A 59-Year-Old College Professor Visits His Physician Because of Muscle

A 59-year-old college professor visits his physician because of muscle fatigue that worsens later in the day. The physician notices that the man has droopy eyelids and seems to have an overall weakness in his muscles. After the intravenous administration of Tensilon, which blocks degradation of acetylcholine, the droopy eyelids and symptoms of muscle weakness appear to subside. Which of the following best describes the patient's condition?

A) Encephalitis
B) Fibromyalgia
C) Flaccid paralysis
D) Myasthenia gravis
E) Poliomyelitis