Myasthenia gravis

Published by Bupa's Health Information Team, June 2010.

This factsheet is for people with myasthenia gravis, or who would like information about it.

Myasthenia gravis is a condition that makes muscles tire easily.

Although there is no cure for myasthenia gravis, for most people there are treatments that can effectively manage the symptoms.

About myasthenia gravis

The name myasthenia gravis comes from Latin and Greek words meaning serious muscle weakness. Myasthenia gravis affects around 15 out of 100,000 people in the UK. Although it can develop at any age, in the UK it's rare before the age of 10. The older you are, the more likely it is to develop.

At younger ages myasthenia gravis is more common in women; between the ages of 15 and 40, three-quarters of people who develop myasthenia gravis are female. However six out of 10 people who develop the condition later in life (between the ages of 50 and 75) are male.

Myasthenia gravis can be life-threatening, but with treatment nine out of 10 people who have myasthenia gravis can live fully active lives.

Symptoms of myasthenia gravis

The main symptom of myasthenia gravis is painless muscle weakness. It is brought on, or made worse, by physical exertion or activity. Your symptoms may be worse towards the end of the day, and can be aggravated by:

• stress
  
• illness (such as an infection)
  
• hot weather
  
• menstruation

The symptoms of myasthenia gravis vary between individuals because different muscles can be affected to different degrees.

For about half of people who have myasthenia gravis, it starts by affecting the muscles that control the eye and eyelid. When these muscles are affected, your eyelids droop (ptosis), causing a tired or sleepy appearance; it can also cause double vision (diplopia).

In some people, myasthenia gravis only affects the eye muscles. This is called ocular myasthenia. More than half of people who have ocular myasthenia will go on to develop generalised myasthenia gravis in the future.

If you have generalised myasthenia gravis other muscles can be affected.

• Muscles in the face are often involved, making facial expressions difficult. Smiling can cause a snarling expression.
  
• Chewing and swallowing can be made difficult by muscle weaknesses. This can increase the risk of choking.
  
• Speech may be affected.
  
• The muscles in your neck may be affected, making your head more likely to droop.
  
• Limb muscles can be weakened, making raising your arms or walking harder.
  
• If myasthenia gravis is severe it can affect your breathing muscles.

Myasthenia gravis doesn't cause tiredness without muscle weakness.

Complications of myasthenia gravis

Myasthenia gravis is characterised by a fluctuating pattern of symptoms; you may have spells of weakness and periods of good health (remissions). A myasthenic crisis is when the symptoms of the illness become severe enough to threaten life - usually by preventing breathing or swallowing. If you have a myasthenic crisis, you will need to be admitted to hospital, and may need to have a tube placed down your throat to help you breathe.

Causes of myasthenia gravis

Myasthenia gravis is an autoimmune disease. This means that it's caused by antibodies from your immune system attacking your body. Antibodies usually attack harmful bacteria or viruses. However, in myasthenia gravis the body attacks its own proteins in areas called neuromuscular junctions - the point where nerve cells, which carry signals from the brain, meet muscle cells.

In neuromuscular junctions, a molecule called acetylcholine transmits signals from your nerves to the muscles. It does this by binding to acetylcholine receptor proteins, causing them to contract. In people with myasthenia gravis, the body produces antibodies that reduce the number of available acetylcholine receptors. This means that the acetylcholine can't transmit the signal to tell your muscle to contract.

Nobody knows exactly why myasthenia gravis develops. However, some people with myasthenia gravis have an enlarged thymus gland or a tumour in the thymus gland called a thymoma, and this is thought to be involved. The thymus gland is in the chest and most thymomas are benign. The thymus gland is an important part of the immune system; one of its functions is creating white blood cells, but people can remain healthy without one.

Congenital myasthenic syndromes (CMS) are a rare group of illnesses that cause similar symptoms of muscle weakness, but are inherited. These are most likely to develop in babies or children but can occasionally occur for the first time in young adults.

Diagnosis of myasthenia gravis

If you think you have the symptoms of myasthenia gravis, go and talk to your GP. If he or she thinks you might have myasthenia gravis, you may be referred to a neurologist (a doctor who specialises in the nervous system). There are a number of tests that you might have.

• Blood tests. These may include tests to look for antibodies against acetylcholine receptors. In most people with the illness, this is sufficient to diagnose the disease. However, some people with the illness don't have these exact antibodies so other tests may be needed. These antibodies are only found in about half of people with purely ocular myasthenia.
  
• Electromyography. A very thin needle is inserted into a muscle to measure its electrical activity. This is a very sensitive test that can identify most people with myasthenia gravis.
  
• Edrophonium test. A drug called edrophonium is injected into your arm. If you have myasthenia gravis this swiftly causes a short-lasting (about 10 - 20 seconds) improvement in symptoms.
  
• CT scan. This test uses X-rays to make a three-dimensional image of part of the body. It may be carried out to examine the thymus gland if a thymoma is suspected.
  
• MRI scan. This test uses magnets and radiowaves to produce images of the inside of your body. It may also be used to examine the thymus gland in your chest.

Treatment of myasthenia gravis

Although there is no cure for myasthenia gravis, there are a number of effective treatments for the condition. With treatment, most people who have the condition can return to living a fully active life.

Some of the treatment options are listed below.

Medicines

Anticholinesterase medication (such as neostigmine and pyridostigmine) prevent acetylcholine from being broken down, so it builds up in the neuromuscular junction. These medicines temporarily improve muscle strength. There is very little research to prove that they improve eye symptoms, or that they prevent ocular myasthenia developing into generalised myasthenia gravis.

These medicines can have side-effects such as nausea, diarrhoea and increased saliva production. Sometimes other medication is used to help reduce the side-effects.

Immunosupressants suppress the immune system to decrease the number of antibodies attacking the neuromuscular junction. This reduces the symptoms of the disease.

Most commonly, you will be prescribed a steroid such as prednisolone. This may be combined with another type of immunosuppressant called azathioprine. Other immunosuppressants include ciclosporin and methotrexate.

When you're taking immunosuppressants, your doctor will need to monitor you to work out the best dose. It may take months for the drugs to have an effect and for the ideal dose to be reached.

Surgery

Many patients with myasthenia gravis experience some improvement in their symptoms after surgical removal of the thymus gland (thymectomy). Not everyone with myasthenia gravis needs to have a thymectomy, and sometimes the surgery is reserved for young patients or those with a thymus tumour.

Non-surgical treatments

If you have a myasthenic crisis that is affecting your ability to breathe or swallow, your doctor may recommend plasmapheresis or plasma exchange. This means going into hospital to have your blood plasma (the clear fluid in your blood) separated from your blood. This reduces the amount of antibodies circulating in your body. Many studies have found that plasmapheresis gives short-term benefit.

Infusing intravenous immunoglobulin or IVIg (antibodies purified from human blood donations) into the bloodstream is sometimes used to help people with worsening myasthenia gravis. This treatment is now used in preference to plasmapheresis because it's easier to administer.

For answers to frequently asked questions on this topic, see Common questions.

For sources and links to further information, see Resources.