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Myasthenia Gravis


The Manual's Editorial Staff

Reviewed/Revised Jul 2022 | Modified Sep 2022
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What is myasthenia gravis?

What causes myasthenia gravis?

Myasthenia gravis is an autoimmune disease Autoimmune Diseases The immune system is your body's defense system. It helps protect you from illness and infection. The immune system usually attacks invading bacteria, viruses, and cancer cells. With an autoimmune... read more . Your immune system is your body's defense system. It helps protect you from illness and infection. But in an autoimmune disease, your immune system attacks parts of your own body.

Your nerves send signals to your muscles to move. Proteins called receptors in your nerves and muscles receive the signals. In myasthenia gravis, your immune system attacks a receptor in your muscles and the signals to move the muscle can’t get through.

Doctors don’t know exactly why this happens, but they think it may involve a problem with the thymus gland. The thymus gland, located in your chest, is part of your immune system. Many people with myasthenia gravis have an unusually large thymus gland or a benign tumor in it.

You're more likely to have myasthenia gravis if you have another autoimmune disease, such as:

Myasthenia gravis may start after:

  • An infection

  • Surgery

  • Taking certain medicines for high blood pressure, malaria, or unusual heartbeats

Sometimes, babies born to mothers with myasthenia gravis have muscle weakness for a few days or weeks after birth.

What are the symptoms of myasthenia gravis?

The main symptom of myasthenia gravis is:

  • Muscle weakness that comes and goes

Your muscles work normally when you start to use them but then get weaker as you keep using them. For example, if you try to blink rapidly, at first you’ll be able to. Then after about 10 seconds, your blinking gets slower and slower.

Other symptoms of weakness include:

Myasthenia affects only your muscles. Even though you're weak, you still have all the feeling in your body and your mind is clear.

What is myasthenic crisis?

Myasthenic crisis is when your myasthenia suddenly gets a lot worse. You get so weak you often have trouble breathing. The crisis is often triggered by an infection.

How can doctors tell if I have myasthenia gravis?

Doctors will ask about your symptoms and do an exam.

If you're weak, doctors may see how your symptoms respond to things that can make myasthenia better. For example, if you have droopy eyelids, doctors may:

  • Hold an ice pack on your droopy eyelid to see if cold improves your muscle strength

  • Have you lie in the dark with your eyes closed for a few minutes to see if rest makes the drooping less

  • Inject you with a short-acting medicine that helps myasthenia to see if it makes the drooping less

If doctors suspect myasthenia after this, they do other tests such as:

Electromyography involves putting small needles in nerves (usually in your arm). The needles record the electrical activity of your muscles. They also record how your muscles and nerves respond to a mild electric shock.

How do doctors treat myasthenia gravis?

Doctors may give you medicines to:

  • Improve your muscle strength

  • Slow down your immune system so it doesn't attack your muscle receptors so much

Medicines to improve your strength act like the chemicals your nerves use to send signals to your muscles. But these medicines work for only a few hours. Also, the medicines don't stop the disease, they just help your symptoms. Doctors adjust the dose based on how you feel. But getting too much medicine can make you weaker. So it's sometimes hard for doctors to tell whether your disease is worse and you need more medicine or whether you're having side effects and need less medicine.

Treatments that slow down your immune system include:

  • Drugs such as corticosteroids that weaken your immune system

  • Immune globulin (medicine that contains certain helpful antibodies)

  • Plasma exchange (a process that filters your blood to take out the antibodies attacking receptors in your muscles)

If you have a tumor in your thymus gland, doctors remove the gland. This often helps the myasthenia. Taking out the thymus sometimes helps even if there isn't a tumor.

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