Gray Matter Thickness and Subcortical Nuclear Volume in Men After SARS-CoV-2 Omicron Infection

This cohort study explores clinical symptoms and changes to gray matter thickness and subcortical nuclear volume in the acute and 3-month follow-up phases of SARS-CoV-2 Omicron infection among adult male patients.


Introduction
According to a report by the Global Initiative on Sharing Avian Influenza Data, 1 genomic surveillance and preliminary phylogenetic analysis of data from China since the abolition of the zero COVID-19 policy (in December 2022) have shown that the patterns of introduced variation and risks in China were similar to those seen globally, and the strains infecting China were dominated by the SARS-CoV-2 Omicron variant.During the Omicron variant phase of the pandemic in China, from December 1, 2022, through March 1, 2023, we collected alveolar lavage fluid from 157 hospitalized patients, of whom 40 were diagnosed with COVID-19.Subsequently, 6 cases underwent genetic sequencing of the Omicron variant, and the results were Omicron BA.5.2.Several follow-up studies [2][3][4] have shown that, similar to infections of the SARS-CoV-2 Delta variant, Omicron infection has multiple systemic symptoms, including respiratory, neurological, and digestive symptoms, and neurological sequelae are becoming the focus of attention.
Long-term COVID-19 neurological sequelae (Ն90 days) are diverse and include clinical symptoms (dizziness, headache, olfactory and taste disturbances, and motor delay), [3][4][5][6] neuropsychiatric symptoms (insomnia, depression, anxiety, and reduced cognitive function), [6][7][8] and structural and functional changes in the brain. 3,4,7,9,10[13] However, few individuals with mild neurological symptoms in the acute phase receive comprehensive neuropsychiatric assessment and magnetic resonance imaging (MRI) examinations, and few studies have focused on neuropsychiatric changes and brain microstructural damage after infection with the Omicron variant.Therefore, we aimed to explore clinical symptoms and brain structural changes in the acute phase of SARS-CoV-2 Omicron infection (hereinafter referred to as the post-Omicron phase) for early detection of and intervention for possible neurological sequelae to alleviate the burden on society and the health care system.
We prospectively collected clinical symptom data, neuropsychiatric findings, and MRI examination results of the same group of participants, with the aim of exploring the changes in brain structure between the pre-Omicron and post-Omicron phases and the changes in symptoms across systems in the post-Omicron phase and 3 months after infection.The changes in gray matter and subcortical nucleus volume were investigated in a data-driven manner.Finally, correlation analysis was performed to explore whether brain microstructure alterations were associated with neuropsychiatric scale scores.

JAMA Network Open | Infectious Diseases
Brain Structure Changes in Men After Omicron Infection

Participants and Study Design
This prospective cohort study was approved by the Ethics Committee of the Second Xiangya Hospital of Central South University, Hunan, China, and all participants gave their written informed consent.When evaluating clinical symptoms, we defined an axillary temperature above 37.5 °C as fever according to the traditional definition of fever.Based on previous studies that found significant neurological effects of axillary temperatures above 38.5 °C, 14 we used the axillary temperature of 38.5 °C as the boundary to divide participants into febrile and nonfebrile groups and to explore structural changes.

This study followed the
After the first and second MRI examinations, the patients completed questionnaires, including the Beck Depression Inventory, Beck Anxiety Inventory (BAI), Insomnia Severity Index, and  and (5) the Word Fluency Test (WFT), in which the participants were asked to name as many animals as possible in 1 minute.Clinical symptoms in the acute phase were compared with those at the 3-month follow-up, and brain gray matter and subcortical nuclear volume changes were compared between the pre-Omicron and post-Omicron groups and the febrile and nonfebrile groups.

