Recovery of olfactory function induces neuroplasticity effects in patients with smell loss

Exploring the Relationship Between Obstructive Sleep Apnea and Olfactory Function

Obstructive sleep apnea (OSA) is increasingly recognized as a chronic condition that is closely interrelated to olfactory disorders, with a significant contribution to quality of health and overall quality of life. This narrative review aims to provide a thorough overview of the emerging evidence that now integrates these two previously considered distinct physiologic systems. Studies published recently have reported a significantly higher frequency of olfactory dysfunction among OSA patients compared to the general population, which raises the possibility of a causal relationship. We explore the postulated mechanisms behind this association, namely, the chronic intermittent hypoxia, local inflammatory effect, and neuroanatomical changes attributed to OSA. The review further explores the clinical impacts of this relationship through proposing the potential for an olfactory assessment to be used as a diagnostic modality for OSA and the effects of OSA treatment on olfactory function. Thus, we explore the difficulties in treating patients who experience both and suggest future areas for research. This review attempts to bridge the gap between the existing literature and impending investigation necessary for a better management of the interaction of sleep apnea and the human sense of smell.

Age-related differences in olfactory training outcomes: A prospective cohort study

INTRODUCTION

While olfactory function decreases with age, it is unknown how age affects olfactory training (OT) efficacy. This study compared OT in two cohorts of subjects: aged ≤50 (younger cohort) and aged 51+ (older cohort) with olfactory dysfunction (OD) primarily from COVID-19 infection.

METHODS

Subjects with OD primarily secondary to COVID-19 infection were prospectively recruited and enrolled into an OT registry. Baseline data were collected and they were provided with a training kit and asked to complete OT at home twice daily for 6 months. Participants were asked to follow-up at 3 and 6 months during training for olfactory testing and quality-of-life surveys (Sino-Nasal Outcomes Test-22 [SNOT-22] and Questionnaire of Olfactory Disorders Negative Statements [QoD-NS]).

RESULTS

Fifty-six participants completed OT (younger cohort: n = 26, older cohort: n = 30). There were no significant differences between cohorts' Affordable Rapid Olfactory Measurement Array (AROMA), QoD-NS, or SNOT-22 scores at any time point. Both cohorts showed significant AROMA score improvement of more than 16 points from baseline to 3 months (younger cohort: p = 0.001; older cohort: p = 0.008). The younger cohort had significant improvements in QoD-NS (p = 0.008) and SNOT-22 (p = 0.042) between baseline and 3 months while the older cohort improved from 3 to 6 months (QoD-NS: p = 0.027, SNOT-22: p = 0.049).

CONCLUSION

Both cohorts demonstrated similar significant improvement in olfactory function after 3 months of OT. The timeline of subjective improvement was different between cohorts, with younger patients experiencing earlier improvement.

Olfactory training affects the correlation between brain structure and functional connectivity

PURPOSE

and background: Neuroimaging studies have increasingly found functional connectivity (FC) changes and structural cortical abnormalities in patients with post-traumatic anosmia (PTA). Training and repeated exposure to odorants lead to enhanced olfactory capability. This study is conducted to investigate the correlations between FC and cortical thickness on the olfaction-related regions of the brain in PTA after olfactory training (OT).

METHODS

Twenty-five PTA patients were randomly divided in three groups: (1) 9 control patients who did not receive any training, (2) 9 patients underwent classical OT by 4 fixed odors, and (3) 7 patients underwent modified OT coming across 4 sets of 4 different odors sequentially. Before and after the training period, all patients performed olfactory function tests, and magnetic resonance imaging (MRI). Sniffin' Sticks test was used to assess olfactory function. MRI data were analyzed using functional connectivity analysis and brain morphometry.

RESULTS

Modified OT resulted in heightened activation in the medial orbitofrontal cortex and anterior cingulate cortex and increased FC between the piriform cortex (PIRC) and the caudate cortex. Conversely, classical OT induced increased activation in the insula cortex and greater FC between the PIRC and the pre-central gyrus. Furthermore, after OT, both training groups achieved significantly improved scores in the changes in brain connectivity associated with OT, which were attributable to anatomical measures.

CONCLUSIONS

This study demonstrates that intensive olfactory training can enhance functional connectivity, and this improvement correlates with structural changes in the brain's olfactory processing areas.

