Can immersive olfactory training serve as an alternative treatment for patients with smell dysfunction?

Abstract

Objectives: Olfactory training (OT) has emerged as a first-line therapeutic approach to the management of olfactory dysfunction. Conventional OT (COT) involves the systematic home-based exposure to four distinct odors. Previous research has demonstrated that immersive OT (IOT) involving full-body exposure to dozens of distinct odors could also improve overall olfactory function. This study compared IOT and COT in terms of efficacy.

Methods: A total of 60 patients were enrolled and assigned to three groups. The IOT group (n = 25) underwent immersive exposure to 64 odors once daily in a specialized theater. COT participants (n = 17) sniffed four typical odors in a set of four jars twice daily at home. A control group (n = 18) underwent passive observation. Olfactory function was assessed before and after training.

Results: Significant improvements in composite threshold-discrimination-identification (TDI) scores were observed after training in both the IOT (mean difference = 2.5 ± 1.1. p = .030) and COT (mean difference = 4.2 ± 1.3, p = .002) groups. No changes were observed in the control group. A significantly higher proportion of patients in the COT group (41%) presented improvements of clinical importance (TDI ≥5.5) compared to the controls (p = .018). The improvements attained in the IOT group (20%) were less pronounced (p = .38).

Conclusion: While IOT did not exhibit the same efficacy as COT in restoring olfactory function, it still demonstrated promising outcomes. Future efforts to advance olfactory recovery should focus on cross-modal integration.

Level of evidence: Level 3.

Keywords: Sniffin' Sticks; olfactory dysfunction; olfactory training.

FIGURE 1

Immersive odor‐presenting theater. (A) Electronically controlled olfactometer, Smell 2.0. (B) Spacious chamber in which the participants underwent immersive exposure to odors.

FIGURE 2

Experimental timeline of each group. OT, olfactory training.

FIGURE 3

Difference between training sessions in terms of measured olfactory function. Error bars represent standard error of the mean. * p < .05; #0.05≦p < .1. The color of asterisk and hashtag represent the corresponding group of significance. TDI, threshold‐discrimination‐identification.

FIGURE 4

Difference between training sessions in terms of self‐rating scales. Error bars represent standard error of the mean. *p < .05. The color of asterisk represents the group of significance.