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Myasthenia Gravis

Definition:
Myasthenia gravis (MG) is a neuromuscular disorder that affects both nerves and muscles throughout the body. Its symptoms may grow progressively more severe over time. This is a potentially serious condition that requires care from you doctor. If you suspect you have this condition, contact your doctor immediately.

Causes:
The root cause of myasthenia gravis is unknown. MG occurs when the body’s immune system attacks muscle receptors. Under normal conditions, these receptors should respond to the neurotransmitter acetylcholine. This allows nerve signals to prompt the muscles to move. However, when these receptors are damaged or destroyed, the muscles can no longer respond to nerve signals. This causes muscles throughout the body to become increasingly weak.

The thymus is an organ behind the breastbone, and it is thought to play a role in causing some cases of myasthenia gravis. Immune cells called antibodies are produced by the thymus. In MG, some of these antibodies may damage or destroy the acetylcholine receptors. It is still not clear why the thymus begins to produce these harmful antibodies.

Risk Factors:
A risk factor is something that increases your chance of getting a disease or condition.

The following factors increase your chance of developing myasthenia gravis.

  • Women are more likely to develop MG between the ages of 20-30.
  • Men are more likely to develop MG between the ages of 60-70.
  • People with certain genetic markers (called HLA-B8, DR3) are more likely to develop MG.
  • Infants of mothers with MG are more likely to develop a temporary form of the condition, called neonatal MG. Neonatal MG occurs because the mother’s abnormal antibodies have entered the baby’s bloodstream. When the baby is born, he or she may exhibit symptoms of muscle weakness. The abnormal maternal antibodies are usually cleared from the baby’s bloodstream within about two months, ending the baby’s symptoms.
Symptoms:
Symptoms include:
  • Muscle weakness that increases with muscle use/exercise, and improves after resting those muscles
  • Weakness of muscles that control:
    • The eyelids
    • Eye movement
    • Facial expression
    • Chewing
    • Swallowing
    • Coughing
    • Breathing
    • Arm and leg movement
  • Drooping eyelids
  • Double and/or blurry vision
  • Difficulty swallowing
  • Difficulty speaking
  • Difficulty walking
  • Weakness of the hand muscles
  • Myasthenic crisis: This is a severe flare of symptoms. Duing an episode, breathing may be significantly impaired.
Diagnosis:
Your doctor will ask about your symptoms and medical history, and perform a physical exam. You may need to see a neurologist, a specialist who is an expert in diseases involving the nervous system.

Tests may include the following:

  • Blood tests can identify the presence of abnormal antibodies
  • Blood tests to look for thyroid disease (increased in patients with MG)
  • Electromyography (EMG) tests can reveal abnormalities in muscle functioning
  • Repetitive nerve stimulation tests will show progressively increasing muscle weakness over the course of the test
  • The “Tensilon test” involves giving a patient a dose of a medication called edrophonium chloride, which will temporarily and briefly improve muscle weakness
  • CT scn or MRI scan of the chest to look for a tumor of the thymus gland (thymoma)
  • Pulmonary function testing to assess how MG may be affecting your ability to breathe
Treatment:
Talk with your doctor about the best treatment plan for you. Treatment options include:

Acetylcholinesterase Inhibitors
These are medications that interfere with the breakdown of acetylcholine. This increases the amount of acetylcholine available to stimulate muscle receptors. These medications include pyridostigmine and mestinon.

Immunosuppressive Therapy
These medications are given to slow down the immune system. As a result, there are fewer antibodies present to attack the acetylcholine receptors. These medications include:
  • Prednisone
  • Azathioprine
  • Mycophenolate mofetil
  • Cyclosporine

Immunoglobulin Therapy
Adminisration of immune globuline intravenously can help reduce symptoms of myasthenia, though the exact mechanism is unclear. This treatment seems to have fewer side effects that immunosuppressive therapy.

Plasmapheresis
This is a procedure which cleans the blood of surplus antibodies. Because the abnormal antibodies will continue to be produced, plasmapheresis may need to be repeated at certain intervals.

Thymectomy
Removal of the thymus gland is necessary when thymoma is present. Thymectomy may improve the symptoms of MG in some patients.

Mechanical Ventilation
Mechanical ventilation may be required if breathing is severely impaired, such as during an episode of myasthenic crisis.

Physical Therapy
Physical therapy and occupational therapy do not generally alter the course of the disease, but may be needed to help the patient cope with changes in muscle strength and coordination. It may also help with learning alternative ways to approach daily activities.

Prevention:
There are no known ways to prevent the development of MG. The following steps may improve muscle functioning in people who already have the condition:
  • Avoid medications that may worsen MG, such as:
    • Beta-blockers
    • Aminoglycoside antibiotics
    • Quinolone antibiotics
    • Class I medications used for abnormal heart rhythms
  • Treat any infections promptly.
  • If you have trouble swallowing, you may wish to consult a dietitian to help you construct a healthful diet that is easier to swallow.
  • If you have trouble speaking, you may wish to consult a speech therapist.
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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