Myasthenia gravis is a rare neuromuscular disease in which the voluntary muscles quickly become tired and weak as a result of dysfunction with nerve and muscle communication.

Myasthenia gravis (MG) is an autoimmune neurological disorder that causes weakness in the muscles that connect to a person’s bones and allow for body movement. It is pronounced my-us-thee-nee-ah gray-vis.

The condition affects 20 people in every 100,000 in the United States. It can happen at any age, but it is more likely to affect people assigned female at birth before age 40 and people assigned male at birth after age 60.

This article covers the symptoms, causes, and treatments for MG.

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MG is an autoimmune disorder that causes muscle weakness. The muscles around the eyes tend to be affected first, causing the eyelids to droop. Symptoms often worsen with physical activity and improve after rest. While there is no cure, treatment can relieve and help manage symptoms.

There are 5 classes of MG:

  • Class 1: Weakness of the muscles around the eye only.
  • Class 2: Mild muscle weakness around the eye or through the body.
    • A: Mainly affecting the limbs or muscles around the head, neck, and spine.
    • B: Mainly affecting muscles in the throat and respiratory system.
  • Class 3: Moderate muscle weakness around the eye or through the body.
    • A: Mainly affecting the limbs or muscles around the head, neck, and spine.
    • B: Mainly affecting muscles in the throat and respiratory system.
  • Class 4: Severe muscle weakness around the eye or through the body.
    • A: Mainly affecting the limbs or muscles around the head, neck, and spine.
    • B: Mainly affecting muscles in the throat and respiratory system.
  • Class 5: Severe muscle weakness requiring intubation and in some cases, mechanical ventilation.

Symptoms of MG vary widely from person to person. They often become progressively worse during periods of activity, but they improve after resting.

Symptoms can include:

  • fatigue
  • weakness of the eye muscles
  • eyelid drooping in one or both eyelids
  • blurred vision or double vision
  • weakness in the limbs and neck
  • difficulty chewing, especially chewy food
  • difficulty swallowing, including food, liquids, and pills
  • difficulty speaking, which makes the voice weak and quiet
  • difficulty breathing and shortness of breath
  • decreased movement of the face muscles, which can cause a weak smile

Research suggests that most people first experience eye symptoms. Many go on to develop additional symptoms within 2 years.

People with MG may also experience temporary or permanent remission, where symptoms disappear or lessen.

What is a myasthenic crisis?

Some people with MG may experience respiratory muscle paralysis and require assisted ventilation.

In people with weakened respiratory muscles, some triggers may cause a myasthenic crisis, including:

  • infection
  • fever
  • adverse reaction to medication
  • emotional stress

MG is an autoimmune disorder. An autoimmune disorder develops when a person’s immune system damages their body tissues. The immune system typically finds and destroys bacteria, toxins, or viruses. In a person with an autoimmune disease, a malfunction of the immune system causes antibodies to damage healthy tissues.

In the case of MG, the antibodies block or destroy muscle receptor cells, resulting in fewer available muscle fibers. As a result, the muscles cannot contract properly and quickly become tired and weak. Exactly why this happens is unknown, but the thymus gland, which is part of the immune system, also plays a role.

The thymus gland is large during infancy and continues to grow until puberty. After this, it gets smaller and eventually is replaced with fat. A significant number of adult patients with MG have an abnormally large thymus gland. About 1 in 10 people with MG may also have a benign tumor in the thymus gland.

Some medications or viruses may trigger the onset of MG. Drugs that may cause a worsening of symptoms in susceptible patients include:

  • beta-blockers
  • calcium channel blockers
  • quinine
  • some antibiotics

Genetic factors may play a role.

Symptoms may also worsen with emotional or mental stress, illness, tiredness, or a high fever.

Neonatal myasthenia affects newborns if they acquire antibodies from a mother who has MG. The symptoms usually disappear before 4 months of age, and MG in infants and children is rare.

A doctor may suspect MG if a person has drooping eyelids but no problem feeling things and if they are prone to muscle weakness that improves after rest.

