myasthenia gravis

a chronic disease marked by abnormal fatigability and weakness of selected muscles, which is relieved by rest. The degree of fatigue is so extreme that these muscles are temporarily paralysed. The muscles initially affected are those around the eyes, mouth, and throat, resulting in drooping of the upper eyelids (ptosis), double vision, dysarthria, and dysphagia. Myasthenia gravis is an autoimmune disease in which autoantibodies bind to cholinergic receptors on muscle cells, which impairs the ability of the neurotransmitter acetylcholine to induce muscular contraction. Treatment with anticholinesterase drugs and surgical removal of the thymus in younger patients (under the age of 45 years) lessen the severity of the symptoms. Steroid therapy or plasma exchange may be used to treat the more severely affected patients.