If a loss of ability to smell after a COVID-19 infection has sapped some of the color from your world, relief could be on the way. (Stephanie Amador, Associated Press)
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TORONTO — A team of researchers in California has found a possible cure for long-term smell loss linked to COVID-19 that uses a blood product from patients’ own bodies.
In a randomized, controlled trial of 26 patients who had lost their sense of smell following COVID-19 infection, half received nasal injections of platelet-rich plasma derived from their own blood, while the others 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 results were published Dec. 12 in the International Allergy and Rhinology Forum.
Dr. Zara Patel, one of the authors and professor of otolaryngology at Stanford Medicine, has for years studied loss of smell as a symptom of viral infections.
“Many viruses can cause loss of smell, so it was not surprising for us rhinologists to learn that COVID-19 causes loss of smell and taste,” she said. in a press release issued on Monday. “It was almost planned.”
Patel knew the illness could last for months, was linked to nerve damage, and few effective treatments were available. She also knew that platelet-rich plasma had been promoted as a treatment for other nerve conditions such as carpal tunnel syndrome.
Platelet-rich plasma is a concentrated form of plasma – the liquid part of blood – minus the 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, COVID-19-related smell loss is a neurological condition in which the virus prevents nerves deep in the nasal cavity from regenerating properly, even after an infection clears. These nerves connect to the brain and normally regenerate every three to four months.
“It’s a nerve damage and nerve regeneration problem that we’re dealing with,” Patel said.
Patel had already completed a small pilot study demonstrating the safety of injections of platelet-rich plasma into the nasal cavity when the pandemic hit, so it was natural to pivot his plans for a larger trial to focus specifically on loss of blood. smell linked to COVID-19.
According to his research, SARS-CoV-2 does not directly target nerve cells. Instead, it attacks supporting cells called sustentacular cells, which have the ACE-2 receptor that the virus uses to infect cells. These cells play a role in the proper regeneration of nerves, 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 her subjects’ nasal nerve damage, she could promote the regeneration of the nerves necessary for smell and taste.
Patients who had suffered from a persistent loss of smell for between six and 12 months received injections – either of platelet-rich plasma or sterile saline solution – 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% of the platelet-rich plasma group showed significant improvement, compared to just 8.3% in the placebo group. All of the people recruited for the study had previously tried other treatments, such as scent training and steroid flushing, without success.
Following the success of the experiment, Patel is now offering nasal injections of platelet-rich plasma to patients outside of the trial.
A survey conducted by Patel with colleagues in California and the UK in 2022 found that around 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,” said- she declared. “People say, ‘My life has turned grey.'”
Patel hopes therapies such as injecting platelet-rich plasma 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 more likely you are to improve.”