Review Question - QID 210928

A 13-year-old teenage girl was brought to the emergency department by her mom after she collapsed. Her mom reports that she was at a birthday party when all of a sudden she fell. She reported left foot weakness and has been limping ever since. The patient has been healthy and had an uncomplicated birth history, though her mom reports that she just recovered from a cold. She currently lives with her younger sister and mother as her parents recently divorced. She does well in school and has a handful of good friends. Her physical exam demonstrated normal bulk and tone, 5/5 strength in all motions, 2+ and symmetric reflexes at biceps, triceps and knees. She had 1+ ankle reflex on left. What is the most likely explanation for her symptoms?