Karen is a 40 year old receptionist who presents with a 4 month history of diplopia and drooping of both her eyelids. Colleagues have commented that her voice becomes quiet after she has been speaking for some time. She has had to stop exercising as her body feels too tired to exert itself. There is no slurred speech, seizures, or weight loss.
Which of the following features would be most in-keeping with her most likely diagnosis?
