Scientists have discovered a potential cure for COVID-related loss of smell

Scientists have discovered a potential cure for COVID-related loss of smell

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If the lost sense of smell following a COVID-19 infection has stripped some of the color from your world, relief may be on the way. (Stephanie Amador, Associated Press)

Estimated reading time: 4-5 minutes

TORONTO — A team of researchers in California have stumbled upon a possible cure for long-term loss of smell related to COVID-19 which uses a blood product from patients’ own bodies.

In a randomized, controlled trial of 26 patients who lost their sense of smell after a COVID-19 infection, half received nasal injections of platelet-rich plasma derived from their own blood, while the rest received a placebo.

The study authors, researchers from the University of California and Stanford University, found that those who received the treatment were 12.5 times more likely to improve than patients who received placebo injections. The the results were published Dec. 12 in the International Forum on Allergy and Rhinology.

Dr. Zara Patel, one of the authors and a professor of otolaryngology at Stanford Medicine, has studied loss of smell as a symptom of viral infections for years.

“Many viruses can cause loss of smell, so it was not surprising to us as rhinologists when we learned that COVID-19 causes loss of smell and taste,” she said in a media release released Monday. “It was almost expected.”

Patel knew that the condition could last for months, that it involved nerve damage, and that there were few effective treatments. She also knew that platelet-rich plasma was touted as a treatment for other nerve-related conditions, such as carpal tunnel syndrome.

Platelet-rich plasma is a concentrated form of plasma – the liquid part of blood – without blood cells and other blood components. It is rich in platelets and growth factors, which are compounds known to help regenerate tissue. Platelet-rich plasma injections have been tested as a treatment for mild arthritis, wrinkles and hair loss.

According to Patel’s research, the loss of smell associated with COVID-19 is a neurological problem in which the virus prevents nerves deep in the nasal cavity from regenerating properly, even after the infection has subsided. These nerves connect to the brain and usually regenerate every three to four months.

“It’s a problem of nerve damage and nerve regeneration that we’re dealing with,” Patel said.

Patel had already completed a small pilot study demonstrating the safety of injecting platelet-rich plasma into the nasal cavity when the pandemic hit, so it was natural to shift her plans for a larger trial to focus specifically on the loss of smell associated with with COVID-19.

According to her research, SARS-CoV-2 does not directly target nerve cells. Instead, it attacks supporting cells known as sustentacular cells, which have the ACE-2 receptor that the virus uses to infect the cells. These cells play a role in proper nerve regeneration, so persistent inflammation and damage to these cells can lead to long-term loss of function.

Patel’s hope was that by injecting platelet-rich plasma into the site of damage to her subjects’ nasal nerves, she could encourage the regeneration of those nerves needed for smell and taste.

The patients, who suffered from a permanent loss of smell lasting between six and 12 months, received injections – either platelet-rich plasma or sterile saline – every two weeks for six weeks. They were then tested on their ability to detect and identify a range of odors for three months afterwards.

Three months after their first injection, 57 percent of the platelet-rich plasma group showed significant improvement, compared to just 8.3 percent of the placebo group. All of those in the study had previously tried other treatments — such as olfactory training and steroid rinses — without success.

Following the success of the experiment, Patel is now offering nasal platelet-rich plasma injections to patients outside the trial.

A study conducted by Patel with colleagues in California and the United Kingdom in 2022 found that about 15 percent of people who experienced loss of smell from COVID-19 — or nine million Americans — continued to have problems for at least six months.

“People tell me all the time that they never realized how important their sense of smell and taste was to them and their quality of life until they lost them,” she said. “People say, ‘My life has turned gray.’

Patel hopes that therapies such as platelet-rich plasma injections will help more of these people regain their sense of smell.

“Our olfactory systems can be resilient,” she said. “But the sooner you do some sort of definitive intervention, probably the better chance you have of getting better.”

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