From what I understand, its from the nerves going crazy or something. I never really understood why this happens. I have seen worse cases that really really bad. That is why Im leaning to amputation before this happens, almost all of the cases Ive seen. It starts with blisters and spreads upward to the thigh. There is a guy I communicate with who is a professional athlete now, after he amputated his leg. Below the knee only.