Treatment of COVID-19 Associated Olfactory Dysfunction: A Systematic Review

PURPOSE OF REVIEW

COVID -19 associated olfactory dysfunction is widespread, yet effective treatment strategies remain unclear. This article aims to provide a comprehensive systematic review of therapeutic approaches and offers evidence-based recommendations for their clinical application.

RECENT FINDINGS

A living Cochrane review, with rigorous inclusion criteria, has so far included 2 studies with a low certainty of evidence. In this systematic review we list clinical data of 36 randomised controlled trials (RCTs) and non-randomised studies published between Jan 1, 2020 and Nov 19, 2023 regarding treatment options for COVID-19 associated olfactory dysfunction. Nine treatment groups were analysed, including olfactory training, local and systemic corticosteroids, platelet-rich plasma (PRP), calcium chelators, vitamin supplements including palmitoylethanolamide with luteolin, insulin, gabapentin and cerebrolysin. Primary objective was the effect of the studied treatments on the delta olfactory function score (OFS) for objective/psychophysical testing. Treatments such as PRP and calcium chelators demonstrated significant improvements on OFS, whereas olfactory training and corticosteroids did not show notable efficacy for COVID-19 associated olfactory dysfunction.

The efficacy of olfactory training in improving olfactory function: a meta-analysis

PURPOSE

Study the efficacy of olfactory training in smell recovery.

METHODS

An extensive search was performed through different databases in order to find articles analyzing the efficacy of olfactory training as a treatment for olfactory dysfunction. Methodological quality of primary studies within the final sample was assessed following PRISMA guidelines. Standardized mean differences in pre-post olfactory training groups, and also in experimental-control and pre-follow up if possible, were computed by Hedges' g effect size statistic. Each effect size was weighted by its inverse variance.

RESULTS

Final sample was composed of 36 articles (45 pre-post effect sizes). Contrasts were performed separately for odor identification, odor discrimination, odor threshold and general olfactory function. Moderate to large and heterogeneous effect was obtained for olfactory function (g = 0.755, k = 45, SE = 0.093, CI 95% = [0.572, 0.937]), different moderators had a significant effects, such as, training duration, age and anosmia diagnosis.

CONCLUSION

Olfactory training was found to have a positive and significant effect on rehabilitating the olfactory function.

Maximizing Participation in Olfactory Training in a Sample with Post-COVID-19 Olfactory Loss

PURPOSE

This study aims to highlight the feasibility of an olfactory training program entirely monitored through online media in COVID-19 patients.

METHODS

Classic olfactory training was performed with a sample with olfactory loss due COVID-19 (n = 11). Participants were engaged on a weekly video call in order to improve adherence and collect information regarding the number of correct answers and the individuals' perception of olfactory function. The olfactory status after training was compared to two groups, one composed of participants who contracted COVID-19 but did not report olfactory loss (n = 11) and a sample composed of healthy participants (n = 11).

RESULTS

The experimental group showed improvements throughout the training period (TDI score on week 0 was 20.3 (5.6) and 24.6 (4.3) for week 12, and on week 24 was 25.4 (6.2) (F = 5.115, df = 2, 20, p = 0.016), and post hoc tests showed that participants significantly improved their TDI score in W12 compared to W0 (SMD = 0.869, p = 0.041) and in W24 compared to W0 (SMD = 0.859, p = 0.041). The experimental group showed lower scores when compared with both groups, and the no OT COVID-19 group showed lower scores than the healthy control group, even though they did not report olfactory alterations.

CONCLUSIONS

Findings suggest that the strategies applied to improve adherence were successful since 100% of the sample completed the training adherence, offering a valuable framework for future olfactory training studies.

Intelligent wearable olfactory interface for latency-free mixed reality and fast olfactory enhancement

Olfaction feedback systems could be utilized to stimulate human emotion, increase alertness, provide clinical therapy, and establish immersive virtual environments. Currently, the reported olfaction feedback technologies still face a host of formidable challenges, including human perceivable delay in odor manipulation, unwieldy dimensions, and limited number of odor supplies. Herein, we report a general strategy to solve these problems, which associates with a wearable, high-performance olfactory interface based on miniaturized odor generators (OGs) with advanced artificial intelligence (AI) algorithms. The OGs serve as the core technology of the intelligent olfactory interface, which exhibit milestone advances in millisecond-level response time, milliwatt-scale power consumption, and the miniaturized size. Empowered by robust AI algorithms, the olfactory interface shows its great potentials in latency-free mixed reality (MR) and fast olfaction enhancement, thereby establishing a bridge between electronics and users for broad applications ranging from entertainment, to education, to medical treatment, and to human machine interfaces.

