How Is Myasthenia Gravis Diagnosed? Antibodies, Ice Pack Test, MRI, and More | MGteam

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How Is Myasthenia Gravis Diagnosed? Antibodies, Ice Pack Test, MRI, and More

Updated on January 23, 2024

If you or a loved one is experiencing symptoms of myasthenia gravis, it’s important to know what’s involved in getting an official diagnosis. If your primary care doctor thinks you may have the condition, they’ll refer you to a specialist who can help. Neurologists diagnose and treat neuromuscular conditions (illnesses related to the connections between nerves and muscles). They’ll use a handful of tests — along with your medical history and physical exam results — to help determine whether you have myasthenia gravis and if so, what type of myasthenia gravis it is.

The information in this article can help prepare you to speak with your doctor about myasthenia gravis and understand what tests are needed to diagnose the condition.

Symptoms of Myasthenia Gravis and When To Seek a Diagnosis

Myasthenia gravis is an autoimmune disorder that causes muscle weakness and ocular symptoms (eye problems). This means that the immune system attacks the body’s healthy cells and tissues. In myasthenia gravis, immune system proteins known as autoantibodies attack the neuromuscular junction, where the nerves and muscles connect. People with this condition can have symptoms including:

  • Fatigue
  • Muscle weakness affecting the neck, arms, legs, hands, and fingers
  • Diplopia (blurry or double vision)
  • Ptosis (droopy eyelids)
  • Difficulty chewing, swallowing, and speaking
  • Changes in facial expressions

If you’re experiencing any combination of these symptoms, it’s time to talk to your doctor or neurologist. They’ll help you get a diagnosis and start a treatment plan. In the meantime, start recording when your symptoms occur and how long they last. Your symptoms may not always show themselves during your doctor’s appointment, so be ready to explain what they look like and how they feel.

Notably, it may take some time for your doctor to confirm a myasthenia gravis diagnosis. This is especially true if you have mild symptoms that affect only a few muscles. According to the National Institute of Neurological Disorders and Stroke (NINDS), a myasthenia gravis diagnosis can be delayed by up to two years for some people.

Medical History and Physical Exam

Your doctor will start by taking your medical history and performing a thorough physical exam. They’ll ask questions about your symptoms and whether you or anyone in your family has a history of myasthenia gravis or autoimmune diseases.

Your doctor may also perform a neurological exam to check your nerve and muscle function. They’ll test your:

  • Muscle strength and tone
  • Balance and coordination
  • Reflexes
  • Sensitivity to touch
  • Sight and any impaired eye movements

The neurological exam will let your doctor know you may have a neuromuscular disorder. However, you’ll need additional tests to confirm whether you have myasthenia gravis or another condition.

Ice Pack Test

The ice pack test is an easy test used to diagnose myasthenia gravis affecting the eyelids. Researchers have found that cold can help improve myasthenia gravis symptoms.

If you have droopy eyelids, your doctor will apply an ice pack on your eyelids for two minutes. After they remove the ice pack, they’ll check to see if your eyelid raises at least 2 millimeters or more. If your eyelids are no longer droopy, it may be a sign that you have myasthenia gravis.

It’s important to note that the ice pack test is accurate only 80 percent of the time. While it can suggest you have myasthenia gravis, your doctor will need to run a few more tests to confirm a final diagnosis.

Antibody Testing

Antibodies are a key part of your immune system that helps protect you against infection. Normally, your immune system makes new antibodies when you’re sick by tagging invading bacteria and viruses for destruction. Your immune system isn’t always perfect — sometimes, it can mistakenly make antibodies targeting your healthy cells and tissues. This is what happens in autoimmune conditions, including myasthenia gravis.

If your physical exam shows you may have a neuromuscular disorder like myasthenia gravis, your doctor will look for autoantibodies. Antibody testing involves a simple blood test. Your doctor will take a small blood sample from a vein in your arm and run tests for the autoantibodies.

The two most common antibodies in myasthenia gravis are acetylcholine receptor (AChR) and muscle-specific kinase (MuSK) antibodies. The chemical messenger acetylcholine makes your skeletal muscles and eye muscles contract, controlling your movement and vision. AChR antibodies interfere with how well acetylcholine works and cause characteristic myasthenia gravis symptoms. Around 85 percent of people with myasthenia gravis have AChR antibodies. If you test positive for AChR antibodies, your doctor will confirm you have myasthenia gravis.

