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:
- Leg or arm weakness
- Swallowing difficulty (dysphagia)
- Speaking difficulty (dysarthria)
- 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.
- 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.
- Other diseases also produce these abnormalities.
- Neurologists need specialized training to perform single-fiber examinations.
- 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?
- 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.
- 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.
- 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.
- 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.
- 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?
- Double vision caused by MG occurs because of misalignment of the visual axes of both eyes (the eyes are not straight).
- 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.
- 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.
- 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!
- Prednisone (see below) will help, but the medication does have many side effects.
- 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.
- 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:
- Severity of symptoms
- Level of physical activity
- Other medical conditions
- 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.
- 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:
- 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:
- Increased blood sugar
- Bone loss with long term use
- High blood pressure
- Weight gain and others
These complications must be weighed against the benefits of treatment.
- 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.
- Some patients develop fever and flu-like symptoms when first starting Imuran. The drug needs to be stopped in such situations.
- 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.
- 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.
- Cyclosporine (Sandimmune, Neoril) is a medication most frequently used for patients who have had organ transplants to prevent rejection. Cyclosporine suppresses the immune system.
- Formal studies of cyclosporine among patients with MG have not been extensive.
- Some patients do respond well and doses of prednisone may be reduced significantly.
- Cyclosporine (within 12 weeks) works more rapidly than Imuran (over months).
- Patients must be watched for high blood pressure, kidney damage (blood creatinine levels), and liver problems.
- Plasma exchange involves putting IV lines into each arm (or a single large catheter into a large vein, usually in the leg or chest).
- Blood is removed and put through a machine that removes antibodies that are causing the MG.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- Like cyclosporine, mycophenolate costs several hundred dollars for a month’s prescription.
- 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.
- No large studies of IVIg have been performed, but one can estimate that sixty to seventy percent of patients benefit from IVIg.
- Improvement usually lasts five to six weeks. Other medications are usually used, which can maintain strength.
- 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?
For more information:
Go to the Myasthenia Gravis health topic.