brain, spinal cord, and nerve disorders
Myasthenia Gravis
Introduction
Myasthenia gravis is an autoimmune disorder that impairs communication between nerves and muscles, resulting in episodes of muscle weakness. Myasthenia gravis results from malfunction of the immune system. People usually have drooping eyelids and double vision, and muscles become unusually tired and weak after they are used and recover when they are rested. Tests using an ice pack or rest to see whether these measures make eyelids droop less, electromyography, and blood tests can help confirm the diagnosis. Some drugs can improve muscle strength rapidly, and others can slow progression of the disorder. If myasthenic crisis occurs, IV immune globulin or plasma exchange is used. (See also Overview of Neuromuscular Junction Disorders .) Myasthenia gravis usually develops in women between the ages of 20 and 40 and in men between the ages of 50 and 80. However, the disorder may affect men or women at any age. Rarely, it begins during childhood. Overview of the Peripheral Nervous System communicate with muscles by releasing a chemical messenger (neurotransmitter), which interacts with receptors on muscles (at the What causes the body to attack its own acetylcholine receptors—an Autoimmune Disorders —is unknown. According to one theory, malfunction of the thymus gland may be involved. In the thymus gland, certain cells of the immune system learn how to differentiate between the body and foreign substances. For unknown reasons, the thymus gland may instruct the immune system cells to produce antibodies that attack the acetylcholine receptors. People may inherit a predisposition to this autoimmune abnormality. About 65% of people who have myasthenia gravis have an enlarged thymus gland, and about 10% have a tumor of the thymus gland (thymoma). About half of these thymomas are cancerous (malignant). Myasthenia gravis also often occurs in people with other autoimmune disorders, such as Rheumatoid Arthritis (RA) , Some people with myasthenia gravis do not have antibodies to acetylcholine receptors but have antibodies to an enzyme involved in the formation of the neuromuscular junction instead. These people may require different treatment. Myasthenia gravis may be triggered by Infections Surgery Use of certain drugs, such asnifedipineorverapamil(used to treat high blood pressure),quinine(used to treat malaria), andprocainamide(used to treat abnormal heart rhythms) Rarely, myasthenia gravis is inherited as an autosomal (not sex-linked) Recessive disorders . That is, two genes for the disorder, one from each parent, are required for a child to have the disorder. 