If you test negative for AChR antibodies, it doesn’t rule out having myasthenia gravis. You may need additional tests to get a final diagnosis. Your doctor may also check for MuSK autoantibodies. According to the University of Rochester Medical Center, up to 40 percent of people with myasthenia gravis who don’t have AChR antibodies are positive for MuSK antibodies. Myasthenia gravis that is positive for MuSK antibodies is called MuSK-MG.

Between 6 percent and 12 percent of people with myasthenia gravis have neither AchR nor MuSK antibodies. When this occurs, it’s referred to as seronegative myasthenia gravis. Interestingly, doctors and researchers have found that around 1 percent of people with seronegative myasthenia gravis have low-density lipoprotein receptor-related protein 4 (LRP4) antibodies. Your doctor may choose to test for LRP4 antibodies if other test results are unclear.

Electromyography

After the physical exam and antibody testing point to myasthenia gravis, the next step is performing electromyography. Also known as a nerve conduction study, electromyography measures the electrical signals in the muscle nerves. It can be especially helpful in diagnosing mild cases of myasthenia gravis that may be missed by other tests.

Your doctor will place sticky patches with electrodes on your skin. Some electrodes will deliver small electrical shocks to your nerves, while others will record how your muscles respond. The most common electromyography test is repetitive nerve stimulation (RNS). This method delivers repeated electrical shocks to the nerves. In people with myasthenia gravis, the muscles quickly become tired after repeated shocks. RNS has 75 percent to 80 percent accuracy.

Doctors may also use another test known as single-fiber electromyography (SFEMG). While SFEMG is more accurate than RNS, it’s less common and harder to use.

Edrophonium Test

Another test used to diagnose myasthenia gravis is called the edrophonium or Tensilon test. During this test, your doctor will give edrophonium intravenously (through a vein) in your arm. If you have myasthenia gravis, this medicine should temporarily improve your muscle weakness. This is because edrophonium helps break down acetylcholine for your muscles to use. If you have droopy eyelids from myasthenia gravis, you’ll likely notice your symptoms get better for a few minutes with edrophonium treatment.

However, an edrophonium test may make some people’s myasthenia gravis symptoms worse. Those who are positive for MuSK antibodies may notice more muscle weakness during this test. If your doctor thinks you have MuSK-MG, they likely won’t perform an edrophonium test.

An alternative to the edrophonium test is taking the drug pyridostigmine (Mestinon). This medication is taken by mouth to treat myasthenia gravis. Your doctor may prescribe you a trial of pyridostigmine to see if your symptoms improve. If they do, it’s more likely you have myasthenia gravis.

Imaging Tests

After doctors confirm a myasthenia gravis diagnosis, the final step is to use imaging tests to look at the thymus gland. This tissue is found above your heart, located behind the sternum (breastbone). The thymus makes specialized immune cells that protect you against infections.

Studies show that around 15 percent of people with myasthenia gravis have a thymoma or a tumor on their thymus. When the immune system tries to fight the cancer, it creates antibodies targeted at the tumor. These antibodies also mistakenly attack the neuromuscular junction in myasthenia gravis. The neuromuscular junction refers to the connection between nerves and muscles that control movement.

Doctors will order an MRI or more commonly a CT scan to take a closer look at the thymus. If you have a thymoma, you’ll be recommended for surgery (known as a thymectomy) to remove it.

Differential Diagnosis

If your symptoms resemble those of another condition, your doctor may perform a differential diagnosis. This is a process to rule out conditions and is often part of diagnosis. Read more about Lambert-Eaton myasthenic syndrome and other conditions that may appear similar to myasthenia gravis.

Find Your Team

On MGteam, the social network for people living with myasthenia gravis and their loved ones, members come together to ask questions, give advice, and share their stories with others who understand life with myasthenia gravis.

What myasthenia gravis symptoms do you experience? How were you diagnosed? Share your experience in the comments below, or start a conversation by posting on your Activities page.

    Updated on January 23, 2024
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    Luc Jasmin, M.D., Ph.D., FRCS (C), FACS is a board-certified neurosurgery specialist. Learn more about him here.
    Emily Wagner, M.S. holds a Master of Science in biomedical sciences with a focus in pharmacology. She is passionate about immunology, cancer biology, and molecular biology. Learn more about her here.

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