I'm not sure about upper arms, but on the subject of extremities...
I have noticed that my left hand (the 'poorly' one) and my left foot are noticeably colder than my equivalent right extremities. (I first noticed this four or five years before diagnosis.)
I mentioned this observation to my consultant, who said it was a simple result of my not making use of the left hand side as much as the right - i.e. the right hand and foot were working harder than the left, and so demanded higher blood flow.
This is, I believe, essentially what Ray is talking about.
I've pretty much always had cold feet. This has the positive side effect that my feet don't, generally, get very pongy. I've usually put this down to long legs and being female (honest, more women have cold feet than men; this in itself is a result of the differences in metabolism between the genders. Basically, us girlies are more efficient than men and exude less heat. Instead, we store our energy as fat.)