Review Question - QID 108649

A 64-year-old man who has not seen a physician in over 20 years presents to your office complaining of recently worsening fatigue and weakness, a decreased appetite, a distended abdomen, and easy bruising. His family history is notable for a mother with Hashimoto thyroiditis, a sister with lupus, and a brother with type 2 diabetes. On further questioning, the patient discloses a history of prior alcohol use disorder as well as intravenous drug use, though he currently only smokes a pack per day of cigarettes. His temperature is 98.6°F (37°C), blood pressure is 106/72 mmHg, pulse is 92/min, and respirations are 14/min. On physical exam, you note the following findings seen in Figure A and Figure B as well as several ecchymoses and telangiectasias. Laboratory values are as follows:

Leukocyte count: 4,100/mm^3
Hemoglobin: 9.6 g/dL
Platelet count: 87,000/mm^3
Prothrombin time (PT): 21.0 seconds
International normalized ratio (INR): 1.8

Serum:
Creatinine: 1.7 mg/dL
Total bilirubin: 3.2 mg/dL
Aspartate aminotransferase (AST): 225 U/L
Alanine aminotransferase (ALT): 103 U/L
Alkaline phosphatase: 162 U/L
Albumin: 2.6 g/dL
Serum thyroxine (T4): 3.1 µg/dL
Thyroid-stimulating hormone (TSH): 3.4 µU/mL

What is the most likely cause of this patient’s low serum thyroxine?