The Efficacy of Olfactory Training as a Treatment for Olfactory Disorders Caused by Coronavirus Disease-2019: A Systematic Review and Meta-Analysis.
Level 3 - non-randomized controlled study
Systematic review and meta-analysis of uncontrolled before-and-after studies
PubMed 36635974 · doi:10.1177/19458924221150977
What was done
Systematic review and meta-analysis searching PubMed, EMBASE, Web of Science, Cochrane database, SCOPUS, and Google Scholar up to May 2022. Studies comparing post-COVID-19 olfactory dysfunction before and after olfactory training were included. Subgroup analyses examined dysfunction duration (acute: <30 days vs chronic: >30 days) and training duration (split at 2 months).
What was found
Olfactory scores improved significantly after olfactory training (SMD = 1.0830, 95% CI [0.6416, 1.5245], P < .0001, I² = 90.4%). The olfactory dysfunction rate decreased significantly post-training (OR = 0.0232, 95% CI [0.0052, 0.1044], P < .0001, I² = 63.1%). Improvements occurred in both acute and chronic groups, but acute-phase training yielded greater score increases (SMD = 1.7779, 95% CI [1.0077, 2.5481] vs 0.6928, 95% CI [0.2143, 1.1712], P = 0.0190). Subgroup analysis using a 2-month training threshold showed no statistically significant difference.
Why it matters
This review synthesizes evidence on olfactory training for COVID-19-induced smell loss and suggests earlier initiation within 30 days provides greater olfactory score recovery.
Limits
The included studies evaluated before-and-after comparisons without parallel control or sham groups, confounding results with spontaneous recovery. Total study count and total participant sample size were not provided in the abstract. Statistical heterogeneity was high across primary outcomes (I² up to 90.4%).