Why does covid cause long-term loss of smell? Scientists have a theory.
A small study published online Wednesday at Science translational medicine and led by researchers from Duke University, Harvard University, and the University of California, San Diego, offers theory and new insight into long-term smell loss.
The scientists analyzed samples of olfactory epithelial tissue – where smell cells live – from 24 biopsies, nine of which were from post-covid patients struggling with permanent loss of smell. Although the sample was small, the results suggest that the sensory deficit is linked to an ongoing immune attack on the cells responsible for smell – which persists even after the virus is gone – and a reduction in the number of olfactory nerve cells.
Bradley Goldstein, an associate professor in Duke’s Department of Head and Neck Surgery and Communication Sciences and Department of Neurobiology, author of the paper, called the results “stunning” and said in statement“It almost resembles some kind of autoimmune process in the nose.”
While there has been research looking at short-term smell loss using animal models, the new study is significant because it focuses on permanent smell loss and uses high-tech molecular analysis of human tissue.
The study reflects the ongoing interest in the mystery symptom. In July, researchers estimated that at least 5.6 percent of patients with covid-19 have chronic problems with smell. That study, published in the peer-reviewed medical journal BMJ, also suggested that women, as well as those who had more severe initial dysfunction, were less likely to recover their sense of smell. The elderly are also particularly vulnerable, writes The Post reported.
Earlier this month, Andnot a small study of patients with Covid-19 suggested long-term olfactory dysfunction may lead to changes in brain regions corresponding to smell. Study published in Februarywhich Duke’s study builds on, found that people who died of covid-19 had fewer membrane-embedded receptors to detect odors than expected.
Loss of smell can have significant implications. It’s a mechanism for detecting threats — from a gas stove you accidentally left on to the foul smell of a rotten egg. And it is a feeling closely related to memories.
Carol Yan, an otolaryngologist and head and neck surgeon at the University of California, San Diego like the author of the new study, he treated patients with permanent loss of smell. “It’s quite devastating for them. And a lot of times, at this point, it’s been more than two years since the loss of smell,” she says. “They ask themselves: ‘Why me? Why do I still have loss of smell compared to so many of my friends, colleagues, family members who have recovered?’”
Doctors struggled to explain what was causing it. “Clinically, when you look at these patients and you look at their nose, everything looks intact,” she says. “So this is happening at the molecular level.”
The study offers some hope, Yan says, because while some have suggested that the lack of smell is related to the central nervous system, this research offers evidence that at least part of the problem is caused by inflammation in the nose, where the virus originally attacked. This could mean there is potential for easier, topical treatments.
For Yan, research on the localized immune response supports others research she conducted in platelet-rich plasma as a treatment for loss of smell. “What we found in the clinical trial is that PRP is actually more likely to improve outcomes for the loss of smell associated with Covid-19 compared to placebo,” she says, cautioning that PRP, which has anti-inflammatory properties, is not a “magic bullet.” ” and needs deeper research — but it seems promising.
And the stakes are high. With smell, says Yan, comes your ability to enjoy food and the environment around you. It even affects how you relate to others. “Patients came to me and said, ‘I’m a little embarrassed to come and see you.’ I didn’t think it was a big deal. I just lost my sense of smell, but it actually significantly affected my quality of life.’”
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