Why do some people lose their sense of smell for a long time after being diagnosed with leukemia? New discoveries may help the nose regain its new life

For some people recovering from COVID-19, loss of smell and taste is often one of the most frustrating complications.

Not only will they miss out on a lot of delicious food, but their normal life will also be affected, and they may even develop problems such as depression, anxiety, loneliness and interpersonal relationship difficulties.

According to relevant statistics, 95% of olfactory disorders caused by COVID-19 infection will recover naturally within 2 weeks, with an average recovery time of 9 days. 5% of patients cannot recover within 2 weeks, which may be related to older age, diabetes, more severe condition, and longer course of disease.

However, some patients do not fully regain their sense of smell even after other symptoms disappear.

Why is this?

A study of biopsies from people infected with the new coronavirus suggests that the loss of smell in infected people may be related to the disruption of immune cells in the smell-sensing tissue in the nose . The findings may help to clarify the mechanisms that lead to long-term smell loss.

The related research paper, titled "Persistent post-COVID-19 smell loss is associated with immune cell infiltration and altered gene expression in olfactory epithelium", has been published in the scientific journal Science Translational Medicine.

Although this long-term loss of smell can last for months after recovery, why it happens in some patients and not others is unclear.

To explore this question, a research team from Duke University School of Medicine and its collaborators analyzed olfactory epithelial cell biopsies from 24 people, including 9 patients who had long-term loss of smell after being infected with the new coronavirus.

The analysis revealed that biopsies from patients affected by anosmia had fewer olfactory neurons and displayed distinct changes in local immune cell populations.

For example, these samples showed abnormally low numbers of M2 macrophages, abnormally high numbers of CD207+ dendritic cells, and evidence of T-cell infiltration.

Although no SARS-CoV-2 RNA was detected, T cells expressed inflammatory molecules and were present, suggesting that these tissue samples were affected by an ongoing inflammatory response.

The research team called for larger studies to clarify how and why immune cell transfer leads to loss of smell in COVID-19 patients.

Furthermore, they speculate that this finding may provide suggestions for therapeutic strategies to reverse smell loss, such as selective blockade of local proinflammatory immune cells or direct inhibition of specific signaling nodes may interfere with circuits that disrupt olfactory epithelial homeostasis or repair, and point out that olfactory epithelial cells are easily accessible by local drug delivery.

However, this study also has some limitations. For example, the experimental samples of this study only came from 24 people , and no batch effect or gene expression changes related to biopsy technology were found. The specific content of each olfactory epithelium biopsy is also inevitably different between samples.

Recently, according to a new study from the University of East Anglia, loss of smell is one of the most common symptoms of COVID-19. Nearly a third of COVID-19 patients suffer from persistent loss of smell , and nearly a fifth of COVID-19 patients also lose their sense of taste.

Lead researcher Professor Carl Philpott, from the University of East Anglia's Norwich Medical School, said: "Long Covid is a complex illness that develops during or after infection with the coronavirus and is defined as long Covid when symptoms persist for more than 12 weeks."

In addition, research teams from Columbia University and the University of Pennsylvania found that the loss of taste or smell after infection with the new coronavirus may be related to the strength of the infected person's immune response.

The official WeChat account of the PLA General Hospital also published an article stating that there are four possible mechanisms for the novel coronavirus to cause olfactory impairment:

(1) Acute infection causes swelling of the nasal mucosa, which prevents odor molecules from binding to olfactory receptors;

(2) Viral infection leads to a decrease in the number of olfactory receptors and olfactory tracts, and a loss of olfactory receptor cilia;

(3) The olfactory epithelium is replaced by the respiratory epithelium or becomes heavily scarred;

(4) The neurotropic properties of the virus cause it to invade the olfactory center along the olfactory pathway.

So, what should we do if our sense of smell does not recover?

Experts suggest that patients can "exercise" their sense of smell by smelling strong odors more often. A study of 140 patients with anosmia found that smelling at least four odors (including lemon, rose and eucalyptus) twice a day for two months significantly improved the subjects' sense of smell. Of course, common strong-smelling spices can also be tried.

In addition to the above-mentioned olfactory training, patients should also maintain a healthy lifestyle and eating habits ; oral vitamin A and vitamin B1 also have a certain auxiliary effect on the recovery of olfactory disorders; in addition, you can also try to add herbs and spices to daily food, such as chili peppers, lemon juice, etc., but for patients with diarrhea or gastrointestinal dysfunction, it is recommended to use it with caution.

If the above methods are ineffective and the problem of loss of smell does not improve over the long term, it is recommended to see an ENT department to rule out other causes.

Reference Links:

https://www.science.org/doi/10.1126/scitranslmed.add0484https://onlinelibrary.wiley.com/doi/10.1002/alr.23103

https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0274611

https://cen.acs.org/articles/100/i34/COVID-19-stole-sense-smell.html