Studies show that about 20% of people around the world still have trouble with their sense of smell even with treatments available. Even long after recovery from the virus, some continue to experience post-viral olfactory dysfunction (PVOD), which can make everyday tasks like enjoying meals or detecting danger such as smoke or gas leaks much more challenging. The emotional toll is also significant, with many sufferers reporting feelings of isolation, depression, and anxiety.
While treatments like smell training, vitamin A nose drops, and omega-3 supplements can help, their effectiveness varies. However, a new study offers hope*: platelet-rich plasma (PRP) injections may provide long-lasting improvements for those with persistent smell loss. Let’s explore what this research tells us and how PRP might work as a treatment.
This idea was tested in earlier studies, where PRP was shown to help some people with PVOD. But it’s still not clear if the benefits last over time. The main goal of this study is to check if PRP continues to help people with PVOD after a year. Another goal is to figure out which factors might predict if the treatment will work for someone.
What Are PRP Injections?
PRP is made from a patient’s own blood and contains concentrated growth factors that can help with healing and tissue repair. Already used successfully in treatments for joint injuries and other conditions, PRP is now being explored as a therapy for smell loss. The idea is that it may help repair the delicate olfactory nerves and tissues in the nose damaged by COVID-19 or other viruses.
The Study: PRP’s Long-Term Effects on Smell Recovery
This study was a prospective cohort study that took place from January 2021 to December 2023. A study of this kind involves researchers who follow a group of people over a period of time to observe how different factors affect their health or behaviours. It was approved by an institutional review board (#38394) to make sure everything was done safely and ethically.
Who took part in the study?
The study focused on adults (over 18 years old) who lost their sense of smell due to an upper respiratory viral illness, like COVID-19. Some of the people in the study were from an earlier trial, and others were new patients who came to the Stanford Sinus Center or the University of California in San Diego after the trial had finished. Because many patients lived far away and were hard to contact, the researchers included both groups for a more complete study.
To be included in the study, patients had to have persistent smell loss lasting between 6 and 12 months. The test used to measure smell was the University of Pennsylvania Smell Identification Test (UPSIT), and only patients who scored 30 or lower out of 40 were included. The reason the study only included patients who had smell loss for more than 6 months was to avoid confusing results from people who might naturally get their smell back after a few months. Patients could have previously used oral or topical steroids, but this was not a requirement to join the study. All patients were asked to do smell training (a special smell exercise) as part of the usual care for this condition. This is because smell training is beneficial across the board.
At the start of the study, each patient was asked to rate how well they could smell on a scale from 0 to 10, and they completed the UPSIT test. They also had a nasal endoscopy, a procedure where a camera is used to look inside the nose, to rule out any physical causes for their smell loss, such as polyps or infections. After 1 year, the UPSIT test was mailed to patients to check in with them without needing them to return to the clinic.
PRP Injections
For patients who received PRP, blood was drawn from them at each injection visit, and PRP was separated from the blood using special equipment. The PRP contains platelets, which are the parts of blood that help with healing. After processing the blood, the PRP was injected into each side of the nose (the superior septum) near the area responsible for smell. This was done in three sessions, two weeks apart.
For the non-PRP group, six patients who had been in the original trial got a “sham” treatment, where they had blood drawn but only received a saline (saltwater) injection instead of PRP. The other ten patients did not receive any injections at all but were told to do the olfactory training.
Improvement was judged in two ways. With a simple questionnaire, asking people how they felt about their sense of smell, and with the UPSIT scratch and sniff test. The minimal clinically important difference (MCID) was considered to be an improvement of at least 4 points on the UPSIT after one year, compared to their starting score.
What Did They Find?
The results were promising. This study shows that PRP injections into the olfactory cleft (the area of the nose that helps you smell) have a long-lasting benefit in improving the sense of smell for people who have persistent olfactory dysfunction (PVOD) caused by COVID-19 or other viral infections. PRP injections were the only factor that helped predict who would improve in the smell tests after one year, even when accounting for things like age, gender, and how long they had lost their sense of smell.
After one year:
- 87.5% of those who received PRP injections showed significant improvement in their UPSIT scores, compared to just 31.2% in the non-PRP group.
- On average, the PRP group’s UPSIT scores improved by 8.9 points, while the non-PRP group’s scores only improved by 1.3 points.
- Participants in the PRP group also reported much higher personal smell ratings (an average improvement of 3.6 points on the VAS scale) compared to the non-PRP group (0.6 points).
These findings suggest that PRP injections not only improve measurable smell test results but also significantly enhance how patients perceive their sense of smell in daily life.
How Does PRP Work?
The olfactory system is delicate, and damage from viral infections like COVID-19 can lead to persistent inflammation in the tissues responsible for smell. PRP is thought to work by reducing this inflammation and encouraging the repair of olfactory nerves and tissues. However, while the results are encouraging, researchers caution that PRP doesn’t work for everyone, and outcomes can vary.
What Makes This Study Stand Out?
This study is notable because it followed participants for a full year, demonstrating that the benefits of PRP injections can be long-lasting. It also used both objective (UPSIT) and subjective (VAS) measures to evaluate improvement, providing a well-rounded view of its effectiveness.
Limitations and Considerations
While the study’s findings are exciting, there are a few limitations to keep in mind:
- The study involved a small group of participants, so larger studies are needed to confirm the results.
- Not all participants responded equally to the treatment, highlighting the need for further research into why PRP works better for some people than others.
There is variation in how PRP is prepared and administered, which could influence outcomes.
Is PRP Right for You?
PRP injections into the olfactory cleft appear to offer long-term benefits for people with persistent smell loss from viral infections like COVID-19. These benefits were seen in both objective smell tests and personal ratings of smell ability. People who received PRP had significantly greater improvements than those who didn’t. The improvements seem to continue over time, suggesting that PRP injections are a promising treatment for those with persistent olfactory dysfunction.
If you’re considering PRP as a treatment for smell loss, it’s important to discuss it with a specialist who can assess whether it might be suitable for your specific situation. Smell training, a simple but evidence-based therapy, remains a key part of any recovery plan and can be combined with other treatments like PRP.
If you’d like to learn more about PRP or explore other treatments, browse the CKOS website for resources and support and sign up for our newsletter.
Key takeaways:
Background: Platelet-rich plasma (PRP) injections have been shown to help people who lose their sense of smell because of COVID-19. However, it’s not clear if the benefits last over time. This study aimed to check how well these injections work one year later.
Methods: The study followed 16 people from an earlier trial (10 got PRP and 6 got a placebo) and 16 more people from a smell clinic, all of whom had their treatment a year ago. They compared the results from two smell tests: the University of Pennsylvania Smell Identification Test (UPSIT) and a personal rating scale of how well they thought they could smell (VAS).
Results: There were no big differences between the groups in terms of age, gender, race, how long they had lost their sense of smell, smoking, diabetes, or other health conditions. However, the group who received PRP injections showed much better improvement in both smell tests a year later. For example, 87.5% of those who got PRP had a significant improvement in their UPSIT score, compared to only 31.2% in the group that didn’t get the injection. Also, the PRP group had a bigger improvement in their smell ratings (VAS).
Conclusion: PRP injections in the nose area seem helpful in providing long-term benefits for both how people rate their sense of smell and how they perform on smell tests. People who received PRP had much better results after one year compared to those who didn’t get the injections.
You can find out more about PRP injections and the procedure from the author of the research, Zara Patel, here.
*The research is behind a paywall, but members of the Network can access it for free
