I have been diagnosed with SFN and dysautonomia, and had a negative skin biopsy. I’m a patient at Mass General, which has a good neurology department. The neuromuscular specialist who ordered the test said that skin biopsies are good for confirming SFN, but not good at ruling it out: few false positives, but relatively many false negatives.

Only an expert could tell you the odds of having SFN given two negative test results, but it probably depends to some degree on who does the biopsy and who evaluates the sample. Mine was done by an expert (Anne Oaklander), but was sent to an outside lab for evaluation. In one of her talks, Oaklamder stressed the importance of having the biopsy evaluated by experts.

Hope that is at least a little helpful Best of luck