Overview and Anatomical Involvement
Translated from Latin and Greek, it means "Grave Muscle Weakness."
Myasthenia gravis is an autoimmune condition, meaning that its symptoms come as a result of a malfunction in the sufferer's immune system. It is (from a physical standpoint) painless, characterized by weakness and fatigue in the skeletal, or voluntary, muscles that is severe during activity and improves during rest. It is brought about by immune system-related deterioration of the connections between the muscles and the nerves that control them.
Normal Versus Myasthenic Transmission
Movement of any particular muscle is initiated by a signal from the brain, which, after being relayed by the various nerves to the muscle, causes the muscle to contract or expand in the desired manner. At the point of connection between nerve and muscle (and between nerves in general) is a tiny gap, or synapse, through which signals go from one unit to the next. These signals are contained in neurotransmitters; in a nerve-muscle type of connection, the nerve end of the connection sends neurotransmitters to the muscle. Receptors in the muscle then sense the presence of the neurotransmitters and begin the process of contraction. At least, that's how it's supposed to work.
In Myasthenia Gravis sufferers, the receptors on the muscles have been destroyed or blocked by agents of the immune system. Consequently, the signal does not reach the muscles properly, and muscles become weak. Repeated attempts to use the affected muscles cause more and more fatigue; consequently, muscles that are used most are quickest to tire out.
Role of the Thymus Gland
The thymus gland, nestled beneath the sternum in the upper chest area, is an important factor in early-life immune development. It is quite large in babies, and grows with the body until puberty; after that, it shrinks and some of its mass is replaced with fatty tissue. Its cells are a supposed to be part of the body's normal immune system. In sufferers of MG, the thymus is abnormal, containing clusters of immune cells that are usually only found in the spleen and lymph nodes during an active immune response. Some MG sufferers develop tumors on the gland which are sometimes malignant.
The relationship between the abnormal thymus and MG is not fully understood; doctors believe that the abnormal cells are a result of incorrect instructions on the production of antibodies, which then set the stage for attacks on muscular receptors.
Types
Drug-Related
Cases of MG have been brought about as a result of penicillamine treatment for diseases such as rheumatoid arthritis. Presumably, the treatment can permanently affect the immune system and produce MG. Several other drugs can worsen symptoms; even small amounts of any drugs that act as neuromuscular blocking agents should be avoided by MG sufferers.
Viral/Bacterial
Some sufferers of MG have developed the disease after an attack by another, asimilar disease, manifested always in bacteria or virus. It is possible that the diseases responsible for the onset of MG are similar in appearance to the receptors on the muscles, and for this reason immune agents continue to attack the receptors long after the virus or bacteria has been eradicated. Herpes Simplex is thought to be a culprit.
Adult-Onset
This most common manifestation of Myasthenia Gravis affects women around age 30 and men around age 50. It carries all the typical symptoms, and generally reaches its greatest severity during the first several years after onset. It can coexist with other autoimmune disorders, and problems with the thyroid can exacerbate symptoms.
Transient Neo-Natal
Transient Neo-Natal Mayasthenia Gravis affects infants with myasthenic mothers. It is caused by exchange of pathogenic immunoglobulins from mother to baby through the placenta. MG occurrs in only about 12% of children born to myasthenic mothers, and becomes apparent within the first week of life. Sometimes the condition will subside without treatment in 1-4 weeks. Although the disease is in this case passed along from the mother, there is no relation between the degree of weakness in the infant and the degree of weakness in the mother.
Symptoms and Signs
The most common symptoms of Myasthenia Gravis involve the eye, and are manifested in ptosis (weakening and drooping of the lids) and double vision. This is because, obviously, the muscles of the eyelids and ocular movement are the most-used muscles in the body. Other symptoms include slurred speech, waddling or unstable gait, weakness in arms, hands, fingers, legs, and neck, a change in facial expression, and difficulty in swallowing and shortness of breath. Symptoms can set on quickly or gradually; in some sufferers, symptoms can be independently diagnosed for years (especially ptosis) without any knowledge of the greater problem they show.
