--small fiber neuropathy is merely a description of a type of neuropathy that preferentially affects the small, unmyelinated fibers that subsume the sensations of pain and temperature.

It is also the variety of neuropathy most likely to be diagnosed as idiopathic--autoimmune, toxic, and/or borderline glucose dysregulation are often suggested as causes but are hard to prove.

The problem may be that as far as I know, Mayo still does not do skin biopsies to document density and condition of those small fibers (which may have something to do with the fact that the procedure, norming, and protocols for skin biopsy were developed at Mayo's great rival, Johns Hopkins).