New research has indicated that hospitalised COVID-19 patients demonstrate substantial cognitive impairment within four months of discharge.
The study, published in the peer-reviewed journal European Neuropsychopharmacology, suggests that within four months of discharge, between 59% to 65% of patients hospitalised due to COVID-19 infection suffer exceptional cognitive impairment.
The researchers from Copenhagen University Hospital have highlighted that due to the small sample size of their study, they will need to conduct further research using a more considerable sample to produce a comprehensive analysis.
Professor Kamilla Miskowiak, the lead researcher of the study, said: “This is the first study we know of which characterises the frequency and pattern of cognitive impairments after hospitalisation with COVID-19. We found that 59-65% of patients had clinically significant problems within learning, memory, and mental flexibility and that this was related to poorer work function and quality of life.”
Investigating cognitive impairment
To conduct their study, the researchers analysed 29 patients after they had been discharged for four months, comparing these results to a match control group of 100 healthy controls – performing an array of cognitive tests, such as memory, verbal learning, processing speed, working memory, verbal fluency, and executive function.
Astonishingly, a distinct cognitive impairment was expressed between the patient group and matched control group – an average global cognition score of 67 was recorded for the patient group, significantly lower than the 75 achieved by the matched control group, with the most notable decline being in mental flexibility and verbal learning.
Miskowiak added: “We need to be cautious expressing the results; it is a small study, and the cognitive impairment in COVID patients is measured against a control group matched for age and education levels, rather than against previous performance (in, e.g., a longitudinal study).
“Nevertheless, the patients in the study and the control group are very well characterised, and the observed differences were of large effect sizes, so the main findings seem robust. Based on this, critical care doctors and psychologists at the University Hospital have now included follow-up cognitive tests in standard post-COVID care.”
The effects of D-dimer levels
The researchers have inferred that cognitive impairment is associated with an increased level of D-dimer – a protein product of cross-linked fibrin degradation contained within the blood that is a marker of blood clots in the lungs throughout COVID-19 infection, which scientists believe may be the cause of the lung dysfunction in patients after discharge. This eludes the fact that the brain is potentially starved of oxygen during the infection. Nevertheless, this claim requires a more in-depth study to be confirmed.
Professor Eduard Vieta, the Editor of European Neuropsychopharmacology, wants to see the study carried out for a wide variety of COVID patients.
He said: “The study does not address the potential occurrence of cognitive impairment in patients with mild-to-moderate COVID-19 (those who were not hospitalised), but given the global spread of the pandemic, it is extremely relevant for a substantial portion of the world’s population.
“The study also suggests that cognition and intellectual abilities should be further studied, especially in the context of Post-Acute COVID-19 Syndrome.”