What Is Myasthenia Gravis? Causes, Types and Outlook

By Anna Curran, RN, BSN, PHN · Last reviewed October 2026

What is myasthenia gravis? Myasthenia gravis (MG) is a long-term autoimmune condition that causes muscle weakness. Your immune system makes antibodies that get in the way of signals passing from your nerves to your muscles, so the weakness gets worse when you use a muscle and better when you rest it.

If you or someone you love just heard these words for the first time, this guide is for you. Here is what is happening in the body, who tends to get MG, the main types and what the future usually looks like.

What Is Myasthenia Gravis?

MG affects the voluntary muscles. These are the muscles you control on purpose, like the ones that move your eyes, eyelids, face, arms and legs. It can also affect the muscles you use to chew, swallow, speak and breathe.

MG is not a disease of the muscle itself. The muscles are healthy. The problem is at the spot where a nerve meets a muscle. This spot is called the neuromuscular junction.

A key feature is that the weakness comes and goes. Many people feel strongest in the morning and weaker as the day goes on. A muscle may work fine at first, then tire quickly with use.

There is no cure yet. But MG is treatable, and most people can manage it well with the right care.

What Causes Myasthenia Gravis?

How nerves and muscles normally talk

When you decide to move, your nerve releases a chemical messenger called acetylcholine. It crosses a tiny gap and attaches to receptors on the muscle. That tells the muscle to contract.

What goes wrong in MG

In MG, the immune system makes antibodies that attack parts of this connection by mistake. The antibodies block, change or destroy the receptors. With fewer working receptors, the signal is weaker, and the muscle cannot contract as well. That is why you feel weak.

Experts do not know exactly what makes the immune system start doing this. MG is not contagious. It is not usually inherited, though it sometimes shows up in more than one person in a family.

The thymus gland

The thymus is a small gland in your upper chest, behind the breastbone. It helps train the immune system when you are young, then it shrinks in adulthood.

In many adults with MG, the thymus stays large or active. Some people have a growth on the thymus called a thymoma. Most thymomas do not spread, but some can be cancerous. Researchers think the thymus may help start or keep up the antibody attack. This is one reason doctors check the thymus with a CT or MRI scan.

Antibody Types: AChR, MuSK and Seronegative MG

A blood test can look for the antibodies that cause MG. Your result helps your doctor understand your type and choose treatment.

Antibody type	What it means
AChR-positive	Antibodies attack the acetylcholine receptor. This is the most common type. Cleveland Clinic reports about 85% of people with MG have them.
MuSK-positive	Antibodies attack MuSK, a protein that helps hold the nerve-muscle connection together. Cleveland Clinic reports about 6% of people have them.
LRP4-positive	Antibodies attack LRP4, another protein at the nerve-muscle connection. This type is less common.
Seronegative	Tests do not find any known antibody. The immune system is still thought to be the cause. The antibody may not be discovered yet.

A negative blood test does not rule out MG. Your doctor may use nerve tests, such as repetitive nerve stimulation or single-fiber EMG, to help confirm the diagnosis.

Types of Myasthenia Gravis

Ocular myasthenia gravis

Ocular MG affects only the muscles that move the eyes and eyelids. You may notice a droopy eyelid or double vision. Eye symptoms are often the first sign of MG. According to Cleveland Clinic, nearly half of people who start with ocular MG later develop the generalized form.

Generalized myasthenia gravis

Generalized MG affects muscles beyond the eyes. It can involve the face, throat, neck, arms, legs and breathing muscles. You may have trouble chewing, swallowing, talking clearly, climbing stairs or lifting your arms.

Neonatal myasthenia gravis

Some babies born to a mother with MG get her antibodies before birth. The baby may have a weak cry or weak sucking. This is temporary and usually clears within a few months.

Congenital myasthenic syndromes

These are rare conditions caused by gene changes, not by the immune system. They can look like MG but are a different condition with different treatment.

Who Gets Myasthenia Gravis?

MG can start at any age, including childhood. It affects all races and ethnic groups. But it shows up most often in two groups:

Women younger than 40
Men older than 60

Cleveland Clinic estimates that about 60,000 people in the United States have MG. The real number may be higher, since mild cases can be missed.

Some things may raise your risk, according to Mayo Clinic:

Having another autoimmune condition, or a family history of one
Having an enlarged thymus or a thymoma

People with MG are also more likely to have thyroid disease and other autoimmune conditions like rheumatoid arthritis or lupus. Your care team may check for these.

What Is the Outlook?

This is often the first thing people want to know. The news is mostly encouraging.

According to NINDS, most people with MG have a normal life expectancy. Symptoms often reach their worst within the first one to three years. With treatment, many people live full, active lives. Some people even go into remission, where symptoms ease or go away for a time, or for good.

The most serious risk is a myasthenic crisis. This happens when the breathing muscles get too weak to work. It is an emergency that needs care right away. NINDS reports that about 15% to 20% of people with MG have at least one crisis.

Call 911 right away if you or someone with MG has trouble breathing, feels short of breath, cannot swallow or cannot clear saliva.

Treatment options have also grown. Several newer, targeted medicines have been approved by the FDA since 2017, and research is ongoing.

Frequently Asked Questions

Is myasthenia gravis fatal?

Most people with MG have a normal life expectancy with treatment. The biggest danger is a myasthenic crisis, when breathing muscles become too weak. That is why it is important to know the warning signs and get emergency care fast.

Is myasthenia gravis hereditary?

MG is usually not passed down in families, though it sometimes affects more than one family member. Congenital myasthenic syndromes are different. They are caused by gene changes and can run in families.

Can myasthenia gravis go away?

There is no cure, but some people go into remission. Symptoms may ease a lot or stop for a time. Any change to your medicines during remission should only happen with your doctor’s guidance.

What kind of doctor treats myasthenia gravis?

A neurologist usually leads MG care. Many people see a neuromuscular specialist, who is a neurologist with extra training in nerve and muscle conditions.

The Bottom Line

Myasthenia gravis is an autoimmune condition where antibodies disrupt the signal between nerves and muscles. This causes weakness that worsens with use and improves with rest. MG can be ocular or generalized, and most people test positive for AChR antibodies, though some have MuSK, LRP4 or no known antibodies. With treatment, most people live full lives with a normal life span.