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Causes
By Mayo Clinic staff
Your nerves communicate with your muscles by releasing chemicals, called neurotransmitters, which fit precisely into receptor sites on the muscle cells. In myasthenia gravis, your immune system produces antibodies that block or destroy many of your muscles' receptor sites for a neurotransmitter called acetylcholine. With fewer receptor sites available, your muscles receive fewer nerve signals, resulting in weakness.
It's believed that the thymus gland — a part of your immune system situated in the upper chest beneath the breastbone — may trigger or maintain the production of these antibodies. Large in infancy, the thymus is small in healthy adults. But, in some adults with myasthenia gravis, the thymus is abnormally large. Some people also have tumors of the thymus. Usually, thymus gland tumors are noncancerous.
Factors that can worsen myasthenia gravis
- Fatigue
- Illness
- Stress
- Extreme heat
- Some medications — such as beta blockers, calcium channel blockers, quinine and some antibiotics
- Myasthenia gravis fact sheet. National Institute of Neurological Disorders and Stroke. http://www.ninds.nih.gov/disorders/myasthenia_gravis/detail_myasthenia_gravis.htm. Accessed July 6, 2010.
- Howard J.F. Myasthenia gravis — A summary. Myasthenia Gravis Foundation. http://www.myasthenia.org/hp_clinicaloverview.cfm. Accessed July 9, 2010.
- Bird SJ. Clinical manifestations of myasthenia gravis. http://www.uptodate.com/home/index.html. Accessed July 7, 2010.
- Bird SJ. Diagnosis of myasthenia gravis. http://www.uptodate.com/home/index.html. Accessed July 7, 2010.
- Bird SJ. Treatment of myasthenia gravis. http://www.uptodate.com/home/index.html. Accessed July 7, 2010.
- Facts about plasmapheresis. Muscular Dystrophy Association. http://www.mdausa.org/publications/fa-plasmaph.html. Accessed July 9, 2010.
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