--come from compromise of nerve roots in the spine, if it is severe enough, one would expect something to show on EMG/NCS--and if that testing was done all up and down the arms and into the neck and shoulder, it may be determinable just where the compromise is coming from.

Spine problems that produce symptoms will usually produce evidence that goes all the way back to the spine, although you may notice it more peripherally. More peripheral problems will show up at and below the area of compromise.

Of course, small fiber problems don't show up on EMG/NCS at all; those nerve are just to small and narrow to be targeted by the currently available technology, which is why quantitative sensory testing, sudomotor testing, and skin biopsies are used to try to determine that.

And, remember, you could have both. I certainly do, and so do many others. In my case, though, the symptoms caused by each tend to be fairly distinct, and in the case of the spinal problems along clearly recognizable body regions--the dermatomes connected to the nerve root levels compromised. But, admittedly, it can be difficult to tease out just what is causing what, as the symptoms CAN feel exactly the same.