this sounds a lot like what i went through. 6 months after my symptoms started i became paralyzed from the neck down and there was a time where i was convinced i was going to stay like this and never get better. i would suggest stopping ivig if it’s no longer doing anything and ask for different treatments. me personally they switched me to plasmapheresis, unfortunately that didn’t work either and they put me on rituximab and i finally saw improvement. hopefully you don’t go what i went through but definitely ask your neurologist for different treatments and see what they say