<p>Change in Functional Brain Activation Patterns Induced by Olfactory Stimulation in Multiple Sclerosis</p>

Abstract

Background: Olfactory disorder is one of the commonly appearing symptoms in diseases like Parkinson's disease (PD) and Alzheimer's disease (AD). However, reports of olfactory changes in multiple sclerosis (MS) are scarce and usually ignored or seldom recognized by clinicians. The majority of current research is based on subjective answers obtained by smelling odorants. Objective: To gain better insights into the central brain regions involved in the olfactory process. We measured preliminary contrast assessment characteristics of brain activation in MS patients and healthy controls using functional magnetic resonance imaging (fMRI) under an odor stimulation task. Methods: Olfactory event-related fMRI was used to assess the olfactory network neuronal activity during passively inhaled volatile gases of lavender and rose solutions alternately in 18 MS patients and 20 healthy sex-and age-matched adults. Spearman correlation analysis was conducted between the lesions in central and olfactory-induced activated brain regions. Results: We observed significant reductions in the number of activated brain areas compared with healthy controls in MS patients under a standard activation mode; the right insula, right amygdala, right inferior frontal gyrus, right frontal middle gyrus, and left supramarginal gyrus were activated in MS patients (t = 2.04, P < 0.05). Meanwhile, the intensity of the activated olfactory brain network revealed attenuation. The Spearman correlation analysis indicated the distribution and number of demyelination lesions, exerting a little impact on major activation of brain regions during olfactory stimulation (r =-0.524, P = 0.054). Conclusion: This study establishes that olfaction-related brain regions were altered in patients with MS confirmed by fMRI. The finding refreshes the awareness that olfactory disturbance involved just in structural pathology like olfactory bulbs and tracts or olfactory sulcus, which reportedly is responsible for the deficits.

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

“…While the activation of cerebral regions in patients with MS, in regions such as the right insular, bilateral hippocampus, and right parahippocampal gyrus, was different from that in healthy adults. OuYang et al (2020) confirmed olfactory-related changes in cerebral networks of patients with MS. Using fMRI imaging, we observed changes in olfactory-related brain regions and differences in the activation of olfactory-related brain regions in NMOSD and MS patients, it suggests that the pathological changes of the two diseases may involve olfactory disorders caused by olfactory networks, but there are different olfactory-related brain networks between the two diseases.…”

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

“…In the present study, the control group represents healthy individuals without any neurologic disorders and/or diseases. The full list of the included studies is available in the reference section [ 1 , 3 , 6 – 8 , 13 , 14 , 16 – 37 ].…”

“…Olfaction is shown to be prone to impairment in three main aspects, including threshold, discrimination, and identification. Olfactory dysfunctions are reported as one the most common manifestations in the initial stages of certain CNS diseases, including Alzheimer’s disease and Parkinson’s disease [ 6 ]. Moreover, numerous studies have pointed out the presumable connection between olfactory disturbances and not only neurodegenerative diseases but also autoimmune ones, such as (MS) [ 7 ].…”

“…Such studies also lack coherence regarding the prevalence they report, with numbers ranging from 20% to 40% [ 13 ]. It is crucial to study olfactory dysfunction as it plays a major role in diminishing one’s quality of life [ 6 ], and also because there is growing evidence that the degree to which MS patients present with olfactory problems can be used as a potential prognostic factor [ 14 ]. On the other hand, the prevalence of olfactory disturbance among MS patients has been reported in various studies, among different sample sizes with different MS subtypes.…”

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

“…Such studies also lack coherence regarding the prevalence they report, with numbers ranging from 20% to 40%. (8,9) It is crucial to study olfactory dysfunction as it plays a major role in diminishing one's quality of life,(10) and also because there is growing evidence that the degree to which MS patients present with olfactory problems can be used as a potential prognostic factor. (11) On the other hand, the prevalence of olfactory disturbance among MS patients has been reported in various studies, among different sample sizes with different MS subtypes.…”