Impact on the microstructure of deep gray matter in unvaccinated patients after moderate-to-severe COVID-19: insights from MRI T1 mapping

Background To determine changes in quantitative T1 relaxation times (qT1) in deep gray matter in patients recovered from coronavirus disease 2019 (COVID-19). Methods Unvaccinated COVID-19 participants >= 3 months after seropositivity and age- and sex-matched controls were examined using 3-T magnetic resonance imaging. Bilateral measures of thalamus, pallidum, putamen, caudate and accumbens nuclei, and hippocampus were extracted from qT1 maps after automated segmentation. Baseline characteristics and results of tests assessing neurological functions (standardized exam), ability to smell (4-Item Pocket Smell Test), depression (Beck Depression Inventory-II), sleepiness (Epworth Sleepiness Scale), sleep quality (Pittsburgh Sleep Quality Index), health-related quality of life (EQ-5D), and cognitive performance (Montreal Cognitive Assessment) were evaluated. Results One hundred forty-five subjects (median age, 46 years; 73 females) were included (11/2020-12/2021): 69 recovered after COVID-19 and 76 controls (age, p = 0.532; sex, p = 0.799), without significant differences in qT1 values overall (all p-values > 0.050). Subgroup analysis of participants aged >= 40 (age, p = 0.675; sex, p = 0.447) revealed higher qT1 values in previously hospitalized COVID-19 subjects (23/69) compared to controls (47/76) in left and right caudate nuclei (p = 0.009; p = 0.027), left accumbens nucleus (p = 0.017), right putamen (p = 0.041), and right hippocampus (p = 0.020). No correlations were found with macroscopic imaging findings, pre-existing conditions, time since COVID-19 diagnosis, inpatient treatment duration, or test results. Conclusion T1 mapping revealed microstructural changes in striatal and hippocampal regions of unvaccinated individuals aged >= 40 who recovered from moderate-to-severe COVID-19 during the pre-Omicron era. Relevance statement This study elucidates brain involvement following severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, underscoring the need for further longitudinal analyses to assess the potential reversibility, stability or deterioration of these findings.