A right-handed man in his 40s with no significant medical history presented with 1 month of fatigue, confusion, and headache. He initially had increased sleep requirements accompanied by poor work performance that progressed to obtundation. Associated with these symptoms, he reported several weeks of night sweats and a 10-lb unintentional weight loss. He denied any history of recent trauma or head injury. Findings from the general examination revealed leftsided cervical adenopathy and splenomegaly. Findings from the neurologic examination demonstrated markedly diminished arousal but normal cranial nerve function, motor strength, and reflexes.