En español | One of the most mysterious and frightening consequences of COVID-19 is its impact on the brain.
Over 80 percent of hospitalized COVID-19 patients have neurological symptoms, a Northwestern Medicine health system study found. Even patients who have mild cases of COVID-19 have reported memory loss, trouble focusing and other related problems that can last for months.
Now, some scientists say there is compelling evidence that the negative effects of the virus could last even longer, possibly creating a surge of cases of dementia and cognitive decline years down the road.
"It's possible — I'd even say it's probable — that having COVID-19 will increase your risk of dementia,” said Gabriel de Erausquin, M.D., a professor of neurology at the University of Texas Health Science Center at San Antonio. “We just don't have enough information yet to answer that question with certainty.”
A global study to find answers
De Erausquin and other researchers have launched a large-scale, global study to investigate the short- and long-term impact of COVID-19 on the brain, including the ways in which it may contribute to Alzheimer's disease and other dementias.
"We want to be out in front of this to minimize the impact, predict who is most at risk and try to identify behaviors or other factors which can help us reduce the impact in older patients,” de Erausquin said.
With funding from the Alzheimer's Association and technical guidance from the World Health Organization (WHO), the study will track more than 40,000 patients age 50 and older, with the first results expected in early 2022.
"The creation of an international group of scientists to further study the virus’ impact on the brain and share information is critically important,” said Sarah Lenz Lock, executive director of AARP's Global Council on Brain Health. “We also need to learn how to better avoid the risks and mitigate the harms of the virus to reduce cognitive decline and dementia in the future."
Other infections linked to dementia
Scientists have been investigating links between infection and dementia for years, said Avindra Nath, M.D., clinical director of the National Institute of Neurological Disorders and Stroke (NINDS) at the National Institutes of Health (NIH). Research shows just one episode of an infection — you get hospitalized with pneumonia, for example — can accelerate cognitive decline, especially if you're already predisposed to memory problems.
"In general, we know that as you get older and get any kind of disease, even a urinary tract infection, it can bring out an underlying dementia,” Nath said.
Respiratory viruses in particular seem to pack a powerful neurological punch.
After the severe acute respiratory syndrome (SARS) outbreak in 2002 and the Middle East respiratory syndrome (MERS) outbreak in 2012 — both syndromes are caused by coronaviruses — 1 in 5 recovered patients reported memory impairment, according to a review in The Lancet Psychiatry.
Before that, scientists studying the 1918 influenza pandemic noted an increase in cognitive decline, psychosis and Parkinson's disease in those who had survived.
The neurological effects of COVID-19 range from mild symptoms such as headache and loss of taste and smell to more severe symptoms such as dizziness, confusion, seizures and stroke.
So-called long-haulers, the survivors of coronavirus infections whose symptoms linger, complain of headaches, fatigue, loss of taste and smell, memory loss, attention difficulties and a “brain fog” that makes it difficult for them to go about their day-to-day activities. In some patients, the problems have dragged on for months.
COVID-19 and the brain
Researchers are trying to tease out exactly how the SARS-CoV-2 virus damages the brain. Is it getting into the brain and attacking it directly? Or is the damage being caused by an inflammatory or autoimmune response?
In a paper published in Alzheimer's & Dementia: The Journal of the Alzheimer's Association, de Erausquin and his coauthors highlighted recent research that suggests the virus may directly invade the brain.
The paper noted the virus has been found in postmortem brain tissue samples and said abnormal brain imaging has emerged “as a major feature of COVID-19 from all parts of the world.”
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When Nath recently used a high-resolution MRI machine to look at the brains of 19 deceased COVID-19 patients for an NIH study published Dec. 30, he saw no signs of the virus, but he did find significant blood vessel damage and inflammation.
Nath said the damage was particularly bad on the brain stem and in the olfactory bulb, which is important for the sense of smell.
"In one or two individuals, [the olfactory bulb] was so bad it was almost destroyed,” he said. “I couldn't even see the architecture of it. It makes you wonder if those areas are more involved than others, and what the consequences of that involvement might be.”
More about the study
The global study will investigate the long-term effects of COVID-19 by age, genetic traits and ethnic background. It will look at whether the virus seems to spur new disease or only accelerate disease in people who are already susceptible biologically or genetically.
Patients who experienced severe illness, as well as those who were asymptomatic, will be included, said Heather Snyder, vice president of medical and scientific relations at the Alzheimer's Association.
The study will also compare cognitive symptoms based on the type of care each patient received, Snyder said.
"We might learn that there are certain types of care that could have better outcomes not just for COVID, but for our brains,” she said.