To further characterize NMOsd with and without anti-MOG.

Demyelination in NMO occurs within longer spinal and optic nerve segments than in typical MS. Brain involvement is usually limited to the brainstem (i.e. area postrema). The serum Aquaporin-4 antibody (anti-AQP4) has been the most significant factor in establishing NMO as a distinct entity. Nevertheless, 30-35%  of patients do not fulfill either radiological or antibody criteria, and are classified as NMO spectrum disorders (NMOsd). Therefore, without anti-AQP4, diagnosis depends on two separate attacks in two of the major areas. However, several of these “seronegative” NMOsd patients have serum anti-MOG, a known, but poorly understood antibody that occasionally appears in ADEM and MS.

Retrospective descriptive case series of patients from a tertiary university-affiliated hospital between October 2016 and October 2018, who were diagnosed with NMOsd based on the 2015 IPND criteria. Patients were divided based on the presence of anti-MOG.

Eight patients were included in the study, with three positive for anti-MOG. All three had evidence of subcortical and neocortical involvement, which was not seen in the antibody-negative group. Conversely, spine involvement was limited to a short segment in one MOG-positive, but occurred exclusively as LETM in all but one MOG-negative patient. Only one anti-MOG exhibited optic neuritis, while it was ubiquitous among the MOG-negative group. There were no differences in brainstem lesions. CSF abnormalities were limited to three MOG-negative patients.

NMOsd with and without anti-MOG exhibit distinct characteristics. The double seronegative patients resemble typical NMO (optic neuritis and LETM), contrasted with the lack of LETM and the prevalence of supratentorial lesions in anti-MOG disease. However, the similarity in brainstem demyelination indicates convergent pathology, and that anti-MOG may be a secondary antibody of NMOsd, rather than an entirely separate demyelinating disorder. Results may be confounded by testing availability, and differing treatment courses.