Myasthenia gravis is an autoimmune disease
that gradually causes muscles to lose their strength and function. Autoimmune
diseases are caused by the body making substances called antibodies that attack a person's own tissues. In myasthenia gravis,
these antibodies are made against receptors in the neuromuscular junction (the area where nerve transmission
makes a muscle do its work). Myasthenia gravis affects individuals differently,
and each person may present with weakness in different sets of muscles. The
April 20, 2005, issue of JAMA includes an article
about diagnosing myasthenia gravis.
Symptoms of myasthenia gravis
Muscle weakness related to myasthenia gravis usually occurs after the
muscle group is used and lessens if the muscle group has some rest. This is
called fatigable weakness and is an important characteristic for the diagnosis
of myasthenia gravis.
Your doctor will take a medical history, asking especially about the
type of muscle weakness, what makes it better, and what makes it worse. A
physical examination may reveal weakness of the extremities, the eye muscles,
or difficulty in facial expression. Several tests may be used to help diagnose
Ice pack or rest test (simple procedures that temporarily
improve eyelid drooping)
Edrophonium test (a medication given
through an intravenous line, temporarily improving strength in patients with
Blood tests may show antibodies to the receptor
at the neuromuscular junction
Nerve conduction studies may show fatigable weakness
in individual muscle groups
Symptoms of myasthenia gravis can usually be improved with medications
that increase the amount of acetylcholine (a neurotransmitter)
at the neuromuscular junction. Treatments involving the immune system include
injections of intravenous immunoglobulin, immunosuppressive medications, and plasmapheresis (removal of antibodies from the blood).
If an individual's myasthenia is found to be related to abnormalities in the thymus gland located at the base of the neck underneath
the breastbone (sternum), a thymectomy (surgical removal of the thymus gland) may help to improve the symptoms.
When respiratory (breathing) muscles fail, this is
called a myasthenic crisis. This type of respiratory
failure is an emergency. It may require intensive care and use of a ventilator
to assist breathing. Some factors leading to a myasthenic crisis include infection,
fever, medication effects, or even stress.
To find this and previous JAMA Patient Pages, go to the Patient Page
link on JAMA's Web site at http://www.jama.com.
Sources: National Institute of Neurological Disorders and Stroke; American
Academy of Neurology; Myasthenia Gravis Foundation of America
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TOPIC: NEUROMUSCULAR DISORDERS