Myasthenia Graves Research Group

 

FAQs

What is a glucose tolerance test (GTT) and why is it relevant to MG?
What is a DEXA scan and why is it relevant to MG?
What are an EMG and NCS?
How is Myasthenia Gravis Diagnosed?
What is Repetitive Nerve Stimulation (RNS)?
What is Single Fiber EMG?
Is Myasthenia Gravis hereditary?
Do I need insurance to participate in a clinical trial?
What is a placebo?
What do trial phases mean?
How will my medical information be used?
What are the benefits of participating in a clinical trial?


What is a glucose tolerance test (GTT) and why is it relevant to MG?
A GTT is a blood test that provides information about how your body utilizes (metabolizes) sugar. The test can be used to determine if you have normal glucose tolerance, diabetes mellitus or an intermediate state referred to as impaired glucose tolerance. To perform a GTT you must not eat or drink (other than water) for about 8 hours. This is best done overnight (e.g. midnight to 8am). A sample of blood is then drawn to determine the fasting blood glucose concentration. You are then given a glucose sample to drink and blood glucose is measured again two hours later. The GTT is the test recommended to determine whether or not you have diabetes or impaired glucose tolerance.

A GTT is important to patients with MG who are contemplating starting treatment with prednisone. If you have impaired glucose tolerance prior to starting prednisone, there is a greater risk that the prednisone will cause diabetes and that you will need additional treatment to control your blood sugars while taking prednisone. We recommend that a GTT be performed before starting prednisone (since prednisone may impair your glucose tolerance or even cause diabetes), and then again once you reach a stable dose of prednisone. This information can be used to determine whether you need any medication to offset the adverse effects of prednisone on your sugar metabolism.

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What is a DEXA scan and why is it relevant to MG?
DEXA stands for dual-emission x-ray absorbitometry, but DEXA rolls off the tongue a lot more easily. DEXA is a test that is used to measure bone mineral density (BMD). BMD is a marker of bone health. A DEXA scan should not be confused with a nuclear bone scan, which is used to detect infections, tumors and fractures in bone.

Having a DEXA scan requires you to lie on your back and to hold still while a scanner (i.e. an x-ray detector) "takes a picture" of your bones. Bones commonly scanned are the spinal vertebrae (back bones) and the hip. There are no special preparations needed before having a bone scan and the scan itself usually takes about 10-20 minutes.

Learning something about your bone health is important in MG because prednisone may cause thinning of the bones (either osteopenia or osteoporosis). The good news is that prednisone-induced loss of bone mineral density is entirely preventable with appropriate prophylactic medication. Using the results of your DEXA scan, your physician will know whether you have reduced bone mineral density and whether you would benefit from some form of prophylactic therapy (e.g. calcium, vitamin D, bisphosphonate, or other treatment) while taking prednisone.

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What are an EMG and NCS?
EMG stands for "electromyography", which refers to a medical test or procedure in which a needle is used to examine the electrical properties of muscles. The test involves the placement of a needle in a variety of muscles (e.g. in the arms or legs). The needle acts like a microphone, relaying information to the neurologist about the health of the muscle. Since the health of a muscle depends in part on its connection to a nerve, EMG can be used to provide information about the health of both nerves and muscles. EMG is an important test in the evaluation of people with suspected diseases of nerve and muscle, including myasthenia gravis.

The term EMG is sometimes used to include other tests of the electrical properties of nerves, including a test known as nerve conduction studies (NCS). Fortunately, NCS do not involve needles, but they do involve repeated small electrical shocks. These shocks are used to stimulate nerves and the neurologist is then able to make recordings from the nerve in order to better understand how well (or poorly) the nerve is working.

NCS and EMG are typically performed together, and in total the testing usually takes about an hour. Most people find the test mildly annoying or uncomfortable, but very few people describe is as painful. Most people are able to tolerate and complete the test without any difficulty.

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How is Myasthenia Gravis Diagnosed?
The diagnosis of MG may be simple, but may sometimes be quite complex and difficult to make. Most people (about 8 out of 10) with generalized myasthenia have antibodies (proteins that are made by the immune system) that react against a structural component of the neuromuscular junction (the side of communication/connection between nerve and muscle). This neuromuscular junction structure is known as the "acetylcholine receptor". These antibodies can easily be measured in the blood. Since there are very few conditions other than MG that lead to production of these antibodies, the presence of these antibodies in the blood is almost diagnostic of MG. So, for those with antibodies, the diagnosis is easily confirmed by measuring the concentration of these antibodies in the blood. Some people without antibodies against the receptor have antibodies against other proteins (e.g. MuSK).

The diagnosis of MG, therefore, typically begins with a clinical suspicion of the diagnosis based on a careful history of the symptoms and findings on neurological examination. The next step is measurement of these antibodies. If the concentration of these antibodies is high, then the diagnosis is established. For those without antibodies, the diagnosis is more difficult. Tests that your doctor might perform include repetitive nerve stimulation (RNS), single fiber electromyography (SFEMG) or a tensilon test. Your doctor may also perform a chest CT scan to look for abnormalities of the thymus gland. While this is an important test, the results of the scan can neither confirm nor refute the diagnosis of MG.

