Thread by @dgurdasani1

More & more evidence accruing that SARS-CoV-2 causes significant persistent effects on the brain. We now have multiple strands supporting this-
-long-term symptoms-brain fog, memory loss
-higher risk of stroke/neuro diseases
-structural brain changes
-virus persistence in brain🧵

We know that SARS-CoV-2 is neuro-invasive. This means that it enters the brain- we think this is through the olfactory nerve (the nerve that helps us smell) through the nose. This has been shown in mice, hamsters and directly in humans in autopsies.

nature.com/articles/s4159…

Replicating SARS-CoV-2 has also been shown to persist in neuro-epithelium (olfactory nerves in the nose) for up to 6 months among people who have recurrent or persistent loss of smell.

stm.sciencemag.org/content/13/596…

Neurological symptoms are significant among people post-COVID, & they persist for long periods of time, even after other symptoms recover. ONS data shows that problems with concentration, memory, brain fog, loss of smell/taste are common persistent symptoms after infection

Symptom based surveys have consistently shown that neurological symptoms are more likely to arise later, and persist over time, and symptom clusters that have neurological symptoms generally also correlate with poorer day to day functioning.

A @TheLancetPsych study showed that neurological & psychiatric diagnosis were very common at 6 months after COVID-19, and the risk for psychiatric disorders, strokes, dementia, muscle disorders was significantly higher, even in those not hospitalised.

There have been earlier studies that have looked at cognitive decline following hospitalisation with COVID-19 suggesting significant reduction after hospitalisation. These studies have been limited by not having measurements pre-COVID-19 to establish that this was the cause.

This is addressed now in a study within UK biobank. This is a cohort of generally healthy people who have had many measurements done as part of the study. ~40,000 people have had brain imaging done for research purposes before the COVID-19 pandemic.

Of the people who have had their second MRI brain scan in the Biobank study, some of them developed COVID-19 before the second scan. We can compare brain changes between those infected vs not infected by comparing the change in brain structure between the two scans.

394 people who were COVID-19 positive (only 15 of these were hospitalised) were imaged after COVID-19 was diagnosed. These were compared with 388 controls (not diagnosed with COVID-19). Both groups had MRI scans done before the pandemic at baseline.

They were compared for volume and thickness in certain areas of the brain. Cases & controls were matched for age, sex, ethnicity & the time between the baseline and repeat MRI scan to ensure any difference in change in brain structure between the two groups was not down to these.

The groups were well matched. Age was between 47-80 (mean age ~59). Similar blood pressure, prevalence of diabetes and BMI. As mentioned, most of the COVID group was people who were infected & tested in the community with non-severe COVID-19.

Most of the patients had been diagnosed Oct 2020 or after, and the duration between infection and scan varied accordingly. Mean duration was 4.5 months post COVID-19

The study found significant reduction in grey matter in certain parts of the brain- especially those associated with smell, and memory. Of note- these are changes in a population of people who mostly had mild COVID symptoms - *greater* reduction from baseline in those with COVID

While correlation isn't causation, the fact that these people were imaged at baseline before COVID-19 - allowing to compare to a group not infected with COVID-19 to look at difference in decline in grey matter after COVID compared to those who weren't infected makes it strong.

Remember, these groups were also the same age, had the same interval between scans, and many similar characteristics, making it unlikely this decline is down to something other than COVID-19

This is very concerning- we are seeing evidence of significant changes in the brain even among people with relatively mild COVID-19. This study was in 46-80 yr olds, and many would've been healthy. We urgently need to understand the impact of COVID-19 in younger age groups too.

This isn't just one study that suggests a link between SARS-CoV-2 and neurodegenerative disease. There have been several care reports of early-onset parkinsonism after SARS-CoV-2 infection, highlighting possible links with neuro-degenerative disease.

thelancet.com/journals/laneu…

Does this happen with other viruses?
Yes, many viruses invade and affect the brain: herpes viruses, Zika virus, measles, polio and of course, Spanish flu (encephalitis lethargica as immortalised in Awakenings). Other coronaviruses are known to invade the brain too.

This has been concerning for a while, but recent reports show us ignoring this will come at a huge cost. We need to stop focusing on hospitalisations & deaths as the only outcome, thinking that it's ok for transmission to continue at such levels. It's not.

This is the sort of thinking that will possibly leave thousands with chronic debilitating neurological illness, as well as other impacts of long COVID. By the time our scientific community & govt are satisfied that there is irrevocable evidence, it'll be much too late.

While I'm not a neuroscientist, I've worked with @HZiauddeen , who is, to make sure my interpretation of the UK biobank study is correct. I've seen several non-experts comment on possible limitations of the study, so wanted to ensure that I'd sought an expert perspective.

Conclusion: This is a robust study that shows significant change in brain structure, and thinning of grey matter in memory, smell and taste associated brain regions post-COVID-19. We should be concerned. This is not a virus we should be happy to expose anyone to.

Link to UK Biobank study here:
medrxiv.org/content/10.110…