Changes in the Brain' Structure Even After Mild Covid-19 Infection

The Covid-19 infection has spread swiftly across the globe, infecting hundreds of millions of people in different parts of the world. Many complications have been linked to Covid-19 infection. For instance, lung fibrosis, thromboembolic events (e.g. stroke, venous thromboembolism), dermatological complications, and mood disorders have all been associated with prolonged Covid infection. The majority of these long term consequences of Sars-CoV-2 infection are seen in people who do not recover quickly. Several studies have shown that chronic COVID infections increases the risk of developing many of these complications. 

However, a recent large study conducted by scientists using Magnetic Resonance imaging scans from the Uk Biobank (A biomedical database and research tool that collects and disseminates genetic and health-related information) revealed significant changes in the brain architecture of people who had mild to moderate Sars-Cov-2 infection. Researchers at Oxford University's Wellcome Centre for Integrative Neuroimaging noted that people who had SARS-CoV-2 infection had more grey matter loss and tissue anomalies, primarily in the parts of the brain responsible for smell, and that their brains shrank more than those who hadn't had the virus.

It is a paradigm-shifting study as it was initially thought that people who suffered from a milder form of the Covid-19 infection were not at much risk of complications. In this article, we will highlight how the research was done and its significance to the growing knowledge about Covid-19.

The Study

This study was carried out by researchers at Oxford University's Wellcome Centre for Integrative Neuroimaging using data from the UK biobank amongst participants who had had a Magnetic Resonance Imaging (MRI) before the pandemic's outbreak and who returned for a second identical scan session. The scientists compared the magnetic resonance imaging of 785 participants for this study. The invited participants for a second scan were aged between 51 and 81 years. The analysis used for the second scan includes;

•  401 case volunteers who had been infected with the Sars-Cov-2 virus. 15 persons (4%) of this group were hospitalized, and two required critical care. Reimaging was performed on the volunteers on an average of three years after initial MRI scans and 4.5 months after COVID-19 diagnosis.
• 384 control volunteers who were not infected with SARS-CoV-2 were matched to the case volunteer group in terms of age, ethnicity, sex, the time between scans, and risk factors such as blood pressure, diabetes, obesity, smoking, and socioeconomic level.

The scientists estimated the changes in each group's brains over time. They then searched for disparities in these changes across the different groups. They also evaluated the variations in cognitive task scores between the groups to see any difference in cognitive deterioration.

The Result

After analyzing the findings of the tests, The researchers noted that people who had been infected with SARS-CoV-2 had alterations in their MRI brain scans and cognitive scores compared to the reported findings before infection. This was not seen in the control group. The differences in brain changes and cognitive scores were more significant among older participants. Although not everyone who became infected with SARS-CoV-2 exhibited these characteristics, the prior-infection group exhibited them on average. The findings include;

• The orbitofrontal cortex and parahippocampal gyrus, which are areas connected with the sense of smell, had a more considerable reduction of grey matter thickness.
• Significant tissue loss occurred in areas associated with the primary olfactory cortex, which is also linked to the sense of smell.
• Significant reduction in the volume of the entire brain and rise in the volume of cerebrospinal fluid
•  The capacity to complete complicated activities was reduced, which was associated with shrinking crus II, a cerebellar area associated with cognition, on brain scans.

Compared with the case-control group, the volunteers with a past SARS-CoV-2 infection experienced an additional 0.2 per cent to 2% grey matter loss or tissue injury on average. The study results were statistically significant even after patients hospitalized with COVID-19 were excluded from the research. The researchers tried to explain the reason for these findings with different hypotheses. They include;

• Diminished sensory input is linked to the loss of sense of smell
• Brain changes might be a consequence of inflammation in the Central Nervous System (CNS)
• The changes might result from direct infection of the brain by the Sars-Cov-2 virus.

Final Consideration

The researchers noted that the study puts into perspective concerns about Covid-19 infections regardless of the severity. They also reported that though the study found that the case-volunteer group had more brain changes than the other group, the clinical relevance of these changes isn't clear cut. Additionally, They thought it was too early to determine whether the alterations noted were reversible. The period between Covid-19 infection among the case volunteers and the second round of MRI brain scans was too short.

Whether this is a transient effect, possibly related to anosmia or inflammation, or a longer-lasting effect, possibly associated with the cognitive and other neurologic and psychiatric changes described in some patients with prolonged COVID, remains an open question," noted Josephson, a professor and chair of the Department of Neurology at the University of California, San Francisco.

Another recent study conducted in Wuhan, China, corroborated the findings of this research. The study noted that the cognitive changes identified in some people with Covid-19 infection persisted, especially in those with a more severe form of the disease. The researchers discovered a greater rate of cognitive impairment among older persons a year after contracting the Sars-Cov-2 virus, compared to their non-infected spouses, even after correcting for age, sex, BMI(body mass index), educational level, and comorbidities.

Finally, the scientists hopefully suggested that because the aberrant alterations observed in the brains of infected participants may be related to their loss of smell, it is likely that when the sense of smell is restored, the brain changes may be reversed over time. Similarly, they hoped that the virus's detrimental effects would diminish with time following recovery from the infection.