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Myasthenia Gravis

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:

  • Blood tests
  • Electromyography (EMG) tests—to reveal abnormalities in muscle functioning
  • Repetitive nerve stimulation (a component of EMG)—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 bodily 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

Plasmapheresis 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 people.

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 Medications That May Worsen Symptoms

Avoid medications that may worsen MG. Some examples include:

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

Prevention

There are no current guidelines to prevent MG.

Revision Information

  • Reviewer: Rimas Lukas, MD
  • Review Date: 08/2014 -
  • Update Date: 00/53/2014 -
  • Myasthenia Gravis Foundation of America

    http://www.myasthenia.org

  • National Institute of Neurological Disorders and Stroke

    http://www.ninds.nih.gov

  • Myasthenia Gravis Association of BC

    http://www.myastheniagravis.ca

  • Public Health Agency of Canada

    http://www.phac-aspc.gc.ca

  • 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. Updated June 27, 2014. Accessed August 21, 2014.

  • 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 April 16, 2014. Accessed August 21, 2014.

  • What is myasthenia gravis (MG)? Myasthenia Gravis Foundation of America website. Available at: http://www.myasthenia.org/WhatisMG.aspx. Accessed August 21, 2014.