Hi again Betty. My doctor doesn't know the cause. We ruled out ALS and MS, ruled out autoimmune disease, B12 deficiency, toxicity to a medication etc. It may be idiopathic. I don't like that answer (stubborn) so I'm still on a search to see if I can find a cause and remedy it before I stop and just focus on symptoms. I'm looking at all the medications I take, and just discovered something about topical metronidazole (which I have used for years for rosacea) can cause neuropathy over time! So I'm going to stop that med and see how it goes.
Also, weirdly, my skin biopsies from my lower left leg (where I'm most symptomatic) were normal! My neurologist still thinks its small fiber polyneuropathy because he says it's diagnosed based on clinical presentation, and it can be patchy in the skin and may not show on the biopsy. I really like him and trust him. Very smart, listens well, and doesn't think I'm crazy.