Q. A 67-year-old man presents to the neurology office with generalized weakness for the past several months. He feels refreshed after taking a nap and first thing in the morning but worse with activity. He has difficulty raising his arms and getting up from a low chair. He also has noticed some double vision, especially late in the day. Vital signs are normal. On exam, he has drooping eyelids that worsen with prolonged upgaze in addition to proximal muscle weakness. Deep tendon reflexes are normal. He has no smoking history. You suspect which of the following diagnoses?