[Laco]

Does the collection of Vets you have seen, include an Internist?

 

[Laco]

What would she be looking with the scope? Perhaps some esophageal inflammation? Seems if steroids make a difference there must be some inflammation, perhaps trachea or esophagus. I'm not a Vet and am only guessing, but it seems the right Vet dedicated to finding the cause could and should be able to find it. Did you take him to a medical center, where collaboration could occur? Don't know where you are located, but is there a university with a Vet program, that you could get to?