Oh, I don't know Rick. It could be a question of not what it is but rather what it is not. Some allergies can be DX'd over the internet or even with a phone call. Especially if its something you have never seen but someone else has.
I spent weeks, months actually, and several thousand dollars with regular vets, specialists, and getting an MRI without resolution or a diagnosis on one of my dogs. All the vet told me was let the dog do what it felt comfortable doing. They didn't know nor did they have an answer. Then a WDF
poster wrote about their BH who presented with a set of symptoms and was DX'd with Fibrocartilagenous Embolism and it sounded hauntingly familiar. When I looked it up - it was my V8 moment. My dog had had exactly the same symptoms, same onset, same presentation as their dog. In fact, my dog had presented with the "classic symptoms". To bad the OP hadn't written about their dog 2 years earlier. It would have saved me 10K in vet bills. When my dog had a reoccurrence of FCE, I recognized it immediately, knew what to call it, whereas I wouldn't have understood prior to the WDF
I have a good vet but they cannot compete with the enormous boots-on-the-ground experiences of this forum.