What Is It?
Myasthenia gravis is a chronic disease that affects the way muscles respond to signals from nerves, leading to muscle weakness. The disease can occur at any age, but it mainly affects women between ages 20 and 40. After age 50, men are more likely to get the disease.
Normal muscle movement relies on chemical signals from the nerves. Nerve signals cause the nerve endings to release a neurotransmitter chemical called acetylcholine into the small space between the nerve and the muscle. This chemical binds to special acetylcholine receptors on the muscle cells and causes the muscle to contract.
Myasthenia gravis is an autoimmune disease, which means the body’s defense mechanism — the immune system — malfunctions and begins to attack the body’s own tissues. In myasthenia gravis, the immune system attacks the acetylcholine receptors with specific antibodies. Some of the receptors are destroyed or blocked, which means that the chemical message cannot be received. Therefore, muscles do not contract properly and become weak. It has been estimated that up to 80 percent of the receptors can be damaged.
Under normal circumstances, the amount of acetylcholine available to be released to muscle cells diminishes with repeated, prolonged or strenuous activity. That normal decrease in the chemical combined with fewer working receptors causes a person with myasthenia gravis to experience increasing weakness, or myasthenic fatigue. Muscles that may seem normal at first become weak with continued use. This is why a person with myasthenia gravis will feel strongest immediately after waking up or resting and weakest at the end of the day when muscles have been in continual use. In fact, this increasing fatigue is a hallmark characteristic of the disease.
Myasthenia gravis typically strikes muscles in the face first. Muscles that control the eyelids and eye movements usually are affected early in the disease. Later, facial weakness can make smiling, chewing, swallowing and talking difficult. In most people, the disease eventually becomes more generalized and can affect the muscles of the arms and legs. Sometimes, the disease affects the muscles that control breathing. In some situations, such as during a respiratory infection, this weakness could lead to a myasthenic crisis during which the person may need help to breathe.
No one knows what causes the body to attack its own cells. The thymus, a gland located in the chest just above the heart, is involved in immunity early in life and seems to play an important part in myasthenia gravis, although its precise role is not yet understood. The thymus is abnormal in a majority of people with myasthenia gravis, and some people develop benign tumors of the thymus.
Although myasthenia gravis is not believed to be inherited or contagious, babies born to mothers who have myasthenia gravis have an increased risk of having the disease at birth. This probably is because the baby acquires the antibodies that attack the body’s cells from the mother during gestation. Usually the symptoms go away within a few weeks after birth.
The primary symptoms of myasthenia gravis are that muscles are weak and quick to fatigue. These symptoms can take many forms, and the symptoms may be more or less severe for different people. Symptoms may include some or all of the following:
- Muscles that become progressively weaker with prolonged use
- Muscle weakness that seems better in the morning or after resting and worse after activity or at the end of the day
- Drooping eyelids
- Blurred or double vision
- A change in facial expressions, such as a smile that looks more like a grimace
- Jaw muscles that tire easily, such as when chewing gum or meat
- Difficulty swallowing
- Slurred or impaired speech
- Weakness in arms, legs, fingers, hands or neck
- Shortness of breath
Sudden, severe weakness (myasthenic crisis) may develop without warning, sometimes triggered by an infection or other stress, causing breathing and swallowing problems.
Your doctor will ask detailed questions about your symptoms and perform a thorough examination, including tests of your muscle strength and reflexes, eyelid strength, and eye movements. If the results suggest myasthenia gravis, some specific tests may be done to confirm the diagnosis. These include:
- Blood test — The test will check for the presence of the specific acetylcholine receptor antibodies that cause myasthenia gravis. High levels of these antibodies will be present in up to 90 percent of people with the disease. Newer tests are more sensitive and can detect antibodies when older tests did not.
- Electrodiagnostic testing — Tiny needles are inserted into muscles and then stimulated to analyze nerve and muscle function. Repeated stimulation will rapidly weaken the muscle response in people with myasthenia gravis.
