Myasthenia gravis

Page last reviewed: 13/07/2011

Myasthenia gravis is an uncommon condition that causes certain muscles to become weak. With treatment,most people can lead a normal life. 

Myasthenia gravis literally means 'grave muscle weakness'.

The condition can affect any muscles that you can control voluntarily. Muscles that you cannot control voluntarily, such as the heart muscles, are not affected.

Myasthenia gravis most commonly affects the muscles that control eye and eyelid movement, facial expression, chewing, swallowing and talking, and the muscles in the arms and legs (see Myasthenia gravis - symptoms). Less often, the muscles involved in breathing may be affected.

The muscle weakness is usually made worse by physical activity and improved by rest.

How common is it?

It is estimated that myasthenia gravis affects about one person in every 10,000. It can develop at any age, but is common in women under the age of 40 and men over the age of 60.

However, in recent years, increasing numbers of patients over the age of 60 are developing the condition.

What is the cause?

Myasthenia gravis is an autoimmune disease, which means that your immune system attacks your own body tissues. In the case of myasthenia gravis, your immune system produces antibodies that block or damage your muscle receptor cells (see Myasthenia gravis - causes). This blocks the messages that pass from the nerve endings to the muscles, so your muscles do not contract well and become weak.

The reason why some people's immune systems make antibodies against muscle receptor cells is not fully understood.

Outlook

There is no cure for myasthenia gravis, but many people with the condition become completely free of symptoms with treatment.

Treatment includes tablets that increase messages from the nerves to the muscles, tablets that suppress the immune system (immunosuppressants) and steroid tablets (see Myasthenia gravis - treatment for more information). Most people with the condition lead a normal, or nearly normal, life.

Page last reviewed: 13/07/2011

Myasthenia gravis causes muscle weakness that gets worse as the day goes on or after activity and improves with rest or a good night's sleep.

Other factors that may make muscle weakness worse include:

  • stress
  • hot weather
  • fever
  • over-exertion
  • infection (such as colds or pneumonia)
  • time of the month - many women find that their symptoms are more severe during their period

Myasthenia gravis is not usually painful. But if it affects your neck muscles, the back of your neck can become painful due to the effort of holding your head up.

For most people, symptoms are mild at first, but get steadily worse over several months. Myasthenia gravis usually reaches its worst within three to five years before levelling off.

Muscle weakness varies in the way that it develops, how severe it becomes and the different muscles that are affected.

Eyes, eyelids and face

For about two-thirds of those with the condition, the eye and eyelid muscles are the first muscles that become affected.

You may experience one or both eyelids drooping, and blurred or double vision.

Almost everyone with myasthenia gravis has problems with their eye muscles at some point, but in some cases these are the only muscles affected (the condition is then known as ocular myasthenia).

Many people with myasthenia gravis show a change in facial expression, such as a 'snarling' smile, as the condition affects the muscles of their face.

Swallowing and breathing

If the muscles around your mouth become affected, you may have difficulty chewing, swallowing and talking. This can lead to slurred speech and a nasal-sounding voice.

Some people with myasthenia gravis also have difficulty breathing, particularly when exercising or lying flat.

When muscle weakness causes severe swallowing or breathing problems, known as myasthenic crisis, the person urgently needs to go to hospital to be put on a ventilator (breathing machine).

Limbs

You may have weakness of the muscles in your arms, legs or neck, which leads to difficulty lifting, walking or holding your head up. Physical activity often leads to tiredness.

Double vision
Double vision is when you see two images of a single object instead of one.

    Page last reviewed: 13/07/2011

    Myasthenia gravis is known as an autoimmune disease because it is caused by the body's own immune system.

    If you have myasthenia gravis, your body's immune system produces antibodies that block or damage muscle receptor cells. This reduces the number of receptor cells on the muscle fibres (see box, right).

    When this happens, the normal communication between your nerves and muscles is affected. Your muscles do not contract well, and they become easily tired and weak.

    It is not fully understood why some people's immune systems make antibodies that act against muscle receptor cells. It is believed that the thymus gland (part of your immune system, located in your upper chest) may be linked to the production of the antibodies. About 10% of those with myasthenia gravis have a benign (non-cancerous) tumour of the thymus gland.

    Myasthenia gravis is known to be triggered sometimes by particular viruses or medicines. It is also thought that some people's genes make them more likely to develop autoimmune diseases.

    Antibodies
    Antibodies and immunoglobins are proteins in the blood. They are produced by the immune system to fight against bacteria, viruses and disease.
    Genes
    Genes contain information that you inherit from your parents, such as eye or hair colour. They are carried by chromosomes.  
    Immune system
    The immune system is the body's defence system, which helps protect it from disease, bacteria and viruses.

      Normal control of muscles

      In order to make a muscle contract (shorten), your brain sends an electrical signal through your nervous system to the nerve endings that lie next to the muscle. There is a tiny gap between the nerve endings and the surface of the muscle fibres.

      The electrical signal from your brain triggers the release of a chemical (called acetylcholine) at the nerve endings. The acetylcholine crosses the gap between nerve endings and muscle fibres and attaches itself to special receptor cells on the muscle, making it contract.

