Review Question - QID 211099

A 17-year-old boy is brought to the emergency room by his mother for altered mental status. His mother reports that over the past month, the patient has been failing his high school exams. She has noticed reduced attention and poor memory. She has had to repeat conversations that they had only hours ago. Then this morning, the patient woke up at home confused, asking where he was. His mother states that he is normally a “bright student” and is in all honors classes. The patient was on a “delayed vaccine schedule" as a child and developed measles at age 6. Since then, he has been healthy. He has no chronic medical conditions and takes only a daily multivitamin. His maternal grandfather has Huntington disease. His temperature is 99°F (37.2°C), blood pressure is 110/82 mmHg, pulse is 86/min, and respirations are 12/min. On physical examination, there is no nuchal rigidity. The patient is disoriented to time and place. His mini mental status exam score is 16/30. The mother adds that 2 months ago her son told her that he was attracted to men. She is not sure if he is sexually active. She denies recent travel. She is unsure about recent sick contacts but says he started volunteering at a local hospital 3 weeks ago and received a flu vaccination. Labs are drawn and a drug screen is pending. Magnetic resonance imaging (MRI) of the brain is obtained demonstrating atrophy. Within 3 days of hospital admission, the patient develops unilateral, slow-myoclonic jerks. Which of the following is the most likely diagnosis?