A new study has presented the most rigorous investigation to date into the long-term cognitive impacts of severe COVID-19. The research, led by scientists from Imperial College London and the University of Cambridge, found persistent cognitive deficits in hospitalized patients equivalent to declines consistent with 20 years of brain aging.
The new research, published in the journal eClinicalMedicine, looked at 46 patients who were hospitalized with severe COVID-19. Sixteen of those patients required mechanical ventilation during their hospital stay.
Around six months after their acute illness the participants completed a barrage of complex cognitive assessments. Each COVID subject was paired with 10 age and demographically matched healthy control subjects.
“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,” explained senior author David Menon.
These COVID patients were slower to respond to tasks and less accurate in their responses, compared to their matched controls. More specifically, the COVID patients performed poorly on “verbal analogical reasoning” tasks which are designed to test particular word-based reasoning cognitive domains.
“On a neurological level, this pattern of impairment aligns with the observation of sub-acute phase hypometabolism within frontoparietal systems after COVID-19 illness that are known to be recruited in different combinations and configurations during the performance of these tasks,” the researchers explained in the new study.
The research found the scale of these cognitive deficits significantly correlated with the severity of each patient’s acute illness. Those with severe COVID requiring ventilation in hospital displayed the most significant cognitive declines.
On average, the research calculated the magnitude of the cognitive deficits to be equivalent to about 20 years of aging. So, a 50 year old hospitalized with severe COVID displayed cognitive test scores similar to what would be seen from a 70 year old.
The findings raise two big questions that the researchers currently have no good answers for. What is specifically causing these persistent cognitive deficits, and do patients recover their cognitive capacities over longer periods of time?
Hypothesizing a potential cause, the researchers indicate these cognitive problems are not likely the result of SARS-CoV-2 infiltrating the brain, despite some prior research finding that is possible. Instead, the most plausible explanation at this point is that severe COVID can cause brain damage due to disruptions in brain oxygen supplies and clotting or bleeds during the acute illness. An excessive immune response is also suspected to play a role in the ongoing cognitive deficits seen in those after a severe illness.
So does it get better over time? Menon said his team has seen some small signals of improvement in patients after long follow-up periods but at best any cognitive recovery is likely to be slow and gradual.
“We followed some patients up as late as 10 months after their acute infection, so were able to see a very slow improvement,” said Menon. “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.”
A study published earlier this year from researchers at the University of Oxford found minor cognitive deficits in subjects experiencing mild COVID-19 up to six months after an acute infection. Alongside these new findings researchers are beginning to paint a clearer picture of the spectrum of cognitive impacts from a COVID-19 infection.
Adam Hampshire, first author on the new study, said these findings indicate a large number of COVID survivors are most likely experiencing significant problems in the months after their acute infection. As vaccinations and more sophisticated treatments begin to reduce the mortality impact of COVID-19 it will be crucial to focus on those survivors experiencing longer-term chronic impacts from this new disease.
“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,” said Hampshire. “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.”
The new study was published in the journal eClinicalMedicine.
Source: University of Cambridge