Myasthenia gravis is a disease that causes weakness in your voluntary muscles. These are the muscles that you control. For example, you may have weakness in the muscles for eye movement, facial expressions, and swallowing. You can also have weakness in other muscles. This weakness gets worse with activity, and better with rest.
Myasthenia gravis is an autoimmune disease. Your body's immune system makes antibodies that block or change some of the nerve signals to your muscles. This makes your muscles weaker.
Other conditions can cause muscle weakness, so myasthenia gravis can be hard to diagnose. Tests used to make a diagnosis include blood, nerve, muscle, and imaging tests.
With treatment, the muscle weakness often gets much better. Medicines can help improve nerve-to-muscle messages and make muscles stronger. Other drugs keep your body from making so many abnormal antibodies. These medicines can have major side effects, so they should be used carefully. There are also treatments which filter abnormal antibodies from the blood or add healthy antibodies from donated blood. Sometimes, surgery to take out the thymus gland helps.
Some people with myasthenia gravis go into remission. This means that they do not have symptoms. The remission is usually temporary, but sometimes it can be permanent.
NIH: National Institute of Neurological Disorders and Stroke