For TOS , I've read that part of the cause is due to women having a general narrower shoulder/upper body build than men. Just a smaller space for all the nerves & blood flow to travel thru. And any injury or trauma in the area can close down those spaces even more.



I found a PDF from 2003 with some info about it -don't have time to read thru all of it, but looked interesting.
http://www.tufts.edu/~ttheoh01/mastc...flammation.pdf