Change in Functional Brain Activation Patterns Induced by Olfactory Stimulation in Multiple Sclerosis

Vitamin D levels and olfactory dysfunction in multiple sclerosis patients

OBJECTIVE

The objective was to explore the possible relationship between the serum vitamin D level and olfactory impairment in a population of multiple sclerosis (MS) patients in Guizhou, China.

METHODS

We included 25 patients with MS and 18 healthy controls (HCs) who were recruited from the Affiliated Hospital of Guizhou Medical University from February 2021 to September 2021. The University of Pennsylvania Smell Identification Test (UPSIT) was used to test the patients' sense of smell, and the level of serum 25-hydroxyethylene polyprotein D was measured.

RESULTS

Serum vitamin D levels and UPSIT scores were significantly different between the MS group and the control group (both p < 0.001). Moreover, a significant positive correlation emerged between vitamin D levels and UPSIT scores in MS patients (r = 0.537, p = 0.021).

CONCLUSIONS

The serum vitamin D level may be involved in the regulation of olfactory dysfunction in MS patients in Guizhou, China.

Longitudinal Olfactory Patterns in Multiple Sclerosis: A Scoping Review and Implication for Use in Management of Disease

BACKGROUND

Although studies regarding multiple sclerosis (MS) and olfactory dysfunction (OD) have been previously described and summarized, there is not a sole review of longitudinal studies regarding the matter. This review examines the existing literature investigating MS and its effect on olfaction. In addition, the role of OD in the diagnosis and prognosis of MS is explored.

METHODS

A scoping review of the literature was performed covering longitudinal studies investigating MS and OD. Systematic searches of PubMed, Google Scholar, Web of Science, Embase, PsycInfo, Cumulative Index to Nursing and Allied Health Literature, AgeLine, and MEDLINE were performed using terms that encompassed MS and olfaction. The aim of this review was to build on the existing literature by summarizing only findings that were demonstrated longitudinally.

RESULTS

Of 6938 articles identified from the search, 9 met the inclusion criteria: longitudinal observation of relapsing-remitting or progressive MS. Olfaction was measured and scored using various testing arrays, and these scores were then correlated with a multitude of clinical markers. Across all studies, patients with MS demonstrated increased OD. Longitudinally, 2 contrasting patterns were identified: (1) clinical markers of acute inflammation correlated with an increased odor threshold and (2) clinical markers of neurodegeneration, or progression of disease, correlated with a decreased ability to discriminate and identify odors.

CONCLUSIONS

These studies suggest that olfaction is a dynamic, dependent variable of neurodegeneration, correlating with inflammation and clinical markers. This opens the door for future exploration of olfaction's relationship with MS diagnosis, characterization, and therapeutic response.

Cerebrovascular Reactivity and Neurovascular Coupling in Multiple Sclerosis-A Systematic Review

The inflammatory processes observed in the central nervous system in multiple sclerosis (MS) could damage the endothelium of the cerebral vessels and lead to a dysfunctional regulation of vessel tonus and recruitment, potentially impairing cerebrovascular reactivity (CVR) and neurovascular coupling (NVC). Impaired CVR or NVC correlates with declining brain health and potentially plays a causal role in the development of neurodegenerative disease. Therefore, we examined studies on CVR or NVC in MS patients to evaluate the evidence for impaired cerebrovascular function as a contributing disease mechanism in MS. Twenty-three studies were included (12 examined CVR and 11 examined NVC). Six studies found no difference in CVR response between MS patients and healthy controls. Five studies observed reduced CVR in patients. This discrepancy can be because CVR is mainly affected after a long disease duration and therefore is not observed in all patients. All studies used CO₂ as a vasodilating stimulus. The studies on NVC demonstrated diverse results; hence a conclusion that describes all the published observations is difficult to find. Future studies using quantitative techniques and larger study samples are needed to elucidate the discrepancies in the reported results.

