Hello @tom01255, Welcome to Connect. It can be a little scary to have a skin punch biopsy and have a neurologist tell you that it gave you no clue to the cause. You are not alone. Many of us have idiopathic small fiber neuropathy and it can be difficult to pin a specific cause when there are so many. I have not had a skin punch biopsy but did have a nerve conduction test along with physical exam. My neurologist thinks mine is mostly likely genetic but doesn't really know. I think what might be helpful for you is to learn as much as you can about your condition and possible treatments available. Two sites that really helped me learn more were:
-- Neuropathy Commons: https://neuropathycommons.org/
-- Foundation for Peripheral Neuropathy: https://www.foundationforpn.org/

Here are a couple of discussions that you may want to scan through to see if some of your symptoms match:
-- Member Neuropathy Journey Stories: What's Yours?: https://connect.mayoclinic.org/discussion/member-neuoropathy-journey-stories-whats-yours/
-- Small Fiber Neuropathy: What helps?: https://connect.mayoclinic.org/discussion/small-fiber-neuropathy/

You mentioned it started in the toes and now has spread to the arms and hands. Do you have pain or is it just numbness and some tingling?