Military版 - Even mild Covid is linked to brain damage, scans s |
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The new British research is the first to reveal striking differences in
areas of the brain based on scans taken before and after a coronavirus
infection.
Washington DC Area Sees Highest Rate Of COVID-19 Infections In U.S.
A medical professional administers a Covid test at a drive-thru testing site
May 26, 2020, in Washington, D.C. Drew Angerer / Getty Images file
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March 7, 2022, 11:01 AM EST
By Benjamin Ryan
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 brain鈥檚 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 disease鈥檚 potential impact
on the brain that is based on brain scans taken both before and after
participants contracted the coronavirus.
鈥淭his 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,鈥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. Gwena毛lle 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 lion鈥檚 share of its participants apparently had mild Covid 鈥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.
Gwena毛lle Douaud, an associate professor at the Nuffield Department of
Clinical Neurosciences at Oxford and the paper鈥檚 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.
鈥淚t is brain damage, but it is possible that it is reversible,鈥she said
. 鈥淏ut it is still relatively scary because it was in mildly infected
people.鈥br />
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 group鈥檚 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 what鈥檚 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 study鈥檚 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 鈥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 what鈥檚 known as
executive function, which is an umbrella measure of the brain鈥檚 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 鈥渉ave 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 don鈥檛 know if the participants
actually lost their sense of smell or have experienced long-term symptoms in
the disease鈥檚 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 study鈥檚 authors don鈥檛 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.
鈥淭he brain is plastic, which means it can reorganize and heal itself. This
is true even in older people.
GWENA脣LLE DOUAUD, UNIVERSITY OF OXFORD
Covid鈥檚 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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鈥淭he brain is plastic, which means it can reorganize and heal itself,鈥
she said. 鈥淭his is true even in older people.鈥br />
Experts in long Covid praised Douaud鈥檚 paper.
鈥淭his 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,鈥said Dr.
Steven Deeks, a veteran HIV researcher at the University of California, San
Francisco. 鈥淚t contributes to an emerging theme that nerve damage was
common during the first few waves of the pandemic.鈥br />
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.
鈥淚t is possible, but perhaps unlikely,鈥he said, 鈥渢hat those who had
higher risk for becoming infected were destined to progress more rapidly in
the changes in their brain for other unmeasured reasons.鈥br />
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.
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