--well-done and well-analyzed skin biopsy results are as valid at test for the presence of small-fiber neuropathy as we currently have; the procedure is, in effect, pretty much accepted as the current gold standard to detect small-fiber syndromes, although the analyses will generally not reveal a cause, just that there is damage.

It is possible to have small-fiber symptoms and not have evident small-fiber damage on skin biopsy, as part of the sensitivity of the test depends on how patchy or widespread the damage is and from where samples are taken. But if small-fiber density is reduced in accordance with the McArthur protocols (and the work was done originally at Johns Hopkins)--that is, density is listed as below the fifth percentile, and there are symptoms, that pretty much cinches the fact that there is some sort of small-fiber syndrome.

Take a look at this:

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

I can also get you to the original papers on the procedure, if needed, though many are available in the index of this article:

http://www.thecni.org/reviews/13-2-p07-treihaft.htm