Review Question - QID 212666

A 65-year-old woman presents to the emergency department with an abnormal appearance of her eye. The patient states she noticed several days ago, and she has some minor pain and double vision as well. The patient has a past medical history of diabetes and hypertension and is not currently taking any medications. She is currently sexually active with 2 male partners. Laboratory values are ordered as seen below.

Serum:
Na+: 139 mEq/L
Cl-: 100 mEq/L
K+: 4.3 mEq/L
HCO3-: 25 mEq/L
BUN: 20 mg/dL
Glucose: 222 mg/dL
HbA1c: 12.8%
Creatinine: 1.1 mg/dL
Ca2+: 10.2 mg/dL

Physical exam is notable for the finding in Figure A. The patient's physical exam is notable for 5/5 strength in the upper and lower extremities with 2+ reflexes throughout. Sensation and proprioception are diminished in a bilateral fashion which the patient states has been gradually occurring over the past several years. Both pupils are equal and reactive to light. Which of the following is the most likely etiology of this patient’s symptoms?