Could viruses cause Alzheimer's? COVID-19 brain studies offer new clues. - National Geographic

Scientists are racing to understand why some patients have persistent symptoms, especially brain fog, after a bout with COVID-19.

Long COVID sufferers describe some cognitive symptoms that neurologists say are very similar to Alzheimer’s disease.

Nearly a quarter of the more than 2,000 clinical trials for Alzheimer’s disease treatments before 2019 tested drugs thought to clear beta-amyloid from the brain.

Scientists are trying to understand why patients like Finley experience ongoing cognitive deficits after COVID-19.

Early-onset Alzheimer’s, which affects only 5 percent of patients, has a strong, well-known genetic link, but little is known about what triggers the much more common late-onset form of the disease.

Autopsy studies of patients who died from severe COVID-19 provide a spectrum of results, with some showing no evidence of the virus in the brain, some showing small quantities hiding in the brain’s blood vessels, and others showing the virus distributed throughout the brain.

One autopsy study from June 2021 took brain samples from eight patients with severe COVID-19.

It showed no signs of virus in the brain, but did find microglia, cells that act as part of the brain’s immune system, with pathological changes resembling those seen in Alzheimer’s patients.

Some of the patients died from the disease, while others lived up to seven months after acute infection.

In October 2020 neurocritical care specialist Jennifer Frontera and her team at NYU Langone Grossman School of Medicine published a study showing that 13.5 percent of patients hospitalized with COVID-19 developed a new neurologic disorder—encephalopathy (cognitive dysfunction triggered by infections and the body’s immune response), seizure, or stroke.

To better understand what was happening to COVID-19 patients specifically, Frontera teamed up with Thomas Wisniewski, head of the Alzheimer’s Disease Research Center, and analyzed blood samples that patients had provided when they were admitted to the hospital.

In a study published this month the scientists wrote that hospitalized COVID-19 patients who had cognitive symptoms but no prior history of dementia had high levels of proteins in their blood that signaled brain damage.

Some of the proteins are commonly seen when patients experience neuronal injury caused by strokes or lack of oxygen, but others, like phosphorylated tau-181 (ptau), are considered likely to be specific to Alzheimer’s disease.

The scientists say it’ll be years, if not decades, before they know if contracting COVID-19 contributes to the risk of developing Alzheimer’s disease.

Alzheimer’s develops gradually over time, whereas brain fog from COVID-19 sets in quickly.

Generally, Alzheimer’s is a disease of those over 65, while cognitive impairment after COVID-19 can occur even in children, explains Ziyad Al-Aly, director of the clinical epidemiology center at the Veterans Affairs St.

Even short-term memory issues may differ between COVID-19 and Alzheimer’s patients.

She feels like the haze has lifted, and that she has a better grasp on her day-to-day life, something that generally never happens to patients with Alzheimer’s disease.