Hello,
I’m sorry to hear about your Skye’s illness. While there is no perfect test, your veterinarian appears to so far have done a fairly good job of narrowing down the possibilities. One non-invasive approach to consider would be an abdominal ultrasound and keep in mind that an endoscopy is minimally invasive. It is correct that without some type of biopsy there isn’t a way to truly differentiate between IBD or lymphoma. If you choose to go down the steroid route, just be aware that it will potentially alter any future results if you later choose to biopsy so there must be a period of time where the medication would have to be stopped.
The steroids may be a reasonable choice as they tend to improve appetite and both conditions often include a steroid as part of their treatment protocol. The tests really are there for information about prognosis and if any additional treatments (chemo) should be added in. It really depends on what your viewpoint is as far as how conservative or aggressive you want to go after this. Over time, the steroids may have other effects on the body or organs but ultimately the focus needs to be on his quality of life. You are trying to make things as good for him as long as possible and a balance will need to be found. He may only get a few years with the steroids before something else happens but at least they may be good ones.
I wish you luck in Skye’s care.
Dr. Ryan Llera