How To Treat Swelling Of Legs And Tiny Holes Causing Burning Sensation?

My mother has some sort of skin disorder, every 2 - 3 years her leg gets swollen, red and very hard. It is also itchy. Then after about a week a tiny hole forms which in 3 days is about 6cm in diameter and 2-3cm deep. Once the hole is there, it is only after 6-7 months that it heals. She also complains that it burns terribly. She has been to several specialist but none has an answer as to what the problem is and how it can be treated. This is quite urgent because this time, the hole is growing bigger that the previous times.
Thanks, Alicia