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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 those 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 GP 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).