Myasthenia Gravis: What to Know About This Autoimmune Disorder

Myasthenia gravis (MG) is a rare condition that causes muscle weakness or fluctuating muscle fatigue. This fatigue can affect your daily life due to trouble with speaking, chewing, breathing, vision, or mobility. The symptoms of myasthenia may be similar to those of other neurological conditions. This can make the diagnosis challenging at times. 

Fortunately, myasthenia gravis can be diagnosed by specialized healthcare professionals. And, once diagnosed, there are treatment options to help with symptoms of myasthenia and improve your quality of life.

Let’s take a closer look at what causes myasthenia gravis, as well as the symptoms, diagnosis, and treatment of this condition.

What is myasthenia gravis?

Myasthenia is an autoimmune disorder that causes muscle weakness in different parts of the body. It’s quite rare, affecting less than 1% of people. It can develop in anyone (including children). But it’s more common in women in their 20s to 30s and men older than 50. 

Myasthenia gravis commonly affects muscles in the following body areas:

• Eyes

• Face

• Limbs

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In severe cases, it may also affect the diaphragm (breathing muscles) and swallowing muscles. Myasthenia gravis may be mild or severe and life-threatening. 

What causes myasthenia gravis?

Experts aren’t sure what causes myasthenia gravis. But a couple of things are clear: It’s not contagious, and it’s not your fault. 

Generally speaking, the cause of myasthenia is a combination of:

• Increased risk from your genes

• Some kind of trigger from the environment (like an infection)

• A family history of myasthenia or autoimmune disease

To understand what causes myasthenia symptoms, 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 ACh receptors (AChR) on the muscle, which causes it to move. 

In myasthenia gravis, the body can make antibodies that block or even destroy the AChRs. This can prevent the brain’s signal to move from getting to the muscle. Antibodies normally protect us against things that don’t belong (like infections). But, in autoimmune conditions, the antibodies target parts of your own body instead.

What are the symptoms of myasthenia gravis?

Symptoms of myasthenia gravis 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, such as:

• 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 symmetrical — that is, it’s 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 myasthenia gravis, a healthcare professional will listen to a history of your symptoms. They’ll then check for muscle weakness using blood tests or special muscle tests to confirm the diagnosis. 

Diagnostic 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 suggests myasthenia. An ophthalmologist (eye specialist) typically does this test, though it isn’t very common.

• Blood tests: Blood tests can check for myasthenia antibodies. But about 10% of people with myasthenia gravis 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 myasthenia have thymomas.

• Repetitive nerve stimulation: This test records nerve signals to see how they respond to repeated electrical impulses.

• 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.

Types of myasthenia gravis

There are five main classes of myasthenia gravis. These classifications are based on how severe the symptoms are:

• Class I: There’s weakness only in the muscles of the eyes with normal strength in the rest of the body, which is known as ocular myasthenia. (Eye symptoms often come first before progressing to generalized myasthenia.)

• Class II: There’s mild weakness in other muscles of the body, with or without eye weakness.

• Class III: There’s moderate weakness in other muscles of the body, with or without eye weakness.

• Class IV: There’s severe weakness in other muscles of the body, with or without eye weakness.

• Class V: The person needs intubation to help with breathing.

Classes II to IV may be further divided into one of two subtypes: A or B. 

Subtype A affects mostly the muscles in the following body parts:

• Arms

• Legs

• Neck

• Back 

Subtype B affects mostly these muscles:

• Mouth

• Throat

• Breathing muscles

What are the treatments for myasthenia gravis?

Treatment of myasthenia gravis includes these three approaches:

1. Cholinesterase inhibitors: Medications called cholinesterase inhibitors are used to slow down the breakdown of ACh in the area between muscles and nerves.

2. Immunosuppressants: Medications called immunosuppressants are used to stop the immune system’s attack on the body. 

3. Thymectomy: Thymectomy is a surgery to remove the thymus gland.

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

Medications for myasthenia gravis

Treatments may include:

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

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

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

• Vyvgart: Vyvgart 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.

• Zilbrysq: Zilbrysq is a complement inhibitor that prevents proteins from being used to create antibodies.

• Rystiggo: Rystiggo is a neonatal Fc receptor blocker which decreases the number of antibodies.

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

• Intravenous immunosuppressants: Examples of these medications include rituximab, eculizumab, and cyclophosphamide.

• Intravenous immunoglobulin (IVIG): These are normal antibodies pooled from healthy donors given through an IV infusion. 

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

Guidelines recommend thymectomy 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 myasthenia gravis need some kind of medication for many years. Some may need medication for life. How long you’ll need to take medication depends on how well symptoms respond to treatment.

What makes myasthenia gravis worse?

People with myasthenia gravis may experience times when their symptoms worsen, called myasthenia flares. 

Triggers for myasthenia 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) 

Complications of myasthenia gravis

Complications of myasthenia gravis can be related to worsening of the condition or its treatment. These include:

• Myasthenic crisis: This is a sudden worsening of myasthenia in which breathing and muscles of the mouth and face become very weak. This is a medical emergency that’s often triggered by infection, stress, or certain medications. To help with breathing, most people with myasthenic crisis need to be intubated 

• Cholinergic crisis: ACh may build up when too much anticholinesterase is used to treat myasthenia. The excess ACh may cause drooling, tearing, blurred vision, wheezing, diarrhea, and paralysis.

If you have myasthenia gravis and notice a sudden shift or flare-up of your symptoms, let a healthcare professional know right away.

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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:

Karla Robinson, MD

Karla Robinson, MD, is a medical editor for GoodRx. She is a licensed, board-certified family physician with almost 20 years of experience in health through varied clinical, administrative, and educational roles.

Reviewed by:

Itza Rivera, MD

Dr. Rivera is a board-certified physical medicine and rehabilitation specialist. She completed her medical degree and residency training at the University of Puerto Rico School of Medicine, and her neuromuscular disorders subspecialty training at Northwestern University.

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