Brain fog in COVID-19 patients can persist for months, even in those who were not hospitalized, study finds

A sign reminds festivalgoers to monitor themselves for possible coronavirus symptoms in the entrance of the Princess of Wales Theatre on day one of the 2021 Toronto International Film Festival, on Sept. 9, in Toronto

A sign reminds festivalgoers to monitor themselves for possible coronavirus symptoms in the entrance of the Princess of Wales Theatre on day one of the 2021 Toronto International Film Festival, on Sept. 9, in Toronto (Chris Pizzello, Invision, AP)

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ATLANTA — Cognitive impairment — described as brain fog — can persist for months in COVID-19 patients, even for some who were not hospitalized, according to a new study.

The research, published Friday in the journal JAMA Network Open, found that nearly a quarter of COVID-19 patients in a Mount Sinai Health System registry experienced some issues with their memory — and although hospitalized patients were more likely to have such brain fog after a coronavirus infection, some outpatients had cognitive impairment too.

"In this study, we found a relatively high frequency of cognitive impairment several months after patients contracted COVID-19. Impairments in executive functioning, processing speed, category fluency, memory encoding, and recall were predominant among hospitalized patients," Jacqueline Becker and her colleagues at the Icahn School of Medicine at Mount Sinai in New York, wrote in the study.

"This pattern is consistent with early reports describing a dysexecutive syndrome after COVID-19 and has considerable implications for occupational, psychological, and functional outcomes," the researchers wrote. Separate research, published in April in the journal Lancet Psychiatry, found that as many as one in three people with COVID-19 had longer-term mental health or neurological symptoms.

The U.S. Centers for Disease Control and Prevention includes difficulty thinking or concentrating — sometimes referred to as "brain fog" — on its list of post-COVID conditions.

"Although most people with COVID-19 get better within weeks of illness, some people experience post-COVID conditions," the CDC notes on its website. "Post-COVID conditions are a wide range of new, returning, or ongoing health problems people can experience four or more weeks after first being infected with the virus that causes COVID-19."

The new study included data, from April 2020 through May 2021, on 740 COVID-19 patients with no history of dementia. The average age of patients was 49. Cognitive functioning was assessed for each patient and the researchers analyzed the frequency of cognitive impairment among the patients.

Among all the patients, the researchers found that 15% showed deficits in phonemic fluency in their speaking; 16% in a set of mental skills called their executive functioning; 18% showed deficits in their cognitive processing speed; 20% in their ability to process categories or lists; 23% in memory recall and 24% in memory encoding, among other impairments.

The researchers noted that hospitalized patients were more likely to have impairments in attention, executive functioning, category fluency and memory.

For instance, when it came to memory recall, the researchers found 39% of hospitalized patients had impairment in that area compared with 12% of outpatients. When it came to memory encoding, the data showed that 37% of hospitalized patients had impairment compared with 16% of outpatients.

The authors noted the possibility for bias in the sample because patients came to Mount Sinai Health System because they were experiencing symptoms.

"The association of COVID-19 with executive functioning raises key questions regarding patients' long-term treatment," the researchers wrote. "Future studies are needed to identify the risk factors and mechanisms underlying cognitive dysfunction as well as options for rehabilitation."

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Jacqueline Howard


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