Myasthenia Gravis

(MG)

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:

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