Loss of sense of smell from COVID-19 caused by damage to brain, study finds

April 11 (UPI) -- COVID-19 causes loss of sense of smell in some of those infected by not only damaging the tissue in the nasal cavity, but also the area of the brain responsible for controlling the senses, a study published Monday by JAMA Neurology found.

Autopsies of 23 patients who died from the virus revealed that those who experienced a loss in their sense of smell had evidence of damage in the white matter of the brain, the researchers said.

The white matter region of the brain plays a key role in communication between cells in the central nervous system, including those that control the senses, according to the National Library of Medicine.

Several of the patients included in this study also had evidence of damage to the brain similar to what is seen in people with Alzheimer's disease, the autopsies revealed.

"COVID-19 not only affects smell function by infecting the cells lining the nasal cavity, but also causes significant damage on the brain region that controls smell," study co-author Dr. Cheng-Ying Ho told UPI by email.

"Since the virus does not infect the nerve cells, the tissue degeneration is either caused by inflammation or reduced blood supply due to damaged vessels," said Ho, an associate professor of pathology at Johns Hopkins University School of Medicine in Baltimore.

Research suggests nearly 2 million people in the United States have experienced long-term declines in their sense of smell due to COVID-19.

A compromised sense of smell can negatively impact quality of life by reducing appetite, among other problems, according to earlier studies.

About one in 10 people who lose their sense of smell following infection with the virus that causes COVID-19 will experience the symptom for six months or more, research indicates.

After the autopsies, the nasal tissue and brains of these patients were compared to those of 14 others who died from causes not related to the virus, they said.

Five of the 23 COVID-19 patients experienced loss of sense of smell, while four others had "diminished" sense of smell before they died, the researchers said.

Only one of these patients had nasal tissue that tested positive for the virus that causes COVID-19 at autopsy, according to the researchers, who are currently working on a study "to see if vaccination [against the virus] causes less smell loss and less olfactory tissue damage."

"I also hope this study may give new ideas about using anti-inflammatory drugs to treat COVID-related smell loss," Ho said.