Cheryl
Years ago I had this on my cat, scraping showed nothing, it started on a small area on her tail, and gradually was her entire back, (not sides or shoulders just slowly spread over her back, and down half her tail). No itching biting just normal looking bare skin.
She was on kibble at the time, from the market, when I was ignorant of things, my others all did fine on grocery canned and dry...
Vet had us try different foods, we progressed to premium foods rather then Kalkan and friskies, no results, tried elimination diets, finding cat foods with no beef, chicken turkey fish in them, that was next to impossible!
No result, then suddenly as it started her hair loss stopped and started growing hair.
She was just 3-4?? And passed just prior to her 19th birthday with a full coat of shining heathy coat, to a stroke we and the vet thinks. She was diabetic but her kidney function was great. She loved Stella and chewys freeze dried raw foods, hydrated of course!