To assess the prevalence of dual positive NMOSD and outline its clinical phenotype.

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.  

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. 

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.  

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.