MRI Acquisition Parameters
We acquired MRI data using one of two 3T scanners (MAGETOM Skyra

MRI Data Preprocessing
The gray matter indexes and subcutaneous nuclear volume were calculated with FreeSurfer, version 6.0. 15The preprocessing steps included checking image quality; motion correction; removing the neck, scalp, and skull; intensity normalization; Talairach registration; segmentation of subcortical white matter and subcortical nuclei; gray matter and white matter boundary delineation; topology correction; surface deformation; registering each person's brain to a common spherical atlas; manual correction for inaccurate cortical segmentation of the image; and calculation of the thickness, curvature, sulcus depth, and subcortical nuclear volume. 16,17atistical Analysis

Main Analysis
Clinical information, neuropsychiatric scale data, and the ratio of 12 subcortical nuclei volumes to the total intracranial volume (TIV) were assessed with SPSS Statistics, version 24.0 (IBM Corporation).
Quantitative data were expressed as the mean (SD) or median (IQR), and categorical data were expressed as numbers and percentages.Paired-sample and 2-sample Wilcoxon-Mann-Whitney tests, 2-sample t tests, χ 2 tests, and McNemar tests were used for various comparisons.In the crosssectional MRI data comparison, general linear modeling was performed, and age and history of nicotine use were included as covariates.Monte Carlo simulation cluster analysis was used to correct for multiple comparisons. 15Two-sided P < .05indicated statistical significance.

Post Hoc Region-of-Interest Analysis
The gray matter indexes were extracted from each participant and displayed in a violin plot.Pearson correlation or Spearman correlation was used depending on whether the variables were normally distributed.All correlation analysis results were corrected by the false discovery rate (FDR) for multiple comparisons.

Participant Characteristics and Clinical Symptoms
A summary of patient characteristics is shown in   2C), but there was no significant difference in the ratio of subcutaneous nuclei volumes to the TIV between the 2 groups.Details and post hoc region-of-interest analyses are shown in eTable 2 in Supplement 1.At the post-Omicron follow-up, the thickness in the left precuneus was negatively correlated with the BAI (Figure 3A) (r = −0.39;P = .002;FDR P = .02),and the ratio of right hippocampus volume to the TIV was positively correlated with WFT scores (Figure 3B) (r = 0.34; P = .007).The correlation analyses between the ratio of the right hippocampus volume and the TIV and WFT scores were not significant after FDR.There was no correlation between the sulcus depth and the neuropsychiatric and neurocognitive test scales in the febrile group.The pre-Omicron measurements were obtained before Omicron infection; the post-Omicron measurements, during the acute phase of follow-up (6-34 days).A, Compared with the pre-Omicron thickness, the post-Omicron thickness was significantly reduced in the left precuneus (red).B, Compared with the pre-Omicron thickness, the post-Omicron thickness was significantly reduced in the right lateral occipital region (red and orange).C, The febrile group had a significantly reduced inferior parietal sulcus depth compared with the nonfebrile group (blue).D, Compared with the pre-Omicron period, the ratio of the right hippocampus volume to the total intracranial volume (TIV) showed a significant reduction in the post-Omicron period.L indicates left; R, right.

