I have read that ice may reduce pain by numbing the nerves, but may also worsen it beyond the immediate effect by damaging the nerves and also constricting the veins and reducing blood circulation. I know Dr Hooshmand's website is very vocal about this, but I seem to recall reading it elsewhere.

In my case cold water (not actual ice) *seemed* helpful when my RSD was not so bad, but harmful when it was more advanced (dramatically increasing stiffness and etc.)