Longitudinally extensive optic neuritis in neuromyelitis optica spectrum disorder

• Distinguishing between causes of optic neuritis is of paramount importance.
• Optic nerve enhancement distinguishes neuromyelitis optica from multiple sclerosis.
• Enhancement greater than 40 mm can be called longitudinally extensive optic neuritis.

BackgroundNeuomyelitis optica, sarcoid, and multiple sclerosis can all cause optic neuritis. Further means of distinguishing the causes of optic neuritis among these etiologies would be valuable for the clinician.MethodsThis is a retrospective, cohort study from a single university based hospital and neuro-ophthalmology clinic. Blinded interpretation of orbit MRIs was performed on patients with acute optic neuritis from multiple sclerosis (n = 25), sarcoid (n = 5) and neuromyelitis optica spectrum disorder (n = 6).ResultsA length of > 40 mm anterior visual pathway enhancement distinguished neuromyelitis optica spectrum disorder from multiple sclerosis (p = 0.0376). No statistically significant differences were found for presence of pain or papillitis, however there was a trend for bilateral involvement and chiasmal involvement in neuromyelitis optica spectrum disorder compared to multiple sclerosis.ConclusionsIn acute optic neuritis, enhancing anterior visual pathway lesion length > 40 mm helps differentiate neuromyelitis optica spectrum disorder from multiple sclerosis. This degree of involvement can be considered longitudinally extensive optic neuritis. Further characterization is necessary as this degree of enhancement occurs in other clinical syndromes besides neuromyelitis optica.