Jill, a 26-year-old gymnastics instructor, presents with complaints of muscle weakness in her face that comes and goes, but has been getting worse over the past two months

Jill, a 26-year-old gymnastics instructor, presents with complaints of muscle weakness in her face that comes and goes, but has been getting worse over the past two months. Most notably, she complains that her "jaw gets tired" as she chews and that swallowing has become difficult. She also notes diplopia ("double vision") which seems to come on late in the evening, particularly after reading for a few minutes. At work, it has become increasingly difficult to "spot" her gymnasts during acrobatic moves because of upper arm weakness.