What Is Myasthenia Gravis?

Myasthenia gravis (MG) — or just myasthenia — is an autoimmune disorder that causes muscle weakness in different parts of the body. It commonly affects the eyes, face, and limbs. In severe cases, it may also affect breathing muscles (diaphragm) and swallowing muscles. MG may be mild or life-threatening. 

MG is a rare condition that affects about 0.02% of people. But it can affect people of any age (including children). It’s more common in women in their 20s to 30s and men older than 50. 

There are several treatments that can improve muscle weakness and save lives when MG affects swallowing and breathing. In this article, we discuss the cause, symptoms, diagnosis, and treatment of MG.

What causes myasthenia gravis?

To understand what causes MG, we first have to understand a bit about how the brain and nerves make muscles move. First, the brain sends a signal down a nerve to the muscle. But there’s not a direct connection between nerves and muscles. 

The neuromuscular junction is the gap between the nerve and muscle. To send the signal across this gap, nerves release acetylcholine (ACh), a type of chemical. ACh floats across and connects with acetylcholine receptors (AChR) on the muscle, which causes it to move. 

In MG, the body can make antibodies to the AChR that prevent the signal from getting to the muscle. The antibodies can block or even destroy the AChRs. Antibodies normally protect us against things that don’t belong (like infections). But in autoimmune conditions, the antibodies target parts of our own bodies instead.

We aren’t exactly sure what causes MG. But a couple of things are clear: It’s not contagious, and it’s not your fault. Generally speaking, the cause of MG is a combination of increased risk from your genes and some kind of trigger from the environment (like an infection). A family history of MG or autoimmune disease might also increase your risk of MG.

What are the symptoms of myasthenia gravis?

Symptoms of MG vary from person to person. Most people (but not all) have symptoms related to eye muscle weakness, such as droopy eyelids and double vision. Eye muscle weakness tends to be worse on one side than the other.

Weakness of other muscles can cause additional symptoms. They may include: 

• Trouble making facial expressions, like smiling or raising eyebrows

• Difficulty chewing tough foods or swallowing

• Slurred speech 

• Shortness of breath or severe breathing problems

• Weakness of the arms, legs, or neck

Limb weakness tends to be worse in areas closest to the trunk, like the thighs and upper arms. This is normally symmetric — that is, equal on both sides. Muscle strength can feel normal in the morning but can get worse with exercise and toward the end of the day. 

How do you diagnose myasthenia gravis?

To diagnose MG, a healthcare provider listens to your symptoms and performs a physical exam to check for muscle weakness. Then they’ll do blood tests or special muscle tests (see below) to confirm the diagnosis. 

Additional tests might include any of the following:

• Ice pack test: This test can help when only eyelid muscles are weak (and not other eye muscles). It involves placing ice packs on closed eyes for 2 minutes and then measuring how far the eyelids can open. If eyelid drooping improves after icing, the test is positive (concerning for MG). An eye specialist (ophthalmologist) typically does this test, though it isn’t very common.

• Blood tests: Blood tests can check for MG antibodies, but about 10% of people with MG have negative antibody tests.

• Chest X-ray or CT scan of the chest: These look for thymoma, a noncancerous tumor of the thymus gland above the heart. About 10% to 15% of people with MG have thymomas.

• Electromyogram (EMG): A specialist inserts a tiny needle (like the ones in acupuncture) into some muscles to see what’s going on at the neuromuscular junction. It can be a bit uncomfortable, but it’s less scary than it sounds!

What are the treatments for myasthenia gravis?

Treatment of MG may includes three different approaches:

1. Medications to slow down the breakdown of ACh in the area between muscles and nerves (anticholinesterases)

2. Medications to stop the immune system attack on the body (immunosuppressants)

3. Surgery to remove the thymus gland (thymectomy) 

Treatment guidelines from a group of international experts were last updated in 2020. The treatment that’s right for you depends on your age, other medical issues, and response to therapies. 

Treatments may include:

• Pyridostigmine: An anticholinesterase that slows breakdown of ACh. This is the first-choice medication for most people.

• Steroids: These turn off overactive parts of the immune system quickly. Prednisone is a common one.

• Immunosuppressants: These help control MG without the use of steroids. Azathioprine is one example.

• Vyvgart: This is a biologic medication that lowers levels of anti-AChR antibodies in the body. So it’s an option if you have anti-AChR antibodies.

Of note, pyridostigmine and Vyvgart are FDA approved for the treatment of MG, but the other listed therapies are considered “off-label.” There are studies to support the use and safety of these medications for people with MG, so doctors commonly prescribe them.

In life-threatening or severe cases that don’t respond to other therapies, options include:

• Intravenous immunosuppressants: Examples of these medications that go directly into the vein include rituximab, eculizumab, and cyclophosphamide.

• Intravenous immunoglobulin (IVIG): These are normal antibodies pooled from healthy donors. 

• Plasma exchange (PLEX): This removes MG antibodies from your body by filtering your blood through a machine.

Recent guidelines recommend thymectomy early on for people ages 18 to 50 who make anti-AchR antibodies. Thymectomy might also help people who don’t have good results with other treatments.  

Most people with MG need some kind of medication for many years. Some may need medication for life. Duration of therapy depends on how well symptoms respond to treatment.

What makes myasthenia gravis worse?

People with MG may experience times when MG symptoms are worse than normal (MG flares). Triggers for MG flares include: 

• Infections

• Stress, depression, or anxiety

• Not getting enough sleep

• Certain types of anesthesia for surgical procedures 

• Certain medications (like some antibiotics and beta blockers) — talk to your provider about medications you might need to avoid or use with caution

Why trust our experts?

Written by:

Samantha C. Shapiro, MD

Samantha Shapiro, MD, is a board-certified rheumatologist and internist with expertise in autoimmune and inflammatory conditions. She founded the division of rheumatology at Dell Medical School at The University of Texas at Austin.

Edited by:

Mandy Armitage, MD

Mandy Armitage, MD, has combined her interests in clinical medicine with her passion for education and content development for many years. She served as medical director for the health technology companies HealthLoop (now Get Well) and Doximity.

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