It won't confirm RSD. It could show nerve entrapment that if surgically repaired could possibly calm things down... Maybe.
Why now, though? Some WC docs just insist that all their patients have them done. Is it being performed at his/her office? If so, it could be for monetary reasons.
Have you had a bad reaction to needles from either blood draws or IV's? If so, this will be significantly worse. That being said, I underwent one rather than jeopardize my WC benefits.
http://www.rsdrx.com/rsdpuz4.0/puz_99.htm
http://www.rsdrx.com/rsdpuz4.0/puz_21.htm