Even mild Covid can cause brain damage, scans show ...
Source:
https://www.nbcnews.com/health/health-news/long-covid-even-mild-covid-linked-damage-brain-months-infection-rcna18959
<begin article>
During at least the first few months following a coronavirus
infection, even mild cases of Covid-19 are associated with subtle
tissue damage and accelerated losses in brain regions tied to the
sense of smell, as well as a small loss in the brainÂ’s overall volume,
a new British study finds. Having mild Covid is also associated with a
cognitive function deficit.
These are the striking findings of the new study led by University of
Oxford investigators, one that leading Covid researchers consider
particularly important because it is the first study of the diseaseÂ’s
potential impact on the brain that is based on brain scans taken both
before and after participants contracted the coronavirus.
“This study design overcomes some of the major limitations of most
brain-related studies of Covid-19 to date, which rely on analysis and
interpretation at a single time point in people who had Covid-19,”
said Dr. Serena S. Spudich, a neurologist at the Yale University
School of Medicine, who was not involved in the research.
The red-yellow regions are the parts of the brain that shrink the most
in the 401 SARS-CoV-2 infected participants
The red-yellow regions are the parts of the brain that shrank the most
in the 401 SARS-CoV-2 infected participants, compared with the 384
noninfected participants. Gwenaëlle Douaud, in collaboration with
Anderson Winkler and Saad Jbabdi, University of Oxford and NIH.
Full coverage of the coronavirus pandemic
The research, which was published Monday in Nature, also stands out
because the lionÂ’s share of its participants apparently had mild Covid
— by far, the most common outcome of coronavirus infections. Most of
the brain-related studies in this field have focused on those with
moderate to severe Covid.
Gwenaëlle Douaud, an associate professor at the Nuffield Department of
Clinical Neurosciences at Oxford and the paperÂ’s lead author, said
that the excess loss of brain volume she and her colleagues observed
in brain scans of hundreds of British individuals is equivalent to at
least one extra year of normal aging.
“It is brain damage, but it is possible that it is reversible,” she
said. “But it is still relatively scary because it was in mildly
infected people.”
Douaud and her team relied on a rich data source: the United Kingdom
Biobank. Before the Covid pandemic began, this mammoth database
already had on hand tens of thousands of brain MRIs of people in
Britain, along with responses to surveys about their diets and
lifestyles and results from cognitive function tests.
The investigators focused on 401 people between 51 and 81 years old
who had tested positive for Covid according to clinical data linked to
the Biobank study. They were invited back for a second brain scan,
which they received an average of about five months after contracting
the coronavirus. Covid was apparently mild in the vast majority of
these participants; only 15 of them were hospitalized with the
disease.
The researchers compared these pairs of scans to those of a control
group of 384 U.K. Biobank participants who had not tested positive for
Covid and were matched according to the Covid-positive groupÂ’s rates
of obesity, blood pressure, smoking and diabetes, as well as their
socioeconomic status, age and sex.
Between the pairs of MRIs, which were separated by an average of about
three years, the researchers observed a striking trend among those who
had Covid: a greater loss of whatÂ’s known as gray matter in the brain,
as well as a higher rate of abnormalities in the brain tissue. Gray
matter, which appears gray on certain brain scans, is comprised of
various cells, including neurons.
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It would be normal for adults within the studyÂ’s age range to lose a
small amount of brain tissue after three years of aging, the
researchers note. But compared with the control group, those who had
Covid experienced an additional 0.2 percent to 2 percent loss of brain
tissue in regions which are mostly associated with the sense of smell
— specifically, in the parahippocampal gyrus, the orbitofrontal cortex
and the insula.
The overall brain volume in people with Covid declined by an extra 0.3
percent over those without the disease.
Older participants experienced all these excess brain-related declines
more profoundly.
The study offers no indication whether a Covid vaccination would
mitigate the risk of such changes. The participants tested positive
for the disease between March 2020 and April 2021, before the vaccines
were widely available in the U.K.
On cognitive function tests, those who had Covid demonstrated a slower
ability to process information and had lower marks on whatÂ’s known as
executive function, which is an umbrella measure of the brainÂ’s
ability to manage complex tasks. Again, these Covid-linked deficits
were more pronounced among older individuals.
Dr. Avindra Nath, clinical director of the National Institute of
Neurological Disorders and Stroke at the National Institutes of
Health, said that these findings “have long-term implications, since
we would be concerned about the possibility of similar cognitive
dysfunction in a large population worldwide."
"It needs to be determined if these patients could further deteriorate
over a period of time," he said.
The investigators had no access to data on any Covid-related symptoms
the participants may have experienced. So they donÂ’t know if the
participants actually lost their sense of smell or have experienced
long-term symptoms in the diseaseÂ’s wake. Some likely had asymptomatic
cases.
That said, the loss of smell was particularly prevalent among those
infected with the coronavirus during the first two major waves of the
pandemic. And when particular regions of the brain go unused, they are
inclined to atrophy. Nevertheless, the studyÂ’s authors donÂ’t know
whether the coronavirus caused a loss of smell through a
nonbrain-based mechanism and this, in turn, prompted the brain damage,
or if possibly the brain damage caused the loss of smell.
How long do Covid brain changes last?
A study published in Cell in February found that a coronavirus
infection of various cells in the nasal cavity gives rise to
inflammation that inhibits the functioning of smell-receptor proteins
on nerve cells, leading to smell loss.
“The brain is plastic, which means it can reorganize and heal itself.
This is true even in older people.
GWENAËLLE DOUAUD, UNIVERSITY OF OXFORD
CovidÂ’s link to declines in the smell-related brain regions, Douaud
said, does not discount the other ways that it might impact the brain
in regions unrelated to smell. The disease has proved maddeningly
variable from patient to patient, and other studies have identified
various means by which severe Covid in particular might damage the
brain. What the study revealed is that changes to the smell-related
regions were the most consistent brain-related trend tied to Covid in
the study cohort.
Whether these changes will persist over the long term remains unknown.
Douaud is hoping to conduct a third round of brain scans.
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“The brain is plastic, which means it can reorganize and heal itself,”
she said. “This is true even in older people.”
Experts in long Covid praised DouaudÂ’s paper.
“This study provides the most definitive clinical data available to
date that SARS-CoV-2 directly or indirectly damages nerves and that
this, in turn, can have systemic effects, including changes in the
brain,” said Dr. Steven Deeks, a veteran HIV researcher at the
University of California, San Francisco. “It contributes to an
emerging theme that nerve damage was common during the first few waves
of the pandemic.”
Deeks, who is directing a major cohort study of people suffering from
persistent symptoms following a coronavirus infection, noted a
limitation of the new study. Those who got Covid, he pointed out, had
some differences in their baseline cognitive function and in some of
the initial brain scans compared with those who did not get the
disease.
“It is possible, but perhaps unlikely,” he said, “that those who had
higher risk for becoming infected were destined to progress more
rapidly in the changes in their brain for other unmeasured reasons.”
That said, having the pairs of brain scans before and after an
infection provided Douaud and her colleagues with a unique ability to
factor out brain abnormalities that might have already been present
before individuals developed Covid and therefore were not likely
connected to the disease.
<end article>
Source:
https://www.nbcnews.com/health/health-news/long-covid-even-mild-covid-linked-damage-brain-months-infection-rcna18959
A shorter more shareable link:
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