The subventricular zone (SVZ), a 2-mm layer alongside brain lateral ventricles, is the largest neural stem cells niche in adult humans. It is likely to exert a neuroprotective role on striatal neurons and its damage has been associated with cognitive decline after brain radiation. Multiple sclerosis (MS) can be considered as a disease-related model of SVZ injury, since periventricular lesions involve this region. In MS, cognitive dysfunction is common and information processing speed is affected from the earliest phases of the disease despite relatively low lesion volume (LV) and atrophy.
In this study, we characterized SVZ damage in terms of focal lesions and microstructural alterations in MS and assessed its association with striatal atrophy and cognitive dysfunction, evaluated with the Symbol Digit Modalities Test (SDMT).
3.0 T brain MRI scans were acquired from 97 MS patients and 43 age- and sex-matched healthy controls (HC). After lesion refilling, normalized (N-) brain volumes and cortical thickness (CT) were obtained. According to anatomical references, SVZ mask was segmented on T1-weighted images in the Montreal Neurological Institute space and then registered on fractional anisotropy (FA) and mean diffusivity (MD) maps. Age- and sex-adjusted linear models, partial correlations, and stepwise multiple linear regressions were used to assess SVZ damage and to identify predictors of N-striatal volume and SDMT scores.
In MS, mean SVZ percentage LV was 4.2%. Compared to HC, SVZ normal appearing (NA) tissue was characterized by increased MD (0.89 vs 0.86, p=0.04) and preserved FA values. N-striatal volume correlated with all measures of brain damage (p range: <0.0001-0.02, r absolute values range: 0.24-0.70), while SDMT correlated with SVZ damage (percentage LV, lesional FA , NA MD, p range:0.028-0.0028, r absolute values range: 0.33-0.36) and brain T2-weighted LV (p=0.0051, r=-0.37). N-brain volume (p<0.0001), white matter MD (p=0.0236), SVZ percentage LV (p=0.0052), and mean CT (p=0.0354) were independent predictors of N-striatal volume (R2=0.67). SVZ percentage LV was selected as the only predictor of SDMT performance (p=0.0018, R2=0.26).
SVZ damage is associated with striatal atrophy and cognitive dysfunction in MS. These results might provide a novel key lecture on cognitive impairment in this disease, suggesting a possible role of periventricular injury in MS cognition.