Hi clarkstar, I can only tell you my experience and what I've learned.
I had an MRI right before starting Tysabri and then one 7 months later, after 7 Infusions. It was supposed to be 6 but, my doctor forgot

I showed no new or active lesions. At approx my 4th infusion I started noticing better balance, better stamina and less fatigue. My understanding of how Tysabri works is that by stopping the T cells from crossing the blood brain barrier it gives the body a chance to heal itself. I don't remember at what point I started walking with 1 cane instead of 2.

I have gotten an MRI every 6 months and they have shown no new or active lesions and as time has gone on many of the old lesions have gotten smaller and some are gone April I will get my 54th infusion-I have been on Ty, at that time, for 4 years 7 months !! I cut back at 3 yrs to every 5 weeks and a few month ago to every 6 wks.

I wish you well and hope Tysabri will be your success story.

Linda