Abstract

Differentiating neuromyelitis optica spectrum disorder (NMOSD) from relapsing multiple sclerosis (MS) can be difficult in aquaporin-4 antibody (AQP4ab) negative cases. Additionally MS like lesions on brain MRI are not uncommon in NMOSD. We were interested to assess if quantitative MRI methods could identify more disease specific features and thus be useful in the diagnostic pathway. To this aim, 18 AQP4ab positive NMOSD patients, 15 age-matched relapsing MS patients and 17 age-matched healthy controls underwent multi-parametric brain MRI at 3 Tesla. MS patients had significantly lower thalamic and whole brain volumes than both NMOSD and controls (p<0.05), and had several other regions of grey matter atrophy identified with voxel-based morphometry. When compared to controls the NMOSD group had localised atrophy within the visual cortex only (p<0.05). This was associated with severe visual impairment and did not occur in NMOSD patients with good vision. Diffusion tensor imaging, which provides a measure of white matter integrity, revealed widespread abnormalities of the non-lesional white matter in MS patients, but only localised changes in the visual pathways and corticospinal tracts in NMOSD. Again the visual pathway changes did not occur in NMOSD patients with good vision. This work demonstrates important differences in regional brain atrophy and white matter damage between patients with NMOSD and relapsing MS, which could provide a means of diagnostic distinction.