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Muscles
Feel Weak?
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Myasthenia
gravis is an unusual disorder affecting muscle function.
Normally, when a person decides to move, an impulse is sent down
a nerve to the muscle. When the impulse reaches the end of the nerve,
the nerve releases a substance called acetylcholine. Acetylcholine
then normally binds to the muscle and causes the muscle to contract,
which creates movement.
In
myasthenia gravis, the body produces antibodies which attack
the acetylcholine receptors found on muscles. The purpose of
these muscle receptors is to bind the acetylcholine that is released
from the nerves, which lets the muscle know when to contract. When
the antibodies bind to these muscle receptors, the receptors are
then blocked or destroyed, making them unable to bind acetylcholine
(See Figure).
This
causes muscle weakness, because the signals sent by the nerve cannot
get to the muscle. So, while the nerves and muscles both technically
are okay in myasthenia gravis, they are blocked from interacting
because of the antibodies that are produced.
Because
the antibodies produced in myasthenia gravis attack the persons
own body, myasthenia gravis is known as an autoimmune disease.
There are many other autoimmune diseases, such as lupus, rheumatoid
arthritis and scleroderma. It is not known why a persons body would
produce antibodies that attack their own body, but unfortunately,
taken as a group, autoimmune diseases are fairly common.
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Myasthenia
gravis tends to affect younger women, however older persons and
males can also be affected. The primary symptom is muscle weakness
and fatigue. Classically, the weakness gets worse as the day progresses.
The
eye muscles are almost always affected, which can lead to a drooping
of the eyelids and double vision because the eyes fail to move in
a coordinated fashion. The more a muscle is used, the weaker it
becomes. If the muscle becomes very weak, a period of rest will
often improve its strength.
When
suspected, a simple test can be done to make the diagnosis of myasthenia
gravis. A short acting medication called an anticholinesterase can
be given. This medicine works by increasing the amount of acetylcholine
around muscles.
|
lupus
|
| any
of several diseases (as lupus vulgaris or systemic lupus
erythematosus) characterized by skin lesions |
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rheumatoid
arthritis
|
| a
usually chronic disease that is considered an autoimmune
disease and is characterized especially by pain, stiffness,
inflammation, swelling, and sometimes destruction of joints |
|
scleroderma
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| a
usually slowly progressive disease marked by the deposition
of fibrous connective tissue in the skin and often in
internal organs |
|
If
a person has myasthenia, this medication will make their weak muscles
stronger. If they dont have myasthenia gravis, their muscles will
not get stronger with the medication. A blood test that detects
the muscle receptor antibodies is often used to confirm the diagnosis.
Once
the diagnosis is confirmed, treatment may be started. The course
of myasthenia gravis is unpredictable and its severity varies widely.
Some people have a very mild disease, which resolves on its own
spontaneously. Others have such severe disease that their respiratory
muscles become paralyzed and they can die without the assistance
of a breathing machine. Because of the unpredictable course of the
disease, treatment may be held initially if symptoms are mild. When
symptoms are interfering with daily life, however, treatment is
started.
Long
acting forms of anticholinesterase medicine are the treatment of
choice. The most commonly prescribed drug in this class is Mestinon
(pyridostigmine bromide). This medication must often
be given four times a day, and if the severity of the disease changes,
the dose will need to be adjusted. Close follow up with a doctor
is usually required.
Another
aspect of treatment is surgery. Removal of the thymus gland often
can produce a permanent relief of symptoms. The thymus gland is
in the chest just above the heart and behind the upper portion of
the breastbone (known as the sternum).
The
thymus has an important role in the development of immune cells
in the body, so it is not surprising that removal of this gland
can improve symptoms in a disease caused by an overactive immune
system. Unfortunately, this treatment is generally not very effective
in other autoimmune diseases.
In
patients who have particularly severe disease or who fail to respond
to having their thymus gland removed, steroid medications, such
as Prednisone
(corticosteroids),
may be needed, usually in high doses. In an acute crisis, hospitalization
may be required to stabilize the patient. Sometimes special procedures,
such as plasmapheresis, that either add or remove antibodies from
the blood may be needed.
Most
patients with myasthenia gravis can be effectively treated with
medications and surgery. This unique disease which affects muscles
is fortunately uncommon. Usually, when our muscles are weak, it
is simply because we need a break!
Copyright
© 1999 PersonalMD.com. All rights reserved.
Copyright
© 1999 PersonalMD.com. All rights reserved.
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