Brain lesion microstructure in neuromyelitis optica spectrum disorder and myelin oligodendrocyte glycoprotein disease

Abstract Background and purpose Neuromyelitis optica spectrum disorder (NMOSD) and myelin oligodendrocyte glycoprotein antibody‐associated disease (MOGAD) diagnosis are based on the presence of serological and magnetic resonance imaging (MRI) biomarkers. Diffusion tensor imaging (DTI), neurites orientation dispersion and density imaging (NODDI), and the Spherical Mean Technique (SMT) may be helpful to provide a microstructural characterization of the different types of white matter lesions and give an insight about their different pathological mechanisms. The aim of the study was to characterize microstructural differences between brain typical lesions (TLs) and nontypical lesions (nTLs). Methods A total of 17 NMOSD and MOGAD patients [9 Aquaporin4 (AQP4) + NMO, 2 seronegative‐NMO, 6 MOGAD] underwent MRI scans on a 3 Tesla MAGNETON PRISMA. Diffusion parameters (fractional anisotropy; mean diffusivity [MD]; intracellular volume fraction [ICVF]; extra‐neurite transverse diffusivity; and extra‐neurite MD; neurite signal fraction) were obtained using DTI, NODDI, and SMT. Microstructural parameters within lesions were compared through a generalized linear model using age, sex, and total lesion volume as covariates. Results In NMOSD/MOGAD whole cohort (total lesions = 477), TLs showed increased MD and decreased ICVF compared to nTLs ( p < .05), indicating higher inflammation and axonal loss. Similar results were found also in the AQP4 + NMO subgroup (decreased ICVF, p < .05). Furthermore, in NMOSD/MOGAD whole cohort and in AQP4 + NMO subgroup, TLs showed a trend toward higher EXRATRANS than nTLs, suggesting a more severe degree of demyelination within TLs. Conclusions TLs and nTLs in NMOSD/MOGAD showed different diffusion MRI‐derived microstructural features, with TLs showing a more severe degree of inflammation and fiber disruption with respect to nTLs.