I am wondering about the same thing. I have atrophy of the traps (mostly middle, but also upper and lower to a lesser extent) as well as weakness and pain in that area. There is also a mild scapular winging.
Symptoms in arms have not been a major issue for me - some on and off pain and weakness which are mostly gone by now,
At least one dr agrees it could be an accessory nerve problem. He suggested an accessory nerve block, but I did not try it yet. Don't know what to expect.