I've read anecdotes that large doses even over a short period can cause long-lasting PN symptoms. These should go away after an indefinite period as long as you stop taking it, though. Also read anecdotes that very large doses of B12 and Riboflavin may help in such cases. I'd guess that chances are, if you were already having symptoms before the B6, it's probably not the cause of anything, but I suppose it's possible.