I have not found one single doctor who will just simply accept that CRPS causes "brain fog." Their reasons are usually
1. Meds
2. Lack of sleep
3. Depression

But if you research yourself online, you can find multiple references to CRPS and memory and cognitive function decline. Not just on any website written by and for people with CRPS, but I have found it on professional sites and in at least one medical study. I met several people in my rehab groups not on meds who had the same symptoms. My symptoms hit rapidly during the first year while my meds were stable. I was fine... and then I wasn't.
I have always had depression and it has never caused any issues even vaguely this severe.
Brain fog, cognitive decline, word finding issues, saying gobblety gook instead of real language, I don't see how ALL of this could be caused by meds, especially as I have changed my meds over time, but the symptoms have been consistent.