Do you have only sensory symptoms--pain, numbness, tingling, shooting, etc.--or does there seem to be some motor involvement?

Any autonomic issues--sweating abnormalities, dizziness, blood pressure drops, heart rate irregularities?

Often, the differences in these can point to what nerves are affected, which might influence a search for a cause and possible treatment.

Part of the problem here is that there are several hundred KNOWN causes of neuropathy--and yet many people still wind up labelled "idiopathic" with no discernable cause. AND--there are other diseases of the nervous system, as well as disorders of the brain/spinal cord, that can mimic the symptoms of peripheral neuropathy exactly, so that investigations are often long and based on process of elimination (and rather expensive).

You've apparently had a good number of tests--but no where near a comprehensive work-up, which can include many of the tests for nerve autoantibodies, genetic abnormalities, toxins, etc. that can be found in the Liza Jane spreadsheets--www.lizajane.org--a great way to track test results and suggest new ones to less aware physicians.

On another thread, I made a long reply about the nature of small-fiber neuropathies not being detectable through most modalities (they will not show up on nerve conduction studies or EMG's which can only measure gross damage to larger, myelinated nerves); it often takes quantitative sensory testing or skin biopsy to show the damage, and these tests are not widely available (one usually has to get them done at a tertiary specialty center).
Take a look at:

http://neurotalk.psychcentral.com/sh...ad.php?t=26824

The information and links posted there--many of which also show up in the Useful Sites section at the top of this board--may help you get a handle on what may be going on.