--that are initially "idiopathic", if one has the time and the (insurance) resources and wants to pursue advanced testing, one can contact one of the tertiary hospital centers that does advanced research in neuropathy and see if one can be worked up there. Often these places will do a much more extensive work-up than the average neurology office.

Among these are

Johns Hopkins in Baltimore
The Cornell Weill Center for Peripheral Neuropathy in New York (part of the New York Presbyterian Hospital system)
Massachusetts General in Boston
Jacksonville Shands in Florida
The Jack Miller Center in Chicago
Washington University Hospital neuromuscular center in St. Louis
University of California at San Francisco Medical Center


These are all places of extensive theoretical and research work in neuropathy and they will often do testing according to algorithmic protocols that most places simply don't have the background to do (and are often the places at which these protocols were devised).