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Myasthenia Gravis (MG)

Myasthenia Gravis (MG)

Table of Contents

What is myasthenia gravis?

Myasthenia gravis (MG) is an autoimmune disease — a disease that occurs when the immune system attacks the body’s own tissues. In MG, that attack interrupts the communication between nerve and muscle — the neuromuscular junction. MG is most often characterized by

autoantibodies against the acetylcholine receptor (AChR-Ab), and less often against a receptor-associated protein called muscle-specific tyrosine kinase (MuSK-Ab).

There are two clinical forms of myasthenia gravis: ocular and generalized. In ocular myasthenia gravis, muscle weakness is restricted to the muscles of the eyelids and other muscles that control movement of the eye (extraocular muscle). In generalized MG, the weakness may involve the ocular muscles and a variable combination of the arm, leg, and bulbar (respiratory, swallowing, speaking, and chewing) muscles.

MG is a relatively uncommon disease, with a prevalence of about 37 cases per 100,000 people in the United States. MG affects both men and women, commonly occurring in women younger than 40 years old and in men older than 60 years old. MG usually begins in adulthood, but can occur in children. Autoimmune juvenile myasthenia gravis accounts for about 10% to 15% of the diagnosed cases in North America.

The disease first appeared in medical reports in 1672, but did not earn its name, which literally means “grave muscular weakness,” until the 1880s.

What are the symptoms of MG?

MG causes weakness in muscles that control the eyes, face, neck, and limbs. Symptoms include droopy eyelids and partial paralysis of eye movements leading to double vision, as well as weakness and fatigue in neck and facial muscles, causing problems with chewing, speaking, swallowing, and holding up the head. The hallmark feature of the disorder is a fluctuating degree and variable combination of weakness in ocular, bulbar, limb, and respiratory muscles. These symptoms may not always be present and may shift from mild to severe repeatedly. The fluctuation of symptoms is an important feature that helps neurologists to distinguish MG from other disorders. Though the diagnostic journey may be long for some, the diagnosis of MG can be established both by clinical and serologic testing (See Diagnosis).

For more, see Signs and Symptoms.

What causes MG?

MG occurs spontaneously for unknown reasons. People with MG have an increased frequency of having other autoimmune diseases, and a small percentage may also have family members with MG. Some gene variants have been linked to a predisposition to MG, but a causative gene has not been identified. It is likely that a combination of a genetic predisposition and triggering environmental factors causes MG.

MG results from an autoimmune response in which components of the body’s immune defenses (i.e., antibodies) inappropriately attack and damage certain receptors on muscle cells, thereby disrupting their ability to communicate with nerve cells. The cause of this autoimmune response in people with MG is unknown. Researchers think that a defect in the part of the body known as the thymus (an organ located behind the breastbone), which plays an important role in making and training the cells of the immune system, could contribute to the development of MG. One theory is that that the thymus of people with MG may not appropriately eliminate the immune cells that produce antibodies that attack their own body tissues.

For more, see Causes/Inheritance.

What is the progression of MG?

MG is treatable with drugs that suppress the immune system or boost the signals between nerve and muscle. Surgery, specifically thymectomy, is recommended in a subset of patients. Most people with the disease manage their symptoms and lead active lives, and many experience pharmacological remission lasting many years. However, about 10-15% of patients are considered refractory, with poor response to currently available therapies. In about 10% to 15% of cases, MG begins in childhood (juvenile onset), which tends to progress slowly and has a high incidence of remission.

What is the status of research on MG?

Scientists in countries around the world, including many supported by MDA, are working to reveal numerous facets of MG, from identifying possible causes and triggers to understanding the disease's molecular underpinnings to developing specific treatment strategies. For more, see Research.

MDA educational resources

Additional reading

  1. Understanding Neuromuscular Disease Care. IQVIA Institute. Parsippany, NJ. (2018).
  2. Beloor Suresh A, Asuncion RMD. Myasthenia Gravis. [Updated 2023 Aug 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK559331/
  3. https://www.ninds.nih.gov/health-information/disorders/myasthenia-gravis

Last reviewed June 2025 by Neelam Goyal, MD.

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