Efficacy of olfactory training in patients with olfactory loss: a systematic review and meta-analysis

Abstract

Objective

Olfactory loss is a challenging clinical problem with few proven therapeutic options. Early experimental results with olfactory training (OT) suggest that this novel therapy may be an effective intervention for olfactory dysfunction of multiple etiologies. The aim of this study was to systematically review currently available studies that assess the efficacy and outcomes of OT in patients with olfactory loss.

Methods

A comprehensive systematic literature review was performed with the assistance of a reference librarian using the Medline, PsycInfo, Google Scholar, EMBASE, and Proquest databases. Eligible studies were extracted based on defined inclusion criteria and the effect of OT on objective olfactory function was evaluated qualitatively and by meta-analysis.

Results

A total of ten studies with 639 patients were identified and systematically reviewed. Sufficient data for meta-analysis was available for 3 studies. Patients receiving OT experienced a statistically significant improvement in the TDI (Threshold, Discrimination, Identification) score compared to control patients (mean difference [MD] 3.77; 95% CI 2.28–5.26). Improvement in olfactory function was observed in discrimination ([MD] 1.92; 95% CI 1.13–2.71) and identification ([MD] 1.61; 95% CI 0.55–2.68), but not in olfactory thresholds ([MD] −0.01; 95% CI −0.42–0.39).

Conclusion

Olfactory training is a promising modality for the treatment of olfactory dysfunction. Results of this systematic review and meta-analysis suggest that it may be an effective treatment for olfactory dysfunction due to multiple etiologies. Additional high quality studies are needed to define indications, outcomes, and duration of therapy for this novel therapy.