Pediatric Myasthenia Gravis

Myasthenia gravis (MG) is a disorder that causes weakness in muscles around the body. This happens because antibodies destroy some of the places where nerves and muscles meet (neuromuscular connections). MG affects the voluntary muscles of the body. It mostly affects the eyes, mouth, throat, arms and legs. It most often affects adults, but it can sometimes happen in children.

There are three types of MG in children:

Transient neonatal MG

This is a temporary form of MG. It can happen in babies born to mothers with MG. It occurs when antibodies from MG cross over to the baby growing in the mother’s uterus. Transient neonatal MG usually lasts only a short time. The symptoms go away weeks or months after birth, as the antibodies are naturally replaced. Babies are not at greater risk of developing MG later in life.

Juvenile MG

This is an autoimmune disorder. It most often occurs in white teen girls. It is a lifelong condition that may go in and out of remission. Treatment is often done by removing the entire thymus gland. This may cure the disorder.

Congenital MG

This is a very rare form of MG. It is not an autoimmune disorder. It is inherited as an autosomal recessive disease. This means that both boys and girls are equally affected. It also means that two copies of the gene, one inherited from each parent, are needed to have the condition. There are about 12 rare genetic disorders that may cause congenital MG. Symptoms of congenital MG usually start at birth and are lifelong. Some forms may be treated with the same medicines that are used for adults.

Myasthenia gravis is not contagious. This means it can’t be spread from person to person. It may be acquired through immune proteins or antibodies to babies born to mothers with MG. Or the disorder may develop by chance later in childhood. Rare forms of MG are caused by gene changes.

A child is more at risk for myasthenia gravis if he or she has a mother with MG, or parents with certain gene changes.

Symptoms can occur a bit differently in each child, and they vary by type of MG. They can include:

Transient neonatal MG

Babies may be weak and have poor sucking. They may have breathing problems. In some cases, a baby’s respiratory muscles are so weak the baby can’t breathe on his or her own. Then the baby may need the help of a mechanical breathing machine (ventilator). Symptoms go away as the mother’s antibodies disappear over time.

Juvenile MG

Symptoms may start slowly over weeks or months. A child may become very tired after very little activity. He or she may start to have trouble with chewing and swallowing. Drooping eyelids may be so severe that the child can’t see or may have double vision. The symptoms tend to be milder in the morning and worse later in the day or after exercise.

Congenital MG

The symptoms are usually noted at birth, but they may begin in the first year. They include overall weakness in the arms and legs. Babies may have delays in motor skills such as crawling, sitting and walking. They may have trouble feeding or breathing. And they may have weak eyelids and poor head control.

The symptoms of MG can be like other health conditions. Make sure your child sees his or her healthcare provider for a diagnosis.

The healthcare provider will ask about your child’s symptoms and health history. He or she may also ask about your family’s health history. He or she will give your child a physical exam. Your child may also have tests, such as:

Electromyogram/nerve conduction study (EMG/NCS).

This is a test that measures the electrical activity of a muscle or a group of muscles. This is the main way to diagnose MG. An EMG/NCS can detect abnormal electrical muscle activity. In some cases, a single-fiber EMG test may be done. This is a more sensitive test. It may not be done in as many healthcare centers.

Tensilon test.

Your child may be given a medicine called an anticholinesterase inhibitor such as neostigmine or pyridostigmine. It may be given by mouth or injected. In some cases, the medicine is given during the EMG test.

Blood tests.

These check for certain kinds of antibodies in the blood.

Genetic tests.

These tests look for conditions that tend to run in families.

Talk with your healthcare provider if you are pregnant and have MG. Your healthcare provider may advise genetic counseling. You can learn more about the risk of MG in a future pregnancy.

Treatment will depend on your child’s symptoms, age and general health. It will also depend on the severity of the condition and the type of MG.

Transient neonatal MG goes away on its own in weeks or months. There is no cure for juvenile or congenital MG, but the symptoms may be controlled. It is usually a lifelong condition.

A child may need:

• Breathing support. Your child may need a mechanical breathing machine (ventilator) to breathe.
• Nutritional support. If your child has swallowing problems, he or she may need tube feeding or other care.

Treatment may also include any of these:

• Medicines. These include cholinesterase inhibitors, steroids and immunosuppressants.
• Thymectomy. This is surgery to remove the thymus gland. The role of the thymus gland in autoimmune MG is not fully understood. A thymectomy may or may not improve a child's symptoms or cure MG. The benefits of a thymectomy in children with MG are not as proven as in adults with MG. The results of the antibody tests may help your child’s healthcare provider assess if a thymectomy may help.
• High-dose intravenous immune globulin. This is a procedure to add a large amount of normal antibodies from donated blood into the child’s bloodstream.
• Plasmapheresis. This is a procedure to remove abnormal antibodies from the blood and replace them with normal antibodies from donated blood.

Talk with your child’s healthcare providers about the risks, benefits and possible side effects of all treatments.

In severe cases, there can be life-threatening weakness of the breathing or swallowing muscles. This is called crises. A child may need a breathing machine (ventilator) to help with breathing during crises.

Issues may come up as a child grows and develops. Children with MG need to see their healthcare team often.

You can help your child strengthen his or her self-confidence and be as independent as possible. The healthcare team will talk with you about the best ways to help your child.

Call the healthcare provider if your child has:

• Symptoms that don’t get better, or get worse
• New symptoms