A 12-year-old female spayed Domestic Shorthair cat is presented with a 2-month history of progressive weight loss despite a ravenous appetite (polyphagia).
The owner also reports occasional vomiting and restlessness.
On physical examination, you note a heart rate of 230 bpm, a thin body condition, and an unkempt haircoat.
Which of the following is the most likely diagnosis?
