Scientists find possible cure for COVID-related loss of smell

If a lost sense of smell following a COVID-19 infection has taken some of the color out of 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 found a potential cure for long-term COVID-19-related smell loss that involves using a blood product from the patient’s own body.

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

The study’s 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 results were published Dec. 12 in the International Forum of Allergy and Rhinology.

Dr. Zara Patel, one of the authors and a professor of ENT at Stanford Medicine, has spent years studying the loss of smell as a symptom of viral infections.

“Many viruses can cause loss of smell, so it wasn’t surprising to us as rhinologists when we discovered that COVID-19 causes loss of smell and taste,” she said in a press release published Monday. “It was almost expected.”

Patel knew that the condition could last for months, that it was related to nerve damage, and that there were few effective treatments available. She also knew that platelet-rich plasma is being promoted 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 — minus blood cells and other blood components. It is rich in platelets and growth factors, substances 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, COVID-19-related smell loss is a neurological problem in which the virus prevents nerves deep in the nasal cavity from regenerating properly, even after an infection clears. These nerves are connected to the brain and normally regenerate every three to four months.

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

Patel had already completed a small pilot study demonstrating the safety of platelet-rich plasma injections into the nasal cavity when the pandemic hit, so it made sense to redirect its plans for a larger trial to focus specifically on COVID-19-related odor loss .

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 cells. These cells play a role in proper nerve regeneration, so continued 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 her subjects’ nasal nerve damage, she could promote the regeneration of those nerves needed for smell and taste.

Patients who had experienced persistent loss of smell between six and 12 months received injections every two weeks for six weeks – either with platelet-rich plasma or sterile saline. They were then tested for three months on their ability to detect and identify a range of odors.

Three months after their first injection, 57% of the platelet-rich plasma group showed a significant improvement compared to only 8.3% in the placebo group. Everyone recruited for the study had previously tried other treatments, such as olfactory training and steroid flushing, without success.

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

A 2022 study Patel conducted with colleagues from California and the United Kingdom found that about 15% of people who experienced smell loss 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 it,” she said. “People say, ‘My life has gone gray.'”

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

“Our olfactory systems can be resilient,” she said. “But the sooner you make definitive intervention, the better the chance of improvement.”

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