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Effectiveness and safety of PRP on persistent olfactory dysfunction related to COVID-19: towards a new therapeutic hope

Introduction and aim Olfactory dysfunction (OD) is a prevalent symptom of coronavirus disease 2019 (COVID-19), accounting for 48 to 85% of patients. In 1 to 10% of cases, patients develop a chronic olfactory dysfunction (COD) lasting more than 6 months. Recently, platelet-rich plasma (PRP) was used in patients with non-COVID-19 COD and authors reported encouraging results. In the present study, we investigated the usefulness and safety of PRP injection in 56 patients with COVID-19 COD. Material and methods 56 adult patients with COVID-19 COD were prospectively recruited from CHU Saint-Pierre. Participants underwent olfactory function testing by means of the Sniffin Sticks Test battery (Medisense, Groningen, Netherlands), resulting in the Threshold Discrimination Identification TDI score, at baseline and 1 month post-injection. PRP injections were performed in each olfactory cleft via nasal endoscopy and under local anesthesia by the same physician (YS), following the protocol of Yan et al. (GS30-PURE II Protocol A: Emcyte, Ft Myers, Florida).1 Olfactory outcome from patients who had PRP injection were compared to a control group made of patient with COVID-19 COD treated with nasal irrigation during a month. Results 36 patients received a PRP injection. Among those, 6 were lost to follow-up and therefore excluded. The control group, matched for age, gender and TDI score at baseline, included 26 patients. Both groups were comparable regarding demographics, duration of OD, and TDI scores. At 1-month post-PRP injection, the mean TDI score significantly improved by 6.7 points in the PRP group (p<.001), while there was no significant change in controls. There was a moderate negative correlation between TDI score difference and duration of OD in the PRP group (r=.387, p=.035) but not in controls. No adverse effects were reported throughout the study Conclusions Our results showed that PRP in the olfactory cleft can increase the olfactory threshold one month after the injection. Moreover, our results suggest that timing of treatment may be an important factor.