my heart goes out to you. We went through something simliar with my dad about ten years ago (he was 74)...his diagnosis turned out to be Creutzfeld-Jakobs disease, but your mom surely doeesn't have that or she would be deterioriating much more rapidly and probably would show on MRI.

Anyway, I remember how difficult it was to deal with that paranoia. I wish your mom and your family the best. Keep us posted when you can.