Neuromyelitis optica: an update.

Neuromyelitis optica (NMO) is an inflammatory condition characterized by the selective involvement of the optic nerves and spinal cord, and by a frequent relapsing course. Many clinical, laboratory and neuroimaging studies have provided useful means to distinguish NMO from multiple sclerosis (MS). The detection of aquaporin-4 (AQP4) antibodies has broadened the spectrum of the disorder, which now includes limited variants (either recurrent myelitis or optic neuritis), Asian opticospinal MS, and "atypical" forms with brain involvement. Many in vitro and in vivo evidence have recently demonstrated that AQP4 antibody plays a relevant pathogenetic role in NMO by inducing an increase of BBB permeability, complement cascade activation and astrocytic cytotoxicity. While corticosteroids and plasma exchange are better therapeutic options during NMO attacks, other treatments should be aimed at the prevention of recurrence, possibly by targeting autoantibody production and/or effector mechanisms. Rituximab and Mofetil Mycophenolate appear at the moment the most promising drugs. Since even the most sensitive AQP4 antibody tests fail to mark about 20-30% of the NMO cases, while 20-30% of positive patients have "atypical" or MS-like variants, it remains to be clarified if NMO, as a clinical entity, can still be considered a disease rather than a syndrome, with more possible pathogenetic mechanisms.