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Myasthenia Gravis (MG) 

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What is it?
Myasthenia gravis is an autoimmune, neuromuscular disease characterized by the varying weakness of voluntary muscle groups. Those commonly affected by myasthenia gravis include the eye muscles, facial and throat muscles, shoulder and hip muscles. Muscles that assist breathing also may be involved. The weakness in the muscles caused by myasthenia gravis fluctuates significantly; it can be made worse by use of the affected muscles and improved partially by rest.

In myasthenia gravis, weakness occurs when the nerve impulse to initiate or sustain movement does not adequately reach the muscle cells. This is caused when immune cells target and attack the body's own cells. This immune response produces antibodies that attach to affected areas, preventing muscle cells from receiving chemical messages (neurotransmitters) from the nerve cell.

What are the symptoms?
Symptoms of myasthenia gravis include:
-- Drooping eyelids
-- Double vision
-- Slurred speech
-- Nasal quality to voice
-- Inability to speak
-- Drooling
-- Problems chewing and/or swallowing
-- Trouble sitting up or holding head erect
or walking
-- Weak cough
-- Shortness of breath
-- Overall fatigue and fatigue of muscles after repetitive movement

Respiratory muscles can become so weak in myasthenia gravis patients that respirations are shallow and ineffective. The airway also can become obstructed due to weakened muscles and accumulated secretions. Failure to treat these symptoms promptly can result in severe low oxygen levels and respiratory arrest.

How is it diagnosed?
Diagnosing myasthenia gravis begins with a complete neurological exam with a review of the patient’s neurological history and clinical evaluation. Specifically, physicians will look for signs of weakness in voluntary muscles that get worse with activity and improve with rest.

In some cases, myasthenia gravis may be associated with tumors of the thymus, an organ of the immune system.

A blood test can detect the presence of immune molecules or acetylcholine receptor antibodies. Most patients with myasthenia gravis have abnormally elevated levels of these antibodies. However, antibodies may not be detected in myasthenia gravis patients with only ocular forms of the disease.

Edrophonium tests require the intravenous administration of edrophonium chloride, a drug that blocks the breakdown of acetylcholine and temporarily increases the levels of acetylcholine at the neuromuscular junction. In people with myasthenia gravis involving the eye muscles, edrophonium chloride will briefly relieve weakness.

Other methods to confirm the diagnosis of myasthenia gravis include a version of nerve conduction study which tests for specific muscle fatigue by repetitive nerve stimulation. A test called single fiber electromyography (EMG) in which single muscle fibers are stimulated by electrical impulses can also detect impaired nerve-to-muscle transmission.

A chest X-ray, CT scan and MRI may be used to detect a tumor in the thymus gland in myasthenia gravis patients.

How is it treated?
Today, myasthenia gravis can be controlled. Several therapies can reduce and improve muscle weakness. Medications used to treat myasthenia gravis include anticholinesterase agents, which improve neuromuscular transmission and increase muscle strength.

Immunosuppressive drugs may also be used to treat myasthenia gravis. The drugs can improve muscle strength by suppressing the production of abnormal antibodies. The medication must be used with careful medical follow up because they may cause major side effects.

Thymectomy, the surgical removal of the thymus gland (which often is abnormal in myasthenia gravis patients), reduces symptoms in more than 70 percent of patients without a tumor on the thymus gland. It may cure some individuals, possibly by re-balancing the immune system.

Other therapies used to treat myasthenia gravis include:
-- Plasmapheresis, a procedure in which abnormal antibodies are removed from the blood
-- High-dose intravenous immune globulin, which temporarily modifies the immune system with normal antibodies from donated blood.

Common-sense lifestyle modifications can also be very effective for myasthenia gravis patients. These include:

-- Getting plenty of rest, specifically resting the affected muscles several times a day.
-- Pacing activities to avoid fatigue.
-- Being vigilant about avoiding infection and exposure to illnesses.
-- Eating a well-balanced diet, with foods high in potassium, such as oranges, tomatoes, apricots and their juices, bananas, broccoli and white meat. Avoid foods that require excessive chewing.

What research is being done?
Some promising research includes testing intravenous immune globulin in patients with myasthenia gravis. The goal is to determine whether this treatment safely improves muscle strength.

Another study, according to the National Institute of Neurological Disorders and Stroke, seeks further understanding of the molecular basis of synaptic transmission in the nervous system. The objective of this study is to expand current knowledge of the function of receptors and to apply this knowledge to the treatment of myasthenia gravis.


Visit the National Institute of Neurological Disorders and Stroke for more details on up-to-date research for myasthenia gravis.

Sources:
-- The Myasthenia Gravis Foundation of America 
-- National Institute of Neurological Disorders and Stroke 



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