Review Question - QID 213604

A 63-year-old woman is brought to her primary care physician by her daughter for worsening memory. She states that she noticed her mother had become more forgetful over the past several months and has several times forgotten simple things like turning off the stove or paying her bills. She has a past medical history of diabetes and hypertension. Her temperature is 99.0°F (37.2°C), blood pressure is 167/98 mmHg, pulse is 70/min, respirations are 17/min, and oxygen saturation is 98% on room air. Physical exam is notable for an obese patient who is alert and oriented to person, but gets the date and the name of her primary care physician incorrect. She is able to recall 2 of 3 objects 5 minutes later. The patient appears fatigued. Laboratory values are ordered as seen below.

Hemoglobin: 13 g/dL
Hematocrit: 39%
Leukocyte count: 6,500/mm^3 with normal differential
Platelet count: 168,000/mm^3

Serum:
Na+: 134 mEq/L
Cl-: 100 mEq/L
K+: 4.3 mEq/L
HCO3-: 25 mEq/L
BUN: 20 mg/dL
Glucose: 159 mg/dL
Creatinine: 1.3 mg/dL
TSH: 7.4 mU/mL
Ca2+: 10.2 mg/dL
AST: 12 U/L
ALT: 10 U/L

Urine:
Color: Yellow
Bacteria: Positive
Leukocytes: Positive
Epithelial cells: Positive

Which of the following is the most likely cause of this patient’s symptoms?