Sometimes, usually when I'm having other issues from my MS, my skin is so terribly itchy and when I scratch it leaves a bad rash. It is not something I have all the time. But miserable when it turns up. I have no idea if it is related to the ms. But I know any kind of skin irritation is no fun.
I am guessing it is related, as I think yours is, IMO. Wish you could get some relief for it.