Review Question - QID 101670

A 37-year-old male with a history of HIV presents to the emergency room with back pain. He reports intermittent fevers for the past week. He reports that he chose to come to the emergency room now because the back pain is more severe and he has also started having trouble controlling his bowels. His vital signs are Temp 38.5 C, HR 100, BP 110/70, RR 16, and O2 99% on room air. Exam of his arm is shown in Figure A. On physical examination of his back and extremities, there is tenderness to palpation along the lower spine, weakness in the bilateral legs (right greater than left), and hyporeflexia bilaterally. Rectal examination reveals saddle anesthesia. Which of the following is the most likely diagnosis?