The Prevalence and Clinical Phenotype of Dual Positive Neuromyelitis Optica Spectrum Disorders (NMOSD) at a National Reference Centre

Objective To assess the prevalence of dual positive NMOSD and outline its clinical phenotype. Background Neuromyelitis Optica Spectrum Disorders (NMOSD) is an autoimmune syndrome that is frequently positive for Aquaporin 4 (AQP4) IgG or Myelin Oligodendrocyte Glycoproteins (MOG) IgG. However, dual positivity to both is rare. Design/Methods This is a retrospective cross-sectional study conducted at a tertiary healthcare center in South Asia between August 2018 and November 2021. The serum and/or CSF samples of suspected cases of NMOSD were tested for both AQP4-IgG and MOG-IgG using an Indirect immunofluorescence test on transfected cells. Results During the study period, 1935 cases of NMOSD were tested for both antibodies- 65 patients (3.36%; 57 females and 8 males) tested positive for AQP4-IgG, 217 patients (11.23%; 122 females and 95 males) tested positive for MOG-IgG and 3 patients (0.15%; 2 females and 1 male) showed dual positivity. There was a strong female preponderance in all three groups (87.69%, 56.22% and 66.66% respectively). This study identified 3 patients with dual positivity. The first patient (42 years, Male) presented with area postrema syndrome initially and subsequently relapsed by developing right-sided numbness of the temporal area and limbs during which he tested dual positive. The second patient (27 years, Female) presented with bilateral optic neuritis (left >right) initially and subsequently relapsed following an episode of a seizure with left-sided hemiplegia and right-sided facial deviation. The third patient (25 years, Female) initially presented with acute bilateral optic neuritis and later developed left-sided hemiplegia post-recovery at which point she tested dual positive. Management using methylprednisolone was ineffective for all three patients, however, plasmapheresis and/or periodic rituximab injections produced an excellent response. Conclusions Our study reports that the prevalence of dual positive NMOSD is 0.15% and its clinical phenotype is more similar to NMO rather than MOG- associated disease.