it isnt easy to answer your questions because you have put down very little information here about your peripheral neuropathy and what type you have and suspected causes. A nerve biopsy should be a last resort and should only be used in certain limited circumstances. it is basically used for a confirmatory diagnosis and will not reveal a cause. it does however cause lasting damage and usually numbness and sometimes pain in the area where the sural nerve was cut. you can look here and get an idea of what type of testing you should be getting for your type PN.

http://www.lizajane.org/