MRCP2-3044

MRCP2-3044

A 32-year-old man presented with gradual difficulty walking and blurry vision over the course of 3 weeks. The day before admission he became excessively sleepy, but still able to be awakened. His partner reported that he had been healthy except for a recent viral illness a month ago.

During the examination, he appeared slightly disoriented and drowsy. His vital signs were normal and there were no abnormalities found during cardiovascular, respiratory, or abdominal examinations. He had reduced upward gaze and bilateral abduction, but all other cranial nerves were normal. His limb examination was unremarkable except for brisk reflexes and up-going plantars.

What is the most probable diagnosis?