Learn The BasicsMyasthenia gravis is a rare autoimmune disease characterized by weakness in the voluntary muscles, or those that a person can move voluntarily.
About 150 to 200 out of 1,000,000 people have MG worldwide. In the U.S., MG is found in about 37 out of every 100,000 people.
MG was first recognised by English physician Thomas Willis in 1672. Another English physician, Samuel Wilks, made the modern description of the disease in 1877.
What causes MG?
MG occurs when the immune system mistakenly attacks components of the neuromuscular junction, or the connection between a motor neuron, a nerve cell that controls muscle movement, and the muscle fibers. This connection between the motor neuron and the muscles is lost, resulting in muscle weakness.
It is not entirely clear why this happens. Researchers think the disease may be linked to problems with the thymus gland, which is situated in the chest. The thymus is usually larger than normal in people affected by MG.
What are the symptoms of MG?
The primary symptom of MG is muscle weakness, which worsens as the disease progresses.
The main muscle groups affected by the disease include those in and around the eyes, face, throat and neck. The disease may also affect the muscles in the arms and legs.
Symptoms of MG include droopy eyelids, double vision or diplopia, which may be horizontal or vertical, and may resolve when one eye is closed. Symptoms may also include difficulty speaking, swallowing and walking. Issues with swallowing may cause patients to choke easily and have difficulty eating, drinking and swallowing pills. Sometimes, swallowed liquids may come out of the nose.
How do doctors diagnose MG?
Doctors diagnose MG based on surveying their symptoms and medical history.
They may also conduct tests like blood tests, nerve conduction studies and electromyography.
During a blood test, doctors are looking to see if a patient is positive for autoantibodies that are specific to MG.
In nerve conduction studies, the nerve fibers are repeatedly stimulated with an electrical signal to see if they become fatigued, a hallmark of MG.
Finally, an electromyogram may be ordered to look for abnormalities in the electrical activity of a muscle caused by disease.
Doctors may also use cholinesterase inhibitors to attempt to improve muscle weakness to reach a final diagnosis of MG.
How is MG treated?
MG may be treated with medications like cholinesterase inhibitors, steroids or immunosuppressants.
Cholinesterase is a natural enzyme that breaks down acetylcholine, a neurotransmitter or chemical signal that carries nerve signals to the muscle. Because one of the chemicals that is mistakenly targeted by the immune system in MG is acetylcholine, cholinesterase inhibits the enzyme that breaks down acetylcholine and can increase the levels available, thereby reducing the symptoms of MG.
Steroids and immunosuppressants may also be used to dampen the immune system and reduce the symptoms of MG.
MG may also be treated with medical procedures like intravenous immunoglobulin, also known as IVIG. This treatment reduces the activity of the immune system through plasma exchange, where antibodies are removed from the blood and replaced with antibodies from a donor’s blood.
The removal of the thymus, also known as a thymectomy, may be performed to treat more severe cases of MG.
Reviewed by Debjyoti Talukdar, M.D., on June 4, 2025.