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by Carson-DeWitt R
(MG)

Definition

Myasthenia gravis (MG) is a problem of the immune system. It causes damage to the connection between the nerves and muscles. It can lead to muscle weakness that gets worse over time.

Infants of mothers with MG can have a temporary form. It is called neonatal MG. When the baby is born, there may be muscle weakness. It often stops in about 2 months.

Causes

The root cause of MG is unknown. Something triggers the immune system to attack healthy tissue. With MG, it attacks a receptor between the muscle and nerves. ACH receptors help nerve signals reach the muscle. When the receptors are damaged signals may not reach the muscle. This is what causes muscle weakness. The more damage there is, the greater the weakness will be.

The thymus is may play a role in some. The thymus is an gland behind the breastbone. It makes antibodies that tell the body what to attack. It is still not clear why the thymus begins to make them.

The Thymus Gland
si2141 97870 1 thymus gland
Copyright © Nucleus Medical Media, Inc.

Neonatal MG is caused by the mother’s abnormal antibodies. The baby gets the antibodies from the mother. The baby will clear these abnormal antibodies in about 2 months. This will stop the muscle weakness.

Risk Factors

MG is most common in:

Symptoms

Symptoms may grow worse over time. MG may cause the following:

  • Muscle weakness that increases with muscle use/exercise, and improves after resting those muscles
  • Drooping eyelids
  • Double and/or blurred vision
  • Trouble swallowing
  • Trouble speaking
  • Trouble walking
  • Weakness of the hand muscles
  • Trouble breathing

Diagnosis

You will be asked about your symptoms and past health. A physical exam will be done. You may need to see a doctor that specializes in the nervous system. Tests may include:

  • Blood tests—to look for antibodies
  • EMG—to check electrical activity of muscles
  • Tensilon test—a medicine which will improve muscle strength in people with MG for a short time

Imaging tests may be done to rule out thymus problems. Tests may include:

Treatment

The goal of treatment is to decrease muscle weakness. It is mainly done by slowing the immune system. A second goal is to avoid a myasthenic crisis. This is when muscles become too weak to let you breathe properly. This is a medical emergency that will need breathing support.

Some may have remission. This is period of time where muscle weakness improves enough to stop treatment. It may be temporary or permanent. Treatment options include:

Medications

Medicine can help to calm the immune system. Options include:

Plasmapheresis

This proceduretakes the abnormal antibodies out of the blood. It will may need to be repeated in cycles.

Surgery

The thymus may be removed. It may improve symptoms or start permanent remission in some.

Supportive Care

  • Mechanical ventilation—if breathing has become difficult.
  • Physical and Occupational Therapy—to improve some muscle weakness. To develop new ways to do daily tasks.

Avoiding Medications That May Worsen Symptoms

Some medicine can worsen MG such as:

  • Beta-blockers
  • Certain antibiotics
  • Certain medicine used to treat psychiatric conditions

The medical team will find a balance of medicine that does not cause further weakness.

Prevention

There are no steps to prevent MG.

RESOURCES

Myasthenia Gravis Foundation of America  http://www.myasthenia.org 

National Institute of Neurological Disorders and Stroke  http://www.ninds.nih.gov 

CANADIAN RESOURCES

Myasthenia Gravis Association of BC  http://myastheniagravis.ca 

Public Health Agency of Canada  http://www.phac-aspc.gc.ca 

References

Juel VC, Massey JM. Myasthenia gravis. Orphanet J Rare Dis. 2007 Nov 6;2:44.

Myasthenia gravis. EBSCO DynaMed Plus website. Available at:  https://www.dynamed.com/topics/dmp~AN~T113873/Myasthenia-gravis  . Updated September 19, 2017. Accessed January 8, 2019.

Myasthenia gravis fact sheet. National Institute of Neurological Disorders and Stroke website. Available at: http://www.ninds.nih.gov/disorders/myasthenia%5Fgravis/detail%5Fmyasthenia%5Fgravis.htm. Updated July 6, 2018. Accessed January 8, 2019.

What is myasthenia gravis (MG)? Myasthenia Gravis Foundation of America website. Available at: http://www.myasthenia.org/WhatisMG.aspx. Accessed January 8, 2019.

11/9/2015 DynaMed Plus Systematic Literature Surveillance  https://www.dynamed.com/topics/dmp~AN~T113873/Myasthenia-gravis  : Kuo CF, Grainge MJ, Valdes AM, et al. Familial aggregation of systemic lupus erythematosus and coaggregation of autoimmune diseases in affected families. JAMA Intern Med. 2015;175(9):1518-1526.

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