Review Question - QID 213689

A 67-year-old woman presents to the emergency department for altered mental status. Her symptoms started roughly 1 month ago and have been gradually worsening. The patient’s daughter states that her mother initially just seemed more forgetful but now is forgetting to turn off the stove, lock the doors, or even how to get home when she goes on walks. Her temperature is 97.0°F (36.1°C), blood pressure is 157/98 mmHg, pulse is 60/min, respirations are 10/min, and oxygen saturation is 98% on room air. Physical exam is notable for an elderly woman who is calm. She is only able to recall 1 of 5 objects and cannot remember what her address is. The patient has gained 20 pounds since she last visited the hospital 1 month ago. Laboratory values are ordered as seen below.

Hemoglobin: 12 g/dL
Hematocrit: 36%
Leukocyte count: 6,500/mm^3 with normal differential
Platelet count: 197,000/mm^3

Serum:
Na+: 130 mEq/L
Cl-: 100 mEq/L
K+: 4.3 mEq/L
HCO3-: 25 mEq/L
BUN: 20 mg/dL
Glucose: 99 mg/dL
Creatinine: 1.1 mg/dL
Ca2+: 10.2 mg/dL
AST: 12 U/L
ALT: 10 U/L

Which of the following is the most likely etiology of this patient’s mental status?