I too have that, and got it once so bad up and down my legs that it even raised the eye brows of the rheumy. Now he didn't mention what it was, but he's concerned that I might also have vasculitis (also have other symptoms).
For years I would get "bruises" and I'd not remember ever bumping into things and stuff like that (the family was convinced that I was pretty clumsy, but I wasn't really (bump into the usual stuff until I got glasses in my teens, then even that stopped)).
Now a days, it can be a "patch" here and there, while other times it would be up and down my legs like someone was a dark painting. I do know that the warmer I get, the more the "patches" appear.
Have you shone the patches to your rheumy yet?
I'm sorry but I can't speak of CREST, and I do hope that you'll get a definitive answer soon. And hopefully another more knowledgeable member will stop by soon with some more answers for you.
Take care of yourself, okay?