Again, thanks for the links, The last one was particularly interesting in that they were measuring serum pyridoxine (not PLP) and that there was significant recovery after cessation of the pyridoxine supplementation.
My own particular interest in B6 toxicity is a result of my flawed attempt to follow the 525 protocol. This may serve as a warning to others.
In order to get sufficient B vitamins (roughly 50mg each of B1, B2 and B3 as in the protocol) I found a B-50 complex. This also had 50mg of B6 which is not part of the protocol. I quickly checked the usual medical websites where the advice was (and is) that B6 deficiency can cause neuropathy and that B6 is not toxic even in large doses of well over 100mg taken for many months. Bad advice.
Unfortunately my PN worsened over the few weeks when I thought that I was following the protocol and I now think that this MAY have been due to B6 toxicity. So I am now back to following the protocol but without the B6.
One ray of hope which could be an extremely rare symptom: While taking the B6 I also developed recurring bouts of very hot and itchy toes, sometimes even waking me up in the middle of the night. Since I stopped the B6 about two weeks ago the hot feet problem has disappeared. Maybe just a coincidence but it gives me some hope that recovery is possible.