Under normal conditions, your nerves direct your muscles to work by sending a message through an area called a receptor. The chemical that delivers the message is called acetylcholine. When acetylcholine binds to a nerve receptor, your muscle knows to contract. In myasthenia gravis, you have fewer acetylcholine receptors than you need.
Myasthenia gravis is considered to be an autoimmune disorder. In an autoimmune disease, some of your body's antibodies (cells in your body that are supposed to be programmed to fight foreign invaders such as bacteria, viruses, or fungi) mistake a part of your own body as foreign, resulting in its destruction. In the case of myasthenia gravis, your antibodies attack and destroy the acetylcholine receptors needed for muscle contraction.
No one knows exactly what causes your body to begin producing the antibodies that destroy acetylcholine receptors. In some cases, the process seems to be related to the thymus gland, which helps produce antibodies.
About 15% of all myasthenia gravis patients are found to have a thymoma, a tumor of the thymus. Although most thymomas are benign, the thymus is usually removed (thymectomy) to prevent the potential spread of cancer. In fact, thymectomy seems to improve symptoms of myasthenia gravis in some patients, even if no tumor is present.
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