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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 speaking.
Sometimes, the muscles that control breathing, neck and limb movements are also affected.
The muscle weakness associated with myasthenia gravis is usually worse during, or just after, physical activity and improves with rest. The symptoms are often described as being at their worst when a person is tired, for example, at the end of the day.
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's not fully understood why some people's immune systems produce specific antibodies that block the nerve's signal to the muscle.
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 common 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're still able to feel things. Around half of people with myasthenia gravis initially develop symptoms of double vision or eyelid droop, with more than 90% of people developing these symptoms at some point during the illness.
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
Although there's no cure for myasthenia gravis, 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 to 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's often abnormal in people with myasthenia gravis.
Read more about how myasthenia gravis is treated.
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. Removing a thymus gland tumour (thymoma) usually has little or no effect on the underlying myasthenia gravis.
Who is affected by myasthenia gravis?
Myasthenia gravis is a rare condition, affecting about 15 in every 100,000 people in the UK.
It can develop at any age, but most commonly affects women under 40 years of age and men over 60. Cases of myasthenia gravis are increasing, particularly in people over 50, but the reasons for this increase aren't fully understood.