Review Question - QID 211072

A 25-year-old woman presents to the emergency department with fatigue and weakness. Over the past 24 hours, she has not felt like herself and has felt like she has no strength. The patient has no significant medical history other than a single episode of blood-tinged diarrhea 1 week ago which resolved on its own. Her temperature is 99.4°F (37.4°C), blood pressure is 124/62 mmHg, pulse is 95/min, respirations are 29/min, and oxygen saturation is 95% on room air. Physical exam is notable for 2/5 strength of the lower extremities and decreased sensation in the lower extremities and fingertips. Which of the following is the most appropriate initial step in management?