The beginning of a rodent ulcer

I just pinned Nathan to the floor with one hand and took a picture of the burgeoning ulcer with the other. Quite proud of myself, and him. He did attempt a scratch with a back leg, but I moved too quickly for him. Dopey cat. Today he managed to get himself lost in a fitted sheet that he was lying on (we are not keen housekeepers) and he's currently having a fight with a curtain. Bless his lack of brain cells.

Anyway, it's rather blurry but I want to document the progression of the ulcer. It's not coming up too quickly, really. With the last one, all of three weeks ago, his lip was swollen on the Monday, and sore, red and weeping by the Wednesday. This has been trying to rise since before the weekend. Of course, he still has some steroid in his system, but perhaps the special diet is helping in some way. I'm sure it'll still come up, and then it's off to the vet for a general anaesthetic and a biopsy, leaving us a little lighter in pocket. All the biopsy will tell us is whether the problem really is eosinophilic granulomae, but doesn't tell us what is causing it.

The vet said 90% of the cause of the condition is an allergy to flea bites. I've read on the internet that just one or two flea bites can cause the ulcer to start. We do treat him with Frontline regularly, and the vet checked him all over again for flea dirt, finding none. But I'm sure a treated cat can be bitten and thus cause a reaction. Apart from keeping him inside, and possibly his sister too, which they'd hate, what else can be done? Then, there's the 10% of cause which may be food allergy.

In order to find out what the food allergy could be, we'd have to cook him food ourselves and a food he's never had before. I read somewhere that cats like variety in their diet, this means that the only meat he's never had is....venison. Yeah, as if I'm going to buy venison for a bloody cat! Not going to happen. Well, I say that now. I also said that I'd never allow a cat on the bed, in case it pissed on it. Guess what happened yesterday morning...This cat is pure trouble, I'm telling you.