Purrley my Andy used to occasionally get something that sounds very similar. It shows up on his leg and sounds quite a bit like what Frisco has (although not really a sore, but looked more like a crusted scratch) and it is accompanied by a swollen lower lip and the vet said the two areas are the same thing just manifesting itself a little differently. He said it was an allergic reaction and told me the medical term for it but unfortunately the name was long and I couldn't remember it once I had left the office. He treats it when it occurs (so far only three times and maybe a year apart between flare-ups) with a steroid injection of some sort. It works immediately. Apparently the condition is not painful but just looks bad. I will be waiting to hear other Pet Talker's responses too. Hope Frisco starts to feel better soon!