Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with your doctor.
Dipolopia is not a typical feature of NMO disease. The so-called "MS hug" is a bandlike sensation around the trunk that occurs due to myelopathy, and may be a feature of NMO. Optic neuritis and cervical myelopathy are part of the diagnostic criteria for NMO, meaning that they must be present in order for the diagnosis to be made. Supportive criteria, meaning criteria that further help in establishing the diagnosis, include myelopathy involving a specific length of the spinal cord, an MRI that does NOT meet criteria for MS, and positive NMO-IgG antibodies.
The NMO-IgG antibodies I have seen are reported as either positive or negative. I am not sure if titers (or antibody levels) are available by some labs. A negative antibody test does not exclude the diagnosis of NMO, a positive test strongly suggests the diagnosis only in the right clinical context. If the diagnosis is suspected and the antibody is negative, additional diagnostic testing may include visual evoked potentials in order to confirm optic neuritis if this has not been definitively confirmed, and serial examination to monitor for signs of developing optic neuritis or myelopathy.
The NMO-IgG blood test is to my knowledge the only available blood test for NMO. Serum and CSF IgG levels are measured sometimes as part of what is commonly known as the tourtellotte panel. This is non-specific, it is used to assess for inflammation/non-specific antibody production within the central nervous system.
MS and NMO have distinctly different clinical and MRI features, but it is not inconceivable that they may be misdiagnosed, particularly by someone without specific education in neurology and specifically demyelinating disorders.
To my knowledge the incidence and prevalence vary by ethnicity, so that it will depend on what patient population they are measured. It is considered to be a rare disorder, though likely under-diagnosed. Some studies have shown its prevalence is 0.32-3.1 per 100000 people, another study showed a 0.05 per 100,000 annual incidence rate.
A patient with NMO should be seen at least periodically by a specialist in demyelinating disorders, these are neurologists trained in multiple sclerosis and other neuroimmunological diseases.
Plasma exchange is effective in some patients but not others, as are newer therapies that are being tried but are still experimental such as rituximab, which is an infusion therapy. These are not offerred in all hospitals, but are offerred in most academic (tertiary care/university) hospitals and some community hospitals.
Thank you for using the forum.