Myasthenia Gravis
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Myasthenia gravis is a chronic autoimmune neuromuscular disease characterized
by varying degrees of weakness of the skeletal (voluntary) muscles of the
body. The hallmark 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. Myasthenia gravis
is caused by a defect in the transmission of nerve impulses to muscles. Normally
when impulses travel down the nerve, the nerve endings release a neurotransmitter
substance called acetylcholine. In myasthenia gravis, antibodies produced
by the body's own immune system block, alter, or destroy the receptors for
acetylcholine. The first noticeable symptoms of myasthenia gravis may be
weakness of the eye muscles, difficulty in swallowing, or slurred speech.
Symptoms vary in type and severity. Myasthenia gravis is not directly inherited
nor is it contagious. The first steps in diagnosing myasthenia gravis include
a review of the individual's medical history and physical and neurological
examinations. If the doctor suspects myasthenia gravis, several diagnostic
tests are available to confirm the diagnosis, including a special blood test
that can detect the presence of immune molecules or acetylcholine receptor
antibodies.
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Myasthenia gravis can be controlled. Some medications improve neuromuscular
transmission and increase muscle strength, and some suppress the production
of abnormal antibodies. These medications must be used with careful medical
followup because they may cause major side effects. Thymectomy, the surgical
removal of the thymus gland, improves symptoms in certain patients and may
cure some individuals, possibly by re-balancing the immune system. Other
therapies include plasmapheresis, a procedure in which abnormal antibodies
are removed from the blood, and high-dose intravenous immune globulin, which
temporarily modifies the immune system and provides the body with normal
antibodies from donated blood.
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With treatment, the outlook for most patients with myasthenia is bright:
they can expect to lead normal or nearly normal lives. Some case of myasthenia
gravis may go into remission temporarily, and muscle weakness may disappear
so that medications can be discontinued. In a few cases, the severe weakness
of myasthenia gravis may cause respiratory failure, which requires immediate
emergency medical care.
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Scientists are evaluating new and improving current treatments for myasthenia
gravis. One study is testing the efficacy of intravenous immune globulin,
and another study seeks to understand the molecular basis of synaptic transmission
in the nervous system.
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Myasthenia Gravis Foundation
of America, Inc.
Muscular Dystrophy Association
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