Myasthenia gravis is a chronic condition that disrupts the way nerves and muscles communicate with each other, leading to muscle weakness that worsens with activity and improves with rest. While this rare autoimmune disease cannot be cured, most people with myasthenia gravis can live full, active lives with proper treatment and management strategies tailored to their individual needs.

Understanding Myasthenia Gravis Around the World

Myasthenia gravis affects approximately 20 out of every 100,000 people worldwide, which means that roughly 60,000 to 75,000 people in the United States live with this condition at any given time^[3][13]. The actual number may be higher because some people with mild symptoms may not realize they have the condition or may not seek medical attention for what they perceive as minor issues.

This rare disease can affect anyone, regardless of race, gender, or background. However, certain patterns emerge when examining who is most likely to receive a diagnosis. The condition most commonly appears in young adult women under 40 years of age and in older men over 60 years of age^[1][2][6]. That said, myasthenia gravis can occur at any age, including during childhood, and no one is completely immune to developing this condition.

The disease does not spread from person to person, meaning it is not contagious. It also is not typically inherited, although occasionally more than one member of the same family may develop myasthenia gravis^[2]. This suggests that while genetic factors may play a role in making someone more susceptible, they are not the sole determining factor.

What Causes This Condition

Myasthenia gravis is an autoimmune disease, which means the body’s defense system mistakenly attacks its own healthy tissues instead of protecting them from foreign invaders^[2][3]. In a healthy body, the immune system produces proteins called antibodies that recognize and neutralize threats like viruses and bacteria. However, in people with myasthenia gravis, the immune system produces autoantibodies—antibodies that react against the body’s own cells and proteins.

These autoantibodies specifically target proteins at the neuromuscular junction, which is the place where nerve cells connect with the muscles they control. The most commonly affected proteins include the nicotinic acetylcholine receptors, muscle-specific kinase, and lipoprotein-related protein 4^[5][7]. When these proteins are attacked and damaged, the normal communication between nerves and muscles breaks down. Nerves send electrical signals to muscles to tell them when to contract, but in myasthenia gravis, these signals cannot get through properly.

The reason why the immune system begins this misdirected attack remains unclear to scientists. However, research has identified a connection to the thymus gland, a small organ in the chest that plays an important role in the immune system. Many people with myasthenia gravis have a thymus gland that is larger than normal, and approximately one in ten people with this condition have an abnormal growth of the thymus called a thymoma^[4][5]. The thymus appears to be implicated in the production of the harmful autoantibodies, though the exact mechanisms are still being studied.

Who Is at Higher Risk

While myasthenia gravis can develop in anyone, certain groups of people face a higher likelihood of developing the condition. Understanding these risk factors can help with earlier recognition and diagnosis.

Age and sex play significant roles in risk. Women are more likely to develop myasthenia gravis when they are younger, typically before age 40. In contrast, men are more likely to develop the condition later in life, usually after age 60^[1][2][6]. The reasons for this difference between men and women are not fully understood, but hormonal factors and differences in how the immune system functions may play a role.

Genetic susceptibility is another factor. While myasthenia gravis is not directly inherited in most cases, having certain genetic characteristics may make someone more prone to developing the condition when exposed to triggering factors^[7]. People who have other autoimmune conditions may also have a higher risk of developing myasthenia gravis, as autoimmune diseases can sometimes cluster together in the same individual or family.

The presence of thymus abnormalities, including an enlarged thymus or a thymoma, is strongly associated with myasthenia gravis. People with these thymus conditions are at increased risk of developing muscle weakness and other symptoms related to the disease^[4][5].

Recognizing the Symptoms

The hallmark feature of myasthenia gravis is muscle weakness that gets worse with repeated use of the affected muscles and improves after periods of rest^[2][3]. This distinctive pattern helps distinguish myasthenia gravis from many other conditions that cause muscle weakness. For most people, symptoms tend to be mildest in the morning after a night’s sleep and worsen as the day progresses and muscles are used.

In more than half of people with myasthenia gravis, the first symptoms involve the muscles that control eye movement^[1]. This can lead to drooping of one or both eyelids, a condition called ptosis. Another common early symptom is double vision, known as diplopia, which may affect horizontal or vertical vision. Some people notice that their double vision improves or disappears when they close one eye. These eye-related symptoms can be distressing and interfere with daily activities like reading, driving, or watching television.

