Our cat has had this problem for about a year now. I included pictures of the problem. We had her go to the vet but everything they did didn't work. It started the heal and the hair started growing back but then boom it came back and was worse then before, and it repeated this process and just kept getting worse. Right now it's just really bad on one leg and it's no where else. She is often licking and nibbling at it and causing it to bleed. We thought it was a problem with the food and litter but we changed them both with no success. Any Idea what this could be? It just won't seem to go away. See pictures of it below.