Myasthenia gravis

About myasthenia gravis

The name myasthenia gravis comes from Latin and Greek words that mean ‘grave muscle weakness’. Myasthenia gravis affects around 15 out of 100,000 people in the UK. It can develop at any age, but it’s most common in women in their 30s and men between 60 and 70.

Myasthenia gravis can affect any muscle that you can control voluntarily. Muscles that you can’t control voluntarily, such as your heart muscles, aren’t affected by the condition.

Most people with myasthenia gravis can live full, active lives with treatment, but occasionally it can be life-threatening.

Symptoms of myasthenia gravis

The main symptom of myasthenia gravis is painless muscle weakness. It can be brought on, or made worse, when you physically exert yourself and usually gets better when you rest. Your symptoms can be worse towards the end of the day and be aggravated by:

  • stress
  • illness (such as an infection)
  • hot weather
  • menstruation (monthly period)
  • having an operation

The symptoms of myasthenia gravis vary between individuals because different muscles can be affected to different degrees. For about half of people, it starts by affecting the muscles that control their eye and eyelid – almost all people are affected at some stage by this. If these muscles are affected, your eyelids droop (ptosis), which can give you a tired or sleepy appearance; it can also cause double vision (diplopia).

Myasthenia gravis may only affect your eye muscles and this is called ocular myasthenia. However, the majority of people go on to develop generalised myasthenia gravis in the future, which affects other muscles and can cause symptoms that include the following.

  • Muscles in your face can be affected, which can cause difficulty with facial expressions, such as smiling.
  • You might find it hard to chew and swallow because of weak muscles around your mouth. This can increase the risk of you choking. Your speech may be affected and you might slur your words.
  • If the muscles in your neck are affected, it can make your head droop.
  • If the muscles in your arms are affected, it can be hard to raise your arms.
  • If the muscles in your legs are affected, it can be difficult to walk.
  • If myasthenia gravis is severe, it can affect your breathing muscles.

These symptoms either stay the same over time or start to improve. If they aren’t treated then they can get slowly worse.

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).

It’s possible that your symptoms can become severe enough to threaten your life – usually by preventing you from breathing or swallowing. This is called a myasthenic crisis and you will need to be admitted to hospital. You 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 antibodies attack areas called neuromuscular junctions – the point where nerve cells meet muscle cells and cause them to contract.

In neuromuscular junctions, a molecule called acetylcholine transmits signals from your nerves to your muscles. It does this by binding to acetylcholine receptor proteins, causing the muscles to contract. In people with myasthenia gravis, the body produces antibodies that destroy acetylcholine receptors. This means that the acetylcholine can't transmit the signal properly to tell your muscle to contract. Your muscles then don’t contract well, and become easily tired and weak.

The exact reasons why you may develop myasthenia gravis aren't fully understood at present. However, some people with myasthenia gravis have an enlarged thymus gland or a tumour in the thymus gland called a thymoma, which is usually benign (non-cancerous), and this is thought to be involved. The thymus gland is in your chest and is an important part of your immune system when you’re a child. As you get older it gets smaller and is eventually replaced by fat.

Myasthenia gravis isn’t inherited. Congenital myasthenic syndromes are a rare group of illnesses that cause similar symptoms of muscle weakness and are inherited. These are most likely to develop in babies or children.

Diagnosis of myasthenia gravis

Your GP will ask about your symptoms and examine you. He or she may also ask you about your medical history.

Your GP may refer you to see a neurologist (a doctor who specialises in conditions that affect the nervous system). You may need to have one or more of the following tests.

  • Blood tests can look for antibodies against acetylcholine receptors. In most people with the illness, this is sufficient to diagnose the disease. However, some people with myasthenia gravis don't have these exact antibodies so you may need other tests.
  • In electromyography, your doctor will insert a very thin needle into a muscle to measure its electrical activity.
  • In an edrophonium test, your doctor will inject a medicine called edrophonium into your arm. If you have myasthenia gravis, this will swiftly cause a short-lasting improvement in your symptoms (usually about five minutes).
  • A CT scan uses X-rays to make a three-dimensional image of your body and can be used to examine your thymus gland.
  • An MRI scan uses magnets and radiowaves to produce images of the inside of your body. It can 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 treatments that should effectively manage your symptoms. With treatment, most people who have the condition can return to living a full, active life. Some of the treatment options are listed below.

Medicines

Anticholinesterase medicines (such as neostigmine and pyridostigmine) are the main treatment for myasthenia gravis and can temporarily improve your muscle strength. They work by preventing acetylcholine from being broken down, so it builds up in the neuromuscular junction. The effect of these medicines usually wears off within three to four hours, so you will need to take tablets at regular intervals throughout the day. These medicines can have side-effects such as pain in your abdomen, 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 that attack the neuromuscular junction. This will help to reduce the symptoms of myasthenia gravis. Your doctor will probably prescribe a steroid such as prednisolone. This may be combined with another type of immunosuppressant called azathioprine. Other immunosuppressants include cyclosporin and methotrexate. These medicines can cause several side-effects, some of which can be prevented by taking additional medicines – ask your doctor for more information.

