In a recently published study, Dr eClinical Medicine, Researchers determined whether the prevalence of substantial cognitive decline could be used as a diagnostic marker of chronic coronavirus disease 2019 (COVID-19).
Study: Prolonged covid is associated with severe cognitive decline: a multicenter cross-sectional study. Image Credit: PeopleImages.com – Yuri A/Shutterstock.com
How long is covid?
Since the emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in late 2019, more than 770 million people have been infected worldwide, of whom nearly 7 million have died from the disease.
Between 30-60% of Covid-19 survivors report experiencing persistent symptoms for weeks to months after recovering from SARS-CoV-2 infection, a condition now commonly referred to as ‘long Covid’. The World Health Organization (WHO) and the United States Centers for Disease Control and Prevention (CDC) define prolonged covid as pre-Covid-19 symptoms that persist or reappear within three months of recovery from infection or the development of new symptoms. At least two months.
‘Brain fog’, a cognitive condition characterized by confusion, forgetfulness, lack of focus and general loss of mental clarity, is one of the most common symptoms associated with prolonged covid. Impairments in sustained attention, memory, and cognitive flexibility have also been reported with prolonged covid, symptoms often associated with structural and functional brain changes.
There are currently no diagnostic tests available for chronic covid, thus diagnosis can be based on patient self-reported assessment. Furthermore, there is a critical need to clearly define and elucidate risk factors associated with prolonged COVID to support the development of future interventions for disease prevention and treatment.
About the study
In the current study, the researchers used a cohort of European participants to determine whether cognitive slowing is strongly associated with prolonged Covid. Importantly, ‘cognitive slowing’ was defined as an increase in the time it takes to process information and respond to it.
Selected participants were divided into three groups, including self-reported prolonged covid (cases), no-covid group (healthy controls) and those with a prior history of COVID-19 but no prolonged covid.
Study participants completed two cognitive function tests, including the Simple Response Test (SRT), which uses a spacebar to respond to monitor-presented visual cues and measure reaction time. In contrast, the Number Vigilance Test (NVT) measures sustained, long-term attention by requiring participants to remain attentive while exposed to a long number with zero as odd. Study participants were also administered six questionnaires measuring mood and mental health, fatigue, sleep, trauma, and intelligence quotient (IQ).
A total of 194 individuals were included in the study, of whom 119 were diagnosed with prolonged covid, 63 of whom had covid-19 but did not have chronic covid, and 75 were healthy controls. Compared to healthy controls, with a mean reaction time (RT) of 0.34 seconds for the SRT test, chronic Covid patients showed a significantly slower reaction time with a mean time of 0.49 seconds. After accounting for the effect of age, the mean RT for long covid patients was significantly longer than for age-matched healthy controls.
Compared to 4% of healthy controls, 53.5% of chronic Covid patients experienced severe cognitive slowing. Similarly, a significantly greater proportion of moderately to severely disabled cases was identified in the long-Covid group compared to both the long-Covid and the healthy controls who survived COVID-19.
Long-term covid patients with low SRT test scores reported significantly lower outcomes on assessments of their mental health, exhibited less restful sleep, and reported higher depression prevalence. Similar to SRT results, NVT estimates differed significantly between COVID-19 survivors and long-Covid patients, with long-Covid patients taking significantly longer to respond to targets. Notably, RT in the NVT was strongly associated with the slower RT observed in the SRT even when age and depression status were taken into account.
During the NVT, chronic Covid patients were less alert to visual stimuli than healthy controls, with their alertness accuracy decreasing over time. Longer Covid patients with normal reaction speed felt significantly more fatigued than other participants with similar RTs, thus indicating that these individuals worked harder to maintain their attention on demanding tasks.
No difference in cognitive slowing was observed in chronic COVID patients who were not hospitalized due to COVID-19 compared to hospitalized chronic COVID patients. Thus, the severity of acute infection with SARS-CoV-2 does not appear to determine the cognitive impact of prolonged covid. Similarly, the presence of pre-existing psychological or neurological conditions, such as depression, did not influence cognitive symptoms in patients with prolonged Covid.
The present study reported significant cognitive slowing in 53% of chronic Covid patients that did not appear to improve over time. Rather, persistent cognitive slowing in chronic Covid patients has been shown to increase the severity of these neurological symptoms in these patients.
Information on the mechanisms responsible for the cognitive deficits observed in chronic Covid patients is lacking. Therefore, additional research incorporating comprehensive neuropsychological assessment in a larger and more diverse group of patients is needed.
- Zhao, S., Martin, E. M., Rieuken, P. A., etc (2024). Prolonged covid is associated with severe cognitive decline: a multicenter cross-sectional study. eClinical Medicine 68. doi:10.1016/j.eclinm.2024.102434.