My dog gets regular cysts all over which will eventually burst. However, at his lower joint on the front of his front left leg, he has developed a large blister, about the size of a dime. In contrasts to his cysts, this is somewhat spongy, appears to be vascular, and is puffed up like a blister from a hot stove. He will lick it, but it appears to be sensitive as he does not like it to be touched. The blister also appears to be hairless, but I do not know if this is due to him pulling the hairs out or etc. On occasion, he will limp with that leg (especially after a long walk or playing/running in the yard). I am taking him in to see the vet, but would just like to know what possibilities could be causing such a blister and any possible recommendations from all sources available. Thanks.