PL, I'm so sorry you got bad news after all these investigations, god, what a shock! But your doctor sounds really positive about your outlook, and there's just so much research going on for MS these days. I actually had one of the new experimental chemo drugs during my bone marrow transplant that they're using to treat MS - Campath.
And from someone's who's been there, there's no easy way to tell your mother. I'd advise doing it asap - today if you can, because there's never going to be an easy or "right" time to do it, and I think it'd be even harder in person. Just ring up, and say it first thing. Though perhaps don't give a big pause after "ok I've got some news" like I did, because then my mom blurted out "ooh you're pregnant, aren't you!". Uhh no mom, that would be infinitely preferable...