is dead on about prediabetes and painful SFPN, also linked to metabolic syndrome too.
There are a number of well documented studies that link particularly painful SFPN to prediabetes and metabolic syndrome. Lifestyle intervention has been shown to delay the onset of PN in prediabetics but also to result in reinervation and pain reduction in those patients who still had demonstrable small fibers.
A couple of good links to studies from Univ of Utah follow. If my memory is correct I believe that Silverlady started a thread much earlier along these lines (related to Sjrogen's syndrome I think) and I believe Wings42 also had some leads but I'll defer to them.
Hope this helps somewhat - I have some other links if you're interested
Alkymst
http://care.diabetesjournals.org/cgi...ract/29/6/1294
http://www.sciencedirect.com/science...d469fd5964375c