Well Pain basically works like this,
In general preferance is given to anesthesia over PM&R if there is an internal anesthesia program. This is primarily because, as you stated previously, most pain programs are run by anesthesia departments. Having said that, the way PM&R can get pain fellowships is:
a) go to a PM&R sponsored pain fellowhship (honestly I don't know how many of those there are...but I'm assuming not many)
b) go to a pain fellowship that isn't interventional (which there are a few of, and usually those are PM&R sponsored I believe)
c) COMPETE WITH ALL THE GRADUATING ANESTHESIA RESIDENTS
Yeah, that last one is daunting, primarily because so many residents are entering back into the field of anesthesia, and pain is a very popular fellowship. Supposedly the gulf in difference in terms of compensation between private and university is one of the largest of any specialty.
Well, with all that said, the key point to remember is...DON'T GO INTO A RESIDENCY BECAUSE YOU ENJOY ONE SUB-SPECIALITY OR FELLOWSHIP. Pain is competitive as hell, with most people staying at the place they did residency to pursue pain fellowships. That is the reality...pick whichever one of those two fields you like more, overall. PM&R has some great aspects too it, so does anesthesia. BUT THERE ARE TOO VERY DIFFERENT PERSONALITIES THAT GO INTO THESE FIELDS. Anesthesia can at times be very lonely as a field, whereas PM&R is in general very collegial. My point is don't base the choice on one sub-speciality part of it. Choose on the overall field, because otherwise you'll be miserable the rest of the time you are there.
OH..just an FYI. They are planning to change the pain fellowship to TWO YEARS. And of course (wouldn't you know it), it'll be during our time in residency. They want to control the numbers going out, and limit interest I think to some degree. Well, c'est la vie.