you seem very articulate about PN.

Since everyone is pointing to Depakote...I'll point some more====>
Depakote depletes l-carnitine from patients. Some people have died as a result.

Also given the increased interest in mito damage --triggers--and autism and possibly other neuro things, first off for you I'd get some L-carnitine or acetyl-l-carnitine and start with 1 or 2 grams a day.

You can have serum carnitine levels drawn as well, if you choose.
Depakote also messes up zinc metabolism. Lowered zinc can set off viruses into replication in the body. Fast progress implies perhaps a viral trigger for you.
Depakote also lowers folic acid. I'd supplement that as folinic acid...the activated form works better.
Depending on what other drugs you use, you may have addition problems with nutrient losses. If you post those I can look that up for you.
It would not hurt to try high dose CoQ-10 as well, since it also helps with mitochondria functions. As the research heats up in the autism world, I think we may see the overflow here. Perhaps mitochondrial malfunction is at the heart of some PN. I know it is for HIV and chemo patients. Their more dramatic reactions to their drug therapies may be a hint for many of us!