pheebs, I am not speaking on lankeela's behalf, as she is perfectly capable of that, but I really wanted to say that in the time I have been using AB, she has been extremely helpful and extremely knowledgable on doggy subjects-scarily so!
Everyone else has given far more comprehensive answers to your Q, but to give you an idea of what may happen, my boss's dog has similar all up his legs, and he has been given steroids and cream. My Border Collie is allergic to fleas, but it took us an age to find this out, after blood tests, skin scrapes etc. I hope your pup is insured, or that you are OK for money, because these diagnostics at our Vet cost in excess of �400-I was so grateful for Pet Insurance when we got the bill! We now flea him every 3 weeks, as opposed to 4.
I hope your pup-pup is OK, give her a tickle from me :)