History of Present Illness:
A patient in their mid-70s with a history of hypothyroidism presents to the hospital with 3 weeks of nausea, vomiting, and diarrhea without blood but with a 30-pound weight loss. Just recently he noticed low-grade fevers up to 100.2 and intermittent mild epigastric pain. He denies any recent antibiotics or recent travel
Vital Signs and Physical Exam:
Vital signs are normal. Physical exam is also normal except for abnormalities noted below in initial diagnostic testing.
Initial Diagnostic Testing:
What is the most likely diagnosis?