Viral Infections USMLE Step 1 Practice Question

A 19-year-old man from rural Bangladesh presents to the emergency department with acute-onset flaccid paralysis of both lower extremities and urinary retention. Two weeks prior, he developed fever (38.5°C), asymmetric proximal limb weakness, and severe myalgias. He reports he has never received polio vaccination due to religious objections. On examination, he is alert and oriented with intact cranial nerves and normal sensory examination. Vital signs are stable with normal respiratory rate. Cerebrospinal fluid analysis shows lymphocytic pleocytosis (85 cells/μL, 90% lymphocytes), normal glucose (55 mg/dL), and normal protein (42 mg/dL). Brain MRI is unremarkable. Which of the following is the most likely diagnosis?