Myasthenia Gravis in Children
What is myasthenia gravis?
Myasthenia gravis (MG) is a complex, autoimmune disorder in which antibodies destroy
neuromuscular connections. It most often affects adults. MG sometimes can happen in
children as well. For example, mothers who have MG can transfer the abnormal autoimmune
antibodies to the fetus, which causes the baby to be born with temporary MG symptoms.
In these babies, the symptoms typically disappear in th e weeks or months after birth,
as the antibodies are naturally replaced.
There are also about a dozen rare genetic disorders involving the proteins and enzymes
of neuromuscular transmission that cause congenital MG. Congenital MG is not an autoimmune
disorder. However, like all forms of MG, it causes problems with the nerves that communicate
with muscles, resulting in weakness of the skeletal muscles. MG affects the voluntary
muscles of the body, especially the eyes, mouth, throat, and limbs.
What causes myasthenia gravis?
Myasthenia gravis is not contagious, but it may be acquired through immune proteins
or antibodies to babies born to mothers with MG, or the disorder may develop spontaneously
later in childhood. Rare forms of MG are caused by genetic mutations.
What are the types of myasthenia gravis?
There are three types of MG in children, including the following:
Congenital MG. This is a very rare nonimmune form of MG that is inherited as an autosomal recessive
disease. This means that both males and females are equally affected and that two
copies of the gene, one inherited from each parent, are necessary to have the condition.
Symptoms of congenital MG usually begin at birth and are lifelong. Some forms may
be treated with the same medications that are used in adults.
Transient neonatal MG. Babies born to mothers with MG may have a temporary form of MG. This occurs when antibodies
common in MG cross the placenta to the developing fetus. Neonatal MG usually lasts
only a few weeks, and babies are not at greater risk for developing MG later in life.
Juvenile MG. This autoimmune disorder develops typically in female adolescents--especially Caucasian
females. It is a lifelong condition that may go in and out of remission. About 10
percent of MG cases are juvenile-onset. Treatment, which may eliminate the disorder,
typically involves the surgical removal of the entire thymus gland.
What are the symptoms of myasthenia gravis?
The following are the most common symptoms of myasthenia gravis. However, each child
may experience symptoms differently. Symptoms may include:
Babies with neonatal MG may be weak with a poor suck, and may have respiratory difficulty.
A few babies may need the help of a mechanical breathing machine if their respiratory
muscles are too weak to breathe on their own. Symptoms go away as the maternal antibodies
disappear over time.
Congenital MG symptoms are usually noted at birth, but may begin in the first year,
with generalized weakness in the arms and legs, and delays in motor skills such as
crawling, sitting, and walking. Babies may have difficulty feeding or breathing and
may have weak eyelids and poor head control.
Juvenile MG symptoms may begin gradually over weeks or months. The child may become
excessively tired after very little activity, and begin to have problems chewing and
swallowing. Drooping eyelids may be so severe that the child cannot see. The symptoms
tend to be milder in the morning and worsen throughout the day.
The symptoms of myasthenia gravis may resemble other conditions. Always consult your
child's doctor for a diagnosis.
How is myasthenia gravis diagnosed?
The diagnosis of myasthenia gravis is made after the sudden or gradual onset of specific
symptoms and after diagnostic testing. During the physical examination, the doctor
obtains a complete medical history of the child, and may also ask if there is a family
history of any medical problems.
The mainstay of the diagnosis of MG is through the performance of an electromyogram/nerve
conduction study (EMG/NCS), which is a test that measures the electrical activity
of a muscle or a group of muscles. An EMG/NCS can detect abnormal electrical muscle
activity due to diseases and neuromuscular conditions. The diagnosis of MG was historically
confirmed with a Tensilon (edrophonium chloride) test in which, a small amount of
the medicine (edrophonium chloride) is injected into the child. If the child has MG,
an immediate, but brief, increase in muscle tone is noted. However, this medication
is no longer made. Doctors sometimes give a different drug instead (an anticholinesterase
inhibitor such as neostigmine or pyridostigmine) , which can be given by mouth or
injected to help test for MG. Sometimes a more sensitive EMG test, known as single-fiber
EMG, can be used to help make the diagnosis. However, this test requires special skill.
A blood test for certain antibodies often provides a diagnosis.
Other diagnostic tests that may be performed to help confirm the diagnosis of myasthenia
Treatment of myasthenia gravis
Specific treatment for myasthenia gravis will be determined by your child's doctor
Your child's age, overall health, and medical history
The extent of the condition
Your child's tolerance for specific medications, procedures, or therapies
Expectations for the course of the condition
Your opinion or preference
There is no cure for congenital MG, but the symptoms can sometimes be controlled.
Myasthenia gravis is usually a lifelong medical condition and the key to medically
managing MG is early detection.
The goal of treatment is to prevent respiratory problems and provide adequate nutritional
care to the child since the swallowing and breathing muscles are affected by this
Treatment may include:
Medications (cholinesterase inhibitors)
Thymectomy. This is the surgical removal of the thymus gland. The role of the thymus
gland in autoimmune MG is not fully understood, and the thymectomy may or may not
improve a child's symptoms, or possibly even cure the MG. The results of the antibody
tests may help your doctor evaluate how likely the thymectomy is to be helpful.
High-dose intravenous immune globulin
Plasmapheresis. A procedure that removes abnormal antibodies from the blood and replaces
the child's blood with normal antibodies through donated blood.
The extent of the problems is dependent on the severity of the condition and the presence
of other problems that could affect the child. In severe cases, a breathing machine
may be required to help the child breathe easier.
The health care team educates the family after hospitalization on how to best care
for their child at home and outlines specific clinical problems that require immediate
medical attention by their doctor. A child with MG requires frequent medical evaluations
throughout his or her life.
It is important to allow the child as much independent function and self care, especially
with juvenile MG, as possible and to promote age-appropriate activities to ensure
a sense of normalcy.