Myasthenia gravis (MG) is an autoimmune, neuromuscular disorder characterized by muscle weakness that worsens after repetitive use and activity and improves after rest.

In people with the condition, the immune system malfunctions, causing a disruption in the normal communication between nerve cells and muscle cells, which results in muscle weakness. This weakness can affect one muscle group, such as the eye muscles, or many muscle groups, including the muscles in the arms and legs, as well as those involved in breathing.

MG affects around 15 to 20 out of every 100,000 people in the United States. It can occur in people of any age, though it is rare in children. It most commonly affects women between the ages of 20 and 40 and men between ages 50 and 80. About 15% of people with MG also have a second autoimmune disorder, most commonly thyroiditis, systemic lupus erythematosus, or rheumatoid arthritis.

Fortunately, various treatment options for MG are available that can effectively improve symptoms and allow people with the condition to live with a good quality of life.

Myasthenia gravis is a chronic autoimmune disorder characterized by skeletal muscle weakness. The skeletal muscles allow for voluntary movement. They attach to the bones and by contracting and relaxing these muscles, people can voluntarily move parts of their body such as their arms or legs.

The disorder most frequently causes weakness in the eye muscles and in other muscles in the face and neck, but it can also affect other parts in the body, including arm and leg muscles as well as the muscles involved in breathing.

In people with MG, the extent of muscle weakness typically varies throughout the day. Usually, the muscle weakness worsens with physical activity and improves when people are well-rested, such as when they first wake up in the morning.

MG is an autoimmune disorder in which the body’s own immune system mistakenly attacks itself.

Normally, to contract a muscle, the brain sends a signal along nerves that join up with a muscle. When the signal reaches the junction between a nerve and muscle, the nerve releases a chemical messenger, called acetylcholine, that binds to special receptors on the muscle. The acetylcholine stimulates the muscle, causing it to contract.

In people with MG, the immune system produces antibodies that block or destroy the receptors on the muscle that bind to acetylcholine, thereby disrupting communication between the nerve and muscle. As a result, affected muscles do not contract properly. (Less commonly, in some cases of MG, the antibodies do not attack acetylcholine receptors, but instead target other proteins involved in communication between the nerve and muscle.)

Doctors do not know what causes the immune system to malfunction, though the thymus gland may be involved in some cases. Around 70% of people with MG have an enlarged thymus and about 10% have a thymoma, a tumor that develops in the thymus. Located behind the breastbone, the thymus plays an important role in the development of immune cells. Moreover, often, surgical removal of the thymus improves or eliminates symptoms.

The main symptom of MG is painless muscle weakness that improves after rest and worsens with repetitive muscle use, such as after exercise or other physical activities. The degree of muscle weakness varies throughout the course of the day and from one day to the next. After waking in the morning, people with the condition may have near normal muscle strength while muscle weakness is usually worse at the end of the day.

Other symptoms may include:

• Drooping eyelid (often affects only one eye, but may affect both)
• Double vision
• Difficulty swallowing, speaking, and/or chewing
• Changes to usual facial expressions, such as difficulty smiling
• Shortness of breath
• Muscle weakness in the arms, legs, neck, hands, and/or fingers

Around 15 to 20% of people with MG will experience a “myasthenic crisis” at least once in their life. A myasthenic crisis is a life-threatening complication of MG in which muscles involved in breathing become severely weakened, leading to respiratory failure. A crisis may be brought on by a current infection, surgery, pregnancy, childbirth, or certain medications. People experiencing a crisis usually need to be connected to a ventilator to help them breathe.

To diagnose MG, your doctor will review your medical history, perform a physical exam, and run one or more diagnostic tests.

Your doctor may begin by asking you about your symptoms including when they began and whether they worsen after physical activity or at the end of the day. You may also be asked whether you have another autoimmune disorder, such as thyroiditis, systemic lupus erythermatosus, or rheumatoid arthritis. During a physical exam, they will examine your eyes, neck, and limbs for signs of muscle weakness. If you have a drooping eyelid, your doctor may perform an ice pack test in which you place an ice pack over the eye for a few minutes. In people with MG, after removing the ice pack, eyelid drooping improves temporarily.

If your medical history and physical exam suggest you may have MG, your doctor will need to order additional tests to confirm the diagnosis. These may include:

• Blood tests to check for the presence of antibodies known to attack acetylcholine receptors and other proteins that can be involved in MG. In some cases, these antibodies may not be present in the blood. This condition is known as “seronegative MG” or “autoantibody-negative MG.”
• Electromyography (EMG), a test to assess the electrical activity of muscles while at rest and while you use them. For this test, a small needle is inserted into a muscle. The needle records the electrical activity of the muscle at rest and when you voluntarily contract it. Often, the test is repeated on different muscle groups.
• Nerve conduction testing with repetitive nerve stimulation (RNS), a test that assesses the speed at which a signal transmits along a nerve. In this test, electrical pulses are delivered to a nerve via electrodes placed on the skin or needles inserted in the nerve. The pulse travels down the nerve, causing it to release acetylcholine which, in turn, stimulates a muscle to contract. Electrical pulses are repeatedly delivered to the nerve. In people with MG, the muscle response weakens with each repetition.

Additional tests may be necessary to exclude other conditions and assess the risk for complications, including:

• Imaging studies such as a computed tomography (CT) scan or magnetic resonance imaging (MRI) of the chest to check for a thymoma (a thymus gland tumor). Imaging studies of the eye orbits or brain may also be necessary.
• Blood tests to check thyroid function and rule out other autoimmune disorders.
• Genetic testing to check for congenital myasthenic syndrome, a condition with symptoms similar to those of MG.
• Pulmonary function testing to assess the strength of breathing muscles.

Treatment for MG may include:

• Anticholinesterases. Often used as the first-line treatment for MG, these drugs improve muscle weakness by helping to maintain acetylcholine levels. They work by preventing its breakdown by an enzyme called cholinesterase. Pyridostigmine is the most commonly used anticholinesterase.
• Corticosteroids. These drugs improve symptoms by suppressing the immune system.
• Other immunosuppressive drugs. Other drugs, such as cyclosporine and azathioprine (among others), that improve symptoms by suppressing the immune system may be used to treat MG.
• Monoclonal antibodies. These medications improve symptoms by suppressing parts of the immune system. They are given intravenously and are usually used to treat people whose symptoms do not respond well to other medications.
• Intravenous Immunoglobulin (IVIG). This medication contains antibodies from the blood of healthy individuals. Given intravenously, IVIG is fast-acting and typically improves symptoms for a period of one to two months.
• Plasma exchange. Also known as plasmapheresis, in this procedure, a machine filters the antibodies that interfere with communication between nerve and muscle cells from the blood plasma of an individual with MG. The plasma, now devoid of the abnormal antibodies, is then returned to the patient. Like IVIG, plasma exchange is fast-acting and provides temporary improvement in symptoms.
• Thymectomy. In this surgical procedure, the thymus gland is removed. Thymectomy is standard treatment for people who have a thymoma (thymus tumor). The procedure may also be an option for those who do not have a thymoma. Thymectomy can improve MG symptoms and allows doctors to reduce the dose of other medications such as corticosteroids.

These treatments are often combined with one another and tailored to meet each individual patient’s needs.

The outlook for people with MG varies depending on the severity of symptoms, how well they respond to treatment, age at onset of the disorder, and which muscle groups are affected by the condition. In general, though, with current treatment options and care, the outlook for people with MG is good. For many, the medications and therapies that are available today can significantly improve the muscle weakness experienced by people with MG.