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What is Myasthenia Gravis (MG)?

Myasthenia Gravis

Myasthenia Gravis is a chronic neuromuscular disease that produces weakness. MG derives its name from Latin and Greek words meaning “grave muscle weakness”. The disease is characterized by abnormal weakness of voluntary muscles (those muscles controlled by will). This weakness increases with activity and decreases with periods of rest.


MG is an autoimmune disease which involves a malfunction at the junctions between nerves and muscles. The body manufactures abnormal antibodies which prevent the muscles from responding properly to the signals from the nerves. To date research has not revealed what activates the malfunction initially.

Current Treatments

The current treatments for MG are effective and the outlook for most patients is bright. Learning to live with MG requires some adjustments that will affect you and your whole family. It is vital that you and your family completely understand the illness and its treatment.   No known cure has been discovered to date.

Positive Future Prospects

Myasthenia Gravis, with proper treatment, is no longer a life threatening disease. Most patients will show significant improvement in their muscle weakness. In some cases, MG may go into remission, in which case the muscle weakness disappears. Remission may last as long as many years and during these periods, treatment may not be necessary. For most MG patients, a new norm quality of life is possible with consistent use of prescribed treatments, adjustment to a less stressful lifestyle, balanced diet, exercise, and more frequent rest.


Could It Be MG? 

Symptoms of Myasthenia Gravis

Symptoms may be any of the following, alone or in combination. Their severity may vary from person to person and from time to time:

  • Drooping eyelids
  • Double vision
  • Difficulty controlling facial expressions
  • Difficulty with chewing and swallowing
  • Slurred speech
  • Weakness in arms, legs or neck, difficulty in climbing, standing or holding head erect
  • Inability to raise arms over the head
  • Difficulty in breathing
  • Difficulty smiling

Who Gets It?

It occurs in both sexes, all races and all age groups. Most commonly it first appears in women between the ages of 20 and 40 and in men over 50. In general MG is being diagnosed more often in the elderly than it was in the past. It is not transmittable to others and with rare exceptions is not hereditary. 

How is Myasthenia Gravis Diagnosed?

Myasthenia Gravis Treatment

If any of the symptoms point to a possibility of MG, the physician in charge many use some of the following tests or procedures.

Laboratory Tests

A blood sample is taken and analysed for the presence of AChR (Acetylcholine receptor), MuSK (Muscle-specific kinase) or rarely LRP4 or Agrin antibodies. Their presence indicates you almost certainly have MG but these antibodies are not found in all patients with MG (‘Seronegative’).

Neurological Exam

This examination tests to see how the nerves and muscles react to certain stimulation. The focus is both on how well and how long you can perform certain tasks with your muscles.

Tensilon™ Test

The drug Tensilon™ is injected into a vein. If your strength improves temporarily it is a sign that you may have MG. This test is rarely done these days.

Ice Pack Test

The local application of ice over a droopy eyelid will sometimes produce temporary improvement for a few minutes after the ice is removed.  This test has mostly replaced the Tensilon Test.

Pulmonary Function Tests

Pulmonary function or breathing tests help the doctor determine whether or not your respiratory muscles are affected.


Electromyography (EMG) is a test for determining how well the muscles respond to electrical stimulation. Several muscles may need to be tested. Although sometimes a little uncomfortable, this test provides valuable information. Two tests are used specifically to diagnose MG; repetitive nerve stimulation (RNS) and single fibre EMG (SFEMG).
Reviewed by:   M. Nicolle, MD, FRCPC, D.Phil                                                       

Information in the Myasthenia Gravis Society of Canada Website express the views of the author and are for information only, not medical advice.  Patients should consult with their physicians for medical treatment.

Which of these treatments should be used for a person with MG depends upon the severity of the weakness, which muscles are affected, the person’s age and other associated medical problems.  The doctor will determine which of these treatments may be best for each patient.

There have been major advances in the treatment of MG in recent years. Although there is no cure for MG yet, the available treatments are sufficiently effective that most patients will experience considerable improvement and can eventually lead near normal lives. The various forms of treatment include medications, plasmapheresis (plasma exchange), IVIg and thymectomy.


Medications are most frequently used in treatment. Anticholinesterase agents (such as Mestinon®) allow the acetylcholine to remain at the neuromuscular junction a little longer than usual so that more receptor sites can be activated. Prednisone, a cortisone-like drug, and/or azathioprine (Imuran®) may be used to suppress the immune system and its production of all antibodies. Other immunosuppressant drugs used in MG include mycophenolate (e.g. CellCept®), cyclosporine, tacrolimus, methotrexate or cyclophosphamide. Close contact with the family doctor is desirable because these drugs may decrease the body’s   natural protection against infection. Some medications (azathioprine in particular) require regular monitoring of blood tests such as liver tests and monitoring of white blood cell counts.

IVIG – Intravenous Immunoglobulin

IVIg is most commonly used for patients with an exacerbation of their MG.  Its effectiveness has been demonstrated in randomized clinical trials.  It is used under similar circumstances to plasmapheresis.


Thymectomy (the surgical removal of the thymus gland) is sometimes used in MG. The thymus lies behind the breast bone and is an important part of the immune system. Younger patients with MG may have a “hyperplastic‟ thymus whereas in older patients there is a chance of a   tumour in this gland (in 10 -15% of patients) called a thymoma. If  there is a thymoma, the thymus is usually removed to reduce the risk of malignancy but usually does not help the MG.   When the thymus is hyperplastic, a thymectomy may reduce the severity of muscle weakness which usually takes months after Surgery.  In a few patients the muscle weakness may completely disappear and this is called a remission.  How much a thymectomy helps varies with each patient but it is most effective when AChR antibodies are positive.


Plasmapheresis may also be useful in the treatment of MG.  This procedure removes the abnormal antibodies from the serum of the blood in patients with MG.  The improvement in muscle strength may be striking but is usually short-lived (weeks to 1-2 months) since the abnormal antibodies continue to be formed.  Therefore, when plasmapheresis is used, it may require repeated use.  Plasmapheresis may be especially helpful during a period of MG crisis or before surgery including a thymectomy.
Reviewed by: M. Nicolle, MD, FRCPC, D.Phil

Information in the Myasthenia Gravis Society of Canada Website express the views of the author and are for information only, not medical advice. Patients should consult with their physicians for medical treatment.