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myasthenia(mī″ăs-thē′nē-ă) [ my- + -asthenia]
myasthenia gravisAbbreviation: MG
Diagnosis is made on the basis of patient history, a thorough neurological examination, electromyography, repetitive nerve stimulation, a Tensilon test, or a combination of these tests. Intravenous injection of Tensilon significantly improves muscle weakness within 60 sec, lasting up to 30 min Acetylcholinesterase receptor antibody titers in the blood are elevated in about 50% to 70% of patients with myasthenia gravis.
Clinical signs include ptosis of the eyelid and double vision due to fatigue and weakness in the extraocular muscles, and difficulty chewing and swallowing from impaired facial and pharyngeal muscles. Speech that becomes progressively more dysarthric during prolonged dialogue is another common symptom. Symptoms are exacerbated by repetitive muscle use, and, in some patients, by menses, emotional stress, prolonged exposure to sunlight or cold, and infections. Myasthenia gravis crisis is a sudden exacerbation of symptoms with respiratory failure.
The primary treatment is with anticholinesterases and immunosuppressive agents. Anticholinesterase therapy often becomes less effective as the disease worsens. In selected patients, removal of the thymus, plasmapheresis, or immunoglobulin therapy is used.
The patient with MG should seek medical attention immediately if he or she experiences difficulty breathing, talking, chewing, or swallowing. These symptoms may herald a myasthenic crisis. In crisis the patient's cardiovascular, neurologic, and respiratory status should be monitored in an intensive care unit. Suctioning the airway and postural changes may sometimes maintain adequate oxygenation and ventilation. If not, the patient will need intubation and positive-pressure ventilation. Exercise, meals, and care activities should be planned around medication-induced energy peaks. The patient should be taught that soft but solid foods are more easily managed than liquids when swallowing is difficult. Additional help for patients is available through support groups and Internet-based resources such as the Myasthenia Gravis Foundation of America (www.myasthenia.org).