Proceedings of the 25th BCTRIMS Annual Meeting

Introduction: Neuromyelitis optica spectrum disorder (NMOSD) is characterized by acute destructive lesions in the spinal cord, optic nerve, and periependymal brain regions. Besides macroscopic visible lesions, it is still a matter of debate whether there is a diffuse damage in normal appearing white matter (NAWM) and gray matter (NAGM).

Objectives: To investigate the presence of diffuse brain parenchymal damage in NMOSD patients by using a multiparametric MRI approach: T1-w/T2-w ratio, Magnetization Transfer Ratio (MTR) and Diffusion Tensor Imaging (DTI). Also, to explore whether there is an association between MRI metrics and clinical variables.

Methods: In this cross-sectional study, we prospectively evaluated anti-aquaporin-4 positive NMOSD patients and healthy controls (HC) matched for age and sex. The mean values of T1-w/T2-w, MTR, fractional anisotropy (FA), axial diffusivity (AD), mean diffusivity (MD), and radial diffusivity (RD) were obtained in NAWM, NAGM and lesion masks.

Results: A total of 105 participants (59 NMOSD patients and 46 HC) were included in the study. T1-w/T2-w was lower in NAWM of NMOSD vs HC (p=0.029), while no significant differences were found in NAWM or NAGM across the following metrics: MTR, FA, AD, MD, and RD. In addition, T1-w/T2-w in NAWM was inversely correlated with time to start immunosuppressive therapy (r=-0.278; p=0.036) and with MD (r=-0.325; p=0.014). Cavitated lesions showed lower mean values of T1-w/T2-w, MTR and FA, and higher diffusivity metrics as compared to non-cavitated lesions (p<0.001).

Conclusion: Diffuse brain damage seems unlikely in NMOSD, according to MTR or DTI metrics, with loss of microstructural integrity restricted to lesional tissue. In this setting, decreased T1-w/T2-w ratio in NAWM may reflect blood-brain barrier dysfunction (subclinical water accumulation) possibly linked to astrocyte pathology. NMOSD cavitated lesions have shown a severe degree of microstructural damage.