A 32-year-old complains of numbness and tingling in his left arm, which began 5 days is ago. dizziness He has also noted some recent "staggering" when walking and he feels quite off balance. There is no dizziness or weakness. He knows of no precipitating event. He has no other complaints. Upon asking about past history, he recalls that about 3 years ago he had an episode of bilateral leg paralysis and poor sensation in the legs. This improved over the course of 2 months and his legs got back to normal. No specific etiology was found at that time. He has not followed up with a doctor.
Examination shows sensory loss and altered sensation to stimulation in the left distal upper extremity and hand. Finger movements in both hands show poor coordination, somewhat more so on the left, but there is no weakness found in the face, arms, or legs. Gait is mildly ataxic. He cannot walk heel to toe in a straight line. Reflexes in the arms are normal, and are brisk at the knees and ankles but not necessarily pathologically SO. Neurologic exam is otherwise unremarkable.
MRIs note several lesions. What is the diagnosis for this man?