What is myasthenia gravis?
Myasthenia gravis is a rare long-term condition that causes certain muscles to become weak.
It mainly affects muscles that are controlled voluntarily – often those controlling eye and eyelid movement, facial expression, chewing, swallowing and talking.
Sometimes, the muscles that control breathing, neck and limb movements are also affected.
The muscle weakness associated with myasthenia gravis is usually worse during physical activity and improves with rest.
Read more about the symptoms of myasthenia gravis.
What causes myasthenia gravis?
Myasthenia gravis is an autoimmune condition that affects the nerves and muscles. Autoimmune conditions are caused by the body's immune system mistakenly attacking healthy tissue.
In myasthenia gravis, the immune system produces antibodies (proteins) that block or damage muscle receptor cells.
This prevents messages being passed from the nerve endings to the muscles, which results in the muscles not contracting (tightening) and becoming weak.
It is not fully understood why some people's immune systems produce antibodies that attack the muscle receptor cells.
Read more about the causes of myasthenia gravis.
Diagnosing myasthenia gravis
The process of diagnosing myasthenia gravis can take a long time because muscle weakness is a symptom of many different conditions.
Your doctor will look at your medical history and symptoms. They may suspect myasthenia gravis if your eye movements are impaired or if you have muscle weakness but you are still able to feel things.
You may be referred to a neurologist (specialist in nervous system disorders), who will carry out some tests to help confirm the diagnosis.
Read more about how myasthenia gravis is diagnosed.
Treating myasthenia gravis
There is no cure for myasthenia gravis, but treatments are available to help control the symptoms and improve muscle weakness.
Medication can be used to improve communication between the nerves and muscles and increase muscle strength.
Immunosuppressants are a type of medication used to improve muscle strength by controlling the production of abnormal antibodies.
In some cases of myasthenia gravis, surgery may be recommended to remove the thymus gland (a thymectomy). The thymus gland is found underneath the breastbone and is part of the immune system. It is often abnormal in people with myasthenia gravis.
Read more about how myasthenia gravis is treated.
In most cases, treatment for myasthenia gravis significantly improves muscle weakness and a person with the condition is able to lead a relatively normal life.
Some people may experience a temporary or permanent period of remission (where there are no longer symptoms) and treatment can be stopped.
Permanent remissions occur in about a third of all people who have a thymectomy (surgery to remove the thymus gland).
Myasthenia gravis symptoms
Muscle weakness is the main symptom of myasthenia gravis. The eye and facial muscles and those that control swallowing are commonly affected.
The symptoms of myasthenia gravis can come on suddenly, but it may take some time before the condition is correctly diagnosed.
Weakness of the eye muscles is often the first symptom to develop, although in some cases slurred speech or swallowing problems can occur first. The severity of muscle weakness varies from one person to another.
The muscle weakness of myasthenia gravis is not usually painful in itself, but people with the condition often experience aching muscles, particularly during periods of physical activity.
Eyes, eyelids and face
Most people with the condition have problems with their eye muscles at some point. In some cases, the eye muscles remain the only muscles affected. This is known as ocular myasthenia.
Where the facial muscles are involved, a person's facial expression may be affected. For example, in some cases, a person may appear to have a "snarling" smile because of lower facial weakness.
Swallowing and breathing
If the muscles around your mouth are affected, you may have difficulty swallowing (dysphagia), chewing and talking. This can lead to impaired speech and a nasal-sounding voice.
Some people with myasthenia gravis also have breathing difficulties, particularly when exercising or lying flat.
A person with moderate to severe swallowing or breathing problems will need to be admitted to hospital to receive urgent medical care (breathing assistance). This is known as a myasthenic crisis.
Limbs and movement
Myasthenia gravis can sometimes affect the muscles of the arms, legs and neck. This can cause mobility problems, such as a waddling gait, head drop and difficulty performing physical tasks such as lifting.
Physical activity often leads to tiredness because the muscles are weak.
Myasthenia gravis causes
Myasthenia gravis is caused by a problem with the transmission of nerve signals to the muscles.
It is an autoimmune condition, which means the body's immune system attacks its own tissues.
Nerve signals travel down the nerves and stimulate the nerve endings to release a chemical substance called acetylcholine.
When acetylcholine comes into contact with the muscle receptors, the receptors are activated and cause the muscles to contract (tighten).
However, in myasthenia gravis the immune system produces antibodies (proteins) that block or damage the muscle acetylcholine receptors, which prevents the muscles contracting.
The disruption between your nerves and muscles means that your muscles become weak and easily tired.
The thymus gland
It is not fully understood why some people's immune systems produce antibodies that act against the muscle receptors.
However, it is thought that the thymus gland, which is part of the immune system, may be linked to the production of the antibodies.
During infancy, the thymus gland is large and gradually increases in size before getting smaller during adulthood.
However, adults with myasthenia gravis may have a large, abnormal thymus gland, and in around 10% of people tumours (thymomas) develop on the thymus gland. These are usually benign (non-cancerous).
In some cases, surgically removing the thymus gland using a procedure known as a thymectomy may be recommended.
Myasthenia gravis diagnosis
Confirming a diagnosis of myasthenia gravis can take a long time because the condition is rare and muscle weakness can be a symptom of many conditions.
