We have had a poster here in the past with a vaccine induced PN.
His doctor gave him a course of steroids, to test to see if they caused a remission or lessening of symptoms, which did result.

Why don't you ask to have this done, before doing IVIG?
Steroids also block autoimmune issues. If you take them a short time in high dose like the MSers do or MGers do, then that would tell more than most tests IMO. There is no cure, but it may reveal much in the way of response. If you don't respond to steroids, then I would question if IVIG would work well. IVIG is not without risk.... some risk of heart attack or stroke exists, plus the discomfort with each infusion.

I would get the autoimmune testing done however... just to see what you might have.