Literature Commentary.

OBJECTIVE To differentiate magnetic resonance imaging (MRI) characteristics of optic neuritis associated with neuromyelitis optica (NMO) and relapsing-remitting multiple sclerosis (RRMS). BACKGROUND Optic neuritis is a common presenting feature of both NMO and MS. Distinguishing between NMO and RRMS is important in guiding treatment, but biomarkers of NMO and MS can be absent early in the disease process. We looked for differences in MRI characteristics of optic neuritis associated with NMO and MS that provide an early clue in the diagnostic workup. DESIGN/METHODS We conducted a retrospective analysis of 26 NMO and 26 RRMS patients presenting to the Johns Hopkins Hospital with MRI-confirmed acute optic neuritis. Magnetic resonance images were assessed to identify the location and longitudinal extent of each contrast enhancing lesion. For the purposes of this study, the optic nerve was divided into intraorbital, canalicular, prechiasmal, chiasmal, and optic tract. RESULTS There are distinct differences in MRI characteristics between NMO-associated and RRMS-associated optic neuritis. The majority of NMO lesions were longitudinally extensive measuring at least 17.6 mm in length and involving at least 3 optic nerve segments. At a cut-off of 17.6 mm of lesion length, the specificity for NMO is 76.9% with a sensitivity of 80.8% and a positive likelihood ratio of 3.50. Conversely, MS lesions were more commonly focal in 1 optic nerve segment localized anteriorly. CONCLUSIONS Optic neuritis in NMO has a distinct pattern on MRI as compared with RRMS and can help differentiate these 2 neuroinflammatory diseases at presentation.