A doctor can confirm a diagnosis of MG through various tests. These can include:

  • An edrophonium test: This test involves injecting a substance into a vein and monitoring the reaction. The muscle weakness may be temporarily relieved.
  • Blood tests: Blood tests can identify specific antibodies.
  • Repetitive nerve stimulation: This involves attaching electrodes to the skin over the affected muscles and sending small electrical pulses through the electrodes to measure how well the nerves transmit the signal to the muscle. If a person has MG, the signals weaken as the muscle tires.
  • Single-fiber electromyography (EMG): This measures the electrical activity that flows between the brain and the muscle. It involves inserting a fine wire electrode through the skin into the muscle.
  • Imaging tests: Imaging, such as a chest X-ray, CT scan, or MRI, may help doctors eliminate other conditions. This can also help identify an enlarged thymus gland or thymus gland tumor.
  • A pulmonary function test (spirometry): This test assesses how well someone can breathe. Performed regularly, it can help monitor the progression of muscular weakness in the lungs.

Because MG shares symptoms with other conditions, in some cases, a person may receive a delayed diagnosis.

There is no cure for myasthenia gravis, but treatment can help control symptoms.

Treatment can include:

  • Monoclonal antibodies: The Food and Drug Administration (FDA) approved eculizumab (Soliris) for adults who test positive for the anti-acetylcholine receptor (AchR) antibody. People must take these daily to prevent symptoms.
  • Cholinesterase inhibitors: Drugs such as pyridostigmine (Mestinon) can improve communication between nerves and muscles. However, these effects only last for a few hours.
  • Immunosuppressants: Immunosuppressive drugs, such as azathioprine and glucosteroids like prednisolone, may alter the body’s immune system to produce fewer of the antibodies that cause MG. Doctors will prescribe these in times of MG crisis, and sometimes for long-term symptom prevention.
  • Thymectomy: This surgery removes the thymus gland and may benefit people with MG, even if they do not have a thymus tumor.

For patients with severe or life threatening symptoms, doctors may administer additional treatments in the hospital. These can include:

  • plasmapheresis, a procedure that remove harmful antibodies in plasma and replaces them
  • intravenous (IV) immunoglobulin, which injects antibodies from donors to change the way the immune system acts

These treatments are effective and work quickly, but the benefits last only a few weeks, so this is a short-term treatment.

People with one autoimmune disease are often susceptible to another. A person with MG may have a second autoimmune condition.

Complications of myasthenia gravis can include:

  • Thyroid problems: These include overactive or underactive thyroid. The thyroid gland is a small gland in the front of the neck that secretes hormones that regulate metabolism.
  • Myasthenic crisis: In a myasthenic crisis, the respiratory muscles become so weak that a person cannot breathe properly. This potentially life threatening complication requires emergency treatment and mechanical breathing assistance. Plasmapheresis and immunoglobulin therapies can help.

Can myasthenia gravis be prevented?

MG cannot be prevented. However, a person can take steps to stop a flare-up of symptoms or prevent them from developing complications.

These include practicing careful hygiene to avoid infections and treating them promptly if they do occur.

It is also advisable to avoid extreme temperatures and overexertion. Effective stress management can also reduce the frequency and severity of symptoms.

Is there a cure for myasthenia gravis?

There is no cure for myasthenia gravis, but treatment can help control symptoms. Some people may also enter remission.

What is the life expectancy of a person with myasthenia gravis?

Most people with MG have a similar life expectancy to a person without the disease, according to the National Institutes of Neurological Disorders and Stroke (NINDS).

Is myasthenia gravis the same as ALS?

MG and ALS are different diseases, though they have some symptoms in common. ALS affects the motor neurons responsible for controlling muscle movement. MG affects the communication between neurons and muscles. Both can cause muscle weakness.

MG is a chronic condition. People with MG may experience periods of disease remission and relapse. While there is no cure, treatment can help manage symptoms.

In most people, the condition spreads over time to affect different body parts.

MG can become life threatening for some people, but most individuals with MG do not see a change in life expectancy.