Background: Neuromyelitis optica spectrum disease [NMOSD] is an inflammatory disease of the central nervous system involving optic nerve, spinal cord, and brain. Asymptomatic brain abnormalities were recorded in some countries but the data in Thailand were limited.

Objective: To evaluate asymptomatic NMOSD brain abnormalities and their relation to clinical relapses in Thai patients.

Materials and Methods: This was a retrospective study, recruiting 27 NMOSD patients in a tertiary care center in Thailand. All patients were seropositive for aquaporin-4 IgG. Magnetic resonance imaging [MRI] of the brain was performed in every case.

Results: Twenty-four cases (88.89%) had asymptomatic hyperintensities on fluid-attenuated inversion recovery images [FLAIR]. These lesions were widespread across the brain even in areas with low density of aquaporin-4. To our knowledge, a fornix lesion was reported for the first time in a patient with acute optic neuritis. By using linear regression analysis, no significant correlation between annual relapse rate [ARR] and the number of asymptomatic FLAIR hyperintensities was established (coefficient 0.02, 95% confidence interval -0.0009 to 0.04, p = 0.06).

Conclusion: Asymptomatic FLAIR hyperintensities on brain MRIs are frequently found in NMOSD. They may not correlate with clinical relapses. Further cohort studies are required. To our knowledge, this is the first report of a fornix lesion in a NMOSD patient presented with acute optic neuritis.

Keywords: Neuromyelitis optica spectrum disease, Optic neuritis, Transverse myelitis, Aquaporin-4 IgG, Asymptomatic brain abnormalities, Fornix lesion