Review Question - QID 214484

A 3-year-old boy presents to his pediatrician for a new patient appointment. The patient was adopted, and his past medical history is not known. The patient was removed from his original home by child protective services yesterday due to inappropriate care and neglect in addition to his parents abusing multiple illegal substances. The patient’s new parents are concerned about a behavioral problem that they noticed. They say that the patient sits, bobs his head, and will not stop despite asking him not to. They note that he recovered from a respiratory infection last week. They have been feeding him appropriately and note that he enjoys eating honey and fruits. His temperature is 97.5°F (36.4°C), blood pressure is 80/40 mmHg, pulse is 105/min, respirations are 21/min, and oxygen saturation is 98% on room air. Physical exam reveals a malnourished child who is playing. Temporal wasting and a protuberant abdomen are noted. The patient is noted to be sitting with his head contracted, turned to one direction, and is bobbing his head. Neurologic exam reveals an uneasy gait, normal strength/sensation in the upper and lower extremities, and the child is able to say his name. A rotary nystagmus is noted on extraocular movements. Which of the following is the most likely diagnosis?