Neuromuscular - Myasthenia Gravis

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 continues to be 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

The following factors increase your chances 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

  • 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-up of symptoms. During an episode, breathing may be significantly impaired.

Diagnosing Myasthenia Gravis

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
  • 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 scan or MRI scan of the chest to look for a tumor of the thymus gland (thymoma)
  • Blood tests to look for thyroid disease (increased in patients with MG)
  • Pulmonary function testing to assess how MG may be affecting your ability to breathe