An 85-Year-Old Man Comes to the Office Accompanied by His

An 85-year-old man comes to the office accompanied by his daughter due to "memory problems."  The patient is a retired accountant who lives alone and had been managing his finances and housework until a month ago.  He says, "I've had to ask my daughter to shop for me and help around the house.  I kept forgetting to turn off the stove and could have easily burned down the house."  The patient has been more tired than usual and sleeps through his favorite television shows.  He previously maintained a rose garden but now feels "it's not worth the effort."  The patient's daughter says, "He was due for a medication refill last week but still has a few pills left because he sometimes forgets to take them."  Medical history includes hypothyroidism, hypertension, hypercholesterolemia, and a transient ischemic attack 2 years ago.  Temperature is 37.2 C (99 F) , blood pressure is 141/87 mm Hg, pulse is 76/min, and respirations are 14/min.  His weight is up 4 kg (8.8 lb) from last month.  TSH is 4.0 µU/mL.  He scores 21/30 on the Montreal Cognitive Assessment (normal: ≥26) , with deficits in delayed recall and attention.  Which of the following is the most likely cause of this patient's cognitive impairment?

A) Alzheimer disease
B) Dementia with Lewy bodies
C) Dissociative amnesia
D) Frontotemporal dementia
E) Major depressive disorder
F) Subclinical hypothyroidism
G) Vascular dementia