A 68-Year-Old Man Is Brought to the Emergency Department Because

A 68-year-old man is brought to the emergency department because of mild headache, confusion, and right-sided upper extremity weakness for the last 2 days.  The patient is accompanied by his wife, who provides most of the history.  The patient was working in his garden 2 days ago when he developed a headache.  He thought nothing of it since he was working outdoors on a hot and humid summer day.  Over the next 24-hours, the patient became lethargic and developed right-sided weakness.  He has not traveled recently and denies insect bites, sick contacts, or flu-like symptoms.  His other medical problems include a history of ischemic stroke without residual neurologic deficits, hypertension, hyperlipidemia, and non-paralytic polio as a child.  His medications include aspirin, simvastatin, and lisinopril.
His temperature is 38.1 C (100.5 F) , blood pressure is 140/90 mm Hg, pulse is 101/min, and respirations are 16/min.  Pulse oximetry shows an oxygen saturation of 98% on room air.  His general physical examination is unremarkable.  On neurological examination, he is obtunded and does not follow commands.  There are no obvious cranial nerve deficits.  He is able to localize briskly to noxious stimuli with the left arm, but he does not move the right arm.  He is able to withdraw briskly to noxious stimuli in the lower extremities (left > right) .  The sensory examination is unreliable.  Reflexes are 2+ on the left side of the body, but absent on the right side.  Plantar responses are downgoing bilaterally.  Superficial abdominal reflexes are present.  Rectal tone is normal. 
Non-contrast CT scan of the head showed no bleeding or masses.
Which of the following is the most likely diagnosis?

A) Acute ischemic stroke
B) Enteroviral meningitis
C) Guillain-Barré syndrome
D) Post-polio syndrome
E) West Nile encephalomyelitis