Myasthenia gravis (MG) tests are used to diagnose MG, a chronic autoimmune disease that causes weakness in muscles throughout the body. An autoimmune disorder causes your immune system to attack your own cells, tissues, and/or organs by mistake. If you have MG, your immune system makes antibodies that block or change the connection between nerves and muscles.
MG affects voluntary muscles in your body. These are muscles that you choose to move. Muscles that control the eyelids are often the first and sometimes the only muscles affected by MG. Other muscles involved can include those in the jaw, neck, and limbs. Muscles that control breathing may also be affected.
MG is not inherited or contagious. It most commonly affects women under age 40 and men over age 60, but it can occur at any age.
MG testing can help you get diagnosed and treated for the disease. While there is no cure for MG, there are treatments that can relieve symptoms and may even allow you to have periods of time without any symptoms (remission).
Other names: Ice pack test, edrophonium test, tensilon test, nerve conduction study
What are they used for?
MG tests are used to diagnose MG.
Why do I need MG testing?
You may need to be tested if you have symptoms of MG. These include:
- Drooping of one or both eyelids
- Double vision
- Weakness in arms, hands, fingers, legs, and/or neck
- Trouble chewing and/or swallowing
- Trouble talking
- Shortness of breath
MG symptoms usually get worse after periods of activity, such as exercise, and improve after periods of rest.
What happens during MG testing?
MG can be hard to diagnose because muscle weakness can be symptom of many disorders. So, your provider may order more than one type of MG test to help make a diagnosis. Types of MG tests include:
Neurological exam. During this test, a provider will take your medical history and conduct a physical exam, which will include checking your:
- Muscle strength
- Muscle tone
- Sense of touch and sight
Ice pack test. This test may be done if you have a droopy eyelid. During the test:
- Your provider will place an ice pack or bag filled with ice on your eyelid.
- The ice will be removed after two minutes.
If drooping improves, it may mean you have MG. This is because cooling temporarily improves muscle weakness that’s caused by MG.
Antibody test. This is a blood test that looks for certain types of antibodies that are found in people with MG. During the test:
- A health care professional will take a blood sample from a vein in your arm, using a small needle.
- After the needle is inserted, a small amount of blood will be collected into a test tube or vial.
Electromyography (EMG). This test measures the electrical signals your muscles make when they are at rest and when they are being used. During the test:
- Your provider will place a needle electrode into your muscle. A needle electrode is a special wire that a mild electric current flows through.
- A machine will record the muscle activity while your muscle is at rest.
- Then you will be asked to tighten (contract) the muscle slowly and steadily.
- The machine will record the muscle activity while your muscle is contracted.
- The electrode may be moved to record activity in different muscles.
- The electrical activity is shown on a video screen.
Nerve conduction study. This test measures how fast and how well the body’s electrical signals travel down your nerves. During the test:
- Your provider will attach one or more electrodes to a certain nerve or nerves using tape or a paste. The electrodes, called stimulating electrodes, deliver a mild electrical pulse.
- These electrodes will record the responses to the electrical stimulation from the nerve.
- Your provider will send a small pulse of electricity through the stimulating electrodes to trigger the nerve to send a signal to the muscle.
- Your provider will record the time it takes for your muscle to respond to the nerve signal.
Imaging tests. Many people with MG have problems with the thymus gland, a small organ in your upper chest. Your provider may order a CT scan (computed tomography) or an MRI (magnetic resonance imaging) to see if you have an enlarged thymus or a thymus tumor, which can be a sign of MG.
During a CT scan:
- You will lie on a narrow table that slides into a scanning machine.
- Once you are in the scanner, the machine will take a series of pictures as it rotates around you.
- You will lie on a narrow table that will slide into a large tunnel-shaped scanner.
- The scanner will take pictures using powerful magnets and radio waves. It does not use radiation.
For both imaging tests, you will need to hold as still as possible. You may also be asked to hold your breath at times while images are being taken.
Edrophonium test. Edrophonium is a drug that briefly relieves muscle weakness in people with MG. It’s mostly used to test weakness in the eye muscles. During the test:
- A provider will inject the drug through an IV (intravenous) line.
- If muscle weakness briefly improves, it may mean you have MG.
Lung function tests. These tests measure breathing and how well your lungs are working. There are several types of lung function tests. For most tests, you will breathe into some type of mouthpiece or machine as your breath is measured. For some tests, you may need to inhale a type of gas or medicine.
Will I need to do anything to prepare for these tests?
You don’t need any special preparations for a neurological exam, ice pack test, or antibody test. For the other tests, you may need to fast (not eat or drink) or avoid certain foods and beverages before the test. Your provider will let you know if you need to make any special preparations.
Are there any risks to these tests?
There is no risk to having a neurological exam or an ice pack test.
There is very little risk to having a blood test. There may be slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.
You may feel a little pain or cramping during an EMG test. During a nerve conduction study, you may have a tingly feeling, like a mild electric shock.
CT scans and MRIs are painless, but can be a little uncomfortable. Some people feel claustrophobic in an MRI scanning machine.
An edrophonium test may cause an allergic reaction. It is not common, but contact your provider if you have breathing problems, vision changes, and/or feel faint after taking the medicine.
There is very little risk to having lung function tests. Some people may feel lightheaded or dizzy during the procedures.
What do the results mean?
If one or more of the tests indicate MG, your provider will probably start you on a treatment plan. With treatment, most people with MG can significantly improve their muscle weakness and have a normal or nearly normal quality of life. Treatment options include:
- Medicines. There are different kinds of medicines used to help improve muscle strength.
- Plasmapheresis. In this procedure, a special machine is used to remove harmful antibodies from plasma, the liquid part of the blood. It then replaces the harmful plasma with normal plasma or a plasma substitute.
- IV Immunoglobulin (IVIG). In this procedure, you receive infusions of antibodies from a healthy donor. IVIG is usually done over a period of two to five days.
- The effects of plasmapheresis and IVIG only last for a few weeks to months. So the procedures may need to be repeated frequently, depending on the severity of your symptoms.
If you have questions about your results, talk to your health care provider.
Is there anything else I need to know about MG testing?
If you’ve been diagnosed with MG, the following lifestyle changes may also help boost muscle strength:
- Eat a healthy diet that includes plenty of protein and carbohydrates.
- Exercise regularly to strengthen muscles, under the guidance of your health care provider.
- Avoid heat and stress, which can make symptoms worse.
- Wear an eye patch if you have double vision.
- Take naps or rest breaks throughout the day.