diagnosing NMO/Devic's

if NMO is suspected in a patient dx'ed with RRMS, and the NMO-IgG test is negative, what would be the appropriate next diagnostic step(s), given the high rate of false negs for that blood test?

Yes, that patient is me.  I don't see my neurologist again till July but if there is further testing that ought to be done sooner rather than later, I can request to have my appt moved up.  

BTW, my only LP, done in 2007 when I was dx'ed with MS, came back neg for O-bands.  

My MS dx was based on two distinct clinical episodes involving multiple symptoms (diplopia, fatigue, Lhermitte's, MS hug, numbness, neuropathic pain) and MRI revealing a lesion on brainstem and one on c-spine.  More c-spine lesions have developed since then, brainstem lesion remains, no other brain involvement has been reported.

I have had 4 distinct attacks from onset in June 2006 to Dec 2008.  Last episode was ON, which got my neuro to considering NMO, in light of my overall history.

Any advice you can offer re: next steps would be appreciated.

Thank you,

~doublevision1~