My knees have been swollen and painful for some time now. I have been on prednisolone for over five years but am nearly off it and I had thought this was the cause. However, when it got particularly bad I took a high dose and it didn t make any difference. So now I am wondering if it could be a side effect of the azathioprine I am on. I also have a kidney problem which I think is a side effect of aza although my consultant will not admit it. It is excruciating to walk at all.