Review Question - QID 212505

A 47-year-old woman presents to her primary care physician for abdominal pain. She states that for the past month she has experienced abdominal pain, diarrhea, bloating, weight loss, and excessive flatulence. Her current medications include metformin and insulin. The patient states that recently she has experienced significant anxiety as well as multiple panic attacks, in addition to worsening GERD. Her diet consists of fruits and vegetables, as well as dairy products for protein. Her temperature is 99°F (37.2°C), blood pressure is 140/87 mmHg, pulse is 90/min, respirations are 13/min, and oxygen saturation is 96% on room air. Physical exam is notable for borborygmi upon abdominal auscultation, and diffuse abdominal tenderness. Inspection of the patient’s extremities reveals the finding in Figure A. Cardiac exam and pulmonary exam is within normal limits. Neurologic exam is notable for decreased sensation bilaterally in the lower extremities, as well as an ulcer on the ventral aspect of the left foot. Laboratory results are ordered and return as follows:

Hemoglobin: 12 g/dL
Hematocrit: 33%
Leukocyte count: 7,500 cells/mm^3 with normal differential
Platelet count: 245,000/mm^3

Serum:
Na+: 140 mEq/L
Cl-: 102 mEq/L
K+: 4.1 mEq/L
HCO3-: 24 mEq/L
BUN: 24 mg/dL
Glucose: 145 mg/dL
Creatinine: 1.4 mg/dL
Ca2+: 9.6 mg/dL

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