If your doctor suspects you have myasthenia gravis (MG), they may recommend getting a magnetic resonance imaging (MRI) scan of your brain. While other tests are typically the main tools for diagnosing MG, an MRI can help rule out other conditions with similar symptoms.

What Is an MRI?

An MRI scan uses powerful magnets and radio waves to create detailed pictures of the inside of your body. The magnets create a strong magnetic field, and the radio waves temporarily disrupt the alignment of atoms in your tissues. The machine detects these changes and translates them into images that can show tissue damage, tumors, blood flow, and other details of your anatomy.

During this noninvasive procedure, you’ll lie on a table that slides into a large, tunnel-shaped machine. You may receive a contrast dye through an intravenous (IV) line in your arm to help certain areas show up more clearly in the images. The procedure is painless, but some people may experience mild side effects from the dye, such as itching or a rash.

Why Might You Need a Brain MRI?

If your doctor or neurologist suspects you have MG or you’ve already been diagnosed, they may recommend a brain or chest MRI for several reasons.

Ruling Out Other Conditions

When doctors evaluate symptoms like muscle weakness or vision problems, they go through a process called differential diagnosis. This means they systematically rule out other possible conditions. For an MG differential diagnosis, they may look for infections, vascular conditions (which affect the blood vessels, such as stroke), and inflammatory diseases.

Multiple sclerosis (MS) is one condition that doctors often check for when evaluating MG. Like MG, MS is an autoimmune disease that can cause muscle weakness and vision problems. However, the conditions’ underlying causes and treatment approaches are very different, so it’s important to get the correct diagnosis. A brain MRI can help distinguish these two conditions because MS often causes characteristic lesions or plaques in the brain and spinal cord, which are not typically seen in MG.

A brain MRI is especially helpful if:

• Your symptoms primarily affect your eye muscles (ocular MG).
• Your blood tests don’t show specific MG-related antibodies (proteins) — these results may mean you have seronegative MG.

“I was just diagnosed with ocular MG,” one MGteam member shared. “It took me three and a half years and several doctors to figure it out. The doctor thought I had a stroke in my eye, so he ordered an MRI and blood work. The MRI came back negative, but the blood work showed I had high antibodies for MG. I finally got lucky.”

Another member wrote, “Doctors have thought many times throughout 30 years that I had MS, but I was finally diagnosed with seronegative MG.”

Why Might You Need a Chest MRI?

Your doctor may also recommend an MRI or CT scan of your chest. This is because some people with MG develop abnormal growths in their thymus gland (a small organ in the chest that helps regulate the immune system). These growths, known as thymomas, can affect MG symptoms. Identifying and treating thymomas is an important part of managing MG.

What Do MRI Results Show?

In MG, chest imaging may reveal an enlarged thymus gland or thymoma. If either is found, your doctor may recommend further evaluation or treatment, such as surgery, radiation, or chemotherapy. Beyond this, MG itself often typically doesn’t cause abnormalities that can be detected through imaging, so MRIs are mainly used to rule out other conditions.

Brain MRI results in people with MG are usually normal. MG primarily affects the neuromuscular junction — the space where nerves communicate with muscles — rather than directly damaging the brain. A normal brain MRI in someone with muscle weakness or vision problems may support an MG diagnosis, especially when combined with medical history, neurological exams (to assess nerve function, reflexes, muscle strength, and coordination), and other diagnostic tests like electromyography (to measure electrical activity in muscles) and antibody testing.

If an MRI shows certain abnormalities, doctors might suspect other conditions, such as:

• Inflammatory conditions that cause muscle weakness, such as MS or amyotrophic lateral sclerosis (ALS)
• Artery problems, such as blood clots
• Muscle disorders, such as muscular dystrophies (a group of inherited conditions that cause progressive muscle weakness and loss of muscle mass)

What Is MRI’s Role in Your Diagnostic Journey?

Although an MRI alone can’t diagnose MG, it’s a valuable tool for ruling out other conditions that could be causing your symptoms. It also helps doctors ensure that nothing requiring a different treatment is being overlooked. An MRI may also be used to check for changes if new symptoms appear or to determine how well treatment is working.

Understanding why your doctor recommends an MRI and what they’re looking for can help you feel more confident about this part of the diagnostic process. When combined with your medical history, symptom patterns, and other diagnostic tests, an MRI can help confirm your diagnosis of MG by eliminating other possibilities.

What Should You Expect During an MRI?

If your doctor recommends an MRI, here’s what you can expect:

• You’ll need to remove metal objects, including jewelry.
• You’ll change into a hospital gown.
• The procedure usually takes 30 to 60 minutes.
• You’ll need to lie very still to ensure clear images.
• The machine makes loud noises, but you’ll get earplugs or headphones.
• You might be allowed to listen to music during the scan.

Throughout the scan, the technologist will be able to see and hear you and can communicate with you.

Some people feel claustrophobic — anxious or uncomfortable in small, enclosed spaces — inside the MRI machine. If this concerns you, talk to your doctor beforehand. They might be able to prescribe a mild sedative or arrange for a wider MRI machine.

Getting an MRI may seem stressful, but this painless procedure provides valuable information. Don’t hesitate to ask your healthcare team any questions you have about the process or the possible results. By understanding the role of MRI in diagnosing MG, you can work closely with your healthcare team to ensure an accurate diagnosis and develop an effective treatment plan.

Talk With Others Who Understand

On MGteam, the social network for people and their loved ones living with myasthenia gravis, more than 2,000 members come together to ask questions, give advice, and share their stories with others who understand life with the condition.

Have you had a brain or chest MRI as part of diagnosing MG? Do you have tips for others who might be getting an MRI? Share your experiences in the comments below, or start a conversation by posting on your Activities page.