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Severe Covid-19 can lead to cognitive impairment equivalent to 20 years of ageing, University of Cambridge and Imperial College find

Severe Covid-19 can lead to cognitive impairment equivalent to 20 years of ageing and the loss of 10 IQ points, a study by the University of Cambridge and Imperial College London has found.

Effects are still detectable more than six months after the acute illness and recovery is at best gradual, the scientists found, and they warned that some may never fully recover.

An illustration of Covid-19
An illustration of Covid-19

There has been growing evidence that Covid-19 can cause lasting cognitive and mental health problems, with reports from recovering patients of ‘brain fog’, problems recalling words, sleep disturbances, anxiety and even post-traumatic stress disorder (PTSD), months after infection.

One UK study found about one in seven individuals surveyed had symptoms that included cognitive difficulties 12 weeks after a positive Covid-19 test.

Between a third and three-quarters of hospitalised patients reported still suffering three to six months later, although even mild cases can lead to persistent cognitive symptoms.

For the new study, researchers explored this link by analysing data from 46 individuals who received in-hospital care, on the ward or intensive care unit, for Covid-19 at Addenbrooke’s Hospital between March and July 2020.

Of them, 16 patients were put on mechanical ventilation during their stay. The patients were recruited to the NIHR Covid-19 BioResource, enabling follow-up study.

The individuals tried computerised cognitive tests about six months after their acute illness using the Cognitron platform to measure mental faculties such as memory, attention and reasoning.

Scales measuring anxiety, depression and post-traumatic stress disorder were assessed against matched controls in what was the first such study of its kind into the after-effects of severe Covid-19.

They found Covid-19 survivors were less accurate and had slower response times, even after six months. The impact was greatest for those who required mechanical ventilation.

Comparing them to 66,008 members of the general public, the researchers estimate that the magnitude of cognitive loss is similar on average to that sustained with 20 years ageing, between 50 and 70 years of age – or the equivalent to losing 10 IQ points.

In particular, the survivors scored poorly on tasks such as verbal analogical reasoning, a finding which backs up the commonly-reported problem of the difficulty in finding words. They suffered slower processing speeds, which aligns with previous observations in post-Covid patients of decreased brain glucose consumption within the frontoparietal network of the brain, which is responsible for attention, complex problem-solving and working memory, among other functions.

Prof David Menon from the Division of Anaesthesia at the University of Cambridge, who was senior author of the study, said: “Cognitive impairment is common to a wide range of neurological disorders, including dementia, and even routine ageing, but the patterns we saw – the cognitive ‘fingerprint’ of Covid-19 – was distinct from all of these.”

A patient on a ventilator
A patient on a ventilator

It is now well known that people recovering from Covid-19 can have a broad spectrum of symptoms of poor mental health, including depression, anxiety, post-traumatic stress, low motivation, fatigue, low mood and disturbed sleep.

But the team found that cognitive deficits were more likely among those whose case of Covid was more severe.

While the patients’ scores and reaction times began to improve over time, the researchers noted that any recovery in cognitive faculties was at best gradual. It is also likely to be influenced by factors including the severity of the illness severity and its neurological or psychological impacts.

Prof Menon added: “We followed some patients up as late as 10 months after their acute infection, so were able to see a very slow improvement. While this was not statistically significant, it is at least heading in the right direction, but it is very possible that some of these individuals will never fully recover.”

The researchers believe several factors could lead to the cognitive deficits. While direct viral infection is possible, they believe it unlikely to be a major cause.

Instead, a combination of factors is more likely to contribute, including inadequate oxygen or blood supply to the brain, blockage of large or small blood vessels due to clotting and microscopic bleeds.

But emerging evidence suggests the most important mechanism involved is damage caused by the body’s own inflammatory response and immune system.

The study examined patients who had been hospitalised, but the team said even those who were not admitted may also have tell-tale signs of mild impairment.

Prof Adam Hampshire from the Department of Brain Sciences at Imperial College London, the study’s first author, said: “Around 40,000 people have been through intensive care with Covid-19 in England alone and many more will have been very sick, but not admitted to hospital. This means there is a large number of people out there still experiencing problems with cognition many months later. We urgently need to look at what can be done to help these people.”

Prof Menon and Prof Ed Bullmore, from Cambridge’s Department of Psychiatry, are co-leading working groups as part of the Covid-19 Clinical Neuroscience Study (COVID-CNS).

This aims to identify biomarkers that relate to neurological impairments as a result of the virus and associated neuroimaging changes.

The research, published in the journal eClinicalMedicine, was funded by the NIHR BioResource, NIHR Cambridge Biomedical Research Centre and the Addenbrooke’s Charitable Trust.

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