Large blister

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.  

[heartfluttersflyawayplz]

hi , i have a shih stuz that does that , he can be walking across the floor and all sudden blood all over floor from one poping. my dr sees them and knows he has them, nothing you can do, they just swell and pop . i would have checked if you never have , my dr says its glans (glands) and they swell and pop.i just clean him up and he goes about his way nothing my dr says to worry about. good luck

[ddeiman]

I would make sure to do bloodwork and biopsy one to rule out autoimmune issues.