Discussion
This was the first study, to our knowledge, in which the same participants were examined with MRI before and after an Omicron infection.The main findings were as follows: (1) BAI scores increased and DES scores decreased at the post-Omicron follow-up; (2) neurological symptoms were more common at the post-Omicron follow-up, and fever, myalgia, and cough had improved significantly at the 3-month follow-up; (3) the thicknesses of the left precuneus and right lateral occipital region and the ratio of right hippocampus volume to the TIV were reduced at the post-Omicron follow-up and the sulcus depth was reduced in the right inferior parietal region in the febrile group; and (4) reduced thickness in the left precuneus was correlated with BAI scores and the ratio of right hippocampus volume to the TIV was correlated with WFT scores.
Compared with pre-Omicron measures, we found a significant increase in symptoms of anxiety and a reduced ability to manage negative emotions in participants in the post-Omicron phase.0][21] A study using the RESE scale to assess mood among patients who recovered from COVID-19 22 found that positive emotions, angerirritation, and DES scores were all decreased.Previous findings showed more pronounced neuropsychiatric health problems than those observed herein, which we believe may be related to 2 factors.First, the participants in this study had a different understanding of SARS-CoV-2.Most of the previous studies were conducted at the early stages of the COVID-19 outbreak or in highly exposed populations, such as physicians.Those participants had more fears and worries regarding SARS-CoV-2.However, our study was conducted 3 years after the beginning of the COVID-19 pandemic, and the participants had a clearer understanding of the process of Omicron infection.Second, previous policies required individuals to be isolated after infection, while our participants could be cared for by family and friends during infection.A previous study 18 found that high levels of isolation were associated with high levels of depression, anxiety, and posttraumatic stress disorder.Therefore, the neuropsychiatric symptoms observed in our study results were milder.
Most studies have focused on comparing the differences in clinical symptoms between the Delta and Omicron variants, and their findings have not been particularly consistent.Reportedly, both variants have similar COVID sequelae in the acute and subacute phases of infection, and the sequelae of Omicron in the chronic phase are milder than those of Delta. 23Menni et al 24 showed that The pre-Omicron measurements were obtained before Omicron infection; the post-Omicron measurements, during the acute phase of follow-up (14-29 days).A, The thickness in the left precuneus was negatively correlated with the Beck Anxiety Inventory (BAI) (false discovery rate P = .02).B, The difference in the ratio of the right hippocampus to total intracranial volume (TIV) was positively correlated with the Word Fluency Test (WFT) scores.
patients infected during the Omicron phase had significantly lower admission rates than those infected during the Delta phase, and the duration of acute symptoms was shorter during the Omicron phase (mean duration of 6.87 days).This finding was consistent with our results; although fever, headache, fatigue, myalgia, cough, and dyspnea were the main symptoms during the post-Omicron follow-up (range of mean [SD] duration, 1.4 [0.6] days for fever to 11.0 [9.5] days for dyspnea), significant improvements in fever, myalgia, and cough were observed at the 3-month follow-up, which is consistent with the view that individuals with an Omicron infection appear to recover more quickly and have milder clinical symptoms than those infected by previous variants. 25,26e thickness of the left precuneus and right lateral occipital were reduced during the post-Omicron follow-up compared with pre-Omicron measurements.However, previous follow-up studies [27][28][29] have shown cortical thickness decreases in areas associated with primary olfactory cortex function during acute, subacute, and 3-month periods after infection with Delta.This may be related to the differences in the mechanism of invasion into the nervous system, neuroinvasiveness, and neurotropism of different variants of SARS-CoV-2 30,31 ; therefore, the damaged brain areas and neurotoxic effects may also differ.Because the olfactory epithelium has the highest viral load (sustentacular cells in the olfactory epithelium express both angiotensin-converting enzyme 2 and transmembrane protease serine 2 [TMPRSS2]), 32 and many patients experience olfactory loss after Delta infection, 33 most researchers believe that the SARS-CoV-2 Delta variant enters the nervous system via the olfactory nerve and causes a decrease in the volume of gray matter in the relevant brain regions. 28Omicron is more likely to enter the nervous system via the terminal nerve pathway, which expresses angiotensin-converting enzyme 2 but not TMPRSS2. 34Omicron may enter the body more efficiently by using endosomal host cells rather than through the TMPRSS2-mediated pathway, 35 so changes in the damaged brain region occur.We found lateralization of the results.The reasons for these lateralized impairments may be different from the mechanism of Omicron damage to the cortex and subcortical nucleus or related to the development of brain lateralization. 36More studies may be needed to explore the mechanisms in the future.In addition, the thickness in the left precuneus was negatively correlated with BAI.The precuneus was involved in the manipulation of mental images and internally directing attention from visuospatial images, indicating their unique ability to represent the inner self psychologically.Some studies have confirmed the importance of the precuneus in anxiety neural circuits and psychological interventions for mood and anxiety disorders. 37,38e ratio of the right hippocampus volume to the TIV was significantly reduced at the post-Omicron follow-up and was positively correlated with the WFT scores.An animal experiment on human coronavirus OC43 infection showed that in the acute phase of the disease, some infected and uninfected neurons, particularly in the hippocampus, underwent simultaneous apoptosis. 39Several studies 40,41 have shown that neuronal cell apoptosis appears to be an important factor in damage to the human central nervous system with influenza and human immunodeficiency virus infection, potentially revealing the cause of cognitive dysfunction in SARS-CoV-2 infection.A 3-month follow-up study after infection with SARS-CoV-2 showed a reduction in hippocampal cortex thickness, 29 and another multimodal MRI study found a significant association between gray matter atrophy and cognitive dysfunction. 7In addition, the febrile group had reduced sulcus depth of the right inferior parietal compared with the nonfebrile group, and there was no correlation between the sulcus depth and the neuropsychiatric and neurocognitive scale results.This may be related to the fact that the nervous system of a patient with fever experiences more severe hypoxia or inflammatory storms.

