I was slightly involved with a research group that worked on MS, but that's probably at a un-usefully detailed level. But a close colleague had both symptoms and lesions a couple of years back when I was worked with her, and would not have diagnosed with MS until a second occurrence. (She had both a professorship, a marriage, and two young children, so she was pretty freaked out about the possibility of her life becoming drastically more limited. As someone who has gone through various phases of chronic illness, we had some pretty intense talks.)

Similar recollections on the number vis a vis non-reoccurence. There might be more information in the particular MRI that leads the doctor to say that... but there's also so much room in terms of different data sets, communication skills and delusions of godhood among physicians, I'd collect all the data first.