Just yesterday we took our cat to the vet for this very thing... Every year at this time he has a problem with what the vet calls "no see ums". His face and ears get spotty then he gets a one time shot, but doesn't stay on continuous steroids. How long has your cat taken steroids? See if your cat will eat yogurt or kefir as probiotic? My cat will eat anything.
This year is different... he's spotty but also really antsy, cleaning himself, and won't stay inside. He chooses to stay outside in the FL. heat? and only comes in long enough to eat and drink. It seems like something about the air condition that sets off the itching, because he's fine outside!
My son found on the cat what looks like a tick, but the vet said could be a spider/mite, that they are all in the same family. Might be too mangled to identify... Is it even the culprit? I don't know but wonder if dusting him with DE would be a good idea?