Olfactory Retraining Protocol for Post-viral Anosmia: A Prospective Cohort Study

Introduction: Olfactory training (OT) is effective for olfactory dysfunction (OD), but the optimal protocol remains unclear. This study compared 4-scent and 14-scent OT protocols in patients with OD, primarily secondary to COVID-19 infection.

Methods: Patients presenting to a tertiary care rhinology clinic with anosmia or hyposmia were recruited from 2021-2024. Participants were randomized to a 4- or 14-scent kit and instructed to complete at-home OT twice daily for 6 months. Olfactory testing was performed using the Affordable Rapid Olfactory Measurement Array (AROMA) with scores ranging from 0 to 100. Participants completed the sinonasal outcomes test (SNOT-22) and Questionnaire of Olfactory Disorders (QoD-NS). Baseline, 3-month, and 6-month scores were compared between groups using Student’s t-test or Mann-Whitney U Test as appropriate.

Results: One hundred five participants completed 3-month OT; 56 completed 6-month OT. Mean AROMA score was 48.1 (SD 22.2) at baseline, 58.4 (SD 22.3) at 3 months, and 64.2 (SD 19.8) at 6 months. Individual changes in AROMA scores were comparable between the 4- and 14-scent groups at 3 months (9.3 vs. 11.2) and 6 months (13.5 vs. 14.7). However, the 14-scent group demonstrated significantly greater improvement in ginger (p < 0.001) and rosemary (p = 0.010), scents included only in the 14-scent OT kit.

The 4-scent group had higher OT compliance at 3 months (88.4% [IQR, 71.5 - 97.1] vs. 69.5% [45.1 - 90.4], p = 0.008), but rates were similar by 6 months (69.8% [44.9 - 95.6] vs. 65.2% [43.9 - 86.7]). The mean QOD-NS score decreased from 21.8 (SD 9.9) at baseline to 17.5 (SD 9.8) at 6 months and SNOT-22 decreased from 27.0 (SD 18.3) to 20.9 (SD 15.6), with no significant differences between groups.

Conclusions: OT using either 4 or 14 scents over 6 months resulted in comparable smell recovery outcomes, with the 4-scent group showing higher compliance at 3 months. These findings suggest that both protocols are effective and achieve similar long-term results, although recovery of specific scents may depend on targeted, scent-specific OT.