Wow...you hit on something that has given me some thought for a few years and I asked my primary the same question who has all my medical history over 20 years. She scratched her head and said...hmmm. When you look at some of the possible causes of PN, I can check off five items right off the bat. A fall, heavy antibiotics, statins, medications, low B-12, both back and knee issues, etc. Or a combination which could possibly explain why the cause is so difficult to determine. Would not be surprised!!