Confuddling the vet...

I talked to the vet this morning, and she's at a bit of a loss at his lack of response to the Prednisolone treatment. I'm bringing him to the clinic to have him scoped after being ridden, she wants to double-tripple check that she hasn't missed a mechanical problem in his palate, larynx, or throat, but I don't think that's it, his symptoms aren't similar to any of the horses I've known with either a low palate or constricted larynx...