Myasthenia gravis (MG) is a neuromuscular condition triggered by an autoimmune response; the disease occurs when the immune system mistakenly attacks healthy cells and tissues, breaking down normal communication between nerve cells and muscles. MG causes weakness and fatigue in voluntary muscles and may also affect the muscles that control breathing.
The disease first appeared in medical reports in 1672 but did not earn its name — which literally means “grave muscular weakness” — until the 1880s. MG most commonly affects women under age 40 and men older than 60, but it can occur at any age, including during childhood.
In MG, the communication between nerve cells and muscles is interrupted at the neuromuscular junction — the place where nerve cell endings connect with the muscles they control. Normally, the nerve cell endings release a neurotransmitter, or signaling molecule, called acetylcholine, which binds to acetylcholine receptors found on the surface of muscle cells, causing them to contract.
In people with MG, antibodies, which normally help fight off infections and threats, mistakenly destroy, damage, or block the acetylcholine receptors. With fewer receptors available, the muscles cannot contract properly and they easily become weak.
In about half of patients, the disease is caused by the immune system attacking other proteins important for maintaining the function of the neuromuscular junction, such as muscle-specific kinase (MuSK). Anti-MuSK antibodies may be more common in female patients.
The specific cause of the abnormal autoimmune response in patients with MG is unknown. However, researchers think that the thymus gland, a part of the immune system, may trigger or maintain the production of antibodies that block the transmission of nerve signals. In about 15 percent of people with MG, the disease is caused by a tumor in the thymus gland.
There is also a distinct type of MG called congenital myasthenic syndrome, which some children have at birth. This is a rare, hereditary form of MG caused by a genetic mutation and not by an autoimmune response.
The first symptom of MG is usually a weakness in eye muscles and sometimes double vision. In some people, it may be difficulty swallowing and talking. The degree of muscle weakness varies greatly among patients, ranging from a localized form limited to eye muscles (ocular MG) to a severe or generalized form in which many muscles — sometimes including those that control breathing — are affected.
Although the disorder usually becomes apparent during adulthood, the onset of symptoms can occur at any age. Symptoms can appear suddenly and are often not immediately recognized as MG. Symptom onset most commonly peaks in women when they are in their 20s or 30s and in men when they are in their 50s or 60s.
When doctors suspect MG due to a patient’s symptoms and after a physical exam, they can perform a series of tests to confirm the diagnosis. Blood tests are used to detect the antibodies that cause MG. If the blood test is negative, the next step is usually a test called electromyography (EMG) to assess muscle activity. Physicians may also use a computerized tomography (CT) scan in which many X-ray images are used to generate a three-dimensional image of the chest to assess the size and shape of the thymus gland.
Physicians may also use the Tensilon test to diagnose MG. A medication called Tensilon (edrophonium) is injected into the bloodstream, and the patient is asked to perform some muscle exercises. Tensilon blocks the breakdown of acetylcholine, meaning that it temporarily increases the amount of acetylcholine present at the neuromuscular junction. If patients experience a temporary improvement in muscle weakness following Tensilon injection, it may indicate that they have MG.
Because muscle weakness is a common symptom of many other disorders, an MG diagnosis is often delayed — sometimes for years — in people who experience mild weakness, or in those whose weakness is restricted to only a few muscles.
There is currently no cure for MG, but there are treatments available that can help control and alleviate the symptoms of the disease. Most people with MG respond well to such treatments. In some people, MG may go into remission, and muscle weakness may go away completely.
Thymectomy, or the surgical removal of the thymus gland, is another treatment option for patients whose disease is caused by a tumor in the thymus gland. Thymectomy may reduce the severity of muscle weakness after some months or years. In some people, the weakness may disappear.
Newer treatments with monoclonal antibodies are emerging as potential new tools to treat MG. For instance, the European Commission (EC) recently approved Soliris (eculizumab) for the treatment of MG. There are also a number of experimental treatments under clinical investigation.
Myasthenia Gravis News is strictly a news and information website about the disease. It does not provide medical advice, diagnosis or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.