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:
- 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 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.
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 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.