The symptoms of MG can mimic the symptoms seen in many other chronic neurologic disorders, such that some call it "the great imitator." Prior to the establishment of a definitive diagnosis, most MG patients have general weakness, especially of the proximal extremities muscle groups, neck extensors, and facial or bulbar muscles. Ptosis and diplopia are the most common presenting symptoms, but oropharyngeal symptoms (dysphagia and dysarthria) and limb weakness also can be seen. Although 10 percent of patients will have weakness that is restricted only to the ocular muscles, most MS patients subsequently will develop weakness in the oropharyngeal and limb muscles. The maximum extent of this weakness usually becomes manifest within the first year of diagnosis. These symptoms can fluctuate throughout the day, usually worsening as the day progresses or with prolonged muscle group use, such as with prolonged reading or prolonged chewing during a meal. Despite the presence of profound muscle weakness, there usually is no deficit in sensory, reflex, or cerebellar functioning. There may be a coexistent endocrine disorder, and the disease is often associated with thymoma.
MG in elderly patients can be misdiagnosed as ischemic stroke, especially when new-onset facial weakness is seen.18 In very rare instances, undiagnosed MG patients may present with extreme weakness in the muscles of respiration, resulting in respiratory failure. This life-threatening situation, termed myasthenic crisis, can be seen prior to MG diagnosis or as a result of inadequate drug therapy or drug tolerance. The complications associated with the respiratory failure seen in acute myasthenic crisis are the leading cause of death in MG patients.
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