Answer

If all of the vets you have seen are stumped, I would certainly pursue help from a dermatologist. Any of the vets you have already seen can do a skin biopsy (which is definitely going to be the next step based on what you have mentioned above) but I think you will have the best chance at a quicker diagnosis and best tailored treatment through a dermatologist. You will probably need a referral to the dermatologist from one of the veterinarians you have already seen. There are some auto-immune skin diseases that can certainly present the way you are describing and would require a (such as pemphigus) skin biopsy to diagnose (and treatment regimens are pretty specific---based on what has been done above it would not have resolved the symptoms). Do you know when the last steroid injection was given? Equally important is biopsy results can be altered by steroids, so these need to be out of your kitty's system before pursuing biopsies, as the results may be inconclusive otherwise.