Hi Nick
Prednisone can make MG worse at first, or if the dose is too high.
I started pred 25mg and Imuran 100mg following IVIg over Christmas along with Mestinon.
Pred was reduced from 25mg to 20mg six weeks ago and will reduce by another 5mg tomorrow, tapering right off over the course of the year. Improvement was noticeable after about a month and I've been steadily improving since, able to reduce Mestinon from 420mg/day to only as required which is hardly any. I take high dose calcium with vit D to offset the calcium reducing effect of pred.
All the best
Marian