--and a lot less invasive.

The punch or skin biopsy is designed to examine intraepdiermal nerve fiber density and condition--specifically, the small, unmyelinated fibers that subsume the sensations of pain and temperature. It's a fairly new procedure, and still is only done at a handful of tertiary centers across the US (Cornell-Weill, Mass General, Jack Miller, Hopkins--though the latter has a program now through which any dermatologist can take the proper 3mm across/1 mm deep skin samples and send them in for analysis, which requires electron microscopy). Often, for people with normal nerve conduction studies and other tests, but painful neuropathies, this will be the only test that shows anything, though it rarely, if ever, points to a cause.

The nerve biopsy, usuallly performed on the myelinated sural nerve, involves a much bigger/deeper incision, as some muscle is normally biopsied as well. It may point to a cause for certain neuropathies--especially autoimmune vasculitic ones secondary to connective tissue disease--but the diagnostic yield may not balance the dangers from the cutting. One should not have this procedure done except by a real, qualified surgeon--there are too many stories of permanent damage/numbness when these are done by your run-of-the-mill neurolgist.