Myasthenia gravis

What is it?

The name myasthenia gravis (MG) comes from Latin and Greek and means 'grave muscle weakness'.

For our muscles to work, electrical signals are sent from the brain to the nerve ending. When these signals reach the nerve ends they trigger the release of a neurotransmitter chemical called acetylcholine, which acts on receptor cells on the muscle causing it to contract.

A different chemical then breaks down the acetylcholine so the muscle relaxes again.

MG is one of the autoimmune diseases where, for an unknown reason, the body attacks itself. In MG the body makes antibodies that destroy some of our muscle receptors. When this happens the muscle contractions are weak.

What are the symptoms?

Affected muscles suffer varying degrees of weakness. Only the muscles under conscious (or voluntary) control are affected, whereas those of the heart and intestine aren't.

The muscles controlling the eyelids are usually affected first, causing them to droop and creating the appearance of looking tired. The muscles controlling eye movements are also commonly involved, causing double vision.

Next the facial muscles may become weak, so any facial expression appears as a grimace. If the jaw and muscles of the gullet are affected then eating and swallowing become difficult. In severe cases, people find themselves unable to speak, lift their arms or walk, and they have difficulty breathing.

Most people find rest and a good night's sleep relieves their symptoms initially. Symptoms may become worse as the day progresses. Any stress worsens the muscle weakness, and women often find their symptoms are more severe during their periods.

Although it's usually a progressive disease this isn't always the case. Some people find their symptoms disappear spontaneously and don't return for many years. Just how weak the muscles are when symptoms do persist also varies from person to person.

Who's affected?

The condition tends to affect men later in life, usually after the age of 60, and under the age of 40. In the UK, it's estimated one in 10,000 people has MG.

How's it diagnosed?

Most people will be seen by a neurologist to confirm the diagnosis. If an injection of a drug that increases the levels of chemical neurotransmitters causes a temporary improvement in symptoms this confirms the diagnosis.

Patients may also have electrical muscle function tests, blood tests to look for the damaging antibodies and CT scans of the chest to look for an abnormality of the thymus gland. This is part of the body's immune system and can be responsible for production of the harmful antibodies that cause MG.

What's the treatment?

For some people, surgical removal of the thymus gland may cure, or at least lessen, the problem. Other people are treated with drugs to stop the breakdown of the chemical neurotransmitter, increasing its level in the body.

In certain situations steroids or other immunosuppressant drugs are used to damp down the immune response.

When symptoms are very severe a process called plasmaphoresis is performed. This involves routing the person's blood supply through a machine to remove the harmful antibody-containing plasma and replace it with antibody-free plasma.

Extremes of temperature, stress, infection and overtiredness can all make symptoms worse and should be avoided.

With current treatments, people with MG are expected to live a relatively normal life and to have a normal life expectancy.

Advice and support

• Myasthenia Gravis Association
• Helpline: 0800 919922
• Email: mg@mg-charity.org
• Website: www.mgauk.org