"The doctor flatly refused -- MRIs were only available after physical symptoms had developed. Of course, at that point, the available treatments for a flare-up of MS are less effective at preventing long-term neurological problems. (Happily, I am back in Japan now.)"

There's your mistake. You didn't see a doctor who owned (or who had bought a share in) an MRI machine. Those doctors are 4.2 times more likely to refer patients for MRI than doctors who don't.