Myasthenia Gravis

(MG)
  • Definition

    Myasthenia gravis (MG) is an autoimmune disease. It affects the connection between the nerves and skeletal muscles. This can cause progressive muscle weakness.
  • Causes

    The root cause of MG is unknown. It occurs when the body’s immune system attacks receptors in muscle. Normally, these receptors respond to the chemical acetylcholine (ACh). This chemical allows nerve signals to prompt the muscles to move. When the immune system prevents these receptors from working well, the muscles cannot respond to nerve signals.
    The thymus is thought to play a role in some cases of MG. The thymus is an organ behind the breastbone. Immune proteins called antibodies are produced there. It is these antibodies that may target the ACh receptors. It is still not clear why the thymus begins to produce these.
    The Thymus Gland
    si2141 97870 1 thymus gland
    Copyright © Nucleus Medical Media, Inc.
    Infants of mothers with MG are more likely to develop a temporary form. It is called neonatal MG. The mother’s abnormal antibodies enter the baby’s bloodstream. When the baby is born, there may be muscle weakness. The abnormal antibodies are often cleared from the baby in about two months. This will end the baby’s symptoms.
  • Risk Factors

    MG is most common in women less than 40 years old and in men over 60 years old.
  • Symptoms

    Symptoms may grow more severe 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
    • Difficulty swallowing
    • Difficulty speaking
    • Difficulty walking
    • Weakness of the hand muscles
    • Difficulty breathing
  • Diagnosis

    Your doctor will ask about your symptoms and medical history. A physical exam will be done. You may need to see a neurologist. This type of doctor is an expert in diseases of the nervous system. Tests may include the following:
    • Blood tests
    • Electromyography (EMG) tests—to reveal abnormalities in muscle functioning
    • Repetitive nerve stimulation—may show progressively increasing muscle weakness over the course of the test
    • Tensilon test—a dose of a medication called edrophonium chloride is given, which will briefly improve muscle weakness
    • Pulmonary function testing
    Imaging tests to see internal body structures may be done with:
  • Treatment

    Treatment is focused on managing MG symptoms. Talk with your doctor about the best treatment plan for you. Options may include one or more of the following:
    Medications
    Your doctor may prescribe the following:
    Plasmapheresis
    This is a procedure that cleans the blood of the abnormal antibodies. This process may need to be repeated at certain intervals.
    Surgery
    Thymectomy is a surgical procedure to remove the thymus gland. Surgery may improve symptoms or bring remission in some patients.
    Mechanical Ventilation
    This may only be needed if breathing is severely impaired. This can happen during an episode of myasthenic crisis.
    Physical and Occupational Therapy
    Therapy does not generally alter the course of the disease. It may be needed to help the patient cope with changes in muscle strength. It may also help with learning alternative ways to approach daily activities.
    Avoiding Medicines That May Worsen Symptoms
    Avoid medicines that may worsen MG. There are many medications, but some examples include:
    • Beta-blockers
    • Certain antibiotics
    • Certain medications used to treat psychiatric conditions
  • Prevention

    There are no current guidelines 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://www.myastheniagravis.ca

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

    References

    Gronseth GS, Barohn RJ. Practice parameter: thymectomy for autoimmune myasthenia gravis (an evidence-based review): report of the Quality Standards Subcommittee of the American Academy of Neurology. Neurology. 2000;55:7-15.

    Myasthenia gravis. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed/what.php. Updated March 7, 2013. Accessed July 19, 2013.

    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 December 4, 2012. Accessed July 19, 2013.

    What is myasthenia gravis (MG)? Myasthenia Gravis Foundation of America website. Available at: http://www.myasthenia.org/WhatisMG.aspx. Accessed July 19, 2013.

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