My husband has been ridden with weakness and pain from PN, which turns out to be just one of the many problems associated with what I've finally learned is his diagnosis. We learned too late that merely testing for B12 levels isn't enough (See the wonderful Mrs. D's posts to learn more (and I meant that wonderful both ways, the posts and Mrs. D!). I'd urge ANYONE facing unexplained and rapid onset of PN and a host of other problems to consider this advice:
"Blood tests, including a complete blood count (CBC), vitamin B12 blood level, or methylmalonic acid blood level are used to diagnose anemia or vitamin B12 deficiency" from the NIH site (haven't posted enough to give the link, googling should get you there, though!)

Anybody else dealing with this? Randy's seems to be progressing, despite daily B12 Methyl.....not sure how much of decline is from being bed bound and/or possibly overmedicated. Thanks as always!