--many, many times, as they are minimally invasive. The frequency recommended depends on the clinical picture (and, often, insurance concerns), but in a neuropathy thought to be progressing, annually is fairly standard.

There really is no way to measure the small nerve fibers FUNCTIONALLY at all, beyond some autonomic tests like the sweat test that do give some information, indirectly, about how that function is working--they are simply to thin to place recording/measuring devices in. Then, too, the symptomology from small fiber damage can vary widely even in people whose biopsies look very similar.

The real value of repeated skin biopsy can be in seeing if the nerve density values rise or fall at consistent sites, what the condition of those fibers looks like, and how this correlates with perceived symptoms.