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Myasthenia gravis

Myasthenia gravis is a condition that makes your muscles tire easily.

Although there is no cure for myasthenia gravis, there are treatments that can effectively manage it.

  • About myasthenia gravis
  • Symptoms
  • Complications
  • Causes
  • Diagnosis
  • Treatment
  • Further information
  • Sources

About myasthenia gravis

Myasthenia gravis affects about one in 10,000 people in the UK. Although it can develop at any age, in the UK it is rare before 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 out of four people with myasthenia gravis are female. At older ages it is more common in men - 60 percent of people with the condition between the ages of 50 and 75 are male.

With treatment nine out of ten people who have myasthenia gravis can live completely active lives.

Symptoms

The main symptom of myasthenia gravis is painless muscle weakness. It is brought on, or made worse, by physical exertion or activity. Stress and illness can make also make it worse. The symptoms of myasthenia gravis vary between individuals because different muscles can be affected to different degrees. It often starts by affecting muscles in the eyelids, making them droop and causing a tired or sleepy appearance. It may also affect muscles in the eye, causing double vision. About one in eight people with the condition only have symptoms in their eyes - this is called ocular myasthenia.

Early on in the disease the symptoms may come and go, and they can progress at different speeds in different people.

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.
  • It can affect muscles in your neck, 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.

It doesn't cause tiredness without muscle weakness.

Complications

A myasthenic crisis is when the symptoms of the illness become severe enough to threaten life - usually by preventing breathing or swallowing. This is rare as symptoms can usually be managed well (see Treatment). It may be caused by having an infection. If you have a myasthenic crisis you will need to be admitted to hospital for treatment. This often consists of plasma exchange or intravenous immunoglobulin (see Treatment), while any other infections are treated.

Causes

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, with myasthenia gravis the body attacks proteins in areas called neuromuscular junctions - the point where nerve cells, which carry signals from the brain, meet muscles.

In neuromuscular junctions a molecule called acetylcholine transmits signals from your nerves to the muscles, causing them to contract. In people with myasthenia gravis the body produces antibodies that attack acetylcholine receptors on the muscle, preventing the signal from reaching the muscle properly and so weakening them.

Nobody knows exactly why myasthenia gravis develops. However, three out of four people with myasthenia gravis have a problem with their thymus gland. The thymus gland is in the chest. It's part of the immune system; one of its functions is creating white blood cells.

About one in ten people who have myasthenia gravis have a tumour in their thymus gland. This is usually benign, which means it doesn't spread.

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

Diagnosis

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 central nervous system). There are a number of tests that you might have.

  • Blood tests. This may include tests to look for antibodies against acetylcholine receptors. In most people with the illness this is sufficient to diagnose the disease. However, about one in eight people with the illness don't have these exact antibodies so other tests may be needed. These antibodies are usually not found in people with the ocular form alone.
  • Electromyography. A needle electrode is inserted into a muscle to measure its electrical activity. Certain types of activity can indicate myasthenia gravis.
  • Tensilon test. A drug called edrophonium is injected into your arm. If you have myasthenia gravis this swiftly causes a short-lasting (about 5 minutes) 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 myasthenia gravis 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

Although there is no cure for myasthenia gravis there are now a number of effective treatments for the condition. Most people who have it can return to living a fully active life.

Some of the treatment options are listed below.

Medicines

Anticholinesterase medication

These drugs work by preventing acetylcholine from being broken down, so that it builds up in the neuromuscular junction. In some people this can help control myasthenia gravis.

Examples of these medicines include neostigmine and pyridostigmine. These need to be taken every few hours, depending on how severe the disease is. These types of drug can have side effects such as nausea, diarrhoea and increased saliva production. Sometimes other drugs are used to help reduce the side-effects.

If you have ocular myasthenia, taking an anticholinesterase medicine may be enough to control your symptoms. If you have generalised myasthenia gravis you may need to take drugs to suppress your immune system as well (see below).

Immunosuppression

Drugs that suppress the immune system are effective in nearly all patients with myasthenia gravis. They reduce the amount of antibodies attacking the neuromuscular junction, so reducing the symptoms of the disease.

Immunosuppressants are used when the condition hasn't responded to other types of treatment. The type of drug used varies. Most commonly you will be prescribed a steroid such as prednisolone. This may be combined with another type of immunosuppressant called azathioprine.

When you are taking drugs to suppress your immune system, 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

Thymectomy

About 85 percent of patients with myasthenia gravis experience some improvement in their symptoms after surgical removal of the thymus gland (thymectomy). It is usually carried out if you have a tumour in your thymus gland, but it can help other patients. This is thought to be especially helpful if you developed the condition before the age of 45. Thymectomy can cause long-term relief from the disease without the need for drugs, so is often offered to younger patients with generalised myasthenia gravis.

There is now a large international trial recruiting patients with myasthenia to determine whether surgery is really necessary in the era of improved drug treatments.

Non-surgical treatments

Plasmapheresis

If you have severe myasthenia gravis that is affecting your ability to breathe or swallow, you may need plasmapheresis. 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. This produces short-term relief from the symptoms.

Intravenous immunoglobulin

Infusing intravenous immunoglobulin (antibodies in plasma pooled from blood donors) into the blood stream improves symptoms in about seven out of 10 people with myasthenia gravis. It isn't known how this works. It can last for weeks to months.

Further information

Myasthenia Gravis Association

Sources

  • MGA publications. Myasthenia Gravis Association. www.mgauk.org, accessed 3 December 2007
  • Vincent A, Palace J, Hilton-Jones D. Myasthenia gravis. The Lancet 2001; 357:2122-2128. www.thelancet.com
  • Kasper DL, Fauci AS, Longo DL, et al., Harrison's Principles of Internal Medicine. 16th ed. New York: McGraw-Hill, 2005: 2520
  • British National Formulary (BNF). BMJ Publishing Group, 2007. 54: 549-550