Your doctor will need to monitor you while you're taking these medicines to work out the best dose for you. This may take some time so it’s important to attend all your appointments.

Non-surgical treatments

If you have a myasthenic crisis that affects your ability to breathe or swallow, your doctor may give you intravenous immunoglobulin or IVIg (antibodies purified from human blood donations) into your bloodstream. You will have a drip inserted into a vein in your hand or arm to give you the immunoglobulin.

Alternatively 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 will reduce the amount of antibodies that are circulating in your body.

Your symptoms should improve in two days but the effects won’t last more than two months. Therefore these treatments are usually just used for situations when symptoms need to be controlled quickly, and aren’t an appropriate long-term treatment.

Surgery

You might experience some improvement in your symptoms if you have your thymus gland removed in a thymectomy operation. However, this isn’t suitable for everyone with myasthenia gravis. Ask your doctor if it’s a suitable treatment option for you.

How quickly does myasthenia gravis develop?

Answer

This can vary between individuals. It can develop gradually, or it may come and go at first.

Explanation

The exact reasons why you may develop autoimmune diseases like myasthenia gravis aren't fully understood at present. Why they develop in some people and not others, and why they develop at different rates, isn't known.

In some people, the condition can develop gradually and in others it may develop rapidly. Myasthenia gravis can become severe quickly or it may remain mild. Research into what causes myasthenia gravis and how it can be treated is continuing. If you think you are developing the symptoms of myasthenia gravis, talk to your GP.

How long do I need to take immunosuppressants like steroids for myasthenia gravis?

Answer

You may need to take them indefinitely. However, over time the dose will be altered so that you take the lowest dose possible to reduce your symptoms – you may only need to take them every other day.

Explanation

Steroids control myasthenia gravis by suppressing your immune system. This means there are fewer antibodies to attack acetylcholine receptors at neuromuscular junctions. This doesn't 'cure' the condition so you need to keep taking the steroids to limit the amount of antibodies. However, for many people, their symptoms improve after three years of having the condition – it’s rare for symptoms to get worse after this time. Therefore, it’s possible that you may only need very small doses, or even none at all if your symptoms go away completely.

Always ask your doctor for advice and read the patient information leaflet that comes with your medicine.

What precautions should I take if I am using immunosuppressant medicines for myasthenia gravis?

Answer

While taking immunosuppressant medicines, it’s important to reduce your chances of catching an infection.

Explanation

Because immunosuppressant medicines suppress all aspects of your immune system, taking them for myasthenia gravis may increase your risk of picking up infections. It’s therefore important to take steps to reduce your chances of getting an infection. For example:

  • keep good dental hygiene
  • stay away from children when they have chickenpox or other viral infections
  • get the flu jab every year

Ask your doctor for more advice about precautions to take while taking immunosuppressant medicines.

What precautions should I take if I need an operation and I have myasthenia gravis?

Answer

Before you have any surgery it’s important to inform your anaesthetist and surgeon that you have myasthenia gravis and about any medicines you take.

Explanation

Myasthenia may affect your reaction to certain general anaesthetics that you may have during a surgical operation. It can also affect your recovery from surgery. Therefore, it's important to let your doctors and anaesthetist know about your condition.

They will use a different selection of anaesthetic drugs to prevent any reaction when you have your operation and will monitor you closely after your operation. Your surgical team will also consider your condition when choosing pain relief for after your operation.

If you have any concerns about your surgery, speak to your anaesthetist or surgeon.

Is it possible to get pregnant if I have myasthenia gravis?

Answer

Yes, but if you’re planning a pregnancy it’s best to wait until your symptoms stabilise before you get pregnant.

Explanation

Pregnancy can affect women with myasthenia gravis in different ways. For some women their symptoms may improve, but for others they can get very severe. Your symptoms may get worse because of the anxiety and stress of pregnancy, for example. Also, there is a risk that you will have difficulty with your breathing during pregnancy because the diaphragm (the main muscle involved in breathing) is affected.

It’s therefore best to wait until your symptoms are controlled before you get pregnant. Symptoms get worse for most people over three years and then either stay the same or start to improve – they rarely get worse after this time. Risks to your health are greatest in the first two years of having the condition and the lowest seven years after, so it’s best to wait at least two years to get pregnant.

Your baby can also be affected by myasthenia gravis. While you’re pregnant you may transfer antibodies across the placenta and your baby can be born with a temporary form of myasthenia gravis. If this happens, your baby can receive treatment and the condition will usually disappear within three weeks and cause no permanent disability. However, it’s possible that your baby may be born with severe symptoms (including deformities in their joints) but this is rare and shouldn’t happen if you receive treatment for myasthenia gravis.

Your doctor will need to monitor your health while you’re pregnant. You should attend all your appointments. It’s also important to get lots of rest both before and after you have your baby and to eat a healthy diet.

Ask your doctor or midwife for more information about myasthenia gravis and pregnancy.