A 67-Year-Old Woman Is Brought to the Office by Her

A 67-year-old woman is brought to the office by her son.  He reports that his mother has had periodic confusion, memory loss, and poor sleep and seems "kind of out of it sometimes."  These symptoms have gradually worsened over the past 1-2 years.  The patient occasionally sees "strangers in the backyard," who are not there when her son looks for them.  More recently, she has begun walking more slowly and has fallen twice in the past month without any significant injuries.  The patient has a history of hypertension and depression.  She does not drink alcohol or use illicit drugs.  On physical examination, she walks slowly and has mild bilateral hand tremors and mild bilateral lower limb rigidity.  On cognitive examination, the patient appears to be oriented to person and place, and can recall 1 of 3 items in 5 minutes; she can state the days of the week forward but does not cooperate with stating them backward.  Chemistries, complete blood count, vitamin B₁₂, and thyroid function tests are normal.  Serum treponemal test is nonreactive.  MRI of the brain shows mild generalized cortical atrophy.  Which of the following is the most likely diagnosis in this patient?

A) Alzheimer disease
B) Dementia with Lewy bodies
C) Major depressive disorder
D) Normal-pressure hydrocephalus
E) Parkinson disease