Myasthenia gravis
Introduction
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 also be affected.
The muscle weakness is usually made worse by physical activity and improved by rest.
How common is it?
Myasthenia gravis affects about one person in every 10,000 in the UK. 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
Many people with myasthenia gravis become completely free of symptoms with treatment. Sometimes, the symptoms may stop altogether and you can come off treatment.
You may be prescribed tablets that increase chemicals in the body and improve messages from the nerves to the muscles. You may also be given 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.
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Symptoms
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 many people, symptoms are mild at first, but can get steadily worse over several months. Many patients first develop eye or eyelid symptoms, with the limbs becoming involved after an interval of months or two to three years.
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, and 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.
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Causes
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.
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.
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Diagnosis
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 and temporarily increases the amount of acetylcholine around the muscle.
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Treatment
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 damp down the body's immune system and reduce the production of the antibodies that cause myasthenia gravis.
Generally, steroids take a month to work. Azathioprine can take up to 6-18 months to work. This medication can reduce or even completely relieve myasthenia gravis symptoms. It is often prescribed to people who would otherwise require too large a dose of steroids for long-term use, 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.
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.
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