Again to Char,
IVIgs and plasmapheresis provide only temporarily relief for MG as they combat or remove the antibodies but they do not attack the primary cause of the desease, i.e. the production of antibodies. That is why they do have to be regularly repeated, each month or so.
For more information about the possible treatments, you may read
http://neurotalk.psychcentral.com/thread246.html
and por the pro and con's for the treatments, specifically the last post (mine...!)
Maurice.