Myasthenia Gravis
Myasthenia Gravis Overview
What is Myasthenia Gravis (MG)?
Myasthenia gravis is an autoimmune disease (where the immune system
attacks the body in some way). Examples of other autoimmune diseases are
rheumatoid arthritis, systemic lupus erythematosis, and Graves disease.
For reasons that are not understood, the body's immune system, which
normally fights infections or cancers, attacks the nerve-muscle
communication point.
Specifically, antibodies (proteins of the immune system) attack the
acetylcholine receptor, which is on the muscle surface, and cause the
signal from the nerve to be blocked.
What are the symptoms of MG?
The major symptom of MG is muscle weakness, which gets worse with
activity. People with MG complain of feeling tired. Often, they may feel
pretty well in the morning, but as the day goes on they become weaker.
The most common problems are double vision and drooping eyelids (ptosis).
Patients often develop:
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Leg or arm weakness
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Swallowing difficulty (dysphagia)
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Speaking difficulty (dysarthria)
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Shortness of breath
How common is MG?
Approximately 50-150 people per million of the population have
myasthenia gravis.
Who can get MG?
MG affects people of any age from 2 to 100. MG affects young women more
than men, but both older men and women are equally affected.
What kind of doctor should a person with MG see?
A person should see his/her family doctor and mention his/her concerns
about the disease. Neurologists (doctors who are experts in the area of
the nervous system) are the most qualified to diagnose and treat MG. If
the symptoms are limited to the eyes, ophthalmologists (eye doctors who
have been to medical school) may take care of myasthenics. Because MG is
not a common disease, many doctors are not familiar with the diagnosis
and treatment of MG.
Diagnosis and Treatment
What kind of tests are there for MG?
A complete history and physical examination is the first step.
Tensilon Test-- This test is given by a neurologist or
ophthalmologist in the office. An intravenous (IV) line
(intravenous-within a vein) is placed in the arm to allow the doctor to
put a chemical called Tensilon (edrophonium) into a vein and watch for
improvement in muscle strength. It is best if the physician looks for
improvement in the strength of an eyelid or muscle that moves the eye.
Immediate improvement of strength after injection of Tensilon tends to
support a diagnosis of MG. The effects of Tensilon last only a few
minutes.
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A patient may "feel" better with administration of the Tensilon, but
this may be a placebo effect, and should not be considered a "positive
test." The placebo effect is a powerful demonstration of the mind-body
connection. Sometimes we feel better just by believing we are getting
a drug that will have the desired effect. The psychological impact of
getting a drug or treatment with the expectation that it will help us
is sometimes enough to improve our physical well-being. Research
studies often use "sugar pills" to control for this effect.
Blood test for Acetylcholine Receptor Antibodies-- Not every
patient with MG has antibodies that can be detected in the blood, and
the level of antibodies are not correlated, or tied to, how bad your
disease is. For example, a high level of antibodies does not necessarily
mean a severe case of MG. On the other hand, a person with a low level
of antibodies could have a severe case of MG.
An electromyogram (EMG) tests the function of nerves and muscles--
The EMG can provide a great deal of information about how the nervous
system works. The examiner first stimulates a nerve with a small
electric shock. A needle is then inserted into several muscles to find
out how they are working. To test for MG, repeated electrical
stimulation of a nerve is done, and the response of the muscle is
measured. Not all patients with MG will show abnormalities or
decreased response on an EMG.
Single-fiber EMG is a specialized type of EMG-- A fine needle
is placed in a muscle and electrical activity is measured. This test
will be abnormal in most patients with MG.
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Other diseases also produce these abnormalities.
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Neurologists need specialized training to perform single-fiber
examinations.
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Usually only specialized centers offer this test.
For more information, see
What are
the Tests for Myasthenia Gravis?
What is the thymus and what is a thymectomy?
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The thymus gland is located behind the breast bone, in front of the
heart, and helps the immune system develop. Thymectomy is removal of
the thymus and is usually performed by cutting through the breast
bone, similar to heart surgery.
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The thymus is frequently removed as a treatment for MG, usually for
individuals in good health under the age of 55. Studies vary as to how
effective thymectomy (removal of the thymus) is, but most experts
agree that thymectomy increases the chance of remission. A remission
is a period during which the symptoms of MG will either partially or
completely disappear for a time. It is not a cure, and no one can
guarantee MG symptoms will not come back.
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All patients with MG should undergo a computed tomogram (CT scan) or
magnetic resonance image (MRI) of their chests. Ten to fifteen percent
of people with MG have a tumor of the thymus gland, a thymoma, which
needs to be removed by a cardiothoracic surgeon experienced in such
surgery.
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The tumor could grow and compress blood vessels, the heart, and lungs,
and any patient with a thymoma should have it removed. Also, MG
may improve after removal of the thymoma. Although the surgery
may sound very frightening and dangerous, most patients do very well
and leave the hospital in less than a week.
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After surgery patients may still need to take Mestinon or medications
to suppress the immune system, like prednisone or azathioprine.
For more information, see
What is
the Role of the Thymus and Thymectomy in Myasthenia Gravis?
What treatments are there for double vision and a drooping eyelid?
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Double vision caused by MG occurs because of misalignment of the
visual axes of both eyes (the eyes are not straight).
