Myasthenia Gravis

Myasthenia gravis (MG) is an autoimmune disease which results in progressive weakness and tiring of the muscles that people can consciously control.  Abnormal antibodies produced by the immune system disrupt communication from the nerves to the muscles.

MG can affect any muscle, but the muscles that control eye and eyelid movement, facial expression, and swallowing are most often affected. Common first symptoms are weakness of the eye muscles, difficulty swallowing, talking, and breathing. Different people have different levels of muscle weakness. The onset of the disorder may be sudden.

Normally, the body releases a molecule called a neurotransmitters (acetylcholine) which binds to the muscle tissue at the nerve-muscle junction, causing the muscle to contract. In MG, the body's own immune system makes antibodies that block the binding of acetylcholine to the muscle.  The thymus gland, part of the immune system, is abnormal in most MG cases.

Most people with MG have good results from treatment. In some people, MG may go into remission for a while and muscle weakness may go away completely. In rare cases, people go into remission or improve without treatment. Treatment for MG may include cholinesterase inhibitors, such as pyridostigmine. These drugs help improve nerve signals to muscles and increase muscle strength. Immunosuppressive drugs frequently are used to suppress the production of abnormal antibodies. Surgical removal of the thymus gland may improve symptoms.

With MG, normal communication between the nerve and muscle is stopped at the place where nerve endings connect with the muscles they control — the nerve-muscle junction. Normally, the nerve endings release a substance called acetylcholine, which binds to the muscle tissue at the nerve-muscle junction, causing the muscle to contract (move). In someone with MG, the body's own immune system makes antibodies that block the binding of acetylcholine to the muscle.

The thymus gland, part of the immune system, is abnormal in most MG cases. Some people with MG have benign tumors of the thymus gland called thymomas. Doctors do not fully understand the relationship between the thymus gland and MG.

See a doctor for muscle weakness that worsens with activity and improves with rest, drooping eyelids, double vision, or trouble chewing. Seek emergency care for trouble breathing or swallowing, which is a medical emergency.