Approximately 15 to 20 percent of people with myasthenia gravis experience at least one myasthenic crisis. However, up to one-half of people may have no obvious cause for their myasthenic crisis.
Certain medications have been shown to cause myasthenia gravis. However, sometimes these medications may still be used if it is more important to treat an underlying condition.
Myasthenia gravis is an autoimmune disease, which means the immune system—which normally protects the body from foreign organisms—mistakenly attacks itself. Myasthenia gravis is caused by an error in the transmission of nerve impulses to muscles. It occurs when normal communication between the nerve and muscle is interrupted at the neuromuscular junction—the place where nerve cells connect with the muscles they control. Neurotransmitters are chemicals that neurons, or brain cells, use to communicate information.
Normally when electrical signals or impulses travel down a motor nerve, the nerve endings release a neurotransmitter called acetylcholine that binds to sites called acetylcholine receptors on the muscle. The binding of acetylcholine to its receptor activates the muscle and causes a muscle contraction. This is most often caused by antibodies to the acetylcholine receptor itself, but antibodies to other proteins, such as MuSK Muscle-Specific Kinase protein, also can impair transmission at the neuromuscular junction.
The thymus gland controls immune function and may be associated with myasthenia gravis. It grows gradually until puberty, and then gets smaller and is replaced by fat.
Throughout childhood, the thymus plays an important role in the development of the immune system because it is responsible for producing T-lymphocytes or T cells, a specific type of white blood cell that protects the body from viruses and infections. In many adults with myasthenia gravis, the thymus gland remains large. People with the disease typically have clusters of immune cells in their thymus gland and may develop thymomas tumors of the thymus gland.
Thymomas are most often harmless, but they can become cancerous. Scientists believe the thymus gland may give incorrect instructions to developing immune cells, ultimately causing the immune system to attack its own cells and tissues and produce acetylcholine receptor antibodies—setting the stage for the attack on neuromuscular transmission. Myasthenia gravis affects both men and women and occurs across all racial and ethnic groups. It most commonly impacts young adult women under 40 and older men over 60 , but it can occur at any age, including childhood.
Myasthenia gravis is not inherited nor is it contagious. Occasionally, the disease may occur in more than one member of the same family.. Although myasthenia gravis is rarely seen in infants, the fetus may acquire antibodies from a mother affected with myasthenia gravis—a condition called neonatal myasthenia.
Rarely, children of a healthy mother may develop congenital myasthenia. This is not an autoimmune disorder but is caused by defective genes that produce abnormal proteins in the neuromuscular junction and can cause similar symptoms to myasthenia gravis. Because weakness is a common symptom of many other disorders, the diagnosis of myasthenia gravis is often missed or delayed sometimes up to two years in people who experience mild weakness or in those individuals whose weakness is restricted to only a few muscles.
Today, myasthenia gravis can generally be controlled. There are several therapies available to help reduce and improve muscle weakness. With treatment, most individuals with myasthenia can significantly improve their muscle weakness and lead normal or nearly normal lives.
Some cases of myasthenia gravis may go into remission—either temporarily or permanently— and muscle weakness may disappear completely so that medications can be discontinued. Stable, long-lasting complete remissions are the goal of thymectomy and may occur in about 50 percent of individuals who undergo this procedure.
The mission of the National Institute of Neurological Disorders and Stroke NINDS is to seek fundamental knowledge about the brain and nervous system and to use that knowledge to reduce the burden of neurological disease. Although there is no cure for myasthenia gravis, management of the disorder has improved over the past 30 years. There is a greater understanding about the causes, structure and function of the neuromuscular junction, the fundamental aspects of the thymus gland and of autoimmunity.
Technological advances have led to more timely and accurate diagnosis of myasthenia gravis and new and enhanced therapies have improved treatment options. Researchers are working to develop better medications, identify new ways to diagnose and treat individuals, and improve treatment options.
Some people with myasthenia gravis do not respond favorably to available treatment options, which usually include long-term suppression of the immune system. Therapeutic algorithms need to be tailored to each myasthenia subtype. Summary: Increasing knowledge about the environmental and genetic risk factors and basic immunopathogenesis of myasthenia gravis, including the role of innate immunity, regulatory T cell impairment and autoantibody heterogeneity, is providing a rationale for treatment with new biological agents.
Current immunotherapies in myasthenia gravis undoubtedly provide benefits, but also cause side-effects. Controlled trials are, therefore, needed to confirm initial results from pilot studies. Abstract Purpose of review: Myasthenic disorders are a well characterized group of diseases of the neuromuscular junction. Publication types Research Support, Non-U. Gov't Review. Substances Autoantibodies Receptors, Cholinergic.
0コメント