I too had that "sudden" onset of PN, but at the time, it was confined to my feet. Just started hurting one morning when I got up. Felt like I was standing on crushed shell.
Several tries with different foot doctors produced a variety of conclusions, none of which worked.
Finally went to a neuro, and he diagnosed it as PN, but said that he wanted to sent me to a hematologist. Kind of surprised, but went anyway.
After some testing, and a bone biopsy, he told me that I had CANCER. Yup, kinda threw me for a loop.
Turned out that I had what is called Waldenstroms Macroglobulinemia. I have a hard time even trying to remember how to spell the darn thing.
Anyway, I have a bad white blood cell that refuses to die, and keeps reproducing itself. You're supposed to have about 350 in your bloodstream at any given time, and I had over 8,000. No more room for red blood cells, so I was also anemic at the same time. The WM is not curable, but thankfully it is treatable. Life expectancy is 5 to 7 years, but some have lived for 10, and even 15 years. Only the Good Lord knows, but that's good enough for me.
I have been on Rituxan infusion every three months now for about two years, and the bad cell count is now down to about 2,000, and falling.
As was hoped, the PN is sort of tracking the WM. As the bad cell count falls, the PM backs off as well. It still gives my feel hell, and there's one finger that still fells like it is always asleep, but the majority of the real pain has diminished quite a lot. I still have trouble if I walk too much, but my neuro has put me on a locally formulated product to use as a foot rub. It contains several products, all of which are geared to reducing PN pain.
I hope you find the answers you seek, and that they lead you in a direction that corrals all your fears. Semper Fi