About Myasthenia Gravis (MG)

About Myasthenia Gravis (MG)

What is MG?

The term “Myasthenia Gravis” comes from Greek and Latin words. In English, this translates to “grave muscle weakness.
MG is a disease that is caused by your body’s own immune system attacking itself. People with MG typically experience many symptoms, which can include muscle weakness in the arms, legs, or neck, double vision, drooping eyelids, difficulty with speech, chewing, swallowing, or breathing as well as mental and physical fatigue.

  • MG can affect different groups of muscles in the body, and this can vary from person to person along with the severity of symptoms.
  • In addition, your symptoms may fluctuate from day to day, depending on the muscles affected at the time. This can cause unpredictability and have a major impact on your ability to manage and plan everyday activities.
  • Sometimes the variation in symptoms can get more serious, resulting in a ‘flare-up’ or exacerbation, also known as a myasthenic crisis, which may mean hospital care is required.

Patient Perspective

“I have to really engineer my life around myasthenia gravis so that I don't have symptoms that flare up out of nowhere, if I can help it. So, I really try to take every possible step in terms of lifestyle management, in order to keep my symptoms under control. And when they are mostly under control, I can live what looks like a pretty normal life on the outside. But I do miss out on a lot of things because I'm very aware of not overextending or asking too much of my body and thereby causing an exacerbation.”– MG Patient, UK
  • Living with MG can have a huge impact on everyday life. People with more severe MG may require hospitalisation and intensive care treatment to manage serious exacerbations.
  • The physical burden of MG and negative impact on quality of life can also lead to mental health problems - many people with MG experience depression and anxiety.
  • Although there isn’t currently a cure, advances in care mean that many people living with MG can now lead relatively normal lives, with careful management of their symptoms.
What causes MG?

MG is not inherited or contagious.

Thymus involvement: Although the cause is not known, about 75% of people living with MG have a problem with their thymus gland but the role of the thymus in MG is not currently understood. The thymus is a small organ that sits behind the breast bone which produces cells that are essential for the body’s immune system to work properly.

Autoantibodies: In healthy individuals, the immune system produces antibodies to protect the body from infections and diseases. However, in the case of MG, this process malfunctions and leads to the production of antibodies that block receptors in the muscles. Antibodies that target the body’s own tissues are called autoantibodies.

When muscle receptors are blocked, as they are by autoantibodies in MG, the muscles themselves receive fewer nerve signals and are unable to contract properly, which leads to muscle weakness and fatigue.

Normally, nerves signal our muscles to contract using a chemical messenger molecule called acetylcholine, which binds to the acetylcholine receptor (AchR). In the most common form of MG, autoantibodies prevent the binding of acetylcholine to AchR, which means the muscles are unable to contract properly, resulting in muscle weakness.

  • Approximately 90% of people diagnosed with MG have autoantibodies which bind to known receptors.
    • This type of MG is known as seropositive myasthenia.
  • The remaining people diagnosed with MG, around 10%, do not seem to have any identifiable autoantibodies at all – this type of MG is called seronegative myasthenia.
  • Your doctor will be able to tell you more about the type of MG you have been diagnosed with and what it means for your care.
    • However, people diagnosed with seronegative MG broadly experience similar symptoms and have a similar response to care to those with seropositive myasthenia.

In MG, when autoantibodies target different muscle groups in the body, that is when the symptoms of the disease start to appear. So, for example, receptors in muscles of the arms and legs when targeted cause limb weakening, receptors in muscles of the mouth, throat, and neck when targeted cause difficulty in speaking, chewing or swallowing.

Because of its rarity and different symptoms, many patients with MG may struggle to receive an accurate diagnosis for months or even years. MG disease can affect anyone, but it is more commonly diagnosed in women aged under 40 years and in men aged over 60.

Tests that can diagnose MG include physical and neurological examinations, tests that stimulate the nervous system and measure muscle response, and blood tests:

  • The main test for MG is a blood test to detect the autoantibody types which are specific to the disease, although as noted above these are not detectable in all forms of MG.
  • Doctors may also use a test called electromyography to check the health of muscles and the nerves that control them. This test measures the electrical activity in muscles when they are activated by nerves."
  • A scan, such as CT or MRI, of the chest can also be used to check for abnormalities in the thymus gland.

In some cases, an injection of a medicine called edrophonium chloride is given. Edrophonium chloride is a drug that temporarily inhibits the breakdown of acetylcholine, a neurotransmitter that is essential for muscle contraction. If a sudden but temporary improvement in muscle strength is seen after the injection, an MG diagnosis is likely.

Janssen and MG

We are dedicated to partnering with the MG community of patients, carers, patient support groups and healthcare professionals, to help transform the lives of people living with MG for the better.

Building on our legacy of innovation, we are committed to leading where medicine is going in autoantibody diseases, such as MG. Together, we aim to make a real difference to the lives of people living with MG.

References

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Myasthenia Gravis Foundation of America (MGFA). Seronegative MG Resource Center. Available at: https://myasthenia.org/Newly-Diagnosed/Seronegative-MG-Resource-Center Last accessed: June 2024.
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