ABSTRACT
Objective: This study investigates the effects of COVID-19 on brain microstructure among those recently recovering from COVID-19 through self isolation. Background: Microstructural differences have previously been detected in comparisons of COVID-19 patients with controls, particularly in regions related to the olfactory system. The olfactory system is connected with the caudate, putamen, thalamus, precuneus, and cingulate regions. Design/Methods: Here we report diffusion magnetic resonance imaging (3 T Siemens MRI) findings from 40 patients (mean age: 43.7, 68% female) who self-isolated after testing positive for COVID (COV+), and 14 COVID negative (COV-) subjects (mean age: 43, 64% female) who had flu-like symptoms. This is part of the Canadian-based NeuroCOVID-19 study. Fractional anisotropy (FA), mean diffusivity (MD), mode of anisotropy (MO), free water fraction (F), tissue-specific FA (FAt) and tissue-specific MD (MDt) were obtained using data with b=700 and 1400 (DIPY free-water model). Regions of interest in the grey matter and white matter were delineated using FreeSurfer. Differences between groups were assessed using an analysis of variance (ANOVA), the Kruskal-Wallis Test and the Mann-Whitney Test, corrected for false-discovery rate of 0.05. Effect size (Cohen's d) was also computed (d>0.45 deemed large effect). Results: In the COV+ group, all three tests revealed decreased FA and FAt in the insula, and increased MD in the parstriangularis cortex. Increased FA and FAt in the cuneus (along with decreased MD) was also found. MD was reduced in COV+ in the temporal and supramarginal areas. MO was lower in COV+ in the insula and amygdala regions. Conclusions: In patients, higher MD with lower FA and MO suggest increased extracellular fluids, while lower MD with decreased FA and MO may suggest necrotic debris built up following inflammation. The cuneus and insula are involved in visual and taste processing, respectively. This study highlights the need to study neurological effects of COVID-19.
ABSTRACT
Objective: This study investigates the chronic effects of COVID-19 on brain microstructure. Background: Microstructural differences have previously been detected in comparisons of COVID-19 patients with controls, particularly in the insula, cuneus, inferior temporal and anterior cingulate regions. Design/Methods: Here we report diffusion magnetic resonance imaging (3 T Siemens MRI) findings from 20 participants (mean age: 45.3, 55% female), both immediately after recovery and at a 3-month follow-up. Fractional anisotropy (FA), mean diffusivity (MD), mode of diffusivity (MO), free water fraction (F), tissue-specific FA (FAt) and tissue-specific MD (MDt) were obtained using DTI data with b=700 and 1400 (DIPY free-water model). Regions of interest in the grey matter and white matter were delineated using FreeSurfer. To assess differences between baseline and follow-up, a paired t-test, the Wilcoxon Test and Friedman Test were performed, corrected for false-discovery rate of 0.05. Effect size (Cohen's d) was also computed (d>0.45 deemed large effect). Results: All three tests revealed decreased F in the hippocampus and decreased MD in the parahippocampal region of the WM at follow-up. In the GM, F was increased in the medial orbitofrontal region. In the WM, MD was increased in the paracentral region and MDt was increased in the parahippocampal and lateral orbitofrontal regions. Conclusions: These results suggest that microstructural abnormalities persist following recovery. Increased extracellular fluid (i.e. F and MD) in the frontal lobe suggest spreading of COVID-19 impact, while decreased F and MD in the hippocampal region suggest debris accumulation as part of the inflammatory process. None of the regions affected in sub-acute COVID-19 appear to fully recover within three months.