My dad has had this issue for some time and unfortunately I do tend to suffer as well...so my conclusion is that it is that it is hereditary. Circulatory system is not the best in the family tree. Even mother side with varicose veins...oh yeah...I like the color blue, when it is not poking out of my skin :P

I have even noticed having it (RS) once in a very AC room.
It is usually affecting only my pointer fingers, so far, but who knows what time will hand me later?!