--CAN be confirmed by certain tests, such as quantitative sensory testing, sudomotor axon reflex testing, and, the most recent gold standard, skin biopsy that shows a reduction in intraepidermal nerve fiber density.

Take a look at this:

http://www.medscape.com/viewarticle/563262_6

None of these are likely to show a cause of the neuropathy, but they can certainly document why you might have symptoms.