Definition

Myasthenia gravis (MG) is a problem of the immune system. It causes damage to the connection between the nerves and muscles. It can lead to muscle weakness that gets worse over time.

Infants of mothers with MG can have a temporary form. It is called neonatal MG. When the baby is born, there may be muscle weakness. It often stops in about 2 months.

Causes    TOP

The root cause of MG is unknown. Something triggers the immune system to attack healthy tissue. With MG, it attacks a receptor between the muscle and nerves. ACH receptors help nerve signals reach the muscle. When the receptors are damaged signals may not reach the muscle. This is what causes muscle weakness. The more damage there is, the greater the weakness will be.

The thymus is may play a role in some. The thymus is an gland behind the breastbone. It makes antibodies that tell the body what to attack. It is still not clear why the thymus begins to make them.

The Thymus Gland Copyright © Nucleus Medical Media, Inc.

Neonatal MG is caused by the mother’s abnormal antibodies. The baby gets the antibodies from the mother. The baby will clear these abnormal antibodies in about 2 months. This will stop the muscle weakness.

Risk Factors    TOP

MG is most common in:

• Women less than 40 years old
• Men over 60 years old
• People with a family history of systemic lupus erythematosus

Symptoms    TOP

Symptoms may grow worse 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
• Trouble swallowing
• Trouble speaking
• Trouble walking
• Weakness of the hand muscles
• Trouble breathing

Diagnosis    TOP

You will be asked about your symptoms and past health. A physical exam will be done. You may need to see a doctor that specializes in the nervous system. Tests may include:

• Blood tests—to look for antibodies
• EMG—to check electrical activity of muscles
• Tensilon test—a medicine which will improve muscle strength in people with MG for a short time

Imaging tests may be done to rule out thymus problems. Tests may include:

• CT scan
• MRI scan

Treatment    TOP

The goal of treatment is to decrease muscle weakness. It is mainly done by slowing the immune system. A second goal is to avoid a myasthenic crisis. This is when muscles become too weak to let you breathe properly. This is a medical emergency that will need breathing support.

Some may have remission. This is period of time where muscle weakness improves enough to stop treatment. It may be temporary or permanent. Treatment options include:

Prevention    TOP

There are no steps to prevent MG.