You are certainly going to the lengths many others would envy to try and get a diagnosis! And, well, it mite not be what you want to hear? Please remember there are over 200+ neuropathies and treatments for most of them are limited. Choices of various meds are about 50+, and other therapies should it have immune implications are down to about five?
That doesn't mean that the docs [if competent] aren't trying? Those not competent wouldn't admit it anyhow..so there. I've been that route as you obviously have.
There is an absence but for few, bits of research about how nerves die, then, if and how they regrow. Most of it is being done on sea animals and rats. I sure wish I could be more encouraging in this quarter? But, know that nerves can and DO die rapidly, but can take YEARS to regrow. Lots and lots of patience is required.... kind of like nuruturing the perfect tree in your yard or a special plant in your house. It is NOT gonna happen overnite!
It's good to see that you seem to have had extensive tests, and as one dear old 'codger' of a neuro would say: That's off the 'lists'! Diagnosing many PN's is truly a process of meticulate elimination of other things. Lots and lots of them! Please review the 'Sticky' important information. Lots of good stuffs there from many here.
Soo, while you are 'basking' in the pain, and chewing on the wood in your furniture? [I've tried, wasn't good on the teeth?] Try the different 'meds menu' and see if something just works? I tried to make friends w/my pains? And well, they just went and kicked it up notches. So I quit that approach.
Mrs D is right to suggest the gluten aspect.... Cutting it[some things?] out or down, is kind of like being a diabetic in that it doesn't have to be blatent? Just some changes... Here is the forum for it here, I am sure there are other sources as well.... http://neurotalk.psychcentral.com/forum13.html I believe this is often called 'lifestyle changes' Blah! But, they can and do work for many. Good luck and keep us all up to date! - j