Goiter? Where and what endocrine glands are involved? That could tell me which sources to refer you to for the 'heavy reading' of sorts.
As for access to IVIG? Take a look at the web site for IG Living, it's a specialty magazine and sign on for free to all prior issues of their magazine. In addition, I can tell you that they've worked with many folks in your situation to try and get aid thru manufacturers and other providers to you could have treatments. While they mite not get back to an e-mail from you right away? They DO get back to you and can help you try and work things out. I have been on IVIG for over 4 years and I can tell you that because of it, I am still mobile and can think clearly, even with some pain. That is a lot to be said given all we go through.
As for an 'excess' of B -12? Never heard of such a thing! Overages of it are like Vitamin C, they just go thru you and out! No harm or foul, ever. B-6 tho is another issue [too much of the B-6 can add to PN issues, I suffered this aspect and changed my regimin a lot because of it] and GOOD metabolic bloodwork should give you a more solid indication of your ranges. Later I'll post some resources about blood tests and results in this quarter.
Also about some autoimmune disease diagnostic procedures....tho nearly all are posted on Liza Janes' website. It will take a while to get acquainted with all the tech and doc speak that goes with the territory tho... But knowing it all is ESSENTIAL for you to get a handle on what is going on!
As for dealing with your sister? Thats a sticky one, for sure. While treatments for MS are at times, similar to PN issues? They are often different and IVIG, Plasmaphersis and steroids are the NORMAL treatments for immune types..... plus pain killers. And, I consider MS and immune PN's sort of distant cousins as they both demeyelinate those danged nerves! Go your own way the best you can here.
While I would like to not have to take some meds? They are essential for being a functional human being at times. I do the minimal possible when really necessary. We do what we have to..to get by!
Enough for now, please don't be shy to ask questions! - j