Myasthenia gravis is a chronic autoimmune neuromuscular disease characterized by varying degrees of weakness of the skeletal muscles of the body, which are responsble for breathing and moving parts of the body, including the arms and legs. In myasthenia gravis, the immune system—which normally protects the body from foreign organisms—mistakenly attacks itself.
Symptoms vary in type and intensity, and may include: muscle weakness in the arms, hands, fingers, legs and neck, weakness of the eye muscles, drooping eyelid, difficulty swallowing, shortness of breath, and impaired speaking.
Myasthenia gravis is caused by an error in the transmission of nerve impulses to muscles. Antibodies (immune proteins produced by the body's immune system) block the normal activity of the neurotransmitter acetylcholine, which prevents muscles from contracting.
The thymus gland also may give incorrect instructions to immune cells and cause the immune system to attack its own cells and tissues.
Myasthenia gravis can generally be controlled. Some medications improve neuromuscular transmission and increase muscle strength. These medications must be used with careful medical follow up because they may cause major side effects.
Thymectomy, the surgical removal of the thymus gland (which often is abnormal in those with myasthenia gravis), improves symptoms in certain individuals.
Other therapies include plasmapheresis, a procedure in which abnormal antibodies are removed from the blood, and high-dose intravenous immunoglobulin, which temporarily modifies the immune system and provides the body with normal antibodies from donated blood. However, their effectiveness usually lasts only a few weeks to months.
With treatment, most individuals with myasthenia can significantly improve their muscle weakness.
Some case of myasthenia gravis may go into remission temporarily, and muscle weakness may disappear so that medications can be discontinued.
In a few cases, the severe weakness of myasthenia gravis may cause respiratory failure, which requires immediate emergency medical care.
New drugs are being tested, either alone or in combination with existing drug therapies, to see if they are effective in treating the disease. Other researchers are trying to find better ways to diagnose and treat this disorder.
For example, NINDS-funded researchers are exploring the assembly and function of connections between nerves and muscle fibers to understand the fundamental processes in neuromuscular development.
Other investigators are developing new tools to diagnose people with undetectable antibodies and identify potential biomarkers (signs that can help diagnose or measure the progression of a disease) to predict an individual’s response to immunosuppressive drugs.