Scenario 9: Myasthenia Gravis (MG)

Scenario 9: Myasthenia Gravis (MG)
61-year-old male complains of intermittent weakness and muscle fatigue that has progressively worsened over the past month. He was an internationally known extreme mountain climber but now he says he has difficulty in getting his morning paper. Initially he thought his symptoms of profound leg weakness and fatigue were due to his age and history of injuries from mountain climbing. Over the past few months, he also reports having noticed “blurriness” when working on his antique train collection or reading for long periods of time. He has developed intermittent double vision that seems to be worse when reading at bedtime. He also reports an occasional “droopy” eye lid. Past medical and social history noncontributory. Physical exam reveals weakness of right extra ocular muscle (EOM) with repetition. There is positive nystagmus and symmetrical upper extremity weakness with fasciculations. Lower extremities within normal limits (WNL).   The APRN suspects the patient has myasthenia gravis (MG).
Question:
What is the underlying pathophysiology of MG?  
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