Myasthenia Gravis

Also called: myasthenia, MG, juvenile myasthenia gravis, JMG

What Is Myasthenia Gravis?

Myasthenia gravis (my-ess-THEE-nee-uh GRAV-iss) is a condition that causes weakness in the voluntary muscles (the muscles we can control). It happens when connections between nerves and muscles get blocked. In children, the condition is called juvenile myasthenia gravis (JMG).

What Are the Signs & Symptoms of Myasthenia Gravis?

The symptoms of muscle weakness will depend on which muscles are affected. Sometimes only a few muscles are involved. For example, ocular (eye) myasthenia gravis is when only muscles in the eyelids and around the eyes are affected. When the condition affects muscles all over the body, it's called generalized myasthenia gravis. Kids with ocular myasthenia gravis may go on to develop generalized myasthenia gravis over time.

Symptoms can look different in each child. Muscle weakness can come and go, and can vary from mild to severe. It often gets worse later in the day or after physical activity.

Ocular myasthenia gravis can affect one eye or both. It causes:

• ptosis (TOE-siss): a drooping eyelid
• double vision: when one eye is slower than the other

Generalized myasthenia affects muscles all over the body. It often causes:

• clumsiness
• frequent falls
• trouble speaking, chewing, or swallowing
• changes in facial expressions
• a weak neck, making it hard to hold up the head

Myasthenia gravis can be life-threatening if it affects breathing muscles or throat and tongue muscles that help keep the airway open. When someone with myasthenia gravis has trouble breathing, it is called a myasthenic crisis. Things that can make symptoms worse and trigger a myasthenic crisis include illnesses, surgery, poor sleep, and some medicines (including common antibiotics).

What Causes Myasthenia Gravis?

Myasthenia gravis is an autoimmune disease. The immune system usually makes to fight infections. Sometimes it makes a mistake and attacks the body's own tissues or organs. This is called autoimmunity. In myasthenia gravis, the immune system makes antibodies that attack the connections between nerves and muscles, making it harder for the muscles to contract. This makes the muscles weaker.

Myasthenia gravis can start at any age. A person is more likely to have the condition if a close family member has it or another autoimmune disease (such as rheumatoid arthritis, scleroderma, or lupus).

Pregnant women who have myasthenia gravis can pass the antibodies to their fetus. In this case, the baby will be born with myasthenia gravis. Symptoms will include weakness, weak cry, poor suck, and sometimes trouble with breathing. But the baby’s symptoms usually go away after a couple of months when the mother’s antibodies have broken down.

How Is Myasthenia Gravis Diagnosed?

If a child has muscle weakness that comes and goes and gets worse as the day goes on or after physical activity, doctors might suspect myasthenia gravis.

To be sure, the doctor will do an exam and order tests such as:

• antibody titer: This blood test checks for antibodies that can cause myasthenia gravis.
• electromyography (EMG): This measures how well muscles respond to signals from the nerves.
• nerve conduction study: This measures how well nerves transmit signals to the muscles.
• Tensilon test: Tensilon is medicine that restores some muscle strength temporarily. It is injected and symptoms are watched closely. If there is a brief improvement in symptoms, the problem is almost sure to be myasthenia gravis.
• CT scan or MRI of the chest to look for problems with the thymus, a gland in the chest that helps the immune system develop.

How Is Myasthenia Gravis Treated?

There is no cure for myasthenia gravis, but treatment options are available.

Some treatments involve the immune system, such as:

• medicines that suppress the immune system and can be taken by mouth (such as prednisone)
• intravenous immunoglobulins (IVIG), which blocks the action of the antibodies causing the condition
• plasmapheresis, which removes some antibodies from the blood
• surgery to remove the thymus (a thymectomy). Removing it can make the immune system less active.

Also, doctors might use medicines that improve the signaling between the nerves and the muscles, which can make muscle strength better.

If symptoms get worse, a child might need to be treated in the hospital. Supportive care can include breathing help through a mask or a breathing machine, and nutritional support through a feeding tube.

What Else Should I Know?

The treatment goal is complete remission. This means all myasthenia gravis symptoms go away and a person can stop taking medicines. But complete remission doesn't happen often.

Most children with the condition must continue treatment during their teen and adult years. Those who had a thymectomy might need less medicine and be more likely to have complete remission.

If your child has myasthenia gravis, tell any doctor caring for your child about the condition, even if a problem doesn't seem related to it.

It can help to talk with other parents who have a child with myasthenia. Ask your doctor to recommend a local support group, or look online at 

• Myasthenia Gravis Foundation of America