Scientists following COVID patients up to 12 months after diagnosis have found that mild cognitive impairment is common even after mild to moderate COVID. The study results, currently in preprint on the medRxiv server awaiting peer review, suggest that cognitive impairment, though barely noticeable, may affect large portions of the global population.
The finding comes as the US Centers for Disease Control reported that up to 1 in 5 Americans experienced at least one symptom that could be attributable to Long COVID.
SARS-CoV-2 is believed to cause lasting cognitive impairment in some cases, though the exact nature of it was not clear. Severe COVID cases risk damage through hypoxia, stroke, as well as the immune and inflammatory response to SARS-CoV-2. Mild to moderate COVID cases are still at risk of brain dysfunction, and cognitive deficits, providing a window into the potential mechanisms of brain injury without the confounding role of severe disease and its complications. Given the large numbers of people who had mild to moderate COVID disease, there would be significant implications for public health.
To assess the effects of the disease, the researchers studied 128 SARS-CoV-2 positive patients, assessing cognition and olfaction at set intervals after COVID diagnosis, along with lung capacity and blood biomarkers including the kynurenine pathway (KP).
After correcting for demographics, mild to moderate cognitive impairment was present in 26% on year post diagnosis, respectively. Overall cognitive performance declined mildly, but was statistically significant. KP metabolites quinolinic acid, 3-hydroxyanthranilic acid, and kynurenine were significantly associated with cognitive decline.
“The immune system reacts first with the virus … tries to basically get rid of the virus,” she said to ABC News. “Then it goes a little bit into overdrive and this overdrive does not fully calm down.”
The KP pathway was seen to be disturbed similarly to the way inflammation is caused by viruses such as HIV.
“I think we’re seeing something a bit akin here, where this low level of inflammation is more and more understood as being able to traffic to the brain, or even being within the brain and affecting those regions of the brain where we process information that demand speed, extra attention and extra cognitive demands,” she explained.
Dr Cysique emphasises that the cognitive decline recorded among most participants in the study is mild and they may not even notice it.
The researchers suggested that as a unique biomarker, the KP offers a potential therapeutic target for COVID-related cognitive impairment.
