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How COVID-19 affects the brain and how it could lead to dementia in older adults

When COVID-19 first began to ravage the globe last year, most of the medical focus lay on patients’ respiratory symptoms. Then, doctors began to notice peculiar patterns. Patients regularly reported impairments to their sense of smell and taste. They suffered from memory loss and confusion. In rare cases, patients showed signs of psychosis. 

It soon became evident that COVID-19 had profound, broad effects on cognitive function ranging from depression to stroke and many conditions in between, according to the Centers for Disease Control and Prevention (CDC). Alarmed researchers are now investigating whether these effects last for years into the future, leading to dementia or other cognitive dysfunctions later in life. 

In a new, global study, doctors are tracking COVID-19 patients for up to three years. “We know that some people manifest psychiatric symptoms,” says Dr. Gabriel de Erausquin, a study lead and neurology professor at the University of Texas Health Science Center at San Antonio. “The purpose of the study is to precisely measure how frequently it might happen, how severe it will be and what mechanisms that will help us prevent it.”

The new study will measure these effects into the future, determining whether COVID-19 is contributing directly to brain disorders such as Alzheimer’s, as well as muscular dysfunction such as tremors. 

Here’s what you need to know about the research, what we know so far and why it matters.

What we know so far

According to a Northwestern University study, 82% of COVID-19 patients reported neurological manifestations ranging from loss of taste to changes in brain function.

Those over age 70 are at high risk for COVID-19-related stroke, according to a Canadian study. Strokes, particularly silent strokes or transient ischemic attacks (TIAs), have been linked to dementia. COVID can also cause encephalitis (swelling of the brain) and a lack of oxygen, which can all lead to various forms of cognitive impairment

Chillingly, patients with no tell-tale respiratory COVID-19 symptoms may still develop these cognitive impairments, according to de Erausquin’s early findings. “It may just be enough to be exposed to the virus. This is a worrisome prospect, and our studies are designed to address it,” says de Erasquin, whose department has published a paper that addresses how the COVID-19 virus may directly invade the brain.

COVID-19 can cause cognitive disruption in a variety of ways. Once inside the nasal or oral cavity, the virus can travel via the bloodstream to attack the central nervous system, leading to symptoms such as dizziness, headache, acute cerebrovascular disease, ataxia and seizure, according to studies. The virus can also reach and travel around the brain via nerve cells.

A small Chinese study found that, in less severe cases, patients later suffered from attention impairments.

And in related research conducted before the pandemic, which looked at people who survived Intensive Care Unit (ICU) stays due to acute respiratory failure or shock, one-third of patients showed memory impairment, including difficulty with reading comprehension and following conversations with friends and family. Those patients also commonly suffered from depression, anxiety and PTSD. 

What the study will look like

The global study, funded by the Alzheimer’s Association and guided by the World Health Organization, will oversee 40,000 patients ages 50 and older who contract COVID-19. The study’s experts hail from more than 30 different countries. 

The study will regularly evaluate the patients based on cognition and behavior. Researchers will also measure patients’ brain volumes using magnetic resonance imaging when possible. Preliminary study results are expected in 2022. 

“At this point, because it’s so recent, we don’t know for sure whether COVID causes a permanent change, whether it will improve over time or whether it will continue to worsen,” says de Erausquin.

De Erausquin notes that the study will factor in biological susceptibility to cognitive disorders, weeding out those generated by COVID. AARP reports that the study will break down its findings based on age, genetic traits and ethnic background, and that it will include both symptomatic and asymptomatic COVID patients.

How other viruses affect the brain and what that can tell us about COVID-19

While anomalous in many ways, SARS-CoV-2, or COVID-19, is not the only virus to cause neurological effects. Researchers have found links between various infections and cognitive decline. 

  • 1918: During the influenza pandemic, researchers noticed an increase in the prevalence of Parkinson’s disease and encephalitis-related cognitive problems. 

  • 2003: An outbreak of SARS (Severe Acute Respiratory Syndrome) or SARS-CoV in China led to a wide variety of neurological impairments, including epilepsy, breakdown of muscle tissue, involuntary movements and stroke. The outbreak lasted about six months.

  • 2012: The Middle East Respiratory Syndrome was linked to brain hemorrhage, stroke and encephalitis. It also caused confusion and seizures.

  • 2020: In July, the University of Texas in Austin found that the flu vaccine reduced Alzheimer’s by 17%. Researchers theorize that proteins in the flu virus — thereby in the vaccine — trains the body’s immune response to protect them against Alzheimer’s disease. 

The bottom line 

Even after COVID-19 stops spreading, it may continue to affect those who contracted the virus. Both symptomatic and asymptomatic patients may be at higher risk for debilitating cognitive impairments years from now. Researchers on the latest study hope to find some answers before then. 

“There’s no question that there will be long-term consequences. What we need to establish with precise measures is how common and how severe these consequences will be,” says de Erausquin. “We want to be ahead of it and prevent more severe consequences in the future.”