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Myasthenia Gravis

Myasthenia gravis is a chronic condition that causes muscles to tire and weaken easily. For example, if you have myasthenia gravis, you may notice that during a meal, your jaw muscles become tired and weak, interfering with your ability to chew food. After you have rested for a little while, the muscles may become strong again, allowing you to resume eating.

This waxing-and-waning weakness of muscles, worsening with use and improving with rest, is a hallmark of this particular disease. There typically are four periods when you may notice symptoms (called an exacerbation), interspersed with periods when symptoms decrease or disappear (remission). 

The disease most commonly affects muscles that control eye and eyelid movement, so the first symptoms you notice may be eyelid drooping and/or blurred or double vision. The majority will go on to develop weakness in other muscle groups within one or two years.

Myasthenia gravis affecting multiple muscle groups throughout the body is called generalized myasthenia gravis. Other common muscle groups that are affected may make it difficult for you to chew, swallow, smile, shrug, lift your arm up, grip, rise to a stand, or walk upstairs. When the muscles necessary for breathing are affected, a patient is said to be in myasthenic crisis. This is a life-threatening situation.

Though anyone can develop myasthenia gravis, those most likely to do so are women between age 20 and 40 or men between age 50 and 70. If a women with myasthenia gravis gives birth, the baby may have some temporary, and potentially life-threatening, muscle weakness (neonatal myasthenia) because of antibodies that have transferred from the mother’s bloodstream.  Typically, during the baby’s first weeks of life, the antibodies are cleared from the baby’s circulation and the baby develops normal muscle tone and strength.

What Causes Myasthenia Gravis?

Under normal conditions, nerves direct your muscles to work by sending a message through an area called a receptor. The chemical that delivers the message is called acetylcholine. When acetylcholine binds to a nerve receptor, your muscle knowns to contract. In myasthenia gravis, you have fewer acetylcholine receptors than you need.

Myasthenia gravis is considered to be an autoimmune disorder. In an autoimmune disease, some of the body’s antibodies (special proteins in your body that are supposed to be programmed to fight foreign invaders such as bacteria, viruses, or fungi) mistake a part of your own body as foreign, resulting in its destruction. In the case of myasthenia gravis, antibodies block, attack, or destroy the acetylcholine receptors needed for muscle contraction.

No one knowns exactly what causes the body to begin producing the antibodies that destroy acetylcholine receptors. In some cases, the process seems to be related to the thymus gland, which helps produce antibodies. 

About 15% of all myasthenia gravis patients are found to have a thymoma, a tumor of the thymus. Although most thymomas are benign (not cancerous), the thymus is usually removed (thymectomy) to prevent to the potential spread of cancer. In fact, thymectomy seems to improve symptoms of myasthenia gravis in some patients, even if no tumor is present. 

What are the Symptoms of Myasthenia Gravis?

The symptoms of myasthenia gravis include:

  • Droopy eyelids
  • Double vision
  • Difficulty swallowing with an increased risk of gagging and choking
  • Change in the quality of one’s voice
  • Increasing weakness of a particular muscle group during continuous use of those muscles and improved strength of muscles after resting those muscle groups
  • Weak cough
  • Difficulty breathing, leading to respiratory failure (myasthenic crisis)

Call Your Doctor if you have the Following Symptoms

  • You notice a droopy eyelid or double vision
  • You have difficulty chewing or swallowing
  • You notice intermittent muscle weakness that improves after rest
  • You already have myasthenia gravis and experience any difficulty breathing

How is Myasthenia Gravis Diagnosed?

During a physical exam, your health care provider may observe signs such as a droopy eyelid, difficulty holding your arms out at shoulder length for a reasonable length of time, or a weak grasp. Blood tests may reveal the presence of acetylcholine-receptor or muscle-specific tyrosine kinase-seropositive (MuSK) antibodies. Specialized tests use electricity to stimulate muscles, and at the same time, measure the strength of muscle contraction.

If you have myasthenia gravis, muscle strength will decrease predictably over the course of testing. You may be given certain medications – edrophonium or neostigmine – as part of a diagnostic exam. In a patient with myasthenia gravis, these drugs will significantly and noticeably improve muscle strength for a short time. This helps to further confirm the diagnosis.

Because other conditions sometimes occur along with myasthenia gravis and can interfere with treatment, your health care provider may order other tests. You may need a CT scan or an MRI to check for a thymoma. You’ll be checked for high blood pressure and glaucoma, and you’ll probably have your blood tested to see if you have thyroid disease, other autoimmune diseases (such as rheumatoid arthritis or systemic lupus erythematosus), diabetes, kidney problems, or any infections.

What are the Treatments for Myasthenia Gravis?

There is no cure for myasthenia gravis, but it is treated with medications and sometimes surgery. You may be put on a drug called pyridostigmine (Mestinon) that increases the amount of acetylcholine available to stimulate the receptors.

If you continue to have symptoms on pyridostigmine, and immunotherapeutic agent is usually added. These include azathioprine (Imuran), cyclosporine (Neoral), eculizumab (Solaris), mycophenolate (CellCept), and prednisone to suppress the immune system.

In severe cases, you may need to have your blood sent through a special machine that removes the antibody-containing plasma and replaces it with antibody free plasma. This is called plasmapheresis. You may also be given a preparation called intravenous immunoglobulin (IVIg) through a needle in a vein.

If you have a thymoma, you will need surgery to remove you thymus (thymectomy). In fact, your doctor may recommend that you undergo this surgery even if no tumor is present because removal of the thymus seems to improve symptoms in many patients.

If you begin to have difficulty breathing due to weakness of the respiratory muscles, you may need to be admitted to the hospital intensive care unit and placed temporarily on a respirator. Myasthenic crisis can occur during a severe infection, so you’ll probably need to be treated with antibiotics as well.

Situations that affect myasthenia gravis include:

  • Changes in thyroid function
  • Surgery
  • Radiation therapy
  • Infection

Certain medications can exacerbate symptoms of myasthenia gravis, including:

  • Antibiotics (particularly those called aminoglycosides)
  • Narcotic drugs
  • Penicillamine
  • Magnesium
  • Anesthesia
  • Muscle relaxants
  • Beta-blockers to treat heart arrhythmias

Some women notice that their symptoms worsen around the time of their menstrual period. Pregnancy’s effect on myasthenia gravis is unpredictable. About one-third of all women have an improvement in their symptoms, one-third have no change, and one-third get worse.

How Can I Prevent Myasthenia Gravis?

There are no known ways to prevent myasthenia gravis. If you already have the condition, take these steps to avoid an exacerbation:

  • Try to prevent infections with careful hygiene and by avoiding sick people
  • Treat infections promptly
  • Do not become overheated or too cold
  • Avoid overexertion
  • Learn effective methods of dealing with stress.