I have never had a cortisone shot for anything, but I do have a relative who has had one for sciatica. She debated whether or not to have it, and decided to go ahead and get the shot.
Unfortunately, things didn't go well at all. In fact, she said it made her sciatica much worse, to the point where she had trouble even sitting in a chair. The last I heard, I think things improved slightly, but she has often mentioned how she regrets agreeing to the cortisone shot, and is pretty upset about
getting it done, especially angry towards the doctor who suggested it to her.
I guess hind-sight is 20/20, right??
Of course, this is just a single example, and there could likely be more positive outcomes. Hopefully, someone here on the forum may have had things turn out better.
My feet don't get to the point where they're purplish or red, but my leg/foot circulation doesn't seem good, especially in cold weather. I try to keep them as warm as possible and walk as much as I'm able, to get the circulation kicked up a bit.
I don't know if this helps you, but just my experience. I often use microwavable 'bed buddy' type of "slippers," which I slide onto my feet if I'm watching a movie or reading in the evenings. It helps to get them warmed up, at least for me.
Obviously, you should first check with your doctor, if you haven't already, especially if you decide to try to apply heat. Also, have you been checked for diabetes? I think that often affects circulation.
I hope you find relief soon. Best wishes!