Myasthenia Gravis (MG)
Myasthenia gravis is a chronic, progressive neuromuscular, autoimmune disease marked by varying degrees of weakness of the skeletal (voluntary) muscles of the body. The body’s immune system attacks and destroys receptors in the muscles. These receptors bind acetylcholine, the neurotransmitter released from motor neurons. (Turkington & Harris, 2009) The main calling card of myasthenia gravis is muscle weakness that increases during periods of activity and improves after periods of rest. Muscles that control eye and eyelid movements, facial expression, chewing, talking, and swallowing are often, but not always, involved. The muscles that control breathing and neck and limb movements may also be affected. (Beers, 2003) Causes
Myasthenia gravis is thought to be caused by the immune system which produces antibodies that attack one type of receptor in the transmission of nerve impulses, especially on the muscle side of the neuromuscular junction. (Beers, 2003) This impairment is what causes the body to attack its own acetylcholine receptors, which in turn causes an autoimmune reaction. (Beers, 2003) 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. (Howard Jr. M.D., 2006) Why the body attacks it own acetylcholine receptors is unknown. One theory is that the thymus gland may be involved. The thymus gland contains muscle cells with acetylcholine receptors. In the thymus gland, certain cells of the immune system learn to distinguish between the body and foreign substances. The theory is that the thymus tells the immune system to attack acetylcholine receptors. (Beers, 2003) Prevalence
Myasthenia gravis is not directly inherited nor is it contagious and it occurs in all races. (Howard Jr. M.D., 2006) The disorder occurs most frequently in 20- to 30 year old women. After the age of 40 the...
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