I could be wrong about this and maybe someone else would be more knowledgable. During the height of my MS scare I remember reading that they check brain and cervical spine for MS, but it would typically be in your brain if it was in your spine. Does that make sense?
On the note of that patient being told it was just anxiety and ended up having MS, was this after any testing was done as you have had? I doubt anxiety was misdiagnosed after the kind of testing you have had (MRI, clean neuro exam I assume).