I was diagnosed with Devic's for almost two years. I had spinal and Optic nerve lesions and nothing on the brain (or in it depending on who you ask). It can be a nasty disease with horrible relapses and can be fatal by affecting the area of your spine where your involuntaries like respiration are controlled. There is a great page like this for people with NMO called Gayle's place. I think the address is http://devic.co.uk
If you can believe it, I was almost relieved when my dx was changed to MS since Devic's can be so serious. It's apparently very prevelant in Asia where they call is OSMS or Optico-Spinal MS. From what I recall, it can attack the entire myelin sheath that surrounds your spinal cord and the lesions can be very long and thin when it's like that.
You are correct that Mayo is the trusted test. We were all set for me to take it (we had to think about it since it 'ain't cheap) right when my dx got changed. It's basically Transverse Myelitis and Optic Neuritis, thus the NMO moniker (Neuro-myelitis optica). The only "positive" thing I remember reading about it is there are more CIS events with Devic's than with MS. They use different techiques for relapses as well. There were many on the Gayle's place board who had undergone plasmapheresis and also IVIG. So devic.co.uk and also myelitis.org are the two best resources for info. that I found.