Long-term olfactory enrichment promotes non-olfactory cognition, noradrenergic plasticity and remodeling of brain functional connectivity in older mice

Brain functional and structural changes lead to cognitive decline during aging, but a high level of cognitive stimulation during life can improve cognitive performances in the older adults, forming the cognitive reserve. Noradrenaline has been proposed as a molecular link between environmental stimulation and constitution of the cognitive reserve. Taking advantage of the ability of olfactory stimulation to activate noradrenergic neurons of the locus coeruleus, we used repeated olfactory enrichment sessions over the mouse lifespan to enable the cognitive reserve buildup. Mice submitted to olfactory enrichment, whether started in early or late adulthood, displayed improved olfactory discrimination at late ages and interestingly, improved spatial memory and cognitive flexibility. Moreover, olfactory and non-olfactory cognitive performances correlated with increased noradrenergic innervation in the olfactory bulb and dorsal hippocampus. Finally, c-Fos mapping and connectivity analysis revealed task-specific remodeling of functional neural networks in enriched older mice. Long-term olfactory enrichment thus triggers structural noradrenergic plasticity and network remodeling associated with better cognitive aging and thereby forms a promising mouse model of the cognitive reserve buildup.

Does Olfactory Training Improve Brain Function and Cognition? A Systematic Review

Olfactory training (OT), or smell training,consists of repeated exposure to odorants over time with the intended neuroplastic effect of improving or remediating olfactory functioning. Declines in olfaction parallel declines in cognition in various pathological conditions and aging. Research suggests a dynamic neural connection exists between olfaction and cognition. Thus, if OT can improve olfaction, could OT also improve cognition and support brain function? To answer this question, we conducted a systematic review of the literature to determine whether there is evidence that OT translates to improved cognition or altered brain morphology and connectivity that supports cognition. Across three databases (MEDLINE, Scopus, & Embase), 18 articles were identified in this systematic review. Overall, the reviewed studies provided emerging evidence that OT is associated with improved global cognition, and in particular, verbal fluency and verbal learning/memory. OT is also associated with increases in the volume/size of olfactory-related brain regions, including the olfactory bulb and hippocampus, and altered functional connectivity. Interestingly, these positive effects were not limited to patients with smell loss (i.e., hyposmia & anosmia) but normosmic (i.e., normal ability to smell) participants benefitted as well. Implications for practice and research are provided.

Determination of Aflatoxin B1 in Grains by Aptamer Affinity Column Enrichment and Purification Coupled with High Performance Liquid Chromatography Detection

Aflatoxin B1 (AFB1) is a highly teratogenic and carcinogenic secondary metabolite produced by Aspergillus. It is commonly detected in agricultural products such as cereals, peanuts, corn, and feed. Grains have a complex composition. These complex components severely interfere with the effective extraction and separation of AFB1, and also cause problems such as matrix interference and instrument damage, thus posing a great challenge in the accurate analysis of AFB1. In this study, an aptamer affinity column for AFB1 analysis (AFB1-AAC) was prepared for the enrichment and purification of AFB1 from grain samples. AFB1-AAC with an AFB1-specific aptamer as the recognition element exhibited high affinity and specificity for AFB1. Grain samples were enriched and purified by AFB1-AAC, and subsequently analyzed by high performance liquid chromatography with post-column photochemical derivatization-fluorescence detection (HPLC-PCD-FLD). The average recoveries of AFB1 ranged from 88.7% to 99.1%, with relative standard deviations (RSDs) of 1.4-5.6% (n = 3) at the spiked levels of 5.0-20.0 μg kg-1. The limit of detection (LOD) for AFB1 (0.02 μg kg-1) was much below the maximum residue limits (MRLs) for AFB1. This novel method can be applied to the determination of AFB1 residues in peanut, corn, and rice.

