myasthenia gravis [key], chronic disorder of the muscles characterized by weakness and a tendency to tire easily. It is caused by an autoimmune attack on the acetylcholine receptor of the post synaptic neuromuscular junction. The initiating event leading to antibody production is unknown. The disease is most common between the ages of 20 and 40 and more frequent in women. The muscles of the neck, throat, lips, tongue, face, and eyes are primarily involved. Exertion quickly brings on difficulty in swallowing, chewing, and talking. The eyelids may droop, and there are visual disorders. Myasthenia gravis is transmitted passively to fetuses from infected mothers, a syndrome call neonatal myasthenia. Congenital myasthenia is a rare autosomal recessive disorder of neuromuscular transmission beginning in childhood, usually with ophthalmoplegia. Life-threatening myasthenic crisis, in which the diaphragm is affected and the patient has respiratory failure, occurs in 10% of the patients. Treatment of the disease includes the use of cholinesterase inhibitors, thymectomy, corticosteroids, and immunosuppressive agents and plasmapheresis (see apheresis). Prolonged rest is likely to restore some of the muscle function; restricted activity at all times and complete rest during periods of aggravation of the illness are necessary.
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