In about 15 percent of people with myasthenia gravis, the initial symptoms involve muscles of the face and throat^[1]. This can make speaking difficult, and speech may sound soft or have a nasal quality depending on which muscles are affected. Swallowing may become challenging, increasing the risk of choking on food or liquids. Chewing, especially when eating tough or chewy foods, may become exhausting. Some people notice that their facial expressions become limited or that they have difficulty producing a smile.

As the condition progresses or in people with generalized myasthenia gravis, weakness can spread to other parts of the body. The muscles in the neck may weaken, making it difficult to hold the head up, especially later in the day. Arms and legs can become weak, making it hard to lift objects, raise the arms overhead, climb stairs, stand up from a seated position, or walk long distances^[3][10].

In rare but serious cases, myasthenia gravis can affect the muscles that control breathing. This leads to shortness of breath and, in severe instances, can result in a myasthenic crisis—a medical emergency requiring immediate hospital care and often mechanical ventilation to help the person breathe^[2]. Approximately 15 to 20 percent of people with myasthenia gravis experience at least one myasthenic crisis, and up to half of those may not be able to identify what triggered it^[2]. Triggers can include infection, stress, surgery, or adverse reactions to medication.

The intensity and combination of symptoms vary greatly from person to person, which is why myasthenia gravis is sometimes called a “snowflake disease”^[6][18]. No two individuals experience the condition in exactly the same way, and symptoms can fluctuate over days, weeks, or months.

Preventing Myasthenia Gravis

Unfortunately, there is no known way to prevent myasthenia gravis from developing^[1]. Because the exact cause of the autoimmune response is not fully understood, scientists have not yet identified specific lifestyle changes, dietary modifications, or other interventions that could stop the condition before it starts.

However, for people who have already been diagnosed with myasthenia gravis, there are important steps to help prevent symptom flare-ups and complications. Identifying and avoiding personal triggers is one of the most valuable prevention strategies. Common triggers include tiredness and exhaustion, so getting plenty of rest and not overexerting oneself may help keep symptoms under control^[9][20].

Stress is another major trigger that can worsen symptoms, so finding ways to reduce stress through relaxation techniques, mindfulness, or other coping strategies can be beneficial^[9][18][20]. Infections can also trigger worsening symptoms or even a crisis, making it important for people with myasthenia gravis to take precautions such as annual flu vaccinations and the pneumococcal vaccine^[9].

Certain medications can trigger or worsen myasthenia gravis symptoms, so it is crucial that every doctor and healthcare provider knows about the diagnosis before prescribing any new medications^[9][17]. People with myasthenia gravis should avoid “live” vaccines unless specifically advised by their healthcare team. Temperature extremes—both very hot and very cold conditions—can also exacerbate muscle weakness, so staying in comfortable environments when possible is helpful^[16][20].

How the Body Changes in Myasthenia Gravis

To understand how myasthenia gravis affects the body, it helps to know how muscles normally receive signals to contract. When the brain decides to move a muscle, it sends an electrical signal down a nerve. When this signal reaches the end of the nerve, it triggers the release of a chemical messenger called acetylcholine. This chemical crosses a tiny gap to reach special receptors on the muscle fiber. When acetylcholine binds to these receptors, it causes the muscle to contract.

In myasthenia gravis, autoantibodies attach to and damage these acetylcholine receptors or other proteins needed for proper nerve-muscle communication^[7][10]. This damage reduces the number of functioning receptors available on the muscle surface. As a result, even when the nerve releases acetylcholine normally, the signal does not get through to the muscle effectively. The muscle receives a weaker signal and contracts with less force than it should.

The reason symptoms worsen with repeated muscle use is that each muscle contraction uses up available acetylcholine and functional receptors. In a healthy person, this system can sustain repeated contractions without difficulty. But in someone with myasthenia gravis, where receptors are already limited, repeated use depletes the system faster, and the muscles become progressively weaker. With rest, the body has time to replenish acetylcholine and recover the ability of receptors to respond, which is why symptoms improve after resting.

The autoantibodies in myasthenia gravis do not attack involuntary muscles, such as those in the heart or digestive tract^[16][18]. They specifically target voluntary muscles—those under conscious control—which is why people with myasthenia gravis can continue to have normal heart function and digestion even when other muscles are weak.