Your sense of smell is often called the mute sense because you experience memories and emotions without words. Normally the main neurological causes for a loss of smell are neurodegenerative disorders such as Alzheimer’s disease and Parkinson’s disease, however, it would now appear MS patients can also be affected.
In a review of thousands of published articles the authors of this pre-print report a 27.2% chance of smell dysfunction in MS. The figures vary from country to country (see plot below) with 0% observed in Austria and 69.6% in Italy. And not surprisingly in their sub-group analysis they found that the prevalence of smell dysfunction is more likely in EDSS >3.0 as opposed to <3.0. However, there was no association with disease duration or the year in which the study was performed.
A smell screen can be performed using a simple scratch card, and may interest some of you. It is likely the olfactory bulb, which is an extension of the brain, maybe involved in the demyelination process leading to the problem. Areas in the brain dealing with smell that are affected by MS plaques may also result in the same.
Olfactory Dysfunction in Patients with Multiple Sclerosis; A Systematic Review and Meta-Analysis
Omid Mirmosayyeb, Narges Ebrahimi, Mahdi Barzegar, Alireza Afshari-Safavi, Sara Bagherieh, Vahid Shaygannejad
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.