Spencer was diagnosed at age 8 via symptoms and ultrasound. He was just coming out of a bad intestinal bacterial infection. Between the two causes, he lost 20 lbs. and was in such poor condition that I couldn't risk a surgical biopsy. (The ultrasound had located the diseased area as where the small intestine meets the large, and a scope wouldn' have reached it.)
For the past two and a half years he has taken an immunosuppressant, budesonide; that is similar to prednisone but targets the gut, so has few side effects. He also takes Flagyl and Tylan. We tried to many different foods before we figured it out that he developed an inflammatory response to chicken, beef, buffalo and rabbit. So now he can only have venison. No grains, just sweet potatoes. So that kind of kibble, dressed with gravy made from canned venison, and one-third of his diet is raw venison. We found by trial and error that that diet and only that diet works for him. He regained 10 lbs. and has done well despite occasional flares.
But we just ran bloodwork that showed his liver enzymes through the roof. Internist says that could be from a situation with his teeth, but it could also be from the long course of budesonide. We will know in about two weeks.
We're near Seattle, so we can't help you with vet recommendations. But hopefully you're already getting good information on that. Were they able to get any samples through the scoping that showed what kind(s) of inflammatory cells are involved? (That may or may not help, but the vets like that info.)