What are myasthenia gravis (MG) tests?

Myasthenia gravis (MG) tests are used to diagnose MG, a chronic (long-lasting) autoimmune disease that causes weakness in muscles throughout your body. In autoimmune diseases, your immune system mistakenly attacks the healthy cells of your organs and tissues. If you have MG, your immune system makes antibodies that block or change the connection between your nerves and muscles.

MG causes weakness in the voluntary muscles in your body. These are muscles that you can control. The symptoms of MG may begin suddenly. There are different types:

• Ocular MG affects the muscles controlling the eyelids. These are often the first and sometimes the only muscles that MG affects.
• In generalized MG, the weakness may also be in your eyelids. But it affects other muscles as well, such as those that control eye movement and those in your neck, arms, and/or legs. If the muscles that control your breathing are affected, this is called a myasthenic crisis. It is a life-threatening emergency.

Researchers aren't sure why people get MG. It is not inherited (passed down in families). But occasionally, the disease affects more than one member of the same family.

What is known is that you may have an increased chance of developing MG if you:

• Have another autoimmune disorder, such as rheumatoid arthritis or systemic lupus erythematosus.
• Have a problem with your thymus gland, a small organ in your upper chest. It is part of your immune system. If you have MG, your thymus gland might be larger than usual, or you may have a thymoma (thymus tumor). These tumors are usually benign (not cancer), but they can become cancerous.
• Are a woman under age 40 or a man over age 60. This is the age range MG most commonly affects (although you can develop it 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 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. Your symptoms will depend on which muscles are affected. The symptoms often include:

• Drooping of one or both eyelids
• Weakness of the eye muscles
• Blurred or double vision
• Changes in facial expression
• Weakness in arms, hands, fingers, legs, and/or neck
• Trouble swallowing and/or chewing
• Trouble talking
• Fatigue
• Shortness of breath

MG symptoms usually get worse after periods of activity, such as exercise, and improve after rest.

What happens during MG testing?

MG can be hard to diagnose because muscle weakness can be a symptom of many disorders. So, your health care 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, your provider will take your medical history and do a physical exam, which will include checking your:

• Reflexes
• Muscle strength
• Muscle tone
• Coordination
• Balance
• 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 looks at the electrical signals your muscles make when they are at rest and when used. A healthy muscle should not give off electrical signals when you aren’t moving. If your muscle is damaged, it may show electrical activity while at rest or activity that is not normal while using it. During the test:

• Your provider will place a small needle with an electrode into your muscle. This is connected to a machine used to record your muscle's electrical activity. You may have slight pain or discomfort when the electrode is inserted.
• 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 recorded and shown on a video screen. The activity may also be sent to an audio speaker. The audio may make popping sounds when you're contracting your muscles.

Nerve conduction study. This test measures how fast and well your body's electrical signals move along your nerves. A damaged nerve has a slower and weaker signal. This test can help check for nerve damage. During the test:

• Your provider will stick electrodes to your skin above a nerve they're checking using tape or a paste. The electrodes, called stimulating electrodes, deliver a mild electrical pulse.
• Your provider will attach recording electrodes to the muscles controlled by those nerves. These electrodes will record the muscle's response 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 signal the muscle. This may cause a mild tingling feeling.
• Your provider will record the time it takes for your muscle to respond to the nerve signal.

Imaging tests. 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 pictures as it rotates around you.

During an MRI:

• 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 a 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. Tell your provider if you are pregnant, have pieces of metal in your body, or if you have a pacemaker or cardiac defibrillator. Special steps may need to be taken before the test. Also, tell your provider if you take any medicines. If you're taking blood thinners, you may need to watch for more bleeding from the needle.

Your provider will let you know if you need to make any additional 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. If your pain becomes very uncomfortable, let your provider know, as this may change your test results. You may feel tingly during a nerve conduction study, like mild static electricity. Your tested muscles may be sore for a few days, and you may have bruises from where the needles were placed.

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 show that you have MG, your provider will work with you on a treatment plan. Treatments can help reduce your symptoms and improve muscle weakness. The treatment options may include:

• Medicines. Different medicines are used to help improve muscle strength and/or decrease your body's immune system responses.
• Plasmapheresis (plasma exchange) and intravenous (IV) immunoglobin. These procedures remove abnormal antibodies from your blood. They are usually only used in severe cases. They can help with your symptoms for a few weeks or months.
• Surgery. Your provider may recommend surgical removal of your thymus gland, which is often abnormal in people with MG. The procedure can reduce symptoms, even in people without thymus tumors.

If you have questions about your results, talk to your provider.

Learn more about laboratory tests, references ranges, and understanding results.

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:

• Eating a healthy diet that includes plenty of protein and carbohydrates.
• Doing regular gentle exercise to strengthen your muscles. But check with your provider before starting any exercise program.
• Avoiding heat and stress, which can make symptoms worse.
• Wearing an eye patch if you have double vision.
• Taking naps or rest breaks throughout the day.