Who Gets Myasthenia Gravis?
MG occurs in all ethnic groups and races and in both genders. It can occur at any age, but typically affects ( as was outlined above) women around age 30 and men at age 50. MG is not directly inherited, and it isn't contagious. Occasionally, the disease may occur in more than one member of the same family (a good reason for this is explained above, in types). In rare instances, children will show signs of congenital myasthenia or congenital myasthenic syndrome. These are not autoimmune disorders; they are genetic, and therefore not the same thing as MG.
Diagnosis
Unfortunately, for reasons outlined above, a delay of years in the diagnosis of myasthenia gravis is not uncommon. Weakness is a symptom in many other disorders as well, and consequently the MG diagnosis is missed in people with a history of mild weakness or weakness restricted to a small area of the body.
First, a review is performed on the individual's medical history. This is accompanied by physical and neurological examinations. The doctor performing the tests looks for muscular impairment that isn't accompanied by loss of feeling in the affected area(s). If the doctor's findings indicate MG, several other tests are subsequently administered in order to confirm the diagnosis.
Blood Tests
A special blood test can detect the presence of immune molecules or acetylcholine receptor antibodies (antibodies that attack the receptors). Most patients with myasthenia gravis have abnormally elevated levels of the antibodies. However, antibodies may not be detected in patients who are affected exclusively at the eyes.
Endrophonium Tests
These tests involve the intravenous injection of edrophonium chloride, which, in cases of weakness about the eye, will temporarily relieve symptoms.
EMG
The single-fiber electromyography (EMG) involves the isolation and electrical stimulation of single muscle fibers. It measures the electrical potential of muscle cells; presumably, muscle fibers stricken with MG are not as receptive to the stimulation.
Prognosis
Myasthenia Gravis is an autoimmune disorder, and like other autoimmune disorders, it comes and goes. It may go into remission, it may come back with a vengeance. Fortunately, the prognosis on people with MG is bright; with treatment, sufferers can expect to lead normal or nearly normal lives. The goal of treatment is a stable, long lasting remission. Occasionally, and MG sufferer will undergo a myasthenic crisis, during which the lungs weaken enough to cause respiratory failure.
Treatment
Luckily, MG can be treated with relative ease; there are several therapies available to help reduce problems associated with symptoms. A neurologist, along with a primary care physician, will determine which treatment option is best for each individual, depending on the severity of the weakness, which muscles are affected, and the individual's age and other associated medical problems.
Through Medication
Sometimes, agents are administered that improve neuromuscular transmission and increase muscle strength. Immunosuppressive drugs may also be used. These medications improve muscle strength by suppressing the production of abnormal antibodies. However, they must be used with careful medical followup because they may cause major side effects. Also, doctors might try high-dose intravenous immune globulin, which temporarily modifies the immune system and provides the body with normal antibodies from donated blood.
Thymectomy
Surgical removal of the thymus is an option, but a rarity in sufferers of MG. It is effective in about half of sufferers, and sometimes actually cures the disease through balancing out the immune system.
Plasmapheresis
Plasmapheresis is a procedure through which abnormal antibodies are actually removed from the blood.
Other Information
Further information regarding myasthenia gravis can be found at the following:
Myasthenia Gravis Foundation of America
5841 Cedar Lake Road
Suite 204
Minneapolis, Minnesota 55416
(800) 541-5454
(952) 545-9438
http://www.myasthenia.org/
Information about research on myasthenia gravis and other related neurological disorders can be found here:
NIH Neurological Institute
P.O. Box 5801
Bethesda, Maryland 20824
(301) 496-5751
(800) 352-9424
http://www.ninds.nih.gov
Sources.
- http://www.nanosweb.org/patient_info/brochures/MyastheniaGravis.htm
- http://www.macalester.edu/~psych/whathap/UBNRP/Gravis/autoimmune_types.html#natal
- http://www.ninds.nih.gov/health_and_medical/pubs/myasthenia_gravis.htm#causes
- http://pages.prodigy.net/stanley.way/myasthenia/diagnose.htm
| 
