Q. A 58 year-old man presents with an abrupt onset of interscapular pain, lower extremity weakness, sensory disturbance, and bowel and bladder incontinence. Neurological exam reveals: - areflexia of the lower extremities; - paraparesis; - loss of pain/temperature sensation with preserved vibration/proprioception sensation in the lower extremities; - anal sphincter atonia; - and a normal motor, sensory, and reflex exam in the upper extremities. Which of the following is the most likely diagnosis?