Review Question - QID 109619

A 53-year-old woman presents to your office with several months of fatigue and abdominal pain. The pain is dull in character and unrelated to meals. She has a history of type 2 diabetes mellitus and rheumatic arthritis for which she is taking ibuprofen, methotrexate, and metformin. She has 2-3 drinks on the weekends and does not use tobacco products. On physical examination, there is mild tenderness to palpation in the right upper quadrant. The liver span is 15 cm at the midclavicular line. Laboratory results are as follows:

Serum:
Na+: 135 mEq/L
Cl-: 100 mEq/L
K+: 3.7 mEq/L
HCO3-: 24 mEq/L
BUN: 13 mg/dL
Creatinine: 1.0 mg/dL
Alkaline phosphatase: 100 U/L
AST: 70 U/L
ALT: 120 U/L
Bilirubin (total): 0.5 mg/dL
Bilirubin (conjugated): 0.1 mg/dL
Amylase: 76 U/L

What is the most likely cause of her clinical presentation?