A 67-Year-Old Man Is Brought to the Physician Because of Increasing

A 67-year-old man is brought to the physician because of increasing forgetfulness, unsteadiness, and falls over the past year. He reports that these symptoms seem to worsen with each fall. Initially, he could not remember directions to his home but now cannot remember recent conversations or appointments he has made. He often repeats questions that he asked shortly before. He has long-standing hypertension, coronary artery disease, and hypercholesterolemia. Current medications include aspirin, carvedilol, enalapril, and atorvastatin. Examination shows a bruise over the left temple and an unsteady gait. On mental status examination, he is oriented to person and place only. Short-term memory is impaired; he can recall 0 out of 5 objects after 10 minutes. Long-term memory is intact. He has no delusions or hallucinations. Muscle strength is decreased in the left lower extremity. Which of the following is the most likely pathophysiologic process underlying this patient's condition?

A) Arteriosclerotic changes affecting small cerebral blood vessels
B) Degeneration of cholinergic neurons in the basal forebrain
C) Degeneration of dopaminergic neurons in the substantia nigra
D) Diffuse shearing and injury of the white matter tracts
E) Neuronal loss and atrophy affecting hypothalamic mamillary bodies