Sean Pittock, MD – Mayo Clinic:
Since the discovery of the aquaporin-4 antibody in 2004 the spectrum of NMO has dramatically changed and evolved to what we now consider NMO spectrum disorder. And animal spectrum disorders are defined by the presence of aquaporin-4 antibodies. So in terms of making the diagnosis, one has to look at the clinical phenotype, the clinical presentation of the patients, but most importantly, the presence of the aquaporin-4 antibody, an antibody that targets a water channel that sits on the astrocyte.
The concept of animal spectrum disorders has expanded to include presentations that are actually outside of the optic nerve and spinal cord. For example, some patients may present with just intractable nausea and vomiting, and if they have aquaporin-4 antibodies they have an NMO spectrum disorder. Other patients can present with muscle problems or brain lesions, and those patients, if they have aquaporin-4 antibodies, can be defined as having an animal spectrum disease.