Hi there, I know you posted this three weeks ago so I hope a late reply is ok.
I was diagnosed with Devic's disease in 2010, although my first attack was in 2004. Multiple brain MRIs in the intervening years showed nothing but dedicated spinal cord and optic nerve imaging showed what everyone had been missing - long fat lesions in both areas. Have you had imaging of all areas or just the brain?
I hope you get a definitive diagnosis soon.