50)On a Monday morning you see a 12-year-old otherwise healthy | Paediatrics videos & books

50)On a Monday morning you see a 12-year-old otherwise healthy boy in the emergency department. The parents brought the boy in because they noticed that he started to have an abnormal gait in the past few days. He seems to be shuffling his feet. The boy complains that his legs feel heavy and are tingling. He relates that his arms feel fine. His past history is significant for attention deficit/hyperactivity disorder (ADHD) for which he is taking methylphenidate. He denies trauma or taking any other medicines or drugs. On examination, he is afebrile with normal vital signs. His entire physical examination is normal with the exception of the examination of his lower extremities. He has 3/5 strength throughout both of his lower extremities with a normal muscle mass. His all joints have a full range of motion, without any pain or swelling. His reflexes are absent and he describes some paresthesias of his feet and ankles. What is the most likely diagnosis?