--damage to both the larger fibers that are measureable by EMG/NCV tests and to the smaller fibers simultaneously. But standard EMG/NCV testing can only isolate fairly large, myelinated nerves and make determinations of fairly gross dysfunction (a "small" ambiguous deviation from norm may or may not get picked up).

Now I have heard of neuros who, after a nomral NCV/EMG series in a person complaining of symptoms, then conclude that the problem must be small-fiber. But they should probably continue attempts to document it, through qualitative sensory testing, autonomic testing, or skin biopsy.