adding that the impairment is “equivalent to losing 10 IQ points.”
In their study, published in eClinicalMedicine, a team of scientists from the University of Cambridge and Imperial College London said there is growing evidence that COVID-19 can cause lasting cognitive and mental health problems. Patients report fatigue, “brain fog,” problems recalling words, sleep disturbances, anxiety, and even posttraumatic stress disorder months after infection.
The researchers analyzed data from 46 individuals who received critical care for COVID-19 at Addenbrooke’s Hospital between March and July 2020 (27 females, 19 males, mean age 51 years, 16 of whom had mechanical ventilation) and were recruited to the NIHR COVID-19 BioResource project.
At an average of 6 months after acute COVID-19 illness, the study participants underwent detailed computerized cognitive tests via the Cognitron platform, comprising eight tasks deployed on an iPad measuring mental function such as memory, attention, and reasoning. Also assessed were anxiety, depression, and posttraumatic stress disorder via standard mood, anxiety, and posttraumatic stress scales – specifically the Generalized Anxiety Disorder 7 (GAD-7), the Patient Health Questionnaire 9 (PHQ-9), and the PTSD Checklist for Diagnostic and Statistical Manual of Mental Disorders 5 (PCL-5). Their data were compared against 460 controls – matched for age, sex, education, and first language – and the pattern of deficits across tasks was qualitatively compared with normal age-related decline and early-stage dementia.
Less accurate and slower response times
The authors highlighted how this was the first time a “rigorous assessment and comparison” had been carried out in relation to the after-effects of severe COVID-19.
“Cognitive impairment is common to a wide range of neurological disorders, including dementia, and even routine aging, but the patterns we saw – the cognitive ‘fingerprint’ of COVID-19 – was distinct from all of these,” said David Menon, MD, division of anesthesia at the University of Cambridge, England, and the study’s senior author.
The scientists found that COVID-19 survivors were less accurate and had slower response times than the control population, and added that survivors scored particularly poorly on verbal analogical reasoning and showed slower processing speeds.
Critically, the scale of the cognitive deficits correlated with acute illness severity, but not fatigue or mental health status at the time of cognitive assessment, said the authors.
Recovery ‘at best gradual’
The effects were strongest for those with more severe acute illness, and who required mechanical ventilation, said the authors, who found that acute illness severity was “better at predicting the cognitive deficits.”
The authors pointed out how these deficits were still detectable when patients were followed up 6 months later, and that, although patients’ scores and reaction times began to improve over time, any recovery was “at best gradual” and likely to be influenced by factors such as illness severity and its neurological or psychological impacts.
“We followed some patients up as late as 10 months after their acute infection, so were able to see a very slow improvement,” Dr. Menon said. He explained how, while this improvement was not statistically significant, it was “at least heading in the right direction.”
However, he warned it is very possible that some of these individuals “will never fully recover.”
The cognitive deficits observed may be due to several factors in combination, said the authors, including inadequate oxygen or blood supply to the brain, blockage of large or small blood vessels due to clotting, and microscopic bleeds. They highlighted how the most important mechanism, however, may be “damage caused by the body’s own inflammatory response and immune system.”
Adam Hampshire, PhD, of the department of brain sciences at Imperial College London, one of the study’s authors, described how around 40,000 people have been through intensive care with COVID-19 in England alone, with many more despite having been very sick not admitted to hospital. This means there is a “large number of people out there still experiencing problems with cognition many months later,” he said. “We urgently need to look at what can be done to help these people.”
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