Severe illness from Covid-19 causes cognitive impairment equivalent to 20 years of ageing, according to a study that exposes the extent of the ‘brain fog’ many long Covid patients report.
The researchers from Imperial College London, Cambridge University and the National Institute for Health Research (NIHR) tested the cognitive abilities of 46 people who were admitted to hospital with Covid-19 in March-July 2020. Sixteen of them were put on mechanical ventilation during their time in hospital.
Six months after their illness they were assessed using the Cognitron platform, which tests different aspects of mental faculties such as memory, attention and reasoning. Scales measuring anxiety, depression and post-traumatic stress disorder were also assessed.
Those who were hospitalised with Covid performed tasks with less accuracy and had slower response times than the control group their scores were compared with. These deficits were still detected when the test was repeated six months later, with the level of impairment strongest among those who required a ventilator.
They scored particularly low on verbal analogical reasoning tasks and showed slower processing speeds.
The researchers estimated that the magnitude of cognitive loss is similar on average to that sustained with 20 years ageing, between 50 and 70 years of age, and that this is equivalent to losing 10 IQ points.
The patients’ scores and reaction times began to improve over time, but the study says that any recovery in cognitive faculties was “at best gradual” and likely to be influenced by a number of factors including illness severity and its neurological or psychological impacts.
The researchers suggested the cognitive defects could have been caused by direct viral infection, inadequate oxygen or blood supply to the brain, blockage of large or small blood vessels due to clotting, and microscopic bleeds. However, emerging evidence suggests the body’s own inflammatory response may have affected cognition.
Professor David Menon from the Division of Anaesthesia at the University of Cambridge 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.
It is very possible that some of these individuals will never fully recover” – Prof David Menon
“We followed some patients up as late as ten 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.”
Even those with Covid who had not been hospitalised may also have suffered minor cognitive impairment, the researchers said.
Professor 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.”