Olfactory functioning in early multiple sclerosis: Sniffin' Sticks Test study

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.

Self-awareness of olfactory dysfunction in elderly individuals without neurodegenerative diseases

PURPOSE

The decrease in smell in the elderly population is frequent and considered a natural process. However, sometimes it can be associated with the decline of cognitive functions, and it is considered a warning for the early stage of neurodegenerative diseases and social impairment.

OBJECTIVE

To assess the prevalence of olfactory dysfunction in previous healthy elderly that attended a tertiary hospital in Brazil as escorts and the clinical alterations associated in this population.

METHODS

Subjects 60 years or over attending the University Hospital of Campinas were evaluated. Each participant answered a questionnaire, followed by an otorhinolaryngological exam with flexible nasal endoscopy and the Connecticut smell test produced by the Connecticut Chemosensory Clinical Research Center (CCCRC). Elderly people with nasosinusal diseases or with a history of nasal surgery were excluded.

RESULTS

Of the total of 103 participants, 16 (15.5%) reported olfactory complaints and 68 (66%) presented impairment in the olfactory test. It was observed that older individuals showed more changes in olfactory function (p = 0.001). Gender, education, lifestyle, comorbidities, medications in use and exposure to pollutants did not influence the impairment olfactory function of this population.

CONCLUSIONS

There is a significant prevalence of olfactory dysfunction in the elderly population evaluated. Most of these elderlies also present an inability to identify odours, not having awareness of this olfactory impairment.

Smell Sensitivity in Primary Open-angle Glaucoma and Pseudoexfoliation Glaucoma

PRCIS

This cross-sectional study of 20 patients with primary open-angle glaucoma (POAG), 20 with exfoliative glaucoma (XFG), 20 with exfoliation syndrome (XS) showed that exfoliative group had a significantly lower smell identification level as compared with the control groups.

PURPOSE

To investigate smell sensitivity in POAG, XFG, and XFS in comparison with healthy controls.

MATERIALS AND METHODS

This prospective, cross-sectional study included 20 patients with POAG, 20 with XFG, and 20 with XFS. The control group consisted of 20 age-matched and sex-matched healthy subjects with no evidence of ocular disease. The Sniffin' Sticks smell test was used to determine the, threshold values, and to assess the ability of smell identification, and differentiation in all patients One eye per patient was included for statistical purposes. One-way analysis of variance was used to compare the differences between the groups. Tukey honestly significant difference was used as a post hoc test when significant differences were detected among the 3 groups.

RESULTS

The XFG, POAG, and control groups showed a significant difference in the odor discrimination, odor identification, and threshold discrimination identification scores. The median (minimum-maximum) smell threshold levels for the POAG, XFG, and XFS groups and healthy controls were 4.5 (0 to 7.5), 4 (0 to 7.5), 5 (4.5 to 6), and 5.5 (4 to 7.5), respectively. The smell differentiation values for the POAG, XFG, and XFS groups and healthy controls were 12 (2 to 14), 8 (0 to 13), 11 (10 to 13), and 12 (9 to 14), respectively. Smell sensitivity for the POAG, XFG, and XFS groups and healthy controls were 26 (4 to 30.5), 19 (0 to 29.5), 28.3 (22.8 to 30.5), and 29 (26.5 to 32), respectively. The smell sensitivity and differentiation were significantly different among the groups (P<0.001). The XFG group had a significantly lower smell identification level than the POAG, XFS, and control groups.

CONCLUSION

Patients with XFS and XFG revealed reduced smell sensitivity and identification compared with patients with POAG and those without glaucoma. These findings provide new insights into neural degeneration and pseudoexfoliation.

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.

Olfactory Dysfunction in Patients With Relapsing-Remitting Multiple Sclerosis Treated With Disease-Modifying Therapies

BACKGROUND

Olfactory dysfunction evaluated with time-consuming tests was more common in patients with multiple sclerosis (MS) than in controls and correlated with neurological deficit. The aim of the present study was to compare olfactory function between patients with relapsing-remitting MS (RRMS) and controls with short and simple screening tool-the Sniffin' Sticks Identification Test (SSIT)-and search for its association with clinical and radiological features of the disease.