The brain functional connectivity alterations in traumatic patients with olfactory disorder after low-level laser therapy demonstrated by fMRI

BACKGROUND

Low-level laser therapy (LLLT) has been clinically accepted to accelerate the nerve regeneration process after a nerve injury or transection. We aimed to investigate the neuronal basis and the influence of LLLT on brain functional networks in traumatic patients with olfactory dysfunction.

METHODS

Twenty-four Patients with traumatic anosmia/hyposmia were exposed to pleasant olfactory stimuli during a block-designed fMRI session. After a 10-week period, patients as control group and patients who had completed the sessions of LLLT were invited for follow-up testing using the same fMRI protocol. Two-sample t-tests were conducted to explore group differences in activation responding to odorants (p-FDR-corrected <0.05). Differences of functional connectivity were compared between the two groups and the topological features of the olfactory network were calculated. Correlation analysis was performed between graph parameters and TDI score.

RESULTS

Compared to controls, laser-treated patients showed increased activation in the cingulate, rectus gyrus, and some parts of the frontal gyrus. Shorter pathlength (p = 0.047) and increased local efficiency (p = 0.043) within the olfactory network, as well as decreased inter-network connectivity within the whole brain were observed in patients after laser surgery. Moreover, higher clustering and local efficiency were related to higher TDI score, as manifested in increased sensitivity to identify odors.

CONCLUSIONS

The results support that low-level laser induces neural reorganization process and make new connections in the olfactory structures. Furthermore, the connectivity parameters may serve as potential biomarkers for traumatic anosmia or hyposmia by revealing the underlying neural mechanisms of LLLT.

The Olfactory System: Basic Anatomy and Physiology for General Otorhinolaryngologists

Olfaction is one of the five basic human senses, and it is known to be one of the most primitive senses. The sense of olfaction may have been critical for human survival in prehistoric society, and although many believe its importance has diminished over time, it continues to have an impact on human interaction, bonding, and propagation of the species. Even if we are unaware of it, the sense of smell greatly affects our lives and is closely related to overall quality of life and health. Nonetheless, olfaction has been neglected from a scientific perspective compared to other senses. However, olfaction has recently received substantial attention since the loss of smell and taste has been noted as a key symptom of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Studies investigating olfaction loss in association with coronavirus disease 2019 (COVID-19) have revealed that olfactory dysfunction can be both conductive and sensorineural, possibly causing structural changes in the brain. Olfactory training is an effective treatment for olfactory dysfunction, suggesting the reorganization of neural associations. A reduced ability to smell may also alert suspicion for neurodegenerative or psychiatric disorders. Here, we summarize the basic knowledge that we, as otorhinolaryngologists, should have about the sense of smell and the peripheral and central olfactory pathways for managing and helping patients with olfactory dysfunction.

Overnight olfactory enrichment using an odorant diffuser improves memory and modifies the uncinate fasciculus in older adults

OBJECTIVE

Cognitive loss in older adults is a growing issue in our society, and there is a need to develop inexpensive, simple, effective in-home treatments. This study was conducted to explore the use of olfactory enrichment at night to improve cognitive ability in healthy older adults.

METHODS

Male and female older adults (N = 43), age 60-85, were enrolled in the study and randomly assigned to an Olfactory Enriched or Control group. Individuals in the enriched group were exposed to 7 different odorants a week, one per night, for 2 h, using an odorant diffuser. Individuals in the control group had the same experience with de minimis amounts of odorant. Neuropsychological assessments and fMRI scans were administered at the beginning of the study and after 6 months.

RESULTS

A statistically significant 226% improvement was observed in the enriched group compared to the control group on the Rey Auditory Verbal Learning Test and improved functioning was observed in the left uncinate fasciculus, as assessed by mean diffusivity.

CONCLUSION

Minimal olfactory enrichment administered at night produces improvements in both cognitive and neural functioning. Thus, olfactory enrichment may provide an effective and low-effort pathway to improved brain health.

