Delaware doctor discusses link between ‘brain fog' and smell to COVID


The Alzheimer’s Association International Conference, held July 31 to Aug. 4 in San Diego, offered some new insights into COVID-19’s impact on memory and thinking skills.

The conference is the world’s largest convening of scientists, clinical researchers, clinicians and the care research community. This year, the conference, held in person and online, hosted more than 9,000 attendees representing 98 countries.

One of the new studies presented at the conference came from a group from Argentina which found that persistent loss of the sense of smell may be a better predictor of long-term cognitive and functional impairment than severity of the initial COVID-19 disease.

Dr. James Ellison, ChristianaCare’s first endowed chair of the Swank Center for Memory Care and Geriatric Consultation, said there has been a lot of data collected already on how COVID-19 affects cognitive behavior, but it’s over a relatively short period of time, so much is still being learned.

“So we’re not sure how long the cognitive effects of COVID will last for everybody,” he said after the conference. “But a number of people who’ve been infected with COVID complain of brain fog or memory difficulties, or impaired concentration or attention, as much as a couple of months or even a couple of years after the infection has passed.”

Dr. Ellison added that makes sense because the virus affects the whole body, including the central nervous system.

“It’s not just a respiratory illness,” he said. “It’s also an illness of the brain, which involves inflammation of the brain and destruction of brain cells in more severe cases.”

Research shows about a quarter of people who are positive for COVID-19 experience loss of smell. Dr. Ellison said this happens because the lining of the nasal cavity is infected with the virus.

“The smell nerve is embedded in that lining up the nasal cavity,” Dr. Ellison said. “But the smell nerve, or the olfactory nerve, which is called the first cranial nerve, is a direct route from the nasal cavity into the brain. So it’s not unknown for infections to track from the nasal cavity into the brain and that’s why the loss of smell is associated with central nervous system effects. The virus travels to the brain within the nerve cells of the olfactory nerve and that is the explanation that researchers are giving for why cognitive symptoms are even more strongly predicted by smell loss.”

Most people who experience loss of smell will regain it, Dr. Ellison said. There is nothing that can be done to expedite the process, which Dr. Ellison called “a waiting game.”

“The cognitive effects of the viral infection are going to be reversible for them in most cases, but some of them will have longstanding cognitive changes or changes that last for a month before they resolve,” Dr. Ellison said.

“So it would make sense that people who develop loss of smell are at greater risk for cognitive sequelae (traumatic brain injury). But that hasn’t been proven yet and I would focus more on the positive aspect, which is that even people who lose their sense of smell are likely to recover from the viral infection and to recover their cognitive functioning.”

For those who might be experiencing memory loss or other cognitive disorders, the Alzheimer’s Association runs a 24/7 helpline at 800-272-3900 and has more information here.

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