A 58-year-old man from Delhi presents to the emergency department with acute onset of vertigo, nystagmus, and ipsilateral facial numbness. On examination, he has ipsilateral loss of pain and temperature sensation over the face, contralateral loss of pain and temperature sensation over the body, and ipsilateral Horner syndrome. MRI brain shows an acute infarct in the lateral medulla. What is the most appropriate next step in management?