Cognitive impairment as a result of severe COVID-19 is similar to that sustained with 20 years of ageing, between 50 and 70 years of age, and is the equivalent of losing 10 intelligence quotient (IQ) points, according to a study.
Cognitive impairment occurs when a person has trouble remembering, learning new things, concentrating, or making decisions that affect their everyday life.
The latest findings, published in the journal eClinicalMedicine, suggest that the effects are still detectable more than six months after the acute illness and that any recovery is at best gradual.
Researchers at the University of Cambridge and Imperial College London, UK, noted that there is growing evidence that COVID-19 can cause lasting cognitive and mental health problems.
COVID-19 recovered patients report symptoms including fatigue, ‘brain fog’, problems recalling words, sleep disturbances, anxiety and even post-traumatic stress disorder (PTSD) months after infection, they said.
The study analysed data from 46 individuals who received in-hospital care, on the ward or intensive care unit, for COVID-19. As many as 16 patients were put on mechanical ventilation during their stay in the hospital.
The patients underwent detailed computerised cognitive tests an average of six months after their acute illness using the Cognitron platform, which measures different aspects of mental faculties such as memory, attention and reasoning.
Scales measuring anxiety, depression and post-traumatic stress disorder were also assessed. Their data were compared against matched controls.
COVID-19 survivors were less accurate and with slower response times than the matched control population — and these deficits were still detectable when the patients were followed up six months later, the researchers said.
The effects were strongest for those who required mechanical ventilation, they said.
By comparing the patients 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 of ageing, between 50 and 70 years of age, and that this is equivalent to losing 10 IQ points.
Survivors scored particularly poorly on tasks such as verbal analogical reasoning, a finding that supports the commonly-reported problem of difficulty finding words.
They also showed slower processing speeds, which aligns with previous observations post COVID-19 of decreased brain glucose consumption within the frontoparietal network of the brain, responsible for attention, complex problem-solving and working memory, among other functions.
“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,” said Professor David Menon from the University of Cambridge, the study’s senior author.
While it is well established that people who have recovered from severe COVID-19 illness can have a broad spectrum of symptoms of poor mental health, the team found that acute illness severity was better at predicting the cognitive deficits.
The patients’ scores and reaction times began to improve over time, but the researchers said 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.
“We followed some patients up as late as ten months after their acute infection, so we’re 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,” Menon added.
There are several factors that could cause cognitive deficits, the researchers said.
They said direct viral infection is possible, but unlikely to be a major cause. It is more likely that a combination of factors contributes, including 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 that the most important mechanism may be damage caused by the body’s own inflammatory response and immune system, according the researchers.
While the study looked at hospitalised cases, the team said that even those patients not sick enough to be admitted may also have tell-tale signs of mild impairment.