Nerve Endings

When I pet my cat anywhere on her back, her head flips up like I'm hitting a nerve. It must hurt her because she softly bites my hand to tell me not to do what I'm doing. Also, the area right above her tail has white flakes almost like dry skin.

I took her to the vet and the first thing she checked for was fleas but she couldn't find any. She was given Revolution as a precaution. That did no good - no change

She was given a dose of Douxo Seborrhea Spot-On - no change

Does anyone have any ideas?

Obviously, I'm not a vet, but the back sensitivity reminds me of what I've read about feline hyperesthesia. You don't mention any of the other symptoms I've heard about (e.g. rippling skin, biting the tail, etc.), though.