Fipronil allergy cat?

[ycbm]

Cat will be seeing vet if things don't resolve very soon.

I'm wondering if one of my cats has an allergy to fipronil flea spot-on or if anyone can suggest what might have given him a very specific dermatitis.

All three were dosed from the same supply for the first time in their lives. My 10 year old neutered male lost a finger nail size/shape patch of hair close to his tail by the side of his spine a few days later. The top layer of skin peeled off but it looked fine, just as if he knocked his hip bone on something. Then he got some more "fingerprints", all close to his spine, traveling towards his head. Today he has a track all the way up the side of his spine from his tail almost to his shoulders. It's very peculiar. I can't see any way, given how it has developed, that this is something which has come from outside his body. No knock or scrape could possibly account for it. The timing and the fact it's tracking his spine makes me wonder about the fipronil. He doesn't seem remotely bothered by it.

Any clue as to what could be going on?
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[chaps89]

I have to be very careful with flea treatment for Stanley, he now has Credelio flea treatment which is a tablet rather than a spot on.
He still has a bald spot from frontline a couple of years later.
However his was only directly where the treatment had been applied.
Has there been any signs of fleas on the cat, or does he seem like an itchy/allergic type more generally?

 

[ycbm]

He's ten and after getting rid of the ones he brought with him as a kitten, he's never needed to be flea treated. There must be cats with fleas on this estate, though, because we now know the youngster has a flea allergy and gets scabs around his ears, and Bob is scabby down his back. His sister is the only one without a problem!

The lack of reaction at the application site seems to suggest it's not fipronil, so I've done them all again today as two are scratching and it was a month ago they were done.

It seems better today, hasn't spread and he's not grooming it as much, so possibly it was something that got on his skin, or a bug that is resistant to fipronil.
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