Myasthenia Gravis
What is it?
Myasthenia gravis is an autoimmune disease that affects
the neuromuscular junction, which is where the nerves
communicate with the muscles and stimulate movement. With
myasthenia gravis, the neuromuscular junction functions
abnormally, which causes muscle weakness.
Who gets it?
Myasthenia gravis can occur at any age, but usually
affects women between the ages of 20 and 40. It is more
common in women than men, and usually affects men after
age 60.
What causes it?
Autoimmune diseases are caused by malfunctions of the
body's immune system, which produces proteins called
antibodies that fight infection. In myasthenia gravis, the
immune system produces antibodies that attack the
acetylcholine receptors. These receptors are located on
the surface of muscle cells, where they receive the nerve
signals through a chemical called acetylcholine. If the
acetylcholine receptors are damaged or destroyed, they are
unable to receive the nerve signal and the muscle cannot
respond with movement. Researchers are not yet sure what
causes this autoimmune response, but believe there may be
a genetic or a viral link. Myasthenia gravis can also be
caused by a tumor of the thymus gland, called a thymoma.
Pregnant women with myasthenia gravis can pass a condition
called neonatal myasthenia on to their babies. Although
symptoms are temporary, they can be life threatening.
What are the symptoms?
The most common and earliest symptoms of myasthenia
gravis are double vision, caused by weakness of the eye
muscle, and drooping eyelids, caused by weakness of the
eyelid muscle. Weakness in the muscles of the mouth and
throat can make swallowing, chewing, and speech difficult.
Weakness in the muscles of the arms and legs may restrict
everyday activities, such as lifting a child or climbing
stairs. If the respiratory muscles become too weak for the
patient to breathe properly, symptoms include rapid
heartbeat, shallow breathing, and pale or blue-tinged
skin. This condition is called myasthenic crisis and
requires emergency medical treatment. Physical exertion
makes the symptoms of myasthenia gravis worse, but they
improve with rest. Symptoms are also affected by heat,
stress, and illness caused by any type of infection.
Muscle weakness can vary from day to day, and many
patients experience periods in which they are symptom free
(remissions). Infants with neonatal myasthenia may have
muscle weakness, lack of muscle tone, a weak cry, and
feeding difficulties. This condition may also affect the
child’s ability to breathe. Symptoms usually resolve
within one month after birth.
How is it diagnosed?
Myasthenia gravis is diagnosed by taking a complete
medical history and performing a thorough physical
examination. Doctors suspect myasthenia gravis when
patients have muscle weakness in the area of the eye and
face, and when muscle strength improves with rest.
However, there are some diagnostic tests that can confirm
the diagnosis and rule out other possible causes of these
symptoms. These tests include electromyography (EMG),
which measures nerve and muscle response, and blood tests
to check for the antibody to acetylcholine. To confirm the
diagnosis, your doctor may perform a test where you are
injected with a drug, such as edrophonium, that increases
the effects of acetylcholine. In patients with myasthenia
gravis, this type of drug temporarily improves muscle
strength. Your doctor may also order a computed tomography
(CT) scan of your chest to check for a thymus gland tumor
(thymoma), which can cause myasthenia gravis.
What is the treatment?
The goal of treatment for myasthenia gravis is to
control symptoms. Drug therapy with medications that
increase muscle strength by increasing the effects of
acetylcholine are often extremely effective. Drugs such as
edrophonium are injected, but other drugs such as
neostigmine or pyridostigmine, can be taken orally and
often have fewer side effects. With long-term use,
however, these drugs can lose their effectiveness. Many
patients with myasthenia gravis see improvement after the
surgical removal of the thymus gland, called a thymectomy.
In fact, thymectomy may cure myasthenia gravis in patients
with thymoma. Patients who do not show sufficient
improvement with drug treatment or thymectomy may need to
take immunosuppressive drugs, such as prednisone,
azathioprine, or cyclosporine. Patients who have weakness
in the muscles used to chew and swallow find that a softer
diet is helpful, while severe cases need a feeding tube
for nourishment. Always follow a doctor’s or registered
dietitian’s dietary recommendations to ensure you are
receiving proper nourishment. Patients in myasthenic
crisis may be treated with plasmapheresis, a procedure in
which the patient’s blood plasma is replaced with plasma
that is free of abnormal antibodies. Immunoglobulin
therapy is another type of blood therapy that can provide
temporary improvement. With this treatment, the patient is
injected with large amounts of immunoglobulins, which are
purified immune proteins. Infants with neonatal myasthenia
may require temporary breathing assistance through a
ventilator.
Self-care tips
If you have been diagnosed with myasthenia gravis,
avoid conditions that make your symptoms worse, such as
heat, stress, and intense exercise. Because some drugs can
also make your symptoms worse, make sure your doctors and
pharmacist are aware of your condition. Take all
medications as prescribed by your doctor, at the same time
each day.
This information has been designed as a comprehensive and quick reference
guide written by our health care reviewers. The health information written
by our authors is intended to be a supplement to the care provided by your
physician. It is not intended nor implied to be a substitute for
professional medical advice.
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