Of course it is possible to build up the muscles and get the function back despite the pain and the RSD...it's just VERY VERY difficult unless you can get your pain to a manageable level. I believe the key is to just keep moving.

Earlier this year my RSD got so bad that I could not stand or walk at all...was stuck in a wheel chair and had to get myself around the house by crawling or scooting. It was awful. But I was lucky and my doctor ordered at home physical therapy and I got a wonderful therapist. We started with small stuff...as small as just sitting in a chair and doing toe and heel raises. From there it was about slowly adding in new things and increasing the difficulty. This therapist was really great at pushing me just enough each time she came and adding something new or increasing the amount I did something just enough so that I kept improving without having many setbacks. But the key is to do these things EVERY day and to incorporate them in a way that you balance the resting with the movement/exercises. 6 months later I am now walking with a walker and able to get around a little bit more.

But you really need to keep looking for something to help get the pain under control. Mine is not well controlled right now...but my doctor was able to get me a portable TENS unit and that helps with my pain enough to allow me to do the exercises. Without it I think I would still be struggling to even stand at all. So even just finding something that can help your pain level even a little can make a big difference in what you are able to accompish with physical therapy and exercise.