David, as far as I can see from PubMed there can be sural nerve involvement in the various transthyretin amyloidoses (which are very rare) and in immunoglobulin light chain amyloidosis.

Obviously check with your health team about this but I would have thought that both could be diagnosed without removing any parts of your sural nerves; there is some information about Dx of immunoglobulin light chain amyloidosis here AL - Amyloidosis Foundation.