Several of us have talked about all sorts of weird rashes. I've had something like it at times, but it always fades away before I can show it to a doc.
One name that I've seen used as a possibility for it is cutaneous vasculitis rash. Here's a site that has pics similar to yours:
Of course, we're not doctors, so I'm guessing as much as you are. Keep that picture, and be sure to show it to your rheumy.
That will be your best bet for getting it diagnosed.