A 56-year-old female presents to the emergency department with double vision, facial deviation, and weakness in both lower limbs for 8 hours. Examination: Alert, normal temperature, normal blood pressure (BP), equal pupils, restricted horizontal eye movements, bilateral facial palsy, inability to protrude tongue. Muscle strength grade 2 in upper limbs, grade 0-1 in lower limbs. No significant sensory deficit. No nuchal rigidity. Brain computed tomography (CT) from another hospital showed no abnormalities. Based on the clinical presentation, the most likely diagnosis is: