I'm not sure. But if you think SFN is a possibility, you will need to get the skin punch biopsy, since it's the only way to diagnose it. It's not 100%, nothing is, but it's pretty accurate/precise, something like 90/95% or some such thing. There are at least a few people on here with SFN and a negative skin biopsy, but most of us have a positive result. Good luck with your appointment.