Olfactory dysfunction in patients with multiple sclerosis; A systematic review and meta-analysis

Background

The importance and prevalence of olfactory dysfunction is recently gaining attention in patients with multiple sclerosis (MS) as a result of their chronic inflammatory disease, 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.

Methods

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) among MS patients and healthy individuals were included. The pooled prevalence was calculated using a random-effects model and a funnel plot and Egger’s regression test were used to see publication bias.

Results

The literature search found 1630 articles. After eliminating duplicates, 897 articles remained. Two conference abstracts 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%. Also, the overall TDI score in MS patients was lower than that in the control group, and the level of Threshold, Discrimination, and Identification per se were lower in MS compared with control respectively.

Conclusion

The results of this systematic review show that the prevalence of olfactory dysfunction in MS patients is high and more attention needs to be drawn to this aspect of MS.

International consensus statement on allergy and rhinology: Olfaction

BACKGROUND

The literature regarding clinical olfaction, olfactory loss, and olfactory dysfunction has expanded rapidly over the past two decades, with an exponential rise in the past year. There is substantial variability in the quality of this literature and a need to consolidate and critically review the evidence. It is with that aim that we have gathered experts from around the world to produce this International Consensus on Allergy and Rhinology: Olfaction (ICAR:O).

METHODS

Using previously described methodology, specific topics were developed relating to olfaction. Each topic was assigned a literature review, evidence-based review, or evidence-based review with recommendations format as dictated by available evidence and scope within the ICAR:O document. Following iterative reviews of each topic, the ICAR:O document was integrated and reviewed by all authors for final consensus.

RESULTS

The ICAR:O document reviews nearly 100 separate topics within the realm of olfaction, including diagnosis, epidemiology, disease burden, diagnosis, testing, etiology, treatment, and associated pathologies.

CONCLUSION

This critical review of the existing clinical olfaction literature provides much needed insight and clarity into the evaluation, diagnosis, and treatment of patients with olfactory dysfunction, while also clearly delineating gaps in our knowledge and evidence base that we should investigate further.

Comparative Study of Brain fMRI of Olfactory Stimulation in Neuromyelitis Optica Spectrum Disease and Multiple Sclerosis

Objective: To observe the characteristics of brain fMRI during olfactory stimulation in patients with neuromyelitis optica spectrum disease (NMOSD) and multiple sclerosis (MS), compare the differences of brain functional activation areas between patients with NMOSD and MS, and explore the characteristics of olfactory-related brain networks of NMOSD and MS.

Methods: Nineteen patients with NMOSD and 16 patients with MS who met the diagnostic criteria were recruited, and 19 healthy controls matched by sex and age were recruited. The olfactory function of all participants was assessed using the visual analog scale (VAS). Olfactory stimulation was alternately performed using a volatile body (lavender and rose solution) and the difference in brain activation was evaluated by task-taste fMRI scanning simultaneously.

Results: Activation intensity was weaker in the NMOSD group than in the healthy controls, including the left rectus, right superior temporal gyrus, and left cuneus. The activation intensity was stronger for the NMOSD than the controls in the left insula and left middle frontal gyrus (P < 0.05). Activation intensity was weaker in the MS group than the healthy controls in the bilateral hippocampus, right parahippocampal gyrus, right insula, left rectus gyrus, and right precentral gyrus, and stronger in the left paracentral lobule among the MS than the controls (P < 0.05). Compared with the MS group, activation intensity in the NMOSD group was weaker in the right superior temporal gyrus and left paracentral lobule, while it was stronger among the NMOSD group in the bilateral insula, bilateral hippocampus, bilateral parahippocampal gyrus, left inferior orbital gyrus, left superior temporal gyrus, left putamen, and left middle frontal gyrus (P < 0.05).

Conclusion: Olfactory-related brain networks are altered in both patients, and there are differences between their olfactory-related brain networks. It may provide a new reference index for the clinical differentiation and disease evaluation of NMOSD and MS. Moreover, further studies are needed.