It could be non related to PD..

Do you have pain & swelling?
How about when you raise your hands like stick em up- do they turn white and get heavy/weaker?
Can you even hold arms above head for more than a few minutes?

Any repetitive or long time desk work?
any previous whiplash or head/neck injury?

If some of these fit I suggest reading on our thoracic outlet syndrome forum- (TOS) the useful sticky threads there are like a crash course of info.
Look or search for VTOS = vascular tos..

http://neurotalk.psychcentral.com/thread84.html
http://neurotalk.psychcentral.com/thread125577.html
http://neurotalk.psychcentral.com/thread135.html