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For double vision to occur, both eyes must be open. If one eye is
covered and there is still double (not just blurred) vision, then the
problem is caused by an eye problem and not MG. If this is the case,
an eye doctor should be consulted.
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Double vision caused by MG is relieved by covering one eye with a
patch. Some patients are happy to do that to avoid taking medications.
Many patients do not like the appearance and it does limit vision.
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Mestinon may help double vision (see below), but often, even with this
medication, the eyes will not work perfectly and double vision may get
worse!
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Prednisone (see below) will help, but the medication does have many
side effects.
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The drooping eyelid can be relieved by taping the eyelid open (ptosis
tape) or a ptosis crutch that is inserted into the frame of your
eyeglasses. Most people do not feel these are appealing treatments,
but often are better then taking medications.
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Mestinon usually will help a drooping eyelid.
What treatments are available for MG?
There are a variety of treatments for MG. The choice of treatments is
based on:
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Severity of symptoms
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Age
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Sex
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Level of physical activity
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Other medical conditions
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Side effects of medications
Treatment decisions should be made after the patient has a more complete
understanding of the disease, the treatment options available, and the
potential side effects or complications of treatment.
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Often the first treatment tried is Mestinon, an anticholinesterase
drug that lets the acetylcholine stay at the neuromuscular junction
longer than usual, improving the manner in which the nerves and
muscles communicate. Patients often feel stronger, and their symptoms
are significantly improved. However, the drug only works for 2 to 6
hours before the effects wear off.
If a patient's symptoms are not adequately treated with Mestinon, the
next step is to try therapies that suppress the immune system. These
therapies include:
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Prednisone is a corticosteroid that helps regulate
the immune system. The majority of myasthenics become stronger within
the first weeks to months of starting prednisone. It has many
potential complications, such as:
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Increased blood sugar
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Bone loss with long term use
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Glaucoma
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High blood pressure
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Weight gain and others
These complications must be weighed against the benefits of treatment.
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Azathioprine (Imuran) can be used alone, but is often
administered in combination with prednisone. When used with
prednisone, Imuran often allows a lower total dose of prednisone to be
administered.
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Some patients develop fever and flu-like symptoms when first
starting Imuran. The drug needs to be stopped in such situations.
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Imuran decreases the white blood cell count and may affect liver
function. Therefore, when taking Imuran , the doctor needs to
check the complete blood count (CBC) and liver function tests
(LFTs). Also, the physician should make sure that the patient is
taking enough Imuran based on body weight to be effective.
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Another difficulty with Imuran is that it takes several months to
work. The side effects of Imuran are fewer than prednisone. Imuran
has been used safely for years. Some studies suggest that
azathioprine may increase the chance of developing a type of
cancer called lymphoma.
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Cyclosporine (Sandimmune, Neoril) is a medication
most frequently used for patients who have had organ transplants to
prevent rejection. Cyclosporine suppresses the immune system.
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Formal studies of cyclosporine among patients with MG have not
been extensive.
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Some patients do respond well and doses of prednisone may be
reduced significantly.
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Cyclosporine (within 12 weeks) works more rapidly than Imuran
(over months).
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Patients must be watched for high blood pressure, kidney damage
(blood creatinine levels), and liver problems.
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Plasma exchange involves putting IV lines into each
arm (or a single large catheter into a large vein, usually in the leg
or chest).
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Blood is removed and put through a machine that removes antibodies
that are causing the MG.
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The patient's own blood with additional fluid is then returned
to the body. A single exchange takes 3-4 hours and is repeated up
to 5-6 times over 2 weeks.
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Patients responded to treatment very quickly (days to a week), but
the improvement only lasts a few weeks. This treatment is only
performed for severe weakness (swallowing problems, difficulty
breathing, inability to walk or use one's arms). Patients who
have not responded to other treatments receive plasma exchange
every few weeks, although this is rare.
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Side effects include low blood pressure during the exchange and
bleeding because of removal of factors that help the blood to
clot. Infections may develop from the catheter placement.
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Mycophenolate Mofetil (Cellcept) is similar to
cyclosporine in that has been used for many years to prevent organ
transplant rejection. Mycophenolate mofetil suppresses the immune
system.
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There have been 2 studies that demonstrate that patients with
severe generalized MG may reduce prednisone doses and have
improved strength when treated with mycophenolate.
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The medication has proved to be safe with MG patients complaining
of mild gastrointestinal upset when starting the medication. Most
neurologists monitor a complete blood count to look for a decrease
in white blood cells, but the studies found no patients who had a
problem with low blood counts.
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Like cyclosporine, mycophenolate costs several hundred dollars for
a month's prescription.
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Intravenous immunoglobulin (IVIg) is given by an IV
infusion over a few hours each day for five days. IVIg is usually used
to treat severe worsening of MG.
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No large studies of IVIg have been performed, but one can estimate
that sixty to seventy percent of patients benefit from IVIg.
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Improvement usually lasts five to six weeks. Other
medications are usually used, which can maintain strength.
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Deciding when to use IVIg is based on the severity of the
patient's symptoms, other medical problems, and the experience of
the neurologist. Sometimes IVIg is used in patients who do not
respond to more standard therapies. In such situations IVIg
is administered every 2 to 3 months or even more often.
For more information, see What
Should I know About Treatment for Myasthenia Gravis?
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Last Reviewed: Dec 29, 2003
