Long-term Outcomes of PRP Injections for Post-viral Olfactory Loss: A Prospective Cohort Study.

Background: Platelet-rich plasma (PRP) injections have previously been shown to benefit coronavirus disease 2019 (COVID-19)-induced smell loss. It is unknown if that benefit is stable over time. The aim of this study was to assess outcomes at 1-year post-intervention.

Methods: Prospective cohort study. Sixteen patients (10 PRP and six placebo) from the original PRP randomized placebo-controlled clinical trial, and a further 16 patients from smell clinic who were a year out from initial treatment (six PRP patients and 10 non-PRP) were enrolled. University of Pennsylvania Smell Identification Tests (UPSITs) and visual analog scale (VAS) subjective scores were compared to initial scores.

Results: There was no difference between groups with respect to age, gender, race, duration of smell loss prior to intervention, smoking or diabetes status, Charlson comorbidity index, presence of phantosmia or parosmia, or baseline UPSIT score. The PRP group had a significantly higher change in UPSIT score at 1 year (p = 0.001), a higher number of patients who met the minimal clinically important difference for the UPSIT (87.5% vs. 31.2%, p = 0.004), and a significantly greater change in VAS at 1 year (p = 0.001), compared to those who did not receive injections. On multivariate logistic regression analysis, no factors appeared to have a significant effect on these findings.

Conclusion: PRP injections into the olfactory cleft now have long-term data suggesting benefit in both subjective and psychophysical measures of smell, and improvements in both realms at 1 year are significantly higher than in those who do not receive the injections.