Myasthenia Gravis

What is myasthenia gravis?

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Myasthenia gravis (MG) is a complex, autoimmune disorder in which antibodies destroy neuromuscular connections. This 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 inherited as a rare genetic disease or 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.

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 in the baby's first year and are lifelong.
• 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.

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 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 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 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/merve 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 neuromuscluar conditions. The diagnosis of MG is occasionally confirmed with a Tensilon or Edrophonium test. With this test, a small amount of medicine (Tensilon or edrophonium chloride) is injected into the child. If the child has MG, an immediate, but brief, increase in muscle tone is noted.

Other diagnostic tests that may be performed to help confirm the diagnosis of myasthenia gravis include:

• Blood tests
• Genetic tests. Diagnostic tests that evaluate for conditions that have a tendency to run in families.
• Muscle biopsy. A small sample of the muscle is removed and examined to determine and confirm a diagnosis or condition.

Treatment of myasthenia gravis

Specific treatment for myasthenia gravis will be determined by your child's doctor based on:

• 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 MG, but the symptoms can sometimes be controlled. Myasthenia gravis is 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 condition.

Treatment may include:

• Medications (cholinesterase inhibitors)
• Thymectomy. This is the surgical removal of the thymus gland. The role of the thymus gland in MG is not fully understood, and the thymectomy may or may not improve a child's symptoms.
• 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.

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