NUMEROUS studies show that covid-19 often affects the brain, having a profound influence on people鈥檚 consciousness, cognition and behaviour 鈥� and possibly even their risk of dementia later in life.
鈥淢ercifully, those affected are a minority of those infected,鈥� says at the University of Liverpool in the UK, 鈥渂ut those affected are severely affected.鈥�
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In addition, given the number of people who have been infected by the coronavirus, the impact of cognitive complications may be large and could have .
How often does covid-19 affect the brain?
Very often. at the University of Oxford and his colleagues of 236,000 people with covid-19. In the six months after infection, 34 per cent were diagnosed with a neurological or psychiatric condition. For 13 per cent, this was their first such diagnosis.
Most people with covid-19 never get tested or seek care, so the 34 per cent figure doesn鈥檛 apply to everyone infected. Nevertheless, the findings still suggest that a large number of people globally have been or will be affected.
What neurological complications can occur?
In a study of in the UK, Michael and his colleagues found that bleeding and clots in the brain were the most common brain complications, affecting around half of the people in the study.
Other complications included delirium, brain inflammation, peripheral nerve damage, psychosis, depression and anxiety. Milder neurological effects included headaches and the loss of smell or taste.
Who is most at risk of neurological problems?
There is a link between disease severity and the severity of cognitive issues, says Michael, but his team has identified some 800 people in the UK for whom the severity of brain complications is disproportionate to the severity of their covid-19. His team is studying whether they have gene variants that predispose them to getting severe brain complications.
One small study in Italy found that brain problems related to covid-19 were worse in those aged under 50 than in older people. Elisa Canu at the San Raffaele Hospital in Milan and her colleagues followed up 50 people in hospital with covid-19. Two months after leaving hospital, half had cognitive issues ranging from impaired memory to trouble judging depth, Canu told a meeting of the
However, Canu suspects this may partly be the result of younger people returning home to recover rather than staying in hospital.
Is covid-19鈥檚 effect on the brain unusual?
Not particularly. Many other viruses, including the measles, polio and Zika ones, . For instance, hospitalisation with pneumonia, which can be caused by viral infection, can lead to that lasts at least a year in a third of those over 60 and a fifth of younger people.
How does the damage actually occur?
The coronavirus can infect the cells lining the blood vessels that supply the brain, says Frank Heppner at Charit茅 University of Medicine in Berlin, causing inflammation and potential complications such as strokes. But the virus doesn鈥檛 seem to cross the blood-brain barrier and attack brain tissue directly.
When Andreas Keller at Saarland University in Germany and his colleagues examined eight people who died of covid-19, they found characteristic of those seen in neurodegenerative conditions such as Alzheimer鈥檚 disease. They think that certain signalling molecules, triggered by the virus, relay information into the brain and cause inflammation and other damage that could help explain symptoms such as the brain fog and fatigue many report.
Can covid-19 lead to Alzheimer鈥檚?
As part of a long-term study called the Biobank, the brains of 40,000 people had been scanned before the pandemic. Now 800 of those people, 400 of whom tested positive for the virus, have been rescanned. The results show a loss of grey matter in some parts of the brains of those infected, including in younger people and those with only mild disease.
A describing these findings has raised alarm bells with some (medRxiv, ). 鈥淚t鈥檚 very concerning,鈥� Scott Gottlieb, former head of the US Food and Drug Administration, . 鈥淚t suggests鈥� covid is a disease that could create persistent symptoms.鈥� The researchers aren鈥檛 discussing the results yet.
Michael thinks that direct infection of the olfactory nerve is causing damage that then affects adjacent areas of the brain, including memory regions.
What has most alarmed people is the possibility that this brain damage could lead to later consequences. The preprint states that the findings raise the possibility that SARS-CoV-2 infection 鈥渕ight in time contribute to Alzheimer鈥檚 disease or other forms of dementia鈥�.
Other researchers say this is plausible, but think at worst it will affect a tiny number of people. 鈥淲e cannot exclude the possibility,鈥� says Heppner. But many viruses have similar effects on the brain without causing such conditions, he says. 鈥淚t won鈥檛 apply to every covid patient for sure.鈥�
Can we treat cognitive problems?
Those severely affected 鈥� because of a stroke, say 鈥� are likely to have significant lifelong disability, says Michael. But for those with milder symptoms, the outlook is brighter. 鈥淚n that group, one would have to be very hopeful that symptoms would improve.鈥�
In a few cases, there are effective treatments. For instance, the virus can cause the immune system to attack the lining of nerve cells, leading to a condition called acute disseminated encephalomyelitis. This is like a one-off hit of multiple sclerosis and can be treated with steroids and immunosuppressive drugs, says Michael.
When it comes to loss of smell, recovery depends on the extent of the damage, says Heppner. If most olfactory nerve cells and the cells that give rise to them are harmed, the problem will be long-lasting.
In Canu鈥檚 study, the proportion of former hospitalised patients with cognitive issues fell from half at two months to just over a third at 10 months. However, 16 per cent reported being depressed and 18 per cent as having post-traumatic stress disorder at two months, and those numbers barely changed at 10 months.
For those with such issues, cognitive stimulation therapy might be helpful, says Canu. This can be done in hospitals or on smartphone apps. Physical exercise is also important, she says.
