The cognitive impairment suffered by patients with a severe bout of Covid-19 is the equivalent of losing 10 IQ points, a new study has found.
According to scientists from the University of Cambridge and Imperial College London, the cognitive loss is similar to ageing two decades, between 50 and 70 years of age.
The study’s findings suggest the effects are still detectable more than six months after the acute illness, and that any recovery is at best gradual.
There is growing evidence that Covid can cause lasting cognitive and mental health problems, with recovered patients reporting symptoms months after infection.
Symptoms suffered by patients include fatigue, ‘brain fog’, problems recalling words, sleep disturbances, anxiety and even post-traumatic stress disorder (PTSD).
A separate UK study found that around one in seven individuals surveyed reported having symptoms that included cognitive difficulties 12 weeks after testing positive.
The researchers claim that between a third and three-quarters of hospitalised patients report still suffering cognitive symptoms three to six months later.
In order to explore further the link between severe Covid and long-lasting cognitive impairment, the team analysed data from 46 individuals who received in-hospital care, on the ward or intensive care unit, for Covid-19 at Addenbrooke’s Hospital - 16 of whom were put on mechanical ventilation during their stay.
The study said that all the patients were admitted between March and July 2020 and were recruited to the NIHR Covid-19 BioResource.
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 results were compared against matched controls.
According to the study’s authors, this is the first time that such rigorous assessment and comparison has been carried out in relation to the after-effects of severe coronavirus.
The study found that Covid survivors were less accurate and with slower response times than the matched control population, adding that these deficits were still detectable when the patients were following up six months later.
It also discovered that those who required mechanical ventilation felt the strongest effect.
By comparing the patients to 66,008 members of the general public, the study estimates that the cognitive loss is similar on average to that sustained between 50 and 70 years of age - the equivalent to losing 10 IQ points.
According to the study, the survivors scored particularly poorly on tasks such as verbal analogical reasoning, which supports the commonly-reported problem of difficulty finding words.
The patients were also found to show slower processing speeds, which aligns with previous observations post-Covid of decreased brain glucose consumption within the frontoparietal network of the brain, responsible for attention, complex problem-solving and working memory, among other functions.
Professor David Menon from the Division of Anaesthesia at the University of Cambridge and the study’s senior author, 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.”
Although it is now widely acknowledged that patients who have recovered from severe Covid can experience a broad spectrum of symptoms of poor mental health – such as depression, anxiety, post-traumatic stress, low motivation, fatigue, low mood, and disturbed sleep – the researchers concluded that acute illness severity was better at predicting the cognitive deficits.
While the survivors’ scores and reaction times improved over time, the team 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.
Professor Menon continued: “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.”
The researchers said that there are several factors that could cause the cognitive deficits.
The first potential factor is direct viral infection is possible, but the researchers added that this was unlikely to be a major cause.
Instead, they said it is more likely that a combination of factors contribute, including inadequate oxygen or blood supply to the brain, blockage of large or small blood vessels due to clotting, and microscopic bleeds.
They also flagged emerging evidence which suggests that the most important mechanism may be damage caused by the body’s own inflammatory response and immune system.
While this study looked at hospitalised cases, the team say that even those patients not sick enough to be admitted may also have tell-tale signs of mild impairment.
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.”
