I don't take IV IG so I don't know. You say you have been taking it 4 years now and lately your MG is acting up, is it possible you are going into remission and your MG is acting up because you don't need as much medication? I know that is how I figured out I went into remission, as my MG started getting worse, so the Dr. and I agreed to wean off the meds and bam it turned out I was in remission and had to much meds.

So talk to your Dr. and good luck!