Clinical Reasoning: A 50-year-old man with headache and cognitive decline.

SECTION 1 A 50-year-old man presented with headache and cognitive decline 10 weeks after undergoing matcheddonor peripheral blood stem cell transplantation for treatment of mixed-phenotype acute leukemia. His pretransplant treatment included systemic chemotherapy (cyclophosphamide, daunorubicin, vincristine, prednisone, L-asparaginase, dasatinib, and cytarabine), intrathecal chemotherapy (methotrexate), and total body irradiation. His posttransplant course had been complicated by cutaneous graft-vshost disease. Over 1 month, he developed holocephalic, throbbing, temporal headache worse when standing and reported feeling confused. His family members reported progressively withdrawn affect, depressed mood, and decreased spontaneous activity. Before his illness, he worked in a cognitively demanding profession with no history of cognitive deficit. On examination, he was arousable to voice but had difficulty sustaining alertness for more than a few seconds and was unable to state the days of the week backward. He was oriented to self, place, and month, but not year. He was able to follow simple 1and 2-step commands but with profound psychomotor slowing and abulia. His cranial nerve examination was notable for mild anisocoria (right pupil being 1 mm larger than left and slightly sluggish in its response) but otherwise unremarkable including funduscopy. There was no weakness or incoordination, but all movements were performed slowly. Sensory and reflex examinations were normal. The patient was able to ambulate slowly with assistance.