METHODS

The study included 30 controls and 30 patients with RRMS treated with disease-modifying therapies-injectables (interferon β or glatiramer acetate, N = 18) and oral drugs (dimethyl fumarate or fingolimod, N = 12). Hyposmia was defined as a score of 6 points or fewer in the SSIT olfactory test. The data concerning number of previous relapses, disability in Expanded Disability Status Scale (EDSS), and recent brain magnetic resonance imaging (MRI) scan were collected. Moreover, thalamic volume and third ventricle width were recorded in every patient. Additionally, cognition and fatigue in patients were evaluated 24 months after olfactory assessment with the Symbol Digit Modalities Test (SDMT) and Fatigue Scale for Motor and Cognitive Functions (FSMC), respectively.

RESULTS

Patients with RRMS had a higher risk of hyposmia than controls (66.7% vs 36.7%, OR = 1.82, 95% CI, 1.10-3.67, P = .02). Neither inflammatory (number of previous relapses or new brain MRI lesions) nor neurodegenerative (EDSS, SDMT, and FSMC scores; thalamic volume; third ventricle width) MS features did not correlate with SSIT score (P > .05). In patients treated with oral drugs, olfactory dysfunction correlated with FSMC cognitive subscale (r = -0.90, P = .006).

CONCLUSIONS

Olfactory dysfunction is nearly twice as common in RRMS as in controls and correlates with fatigue level in patients treated with dimethyl fumarate or fingolimod.

Gene Expression Profile of Olfactory Transduction Signaling in an Animal Model of Human Multiple Sclerosis

Olfactory dysfunction occurs in multiple sclerosis in humans, as well as in an animal model of experimental autoimmune encephalomyelitis (EAE). The aim of this study was to analyze differentially expressed genes (DEGs) in olfactory bulb of EAE-affected mice by next generation sequencing, with a particular focus on changes in olfaction-related signals. EAE was induced in C57BL/6 mice following immunization with myelin oligodendrocyte glycoprotein and adjuvant. Inflammatory lesions were identified in the olfactory bulbs as well as in the spinal cord of immunized mice. Analysis of DEGs in the olfactory bulb of EAE-affected mice revealed that 44 genes were upregulated (and which were primarily related to inflammatory mediators), while 519 genes were downregulated; among the latter, olfactory marker protein and stomatin-like 3, which have been linked to olfactory signal transduction, were significantly downregulated (log2 [fold change] >1 and p-value <0.05). These findings suggest that inflammation in the olfactory bulb of EAE-affected mice is associated with the downregulation of some olfactory signal transduction genes, particularly olfactory marker protein and stomatin-like 3, which may lead to olfactory dysfunction in an animal model of human multiple sclerosis.

Olfactory Dysfunction in CNS Neuroimmunological Disorders: a Review

Olfactory dysfunction is deeply associated with quality of human life in the aging population. Olfactory dysfunction is an occasional presymptomatic sign of neuroimmunological multiple sclerosis, neuromyelitis optica, and systemic lupus erythematosus. Olfaction is initially processed by olfactory receptor cells that capture odor molecules, and the signals are transmitted to the glomeruli in the olfactory bulbs via olfactory nerves and processed in the primary olfactory cortex in the brain. Damage to either the olfactory receptor cells or the olfactory bulb and primary olfactory cortex may influence olfactory functioning. A close link between neuroimmunological disorders and olfactory dysfunction has been reported in patients and animal models. This review summarizes the literature data concerning olfactory dysfunction in autoimmune diseases including multiple sclerosis, neuromyelitis optica, and systemic lupus erythematosus; animal models thereof; and inflammation in the olfactory bulb.

Olfactory Dysfunction as a Global Biomarker for Sniffing out Alzheimer's Disease: A Meta-Analysis

Cases of Alzheimer’s disease (AD) are rising exponentially due to increasing global life expectancy. There are approximately 50 million sufferers worldwide, with prevalence rising most rapidly in low-income countries such as Africa and Asia. There is currently no definite diagnosis of AD until after death, thus an early biomarker for AD is urgently required in order to administer timelier and more effective interventions. Olfactory dysfunction (problems with the sense of smell) is one of the earliest, preclinical symptoms observed in AD. Olfaction is a promising early biomarker for use worldwide as it is easy, cheap to measure, and not reliant on specialist clinicians or laboratory analysis. We carried out a meta-analysis to determine the credibility of olfaction in diagnosing AD in the preclinical stages, by comparing olfaction in healthy controls against AD patients and patients with mild cognitive impairment (MCI). Data from 10 articles were subjected to two comparative meta-analyses. In the case of AD, the results illustrated that the overall magnitude of effect size was more apparent, d = −1.63, 95% CI [−1.95, −1.31], in comparison to that of MCI, d = −0.81, 95% CI [−1.08, −0.55]. This shows that olfaction worsens progressively as patients progress from MCI to AD, highlighting the potential for olfactory dysfunction to identify AD in the preclinical stages prior to MCI.

