Myasthenia gravis (MG) is a neuromuscular condition triggered by an autoimmune response. This happens when the immune system mistakenly attacks healthy cells and tissues, breaking down normal communication between nerves and muscles. MG causes weakness and fatigue in voluntary muscles.
The disease first appeared in medical reports in 1672, but didn’t earn its name — which literally means “grave muscular weakness” — until the 1880s. It most commonly affects women under age 40 and men older than 60, but it can occur at any age, including during childhood.
In MG, normal communication between nerves 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 chemical substance or neurotransmitter called acetylcholine, which travels from the nerve ending and binds to acetylcholine receptors found on the surface of the muscle cells, activating the muscle and causing it to contract.
In people with MG, antibodies, which normally help to fight off infections and threats, mistakenly destroy the acetylcholine receptors. With fewer receptor sites available, the muscles cannot contract properly and they easily become tired and weak.
The specific cause of this abnormal autoimmune response in patients with MG is unknown. However, researchers believe 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, this is caused by a tumor in the thymus gland.
There is also a distinct type of myasthenia called congenital myasthenic syndrome, which some children are born with. This is a rare, hereditary form of myasthenia caused by 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 individuals, ranging from a localized form limited to eye muscles (so-called ocular myasthenia) 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 the symptoms may occur at any age, be sudden, and often not immediately recognized as MG. Symptom onset most commonly peaks in women during their 20s or 30s and in men 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, and a chest CT scan to assess the size and shape of the thymus gland.
Because muscle weakness is a common symptom of many other disorders, an MG diagnosis is often delayed — sometimes up to two years — in people who experience mild weakness, or in those whose weakness is restricted to only a few muscles.
MG has no cure, but the available treatments can help control and alleviate signs and symptoms of the disease. Most people with MG have good results from treatment and in some people, MG may go into remission for awhile, and muscle weakness may go away completely.
Thymectomy, or 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 lessen the severity of muscle weakness after some months or years. In some people, the weakness may completely disappear.
Newer treatments with monoclonal antibodies are emerging as potential new tools to treat MG. For instance, the European Commission recently tly approved Soliris (eculizumab), and Rituxan (rituximab) is under clinical investigation.
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