the Dx for MS involves both damages on a MRI, and a spinal tap to see if MS fatty stuff is sloughed off in your fluid. You usually have to have both show MS, sometimes a clean spinal tap is found, if so, it opens up the possibility of a group of diseases called leukodystrophies.With a clean spinal tap, they go back to your MRI and look really closely to see if the pattern of your damages line up with MS damages or are consistent with some of the leukos. It can take time to get all this done. The trouble with doing it is that if leukos are Dx'd there is nothing they can do but treat symptoms, so doctors are tempted to say MS because at least there are treatments for MS....not very good ones, admittedly, but treatments nonetheless. And most leukos cannot be identified anyhow (the second largest group of people with white matter damages are those with undiagnosed leukos), so you stay in limbo with a leuko Dx.