Olfactory dysfunction in multiple sclerosis

BACKGROUND

Multiple sclerosis (MS) is a common chronic neurological disease that causes disability. MS can have various clinical manifestations, one of which is olfactory dysfunction. In clinical practice, olfactory disturbances are usually underdiagnosed. The aim of our study is to assess olfactory function and its relationship with MS disease duration, disability and cognition.

METHOD

We assessed 31 MS patients and 24 healthy controls matched in sex and age at our MS outpatient clinic of the Istanbul Education and Research Hospital Neurology Department. Each subject was interviewed to obtain demographic data. The Connecticut Chemosensory Clinical Research Center (CCCRC) olfactory test and Montreal Cognitive Assessment (MOCA) were applied to each participant.

RESULTS

The CCCRC test scores of the MS patients were lower than those in the control group (p < 0.05). Patients with a longer disease duration and more frequent attacks had lower CCCRC scores (p < 0.05). The Expanded Disability Status Scale scores had no correlation with the CCCRC test scores. The MOCA score was positively correlated with all domains of the olfactory test scores.

CONCLUSION

This study supports the presence of olfactory dysfunction in early stages of MS and the correlation of cognitive impairment with olfactory dysfunction, even in the early stages of the disease in young and less physically- disabled patients. The assessment of olfaction may be helpful as a surrogate method for tracking disease progression in patients over time.

Olfactory function in systemic lupus erythematosus and systemic sclerosis. A longitudinal study and review of the literature

BACKGROUND/PURPOSE

To evaluate olfactory function in systemic lupus erythematosus (SLE), systemic sclerosis (SSc) and healthy controls over a 2-year period, and to determine the association of olfactory dysfunction with age, disease activity, disease damage, treatment, anxiety and depression symptoms and limbic structures volumes.

METHODS

Consecutive SLE and SSc patients were enrolled in this study. Clinical, laboratory disease activity and damage were assessed according to diseases specific guidelines. Olfactory functions were evaluated using the Sniffin' Sticks test (TDI). Volumetric magnetic resonance imaging (MRI) was obtained in a 3T Phillips scanner. Amygdalae and hippocampi volumes were analyzed using FreeSurfer® software.

RESULTS

We included 143 SLE, 57 SSc and 166 healthy volunteers. Olfactory dysfunction was observed in 78 (54.5%) SLE, 35 (59.3%) SSc patients and in 24 (14.45%) controls (p<0.001) at study entry. SLE and SSc patients had significantly lower mean in all three phases (TDI) of the olfactory assessment when compared with healthy volunteers. In SLE, the presence of olfactory dysfunction was associated with older age, disease activity, higher anxiety and depression symptoms score, smaller left hippocampus volume, smaller left and right amygdalae volume and the presence of anti-ribosomal P (anti-P) antibodies. In SSc the presence of olfactory impairment was associated with older age, disease activity, smaller left and right hippocampi volumes and smaller right amygdala volume. Olfactory function was repeated after a 2-year period in 90 SLE, 35 SSc and 62 controls and was stable in all three groups.

CONCLUSION

Both SLE and SSc patients with longstanding disease had significant reduction in all stages of TDI that maintained stable over a 2-year period. Olfactory dysfunction was associated with age, inflammation and hippocampi and amygdalae volumes. In SLE, additional association with anti-P, anxiety and depression symptoms was observed.

Anosmia and Ageusia in Parkinson's Disease

Anosmia, the loss of sense of smell, is a common nonmotor feature of Parkinson's disease (PD). Ageusia, the loss of sense of taste, is additionally an underappreciated nonmotor feature of PD. The olfactory tract is involved early in PD as indicated by frequent occurrence of hyposmia or anosmia years or decades before motor symptoms and by autopsy studies showing early synuclein pathology in the olfactory tract and anterior olfactory nucleus even in the early stages of PD. Testing for olfaction consists of evaluation of olfactory thresholds, smell identification and discrimination, and olfactory memory. Testing for gustation involves evaluating thresholds and discrimination of five basic tastes (salty, sweet, bitter, sour, and umami). The presence of a specific pattern of loss in both olfaction and gustation in PD has been proposed, but this has not yet been confirmed. Within PD, olfactory loss is strongly tied with cognitive status though links to other features of PD or a particular PD phenotype is debated. Hyposmia is more often present and typically more severe in PD patients than other parkinsonian syndromes, making it a potentially useful biomarker for the disease.