1 .
Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guidelines for cohort studies.The experimental design is shown in Figure The inclusion criteria were as follows: (1) a certain frequency of nucleic acid tests was maintained and none of the test results were positive; (2) no typical symptoms of SARS-CoV-2 infection; (3) a self-reported first infection of the virus in December 2022 and a positive nucleic acid test result; and (4) a complete set of first and second MRI and neuropsychiatric scale data.The exclusion criteria were as follows: (1) a negative nucleic acid test result; (2) an MRI contraindication; (3) a history of structural brain abnormalities, such as intracerebral hemorrhage, encephalitis, epilepsy, and psychiatric illness; and (4) a history of tumor or endocrine diseases.Ultimately, 61 individuals were included in our study.Seventeen individuals completed follow-up of clinical symptoms 3 months after infection via a web-based questionnaire.Pre-Omicron data collection occurred from August 28 to September 18, 2022; post-Omicron follow-up data collection, January 6 to 14, 2023; and 3-month follow-up data collection, April 17 to 27, 2023.All participants were Chinese Han ethnicity.

Figure 1 .
Figure 1.Flowchart of the Study

1 mm 3 ,
[Siemens Healthcare] and uMR 790 [United Imaging Healthcare]) with 32-channel head coils.To minimize motion artifacts, participants were kept in a supine position while wearing earplugs, and a foam pad was placed between their head and the coil.The MRI scanning sequences included T1-weighted imaging, T2-weighted imaging, fluid-attenuated inversion recovery imaging, and 3-dimensional magnetization-prepared rapid acquisition gradient echo (3D-MPRAGE).The 3D-MPRAGE scanning parameters for the MAGETOM Skyra scanner were as follows: 176 sagittal sections, repetition time of 2000 milliseconds, echo time of 2.26 milliseconds, flip angle of 8°, voxel size of 1 × 1 × section thickness of 1 mm, and field of view of 256 × 256 mm 2 .The 3D-MPRAGE scanning parameters for the uMR 790 scanner were as follows: 160 sagittal sections, repetition time of 2000 milliseconds, echo time of 3.1 milliseconds, flip angle of 10°, voxel size of 1 × 1 × 1 mm 3 , section thickness of 1 mm, and field of view of 256 × 256 mm 2 .

Table 1 .
This study included 61 men with a mean

Table 2 .
Clinical Information in the Acute Phase and 3-Month Follow-Up Assessments for Omicron Infection Figure 2. Results of Gray Matter and Subcortical Nuclear Volume Analysis and Post Hoc Region of Interest Analysis Comparing Pre-Omicron and Post-Omicron Evaluations and the Febrile and Nonfebrile Groups a Calculated using the McNemar test.bDefined as an axillary temperature above 37.5 °C.JAMA Network Open | Infectious DiseasesBrain Structure Changes in Men After Omicron Infection JAMA Network Open.2023;6(11):e2345626. doi:10.1001/jamanetworkopen.2023.45626(Reprinted) November 30, 2023 6/13 Downloaded from jamanetwork.comby guest on 12/22/2023 29,42 Limitations 42.Duan K, Premi E, Pilotto A, et al.Alterations of frontal-temporal gray matter volume associate with clinical measures of older adults with COVID-19.Neurobiol Stress.2021;14:100326.doi:10.1016/j.ynstr.2021.100326SUPPLEMENT 1. eFigure.Clinical Symptoms in the Acute Phase and 3-Month Follow-up eTable 1. Characteristics of the Febrile and Nonfebrile Groups eTable 2. Significant Index Differences Between Pre-Omicron and Post-Omicron Groups and Febrile and Nonfebrile Groups