Clinical Reasoning: A 46-year-old man with persistent hiccups, cognitive dysfunction, and imbalance

A 46-year-old, right-handed, African American man presented to the emergency department after 1 week of persistent hiccups and 3 days of nausea and vomiting. His family member also noted that he had been experiencing right-hand tremor and gait imbalance for the last 3 months. Over the 6 months prior to presentation, the patient's coworkers had noticed that he was completing his work more slowly, that he was forgetting how to perform simple tasks, and that several times he had come to work at the wrong hours. The patient had a history of HIV diagnosed 10 years earlier and reported good adherence to an antiretroviral regimen consisting of tenofovir, emtricitabine, and atazanavir boosted by ritonavir, without any changes for several years. His viral load was undetectable when tested 8 months prior to presentation.