--it may take a long time for obvious signs of neuropathy to show up on NCV/EMG studies, if at all; these measures are still very gross in aspect.

And, further, if the damage is primarily or exclusively to the small-fiber nerves, NCV/EMG studies would not show abnormalities--those fibers are too small to measure by that method. Quantitative sensory testing, sudomotor axon reflex testing, and/or skin biopsy would be needed to document damage there.