medical needs?
What can you tell me about research fellowships and scholarships?


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