For me...the spread was gradual. Mine spread after a lumbar sympathetic block. After the block...my back started to ache and burn...and then it got worse...and then it went up my spine to my neck, and then my shoulders and around the front to my chest and abdomen, and then down my arms, and then to my hands. It was definitely burning RSD pain and flare ups felt the same as in my ankle.

I also experienced spread about a year after that that went up my left leg and ended in my left hip after my nephew accidentally kicked my ankle while rough housing with my boyfriend. It was also definitely the RSD burning.

But as much as it was the same pain...it wasn't the same experience as my initial onset of RSD. Part of that was probably because I was used to the high pain levels...but there were other differences. I didn't have the drastic temperature differences I had when I first got RSD in my ankle. There was inflammation but it presented differently...more like a slight sunburn over all of my RSD spread areas vs. the severe swelling and color differences in my ankle when that first started.

The extreme sensitivity to touch and cold was the same in the spread areas though...

Not sure if any of that info helps...but that's what it was like for me.