COVID-19 may cause cognitive deficits equivalent to 20 years of aging

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New research assesses cognitive impairment found in people hospitalized with COVID-19. Jeff J Mitchell/Getty Images
  • A recent study suggests a link between severe COVID-19 requiring hospitalization and deficits in cognitive function that persist 6-10 months after disease onset.
  • The cognitive deficits in COVID-19 survivors were of a similar magnitude to the decline in cognitive function that normally occurs in individuals between the ages of 50 and 70.
  • The gradual recovery, if at all, of these persistent cognitive deficits highlights the importance of understanding the underlying mechanisms and developing treatment strategies.
  • Mild COVID-19 cases may report persistent cognitive symptoms, but the study authors report that the incidence is higher in severe cases, with 33-76% with cognitive symptoms 3-6 months after hospitalization.

A recent study appearing in the journaleClinical Medicinesuggests that severe COVID-19 may be associated with persistent cognitive impairment, equating to a 10-point IQ decrease. In this study, severe COVID-19 was defined as COVID-19 requiring hospitalization and critical care.

These cognitive deficits persisted for at least 6 months after contracting SARS-CoV-2 infection, with gradual improvement, if any, in these cognitive symptoms. These results underline the importance of long-term support for patients who have recovered from severe COVID-19.

According to official data from 2020, the same year this study collected its data, in the United States about 4 in 10 adults over the age of 18 are at risk of developing severe COVID-19.

A significant minority of individuals with SARS-CoV-2 infection experience persistent cognitive symptoms after the first 4 weeks after the onset of COVID-19 symptoms. Some of the most common cognitive symptoms are problems with concentration, “brain fog”, memory and executive function.

While persistent cognitive symptoms are also seen in individuals with mild COVID-19, such impairments in cognitive function are more common in individuals with severe COVID-19. Previous studies suggest that 36%–76% of individuals with severe acute COVID-19 show cognitive impairment 6 months after disease onset.

However, further research is needed to understand the specific aspects of cognitive function that are affected after severe COVID-19 and the factors that predict these cognitive symptoms.

Previous studies characterizing persistent cognitive symptoms in COVID-19 patients have been based on self-reports, which are prone to bias. Other studies have used pen-and-paper neuropsychological tests to assess cognitive function.

However, these tests do not have the sensitivity to detect small changes in cognitive function or distinguish the different domains or aspects of cognitive function affected by SARS-CoV-2 infection.

To address these concerns, the authors of the present study used automated cognitive tests to objectively characterize specific domains of cognitive function affected after severe acute COVID-19. These automated tests also allowed the researchers to assess the extent of these cognitive deficits.

Individuals with COVID-19 also experience persistent psychological symptoms such as anxiety, depression, fatigue and post-traumatic stress disorder (PTSD), which can contribute to the deficits in cognitive function.

Another aim of the current study was to determine whether these psychological symptoms mediate the persistent cognitive deficits in COVID-19 patients.

The current study included 46 patients previously hospitalized for severe COVID-19 receiving critical care at Addenbrooke’s Hospital in Cambridge, England. The former COVID-19 patients took a battery of computer-aided cognitive tests during a return visit to the hospital, an average of 6 months after the onset of the disease.

The performance of the 46 participants on the cognitive tests was compared with that of 460 people in the control group. The subjects in the control group were not hospitalized for COVID-19 and were matched for age, gender and education level. The researchers also used self-reports to assess symptoms of anxiety, depression, and PTSD.

The researchers found that the COVID-19 patients had a lower score and slower response time in the cognitive tests than the matched controls. People who had COVID-19 showed more pronounced deficits in specific domains of cognition, including processing speed, attention, memory, reasoning and planning.

Notably, the cognitive function deficits in the COVID-19 survivors were not associated with psychological symptoms present at the time of the cognitive tests, such as depression, anxiety, and PTSD.

Instead, performance in the cognitive tests was correlated with acute illness severity. For example, cognitive impairment was more pronounced in individuals requiring mechanical ventilation.

The researchers then compared the performance of COVID-19 survivors with more than 66,000 individuals from the general population.

The magnitude of cognitive impairment in COVID-19 survivors was similar to the age-related cognitive decline expected over the 20-year period between the ages of 50 and 70.

The study’s lead author, Professor David Menon, head of the Department of Anesthesia at the University of Cambridge, says: “Cognitive impairment is common in a wide variety of neurological disorders, including dementia and even routine aging, but the patterns we saw – the cognitive ‘fingerprint’ of COVID-19 – was different from all of these.”

dr. Betty Raman, a cardiologist at Oxford University, said: Medical news today“This prospective cohort study of 46 individuals recovering from severe COVID-19 and a large normative reference population by Hampshire and colleagues has demonstrated a clear association between the severity of infection and the degree of cognitive impairment.”

“This multidimensional characterization of cognition provides a nuanced understanding of different patterns of cognitive impairment during the recovery phase from severe COVID-19. Future efforts are needed to understand how this pattern varies in the context of other post-infectious syndromes and critical illnesses.”

The study found that these cognitive impairments persisted for up to 6-10 months after the onset of COVID-19, with only a gradual improvement, or already present, in cognitive performance. The persistence of these cognitive deficits highlights the importance of understanding the mechanisms underlying these symptoms.

Scientists have proposed multiple mechanisms, such as direct infection of the brain by SARS-CoV-2 and disruption of blood flow to the brain, to explain the persistent cognitive symptoms in COVID-19 patients. Among these mechanisms, systemic or whole-body inflammation has emerged as the leading candidate responsible for persistent cognitive symptoms.

dr. Roger McIntyre, a professor of psychiatry and pharmacology at the University of Toronto, said: MNT“Inflammatory activation appears to mediate these findings, highlighting the dangers of long-term immune activation. The next steps are to more fully unravel biological mechanisms and identify prevention and treatment strategies.”

dr. Paul Harrison, a professor of psychiatry at the University of Oxford, discussed key questions to be answered:

“This study shows that these deficits can be significant and persist for more than 6 months after the acute illness. The results are convincing and important and raise new questions. For example, what happens after a less severe infection? How long will the shortages last? What causes them and, critically, how can they be treated or prevented?”

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