Felipe,
Many surgeons will perform the Sural Nerve Biopsy where they cut out an inch or more of the nerve in the ankle region, leaving a nerve gap that may never repair correctly, leading to pain and discomfort that can exceed the original PN pain, and can be a lasting complication to post surgery.
I would leave that procedure as a very last effort for Dx, or never have it at all, since the results usually only confirm a prior Dx.
This will sometimes have pain and discomfort left........ forever.

The Skin Punch Biopsy, usually taken at 3 places, only removes the top layers of skin about the size of a US dime and heals with 3 small Band-Aids. No after affects whatsoever- a practically non-invasive procedure.
But it is only done in a few places in the US.
But...... Johns Hopkins has a mail-in kit that instructs how to take the samples, that are then sent by mail to Hopkins, for proper preparation and microscopic evaluation by experts.