Dahlek,
I'm really sorry to hear that you've been diagnosed w/ Hashimoto's too. You are right though that Synthroid will probably help you and might not pose a huge medication complication - another plus it's relatively inexpensive so it may not break the bank.

You pose a really interesting chicken and egg question re: the CIDP and the HT. I've had HT for >10yrs now, well before my PN - idiopathic at last count but who knows - and I've often wondered whether the HT was a harbinger of other auto-immune disorders too. I've looked but I haven't found a definitive correlation between HT and PN but maybe I've not looked hard enough or in the right places but I'll keep my eyes open.

In our family only my mama and I have ever had any thyroid problems, both sides of the family and back 3 generations. She and I both wound up having surgery, hers >30yrs ago and mine 7 but I still have my thyroid - only lost the isthmus. It got so large that it compressed my esophagus which the first surgeon told me was anatomically impossible and which the second, and my surgeon found to true as the isthmus was so large that he could not see the thyroid gland until he removed the isthmus.

In any case I do wish you well and hope that a daily little Synthroid pill will keep your thyroid functions as normal as mine have been for years - this is one of the few areas that has been on autopilot for me for years. The endo does a complete thyroid work-up every 6 months or so and I've not had a problem to date but I know this doesn't help your situation or in any way answer your question.
Take good care of yourself.
Alkymst