How sensitive is the biopsy test for small fiber neuropathy?

Not very: Generally nerve biopsy is done for suspect vasculitis (blood vessel disease) or amyloidosis (amyloid deposition). It doesn't,t add much that clinical evaluation, lab tests and nerve conduction studies can do. So it isn't very sensitive for small fiber neuropathy itself.

Pretty good: Overall the tests are pretty good - there may be some small issues with the threshold for a diagnosis however overall very sensitive.