Severity of Anosmia as an Early Symptom of COVID-19 Infection May Predict Lasting Loss of Smell

Abstract

Introduction: To evaluate the recovery rate of loss of smell (LOS) with objective olfactory testing in COVID-19 patients. Methods: Adults with confirmed COVID-19 and self-reported sudden LOS were prospectively recruited through a public call from the University of Mons (Belgium). Epidemiological and clinical data were collected using online patient-reported outcome questionnaires. Patients benefited from objective olfactory evaluation (Sniffin-Sticks-test) and were invited to attend for repeated evaluation until scores returned to normal levels. Results: From March 22 to May 22, 2020, 88 patients with sudden-onset LOS completed the evaluations. LOS developed after general symptoms in 44.6% of cases. Regarding objective evaluation, 22 patients (25.0%) recovered olfaction within 14 days following the onset of LOS. The smell function recovered between the 16th and the 70th day post-LOS in 48 patients (54.5%). At the time of final assessment at 2 months, 20.5% of patients (N = 18) had not achieved normal levels of olfactory function. Higher baseline severity of olfactory loss measured using Sniffin-Sticks was strongly predictive of persistent loss (p < 0.001). Conclusion: In the first 2 months, 79.5% of patients may expect to have complete recovery of their olfactory function. The severity of olfactory loss, as detected at the first Sniffin-Sticks-test, may predict the lack of mid-term recovery.

Keywords: COVID-19; anosmia; neuroepithelia; objective test; recovery.

Figure 1

Flow Chart. 1. The included patients had mild-to-moderate COVID-19 form, defined as a disease that not required hospitalization. 2. To be included, patients had to present sudden loss of smell related to COVID-19. Patients with a history of olfactory dysfunction before the pandemic, history of nasal surgery, chronic rhinosinusitis, head and neck trauma, or degenerative neurological disease were excluded from the study. 3. Seven patients did not present to the second evaluation and were excluded. 4. The extraction of epidemiological and clinical data and the psychophysical olfactory evaluations were made at the same times (24- to 48-h maximum gap). Regarding the risk of contamination for investigators, patients were assessed when the “acute course of the disease” was resolved, corresponding to the 20 first days following the loss of smell appearance. 5. Regarding objective testing, 22 patients recovered olfaction over the 15 first days following the onset of the loss of smell.

Appendix 1

Sniffin-Sticks-test features and imaging of olfactory bulb. The first Sniffin-Sticks-tests (SST) of COVID-19 patients are represented in (A). The median value of SST was presented regarding the following patient recovery subgroups: 1 (recovery: 1–14 days), 2 (15–30 days), 3 (31–45 days), 4 (45–60 days), and 5 (no recovery). Patients of group 5 had a lower baseline SST compared with other groups (p < 0.001). The mean value of SST of patients of group 5 significantly improved throughout the first 2 months following the onset of anosmia, represented in (B). Comparison of T2/FLAIR coronal views centered on the olfactory bulbs showed normal signal in a normosmic (C) and T2/FLAIR hyperintensity of the olfactory bulbs in a patient with anosmia (D).