What is myasthenia gravis?
Myasthenia gravis (MG) is a neuromuscular disorder that causes muscle weakness. It affects muscles that a person can usually control consciously like those controlling the eyelids, eye movement, breathing swallowing as well as the facial and shoulder muscles.
The weakness tends to temporarily worsen with activity and improves with rest. MG is an autoimmune disorder. This means the body's immune system mistakenly attacks the connection between the nerve and muscle. In MG, the muscle cells have problems responding to the nerve impulses that normally signal them to contract and this result in weakness.
The disease usually does not reduce life expectancy. Most people with MG manage their symptoms and lead active lives. MG affects people of all ages and ethnic groups. Women are most often affected in their 20s and 30s. Men usually develop MG in late middle age.
What causes myasthenia gravis?
MG is caused by a problem with nerve impulses getting to muscles. Normally when impulses travel down the nerve, the nerve endings release a protein called acetylcholine. Acetylcholine is like a key that fits into the acetylcholine receptor which is like a lock. With the proper fit, the door opens and a signal is sent to the muscle to do its job. Antibodies are proteins produced by the body in response to harmful substances. In MG, the body mistakenly makes antibodies to the acetylcholine receptor.
Acetylcholine receptor antibodies fit into the receptor and cause it to be destroyed so the door does not open and no signal is received by the muscle. This leads to muscle weakness. It is thought that the thymus gland may instruct the immune system to produce the antibodies. The thymus gland is in the chest. In some people with MG, the thymus becomes enlarged. In others, tumours of the thymus may develop.
In rare cases, children develop MG symptoms due to a genetic defect. In these children, acetylcholine antibodies cannot be detected in the blood.
Women with MG who are planning pregnancies should talk to their physicians. Temporary MG occurs in about 15% of infants born to women with MG due to the transfer of antibodies across the placenta. The condition lasts for only a few weeks, but it needs to be recognised. These infants often need to be treated in an intensive care unit until the weakness is gone.
What are the symptoms?
The symptoms of MG vary from person to person. For some, only the muscles that control eye movements and the eyelids are affected. In others, the muscles that control swallowing and speech are affected. Some muscles are weaker than others. In some people, breathing can be affected. This is due to the weakness of the throat or diaphragm muscles. In a few cases, weakness can cause respiratory failure that requires emergency medical support. In contrast to many other diseases producing weakness, the legs are less commonly involved in MG.
How is myasthenia gravis diagnosed?
Many disorders can cause weakness. The diagnosis of MG should be made by a neurologist. The evaluation may include:
- Medical and neurological evaluation
- Blood tests to check for antibodies
- Blood tests or other studies to rule out other causes of weakness
- Imaging scans
- Electrical tests of nerve and muscle function (electromyography and nerve conduction studies)
- Ice pack test to improve the strength of the eyelid
What are the treatment options?
MG does not have a cure yet but effective treatments are available. It can take time to find the right combination of treatments for each person. In up to 20% of the people, symptoms may improve or disappear for up to a year or more. Occasionally, the disease may disappear permanently, although this is rare. No one knows why these remissions occur.
Medication: include drugs to suppress the immune system and decrease the autoantibodies or drugs that slow the breakdown of acetylcholine and prolong its action at the nerve-muscle connection
Surgery: The thymus gland may be removed if it is suspected to be the cause. It is still not clear whether removal of a thymus that appears normal on imaging is a useful treatment.
Plasma exchange: In plasma exchange, abnormal antibodies are removed from the blood. Then red blood cells are returned in artificial plasma. Antibody removal in this way produces temporary improvement in most patients but also requires some form of immune suppression so that the antibodies do not rebound.
Intravenous immunoglobulin (IVIG): may temporarily modify the immune system and provide the body with normal antibodies from donated blood
Living with myasthenia gravis
With treatment, the outlook for most people with MG is bright. You can have a full, productive life.
Learning to manage the symptoms of MG can make it easier.
- Schedule regular rest periods during the day.
- Delegate tasks to other family members.
- Learn to manage and reduce your stress.
- If your swallowing is affected, plan meals at times when your muscle strength is greater.
- Fasting and skipping meals should be avoided. When hungry, eat solids as food is the pillar of your health.
Partnering with your neurologist
To provide the best care, your neurologist needs to know all about your symptoms and medical history. Likewise, you need to get answers to your questions. Keeping a notebook about your condition and bringing a few well-organised questions to your appointments can be helpful.