Joanna my rheumo had me on both enbrel and IVIG. I didn't stay on the enbrel long though because I had a reaction at the injection site that got worse each time I injected. I don't think it was doing anything for me anyway.
I would think a lot of the proof as to whether or not the IVIG is working would be subjective. I don't know if your doctor or you go to the panel but I would think that your subjective findings will count for something.