Juvenile Myasthenia Gravis

Juvenile Myasthenia Gravis (Ju-ven-ile My-as-theen-ia Grav-is – or JMG) is a childhood form of myasthenia gravis (MG), which is seen in adults. It’s an autoimmune disease, which means that the immune system (a system that usually protects the body from sickness) attacks the body instead of the germs. The disease does this by stopping some of the connections between the nerves and muscles (the parts of the body that allow us to move).

What causes Juvenile Myasthenia Gravis?

In a person who doesn’t have JMG, the body contracts a muscle (necessary for movement, swallowing, smiling, etc.), by doing the following:

1. The brain sends what’s called a nerve impulse (or signal) to the muscle it controls.
2. The nerve impulse travels along nerve cells and releases a substance called a neurotransmitter to communicate the message from the nerve to the muscle. The name of the neurotransmitter released at the nerve-muscle contact point is acetylcholine.
3. The muscle has special spots called receptors where acetylcholine can attach itself, which gives the muscle the signal to contract (tighten and release).
4. After receiving the signal, the muscle contracts, allowing movement.

In a person with JMG, the body either blocks, changes, damages, or destroys the receptor sites where acetylcholine attaches to the muscle. When these receptor sites are damaged or destroyed, the affected muscles don’t receive enough acetylcholine. Over time this causes certain muscles to become weak because they don’t receive the full message to contract.

How does Juvenile Myasthenia Gravis (JMG) affect the body?

Most often, JMG affects the muscles of the face, especially those that are in charge of eye movements, facial expressions, talking, and swallowing. JMG can also weaken “voluntary” muscles, which are the muscles and movements we can control (such as moving our arms and legs).

Every person with JMG is affected differently, because JMG can affect different muscles in the body. Symptoms usually get worse at the end of the day, or after a person has been active and/or using the affected muscles a lot. However, symptoms can change, which makes it hard to know if they’re caused from JMG or something else. Symptoms can improve with rest.

Symptoms include:

• Droopy eyelids
• Blurry and/or double vision
• Uneven facial expressions
• Choking or trouble swallowing
• Trouble speaking
• Trouble walking
• Changing muscle strength-sometimes strong and sometimes very weak
• Muscle tiredness and physical exhaustion that lasts a while
• Difficulty breathing

The symptoms can change over time, and young people with JMG may not have all of them. Although these symptoms may make a health care provider(s) think a patient has myasthenia gravis, tests are necessary to be sure.

Is there anything that makes the symptoms of JMG worse?

Yes. Alcohol, tonic water with quinine, and certain medications, along with tiredness, not enough sleep, illness, and stress can make JMG symptoms worse.

How is Juvenile Myasthenia Gravis (JMG) diagnosed?

If a health care provider thinks a patient may have JMG, they’ll likely need to have testing done. The tests may include one or more of the following:

• Antibody titer test: This is a blood test that checks for the type of antibodies that attack the neuromuscular system. If the test is positive the patient most likely has JMG.
• Repetitive nerve stimulation: This test is done during an electromyography study (EMG). Certain nerves are stimulated a few times using a low electric signal to see if specific muscles are moving normally.
• Tensilon test: This test may be done after other tests show that JMG is likely. A small amount of medicine called Tensilon is given to the patient in the form of a shot. The person doing the test will then watch for a quick return of muscle tone. This test is less commonly used than in the past.
• Single fiber EMG (SFEMG): This is a special test that is done when other test results are unclear, but the patient still has symptoms. It stimulates one nerve cell and sees how associated muscle fibers respond.
• Genetic testing: This test looks at a patient’s blood sample to see if “congenital” myasthenia gravis (CMG) is present. This test is not used to diagnose JMG.

Is JMG common?

JMG is rare. About 10 in 1 million people are diagnosed with myasthenia gravis each year and about 10% of them are children, which is JMG.

Is JMG the same as Congenital Myasthenic Syndrome (CMS)?

No. CMS is a similar, but different disease of the neuromuscular junction. It’s a genetic disease, not an autoimmune disease.

How does someone get JMG?

Although the cause of JMG is unknown in most cases, JMG is not contagious, and is not passed down from parent to child (it is not “hereditary”). What health care providers do know is that the receptors on the muscles have been damaged in a way that prevents them from working properly.

How is Myasthenia Gravis treated?

Although there isn’t a known cure for JMG yet, there are effective treatments that allow teens to have long periods without symptoms and live a healthy life. JMG can also spontaneously go into remission (no symptoms are shown and no treatment is necessary) or improve.

Treatment options depend on a person’s symptoms, and include:

Acetylcholenesterase inhibitors: These medicines (ex. Pyridostigmine) increase the amount of acetylcholine at the nerve-muscle contact point, so the signal to move muscles is sent many times. The more signals sent, the better the chance that receptors will receive them.

Immunomodulatory therapy: This therapy lowers the number of harmful acetylcholine antibodies. Treatments in this category include:

• Immunosuppressive medicine: Steroids are a type of immunosuppressive medicine that help to strengthen muscles. Unfortunately, this type of treatment stops the immune system from performing other jobs, such as protecting the body from bacteria and viruses.
• Plasmapheresis: This is a special technique that removes harmful antibodies from the blood. The antibodies are replaced with clean blood.
• Intravenous immunoglobin (IVIG): This is a technique that lowers the amount of harmful antibodies made by the immune system.

Surgical treatment:

• Thymectomy: Thymectomy is an operation that removes the thymus gland (an organ that’s part of your immune system). The thymus is located in the chest. Many health care providers who treat patients with JMG believe that the thymus gland makes the antibodies that stop the signal from the brain to the muscles. Health care providers hope that by removing the thymus gland, the muscles will be able to function more normally.

When is a thymectomy needed?

The thymus gland may need to be surgically removed if a child/adolescent has:

• A rare tumor of the thymus gland called a “thymoma”
• Symptoms affect many muscles
• Symptoms do not improve with medical therapies

How does JMG affect chewing and swallowing?

Because chewing and swallowing need repeated muscle movement, chewing and swallowing can sometimes be a challenge for patients with JMG. This can make it hard for people with JMG to get the right amount of nutrients to keep them healthy. Because of these difficulties, mealtime can be exhausting. In order to prevent choking and to make sure to get enough nutrients (vitamins and minerals important to your health), eating foods that are easy to chew and/or swallow are recommended.

What can I do to help myself?

You can help yourself by learning about your condition and taking an active role in your medical care. You should also:

• Take your medicine on time.
• Be sure to refill your prescriptions before you run out of medicine.
• Never take any over-the-counter medicine such as herbs or dietary supplements without checking with your health care provider first.
• Report new symptoms or changes in your symptoms to your parent(s) or guardian and your health care provider.
• Plan rest periods during the day and get plenty of sleep at night.
• Talk with your school nurse or a teacher about any limitations you might have.

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