Your doctor will look at your medical history and your symptoms. They may suspect myasthenia gravis if your eye movements are impaired or you have muscle weakness but are still able to feel things.
However, as these symptoms are common in a number of different conditions, you will need to have some tests before a diagnosis of myasthenia gravis can be confirmed.
If your doctor thinks you may have myasthenia gravis, they will refer you to a neurologist (specialist in nervous system disorders). They will carry out some tests that will confirm whether or not you have the condition.
There are a number of tests that can be used to help diagnose myasthenia gravis.
A special type of blood test can be used to detect the antibodies (proteins) that block or damage the muscle receptors. Most people with myasthenia gravis have an abnormally high number of these antibodies.
The antibody blood tests are quite specific, which means that these antibodies are almost never detected in patients who do not have myasthenia gravis.
However, in people whose symptoms are limited to the eyes, (ocular myasthenia), high levels of antibodies are not always present.
An edrophonium test involves having an injection of a type of medication called edrophonium chloride. Edrophonium chloride prevents the substance acetylcholine from being broken down, which temporarily increases the amount of acetylcholine around the muscle.
In people with myasthenia gravis, the increased amount of acetylcholine produces a sudden but temporary improvement in muscle power. However, this will not usually occur in people with other causes of muscle weakness.
There are significant side effects associated with the edrophonium test, such as heart rate and breathing problems, that may occur during the investigation.
Therefore, the test should only be carried out if myasthenia gravis is still suspected despite negative blood and electrical tests. The test should only be carried out by experienced neurology doctors in specialist centres.
Nerve conduction tests
Electromyography is a procedure that can be used to identify communication problems between the nerves and muscles. It involves inserting a needle electrode through the skin into the muscle.
This produces an electrical recording of the muscle activity. If you have myasthenia gravis, your muscles will not respond very well to the electrical stimulation.
A nerve conduction study can also be used, which uses repeated nerve stimulation to test for muscle fatigue (weakness). In myasthenia gravis, the transmission of signals between the nerve and muscle will be poor.
Single-fibre EMG is the most sensitive electrical test for detecting disruption of the signal between the nerve ending and the muscle membrane (as in myasthenia gravis). It usually involves taking a recording from a very small needle in one of the muscles around the eye, forehead, or sometimes in the forearm.
Myasthenia gravis treatment
There is no cure for myasthenia gravis, but treatments are available to help control the symptoms.
In many cases, treatment for myasthenia gravis can significantly improve muscle weakness and a person with the condition is able to lead a relatively normal life.
If your symptoms are mild, you may find that getting plenty of rest helps improve your symptoms without the need for additional treatment.
Medications such as [pyridostigmine], and less commonly [neostigmine], can be prescribed for myasthenia gravis. They prevent the breakdown of acetylcholine, an important chemical that helps the muscles contract (tighten).
These medicines tend to work best in cases of mild myasthenia gravis. They can improve muscle contractions and strength in the affected muscles. They are often used as the first line of treatment for myasthenia gravis if the initial symptoms are not too severe.
However, they can sometimes cause side effects, such as stomach cramps, muscle twitching, diarrhoea and nausea. Your doctor will be able to prescribe additional medication for you if you experience these.
Steroid tablets, such as prednisolone, are used if the symptoms of myasthenia gravis worsen despite using pyridostigmine. Initially, these steroid tablets are usually given in hospital and the dose is quickly increased to a high level.
At the same time, doctors often prescribe additional medication that suppresses the immune system, such as [azathioprine], methotrexate or mycophenolate.
It is hoped that these tablets will act alongside the steroids to reduce the level of harmful antibodies. Doctors may allow the steroid dose to be reduced over time, but probably not within the first four to six months.
Regular blood monitoring is required for all people taking these immunosuppressants. All of these medications have associated side effects that your doctors will discuss with you.
Some people respond well and are able to stop using all steroids in remission, while continuing to take secondary immunosuppressant medication. In time (usually years), it may be possible to stop all immunosuppressant medication if you remain well.
In some cases of myasthenia gravis, surgery to remove the thymus gland (a thymectomy) may be recommended.
Thymectomy can improve the symptoms of people who do not have tumours (thymomas) on their thymus gland. It is thought that the immune system rebalances itself after the thymus gland is removed.
However, the improvement may take some time to occur. It is usually seen within the first year, although in some cases it can take up to three years.
Thymectomies are usually only recommended for people under 60 years of age, although research is ongoing to establish exactly which non-thymoma myasthenia gravis patients benefit from this type of surgery.
Plasmapheresis and immunoglobulin therapy
Plasmapheresis or intravenous immunoglobulin therapy may be needed in very severe cases of myasthenia gravis, where a person has such severe muscle weakness that it is causing life-threatening breathing or swallowing problems.
These treatments are given in hospital and involve:
- plasmapheresis, where your blood is circulated through a machine that removes the plasma containing the harmful antibodies
- intravenous immunoglobulin therapy, where you are injected with normal antibodies from donated blood that temporarily change the way your immune system operates
Both treatments can produce a rapid improvement in the symptoms of myasthenia gravis, but the benefits usually only last a few weeks. They are therefore not suitable as long-term treatments for myasthenia gravis, and are usually only used to treat people who are seriously ill.