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What is Repetitive Nerve Stimulation (RNS)?
RNS is a type of nerve conduction study that is used specifically in the diagnosis of myasthenia gravis and other disorders of the neuromuscular junction. The test involves the rapid administration of a series of electrical shocks, with recording of the response from muscles. This test, like many others in medicine, can be done well or badly. It is easy to make technical mistakes and to misinterpret the results. It is very important, therefore, that an experienced person perform the test. People often find this test a little uncomfortable, but most people donít find it painful. Also, the shocks are quite brief and so the discomfort is very short-lived and disappears immediately after the shocks are given. If you're anxious about having this test, please let your neurologist know.

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What is Single Fiber EMG?
Single fiber EMG is a special kind of EMG that involves very careful measurement of the electrical activity in a muscle. The test is difficult to perform and the test is not as widely available as some of the other tests used in the diagnosis of MG. However, single fiber EMG may be very useful for diagnosis, sometimes being the only test that confirms the diagnosis of MG, when all other tests have been negative.

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Is Myasthenia Gravis hereditary?

In order to answer this question, we need to first explain that there are different types of myasthenia. The most common type is what is known as auto-immune MG Ė this is the form of MG that is described on this website (About MG). However, there are two other important, albeit relatively rare, forms of myasthenia - "neonatal myasthenia" and "congenital myasthenia". Neonatal myasthenia occurs in newborns of mothers with MG. What happens is that antibodies (the immune system proteins that cause MG) cross the placenta and interrupt communication between nerves and muscles in the newborn. Since the newborn is not making these auto-antibodies (remember they had passed from mother to child through the placenta prior to birth), they are gradually destroyed and not replaced. The result is that the weakness due to neonatal myasthenia gradually improves, usually over a period of about 2-3 months.

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Do I need insurance to participate in a clinical trial?
It is important to inquire as to how medical costs will be covered prior to enrolling in a research study. Some costs are considered 'research' costs, meaning they are usually covered by the sponsor, or organization conducting the trial. Other costs may fall under 'stand of care' meaning they are typically covered by the participant's private health insurance or Medicare. If you do not have health insurance, you should discuss with research staff whether you will be responsible for paying any costs associated with participation in the study before you make the decision to enroll.

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What is a placebo?
A placebo drug, sometimes referred to as a "sugar pill," is a term used to describe a substance that looks exactly the same as the drug or treatment being tested, however it has no active medicine in it. Clinical trials involving treatment with a placebo are used as a method to test or compare the effects of an active drug to the effects of the placebo in an effort to determine whether the active drug is beneficial in the treatment of a disease. If an MG research study involves a placebo drug, this information will be disclosed to participants prior to their enrollment.

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What do trial phases mean?
Clinical trials are classified by a phase I-IV, which represents what stage the investigational treatment is in the research process.

Phase I: These trials seek to evaluate the safety of a particular treatment or intervention. Researchers are also learning about the maximum dose of a drug that can be safely administered, as well as collecting information about possible harmful side effects. At this stage in the research process, doctors are not yet determining how effective the intervention is at treating the disease.

Phase II: These trials continue to evaluate safety, and begin to test the effectiveness of the intervention or treatment for a particular disease.

Phase III: These trials are examining how the new treatment or intervention compares with the current standard of care as it relates to effectiveness. Researchers are also looking to see if the side effects of the study treatment are more or less frequent than what is considered usual care. If the new intervention is proven to be better tolerated because there are fewer side effects, and it is equal to or better at treating a disease than what is currently available, then it may become the new standard of care.

Phase IV: These trials continue to examine the long-term safety and effectiveness of an agent or intervention, usually after the treatment has already been approved for such use by the FDA.

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How will my medical information be used?
The medical information collected during your participation in a clinical trial will be used by researchers for analysis once the trial is complete. They will use this information to draw conclusions about the drug or intervention that was being tested. These results are often published in the form of medical journal articles, or presented at scientific conferences. It is important to note however that medical information collected from patients when they participate in a study will be de-identified, and participants will be assigned a study ID which will be used instead of a name. Furthermore, a patientís name will not appear in any published results, journal articles, or presentations. If the results of a particular treatment that was being studied look promising, then doctors may decide that additional research may help to learn even more about the agent, and they may use the data from the clinical trial to plan new studies.

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What are the benefits of participating in a clinical trial?
Although you may not directly benefit from participating in a clinical trial, many patients report a positive feeling associated with knowing they are playing an active role in contributing to medical knowledge and scientific research, thereby helping future MG patients. In addition, one possible direct benefit of participating in a clinical trial is that you could have first access to new treatments or interventions that may become the future standard of care in MG before they are available to others with the same disease.

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