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Purpose To evaluate the evolution of chemosensation via extended psychophysical testing in patients who suffered from sudden chemosensory loss due to coronavirus disease 2019 (COVID-19). Additionally, this study sought to determine whether odor threshold testing provided additional information on olfactory loss due to COVID-19 compared to the more common odor identification testing. Methods Prospective cohort study of patients with sudden chemosensory loss since February 2020 and confirmed COVID-19 infection via RT-PCR or serology testing. Olfactory function was tested extensively using the “Sniffin Sticks” test battery. In addition, we screened gustatory perception and nasal cooling sensations using psychophysical tests. Results Seventy-two patients completed the study. After a mean of 37 days, 37% of patients showed olfactory dysfunction, 7% were dysgeusic, and 48% showed signs of low sensitivity for cooling sensation. A longer duration of anosmia before smell improvement was correlated with lower olfactory function at 5 weeks. Odor threshold detection was more affected by COVID-19 compared to odor identification. Conclusion Five weeks after developing sudden chemosensory loss due to COVID-19, a high proportion of patients were dysosmic and showed signs of low nasal cooling sensitivity, whereas most of them had normal taste function. SARS-CoV-2 affected mainly odor thresholds, possibly suggesting that the major cause of loss of smell lies at the level of the olfactory neuroepithelium, rather than in the central nervous system.

Introduction Olfactory dysfunction (OD) is a well know 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. Methods In the present study, we investigated the usefulness and safety of PRP injection in 56 patients with COVID-19 COD by the Sniffing Stick test (TDI score) and a linker-scale from 0 (none) to 3 (strong) and we compare the result to a control group. Results At 1 month post-PRP injection, the mean TDI scores significantly improved by 6.7 points in the PRP group ( p < 0,001), the mean self-assessment of improvement in smell function was 1.8 (mild-to-moderate) in the PRP group, which was significantly higher than the score (0.3) in the control group ( p < 0,001). Conclusion Our results showed that PRP in the olfactory cleft can increase the olfactory threshold 1 month after the injection. Moreover, our results suggest that timing of treatment may be an important factor and that PRP is a safe treatment, because no adverse effects were reported throughout the study. Trial registration number: NCT05226546.

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