CADASIL is a genetic condition, which is now recognized by the National Multiple Sclerosis Society on their diagnosis page as needing to be excluded before dubbing somebody as having MS.
Both MS and CADASIL appear similar on MRI's, but there is a DNA blood test which will definitely include or exclude you from this diagnosis. There is also a skin biopsy test (where the docs look for GOM, Granular Osmiophilic Material -- which, if found, is 100% proof that a person has CADASIL).
Because treatment for MS can greatly disable and harm a person with CADASIL and because most doctors are still unaware of CADASIL (and it's close relative CARASIL), it is important that we spread the word. Another wrongful diagnosis for CADASIL would be Atherosclerosis (hardening of the arteries).
Please come to Facebook CADASIL Support (see the purple brain icon) and learn more about it. It could help you live a healthier life.