Scott,

Could be a number of things causing this. More often than not, it's decreased circulation caused by arterial sclerosis, which can easily be checked with some non-invasive tests. The other cause is usually nerve compression, which is more difficult to detect, but still a non-invasive procedure done with electrical stimulation. Carpal tunnel disease would be the first thing that comes to mind with musicians that primarily use their hands to play.

Good luck,

Gary