Olfactory Dysfunction in Patients with Multiple Sclerosis; A Systematic Review and Meta-Analysis

Abstract

Objectives: Olfactory dysfunction is a major comorbidity observed in patients with multiple sclerosis, yet different prevalence rates are reported for it. Therefore, we have designed this systematic review to estimate the pooled prevalence of olfactory dysfunction in patients with MS. To our knowledge, this is the first systematic review and meta-analysis on the prevalence of olfactory dysfunction in MS patients. Method: We searched PubMed, Scopus, EMBASE, Web of Science, ProQuest, and gray literature including references from the identified studies, review studies, and conference abstracts which were published up to January 2021. Articles that were relevant to our topic and could provide information regarding the prevalence of olfactory dysfunction, or the scores of smell threshold, discrimination, or identification (TDI scores) among MS patients and healthy individuals were included; however, articles published before 1990 and after the end of 2020 were excluded. Results: The literature search found 1630 articles. After eliminating duplicates, 897 articles remained. two abstract conference papers were included for final analysis. A total of 1099 MS cases and 299 MS patients with olfactory dysfunction were included in the analysis. The pooled prevalence of olfactory dysfunction in the included studies was 27.2%. (95% CI: [19.7%, 35.4%]) Also, the overall TDI score in MS patients was lower than that in the control group (SMD=-1.00; 95% CI: [-1.44, -0.56]), and the level of Threshold (SMD= -0.47; 95% CI: [-0.75, -0.19]), Discrimination (SMD=-0.53; 95% CI: [-0.96, -0.10]), and Identification (SMD=-1.02; 95% CI: [-1.36, -0.68]) per se were lower in MS compared with control respectively. Conclusion: The results of this systematic review shows that the prevalence of olfactory dysfunction in MS patients is high and more attention needs to be drawn to this aspect of MS.