- Tensilon test, also called the edrophonium test — Edrophonium (brand name Tensilon) is a drug that temporarily increases the amount of acetylcholine in the neuromuscular junction. That means that more of the chemical signal is available to activate the muscle. In people with myasthenia gravis, this can reduce muscle weakness temporarily. This test sometimes shows normal responses even in people who have the disease, and some people with an abnormal response turn out to have a different neuromuscular problem.
In addition, magnetic resonance imaging (MRI) scans or computed-tomography (CT) scans may be performed to look for abnormalities of the thymus. Pulmonary function tests, which measure breathing strength, also may be recommended, because they can alert doctors to any potential breathing problems.
Myasthenia gravis is a chronic disease that usually progresses slowly over time. Although symptoms may fluctuate in severity over the years, the disease rarely goes away on its own. It is likely to recur even after periods when the disease has not been active.
Because the cause of myasthenia gravis is unknown, there is no way to prevent it. However, once the disease has developed, there may be ways to prevent episodes of worsening symptoms or flare-ups:
- Give yourself plenty of rest to allow recovery of proper nerve-to-muscle communication.
- Avoid strenuous, exhausting activities.
- Avoid excessive heat and cold.
- Avoid emotional stress.
- Whenever possible, avoid exposure to any kind of infection, including colds and influenza (flu). You should be vaccinated against common infections, such as influenza.
- Work with your doctor to monitor your reactions to prescription medications. Some drugs commonly prescribed for other problems, such as infections, heart disease, or hypertension, may make myasthenia gravis worse. You may need to choose alternative therapies or avoid some medications entirely.
There are many possible treatments for myasthenia gravis. You and your doctor should work together to determine the best course of treatment for you.
- Medications that improve symptoms of myasthenia gravis work by allowing more acetylcholine to accumulate in the neuromuscular junction. This increases the chances that receptors will be activated, so that the nerves and the muscles will have better communication and the muscles won’t weaken as quickly. Pyridostigmine (Mestinon) is the most commonly prescribed medication for this condition. Drugs that suppress the immune system, such as corticosteroids and azathioprine (Imuran), work for some people, probably by reducing the amount of receptor antibodies in the body.
- Surgical removal of the thymus (thymectomy) improves symptoms in some people with myasthenia gravis, although experts disagree about who should have the surgery and when it should be performed. Thymectomy is recommended routinely for people who have a tumor. It is thought that removing the thymus may somehow re-balance the immune system. Occasionally, radiation of the thymus is offered when complete removal cannot be achieved.
- Plasmapheresis is a process in which plasma is separated from the blood, cleansed of abnormal antibodies, and then replaced. Plasmapheresis can increase muscle strength for many people with myasthenia gravis, perhaps because it lowers the amount of abnormal antibodies. The technique is used mainly in severe cases that may be life threatening.
- Some people have been helped with intravenous immunoglobulin therapy, which involves infusions of certain antibodies into a vein to alter the immune system temporarily.
- Experimental therapies often are offered as part of a research study or if conventional treatments have not been effective.
When To Call A Professional
See your doctor if you experience any unexplained muscle weakness or fatigue.
If you have been diagnosed with myasthenia gravis, it is critically important to be prepared to seek help in case of a myasthenic crisis. If the muscles that control your breathing are affected, call your doctor if you develop a respiratory infection, even a small breathing difficulty. Seek immediate help if you have difficulty breathing or swallowing.
Myasthenia gravis is a chronic disease, although there may be periods of remission, when symptoms disappear. Current treatments, however, can allow most people with myasthenia gravis to live normal or near-normal lives. Other autoimmune disorders, such as systemic lupus erythematosus (SLE or lupus) or rheumatoid arthritis, may be associated with myasthenia gravis and may develop either before or after the weakness is noticed.
Diseases and Conditions Center
All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.