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Wednesday, April 23, 2014
- What are the specific causes/links of Myasthenia Gravis?
- Is Myasthenia Gravis hereditary?
- Can Myasthenia Gravis be caused by trauma?
- Does Ocular Myasthenia Gravis progress to generalized Myasthenia Gravis?
- How does Myasthenia Gravis affect the signals between the brain and the muscles?
- How common is Myasthenia Gravis?
- What are the types of Myasthenia Gravis?
- What should I know about doctor selection and appointments with Myasthenia Gravis?
Myasthenia Gravis is an autoimmune disease. For reasons that are not understood, the body's immune system, which normally fights infections or cancers, attacks the nerve-muscle communication point. In about one in ten Myasthenia Gravis patients, the disease is caused by a tumor called a thymoma that stimulates the immune system to attack the nerve-muscle junction. It is thought that what causes the disease in other patients is a combination of genetic factors and one or more environmental problems. The best guesses of environmental causes are viruses or bacteria (germs) that stimulate the immune system at the "wrong" time in a patient with genetic background that puts them at risk for this autoimmune disease. An example might be that some types of thyroid disease are caused by problems with the immune system and a similar autoimmune condition can cause MG.
In general, Myasthenia Gravis is not an inherited disease. It is not normally passed down from parent to child. If a patient who does not have a strong family history of MG has the disease, it is very unlikely they will pass the disease on. There are some families that appear to have a genetic predisposition (they possess a gene that increases the risk of developing MG), but it does not necessarily mean that everyone in the family will get the disease. There is no scientific proof to determine what genes could place a person at risk for MG and there are no tests for genetic screening.
Infants of mothers with Myasthenia Gravis may be born with neonatal Myasthenia Gravis. The child is weak at birth, but within a few weeks attains normal strength. This is NOT a permanent condition. The antibodies causing the disease in the mother are transferred to the child and then are eventually cleared for from the baby's body. The child does not have Myasthenia Gravis. It is very rare for children of myasthenics to develop Myasthenia Gravis.
There is no reason to believe that trauma, such as an automobile accident, a fall, or a gunshot wound, can cause Myasthenia Gravis. There is also no proof that the stress of these events can cause or "set off" the disease.
About eight out of ten patients with Ocular Myasthenia Gravis proceed to develop generalized MG. The longer a patient remains with only ocular symptoms, the more likely it is that it will not become will not generalized. Unfortunately, there is no clear answer on how to prevent general disease. Some neurologists believe that using prednisone to treat ocular symptoms may decrease the chance of generalization, but this has not been established with any certainty.
Antibodies (proteins of the immune system) attack acetylcholine receptors on the surface of the muscle. This impairs the ability of the nerve to communicate with the muscle and causes it to contract.
The overall prevalence (all cases of disease at one time) of MG varies. In adults, estimates vary from 50-200 patients with the disease per million people. For children, an estimate would be 20-50 children with the disease per million children. Another way of measuring Myasthenia Gravis in children is to say a children's hospital may see one child every one or two years with the disease. MG is more prevalent in women than in men. It is not absolutely understood why this is the case. It is likely the differences in levels of sex hormones contribute to this difference.
The best review regarding the epidemiology of myasthenia appeared in the journal, Neurology, November, 1996, volume 47, pages 1233-1238, by Phillips and Torner entitled "Epidemiologic Evidence for Changing Natural History for Myasthenia Gravis".
Sero-negative: Patients without antibodies against the acetylcholine receptors detected by the standard blood tests are described as having "seronegative" myasthenia. Some of these patients have been found to have antibodies against a protein called, MuSK. Tests for antibodies against MuSK can be performed.
Bulbar Myasthenia Gravis includes a range of symptoms. This term refers to weakness of muscles supplied by an area of the brain called brain stem (or bulb). Some have only weakness of eye muscles (ocular myasthenia). Others have weakness only (or much more severely) of the bulbar muscles. These muscles are those of the throat and face. Patients have speaking and swallowing difficulties. At present, it is not known why some patients have particular involvement of these muscles.
Congenital Myasthenia Gravis is caused by genetic disorders of the nerve-muscle communication point. Usually patients are weak from birth. In some patients, weakness and fatigue become more evident with age. Congenital Myasthenia Gravis is not an autoimmune disease and therefore surgery and/or medications directed at the immune system do not help.
Patients with Myasthenia Gravis should be treated by a neurologist (doctors who are experts in the area of the nervous system) who has some experience with the disease. If surgery to remove the thymus is recommended, the surgery is done by a chest surgeon. If the symptoms are limited to the eyes, ophthalmologists (eye doctors who have been to medical school) may be able to treat the disease. A neuro-ophthalmologist is also a specialist who can treat the ocular symptoms of Myasthenia Gravis.
The frequency of visits with the neurologist depends on the severity of the disease. A patient receiving immune suppression treatment needs frequent observation monitoring of laboratory tests.
Last Reviewed: Dec 29, 2003
Henry J Kaminski, MD
Formerly, Professor of Neurology
School of Medicine
Case Western Reserve University