      Another chemical (acetylcholinesterase) then breaks down the acetylcholine, making the muscle relax.

      Page last reviewed: 13/07/2011

      Your GP may suspect that you have myasthenia gravis if they can see you have impaired eye movements or muscle weakness without any change in your ability to feel things.

      However, these symptoms can indicate a variety of conditions, not just myasthenia gravis, so the diagnosis needs to be confirmed.

      You will usually be referred to a neurologist (specialist in disorders of the nervous system) to have your diagnosis confirmed.

      There are several tests that can confirm a diagnosis of Myasthenia gravis. Some are listed below:

      • A blood test may be able to detect the abnormal antibodies that cause myasthenia gravis, although in about a quarter of those with the condition the levels may not be high enough to be detectable.
      • An electromyogram can measure muscle responses to an electrical stimulus. A needle electrode is inserted through the skin and into the muscle. It gives an electrical recording of muscle activity when nerves to the muscles are stimulated.
      • An injection of the drug edrophonium can be given, which causes a rapid but brief improvement in muscle strength for people with myasthenia gravis. This is because edrophonium blocks the breakdown of acetylcholine (see Myasthenia gravis - causes) and temporarily increases the amount of acetylcholine around the muscle.

      Antibodies
      Antibodies and immunoglobins are proteins in the blood. They are produced by the immune system to fight against bacteria, viruses and disease.
      Blood test
      During a blood test, a sample of blood is taken from a vein using a needle, so it can be examined in a laboratory.

        Page last reviewed: 13/07/2011

        Although there is no cure for myasthenia gravis, a range of treatments can control the symptoms for most people very effectively.

        Many people with the condition become completely free of symptoms with treatment, and most can lead a normal, or nearly normal, life.

        Some people with very mild symptoms find that resting and getting a good night's sleep is all they need to relieve their symptoms without any additional treatment.

        Cholinesterase inhibitors

        Medicines known as cholinesterase inhibitors (such as pyridostigmine) can block the action of the chemical that normally makes the muscles relax once they have contracted. These medicines work best with mild myasthenia gravis, and can improve muscle contractions and muscle strength in the affected muscles.

        Cholinesterase inhibitors sometimes cause side effects, such as stomach cramps and nausea. Your doctor will give you tablets to stop these.

        Removal of the thymus gland

        Surgical removal of the thymus gland (thymectomy) improves the symptoms of myasthenia gravis in more than 70% of those who have it. Symptoms disappear completely in about 30% of people.

        However, the improvement may take some time to appear. It is usually seen within the first year, but may take up to three years.

        A thymectomy is generally only recommended for people under the age of 60.

        Medication to alter the immune system

        Steroids (such as prednisolone) or immunosuppressant drugs (such as azathioprine) can alter the body's immune system and reduce the production of the antibodies that cause myasthenia gravis.

        Generally, steroids take a month to work. Azathioprine takes at least three to six months to work.

        Although it may take several months, this medication can reduce or even completely relieve myasthenia gravis symptoms. It is often prescribed to people who cannot have a thymectomy, or to those whose symptoms have not been improved by a thymectomy.

        Plasmapheresis and immunoglobulin therapy

        If myasthenia gravis muscle weakness becomes so severe that it causes life-threatening breathing or swallowing problems, plasmapheresis or intravenous immunoglobulin therapy can be given in hospital:

        • In plasmapheresis, your blood is routed through a machine that removes the plasma containing the harmful antibodies, and replaces it with antibody-free plasma before returning it to your body.
        • In intravenous immunoglobulin therapy, you are injected with normal antibodies that change the way your immune system acts.

        Both of these treatments can produce a rapid improvement in myasthenia gravis symptoms, but the benefits only last for a few weeks, so they are not suitable as long-term treatments and are usually used only if you are seriously ill.

        Antibodies
        Antibodies and immunoglobulins are proteins in the blood. They are produced by the immune system to fight against bacteria, viruses and disease.
        Immune system
        The immune system is the body's defence system, which helps protect it from disease, bacteria and viruses.
        Immunoglobulin
        Immunoglobulins (antibodies) are types of proteins in the body that fight off infection.
        Intravenous
        Intravenous (IV) means the injection of blood, drugs or fluids into the bloodstream through a vein.
        Plasma
        Plasma is the liquid part of blood, which holds other blood cells together.

          Self-care advice

          There are things you can do to make it easier to deal with the symptoms:

          • If the muscles you use for speaking, chewing and swallowing are affected, try to eat softer foods that are easier to swallow and avoid foods that need a lot of chewing. Try to eat when your muscles are at their strongest, take your time eating and rest between mouthfuls. Eating smaller meals but more often may be easier than eating a large amount three times a day.
          • Save your energy around the house by using electric items such as electric toothbrushes, can openers and screwdrivers.
          • Plan your activities to coincide with the time when your energy levels are at their highest. This may be early in the day or soon after you have taken your medication.

          Content provided by NHS Choices www.nhs.uk and adapted for Ireland by the Health A-Z.

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