A Pilot Study of Short-Course Oral Vitamin A and Aerosolised Diffuser Olfactory Training for the Treatment of Smell Loss in Long COVID

Background: Olfactory dysfunction (OD) is a common neurosensory manifestation in long COVID. An effective and safe treatment against COVID-19-related OD is needed. Methods: This pilot trial recruited long COVID patients with persistent OD. Participants were randomly assigned to receive short-course (14 days) oral vitamin A (VitA; 25,000 IU per day) and aerosolised diffuser olfactory training (OT) thrice daily (combination), OT alone (standard care), or observation (control) for 4 weeks. The primary outcome was differences in olfactory function by butanol threshold tests (BTT) between baseline and end-of-treatment. Secondary outcomes included smell identification tests (SIT), structural MRI brain, and serial seed-based functional connectivity (FC) analyses in the olfactory cortical network by resting-state functional MRI (rs-fMRI). Results: A total of 24 participants were randomly assigned to receive either combination treatment (n = 10), standard care (n = 9), or control (n = 5). Median OD duration was 157 days (IQR 127-175). Mean baseline BTT score was 2.3 (SD 1.1). At end-of-treatment, mean BTT scores were significantly higher for the combination group than control (p < 0.001, MD = 4.4, 95% CI 1.7 to 7.2) and standard care (p = 0.009) groups. Interval SIT scores increased significantly (p = 0.009) in the combination group. rs-fMRI showed significantly higher FC in the combination group when compared to other groups. At end-of-treatment, positive correlations were found in the increased FC at left inferior frontal gyrus and clinically significant improvements in measured BTT (r = 0.858, p < 0.001) and SIT (r = 0.548, p = 0.042) scores for the combination group. Conclusions: Short-course oral VitA and aerosolised diffuser OT was effective as a combination treatment for persistent OD in long COVID.

Aberrant olfactory network functional connectivity in people with olfactory dysfunction following COVID-19 infection: an exploratory, observational study

BACKGROUND

Olfactory impairments and anosmia from COVID-19 infection typically resolve within 2-4 weeks, although in some cases, symptoms persist longer. COVID-19-related anosmia is associated with olfactory bulb atrophy, however, the impact on cortical structures is relatively unknown, particularly in those with long-term symptoms.

METHODS

In this exploratory, observational study, we studied individuals who experienced COVID-19-related anosmia, with or without recovered sense of smell, and compared against individuals with no prior COVID-19 infection (confirmed by antibody testing, all vaccine naïve). MRI Imaging was carried out between the 15th July and 17th November 2020 at the Queen Square House Clinical Scanning Facility, UCL, United Kingdom. Using functional magnetic resonance imaging (fMRI) and structural imaging, we assessed differences in functional connectivity (FC) between olfactory regions, whole brain grey matter (GM) cerebral blood flow (CBF) and GM density.

FINDINGS

Individuals with anosmia showed increased FC between the left orbitofrontal cortex (OFC), visual association cortex and cerebellum and FC reductions between the right OFC and dorsal anterior cingulate cortex compared to those with no prior COVID-19 infection (p < 0.05, from whole brain statistical parametric map analysis). Individuals with anosmia also showed greater CBF in the left insula, hippocampus and ventral posterior cingulate when compared to those with resolved anosmia (p < 0.05, from whole brain statistical parametric map analysis).

INTERPRETATION

This work describes, for the first time to our knowledge, functional differences within olfactory areas and regions involved in sensory processing and cognitive functioning. This work identifies key areas for further research and potential target sites for therapeutic strategies.

FUNDING

This study was funded by the National Institute for Health and Care Research and supported by the Queen Square Scanner business case.

Association between cognition and olfaction-specific parameters in patients with chronic rhinosinusitis

BACKGROUND

Patients with chronic rhinosinusitis (CRS) have reported significantly cognitive and olfactory dysfunction. This study aimed to explore the relationship between cognitive function and olfaction-specific parameters in patients with CRS.

METHODS

A cross-sectional survey method was used to investigate 98 participants, including 75 patients with CRS and 23 healthy controls. Cognitive function and psychophysical olfactory tests were performed. Olfactory cleft endoscopy scale and olfactory cleft computed tomography (CT) scores were obtained. Multivariate logistic regression was used to analyze the risk factors of Mild Cognitive Impairment (MCI) in patients with CRS.

RESULTS

There are significant differences in age, Montreal Cognitive Assessment (MoCA) scores, number of MCI, Lund-Mackay olfactory cleft (LM-OC) score, and blood eosinophil count between CRS with and without olfactory dysfunction groups (all P < 0.05). Total MoCA scores were positively correlated with thresholds-discrimination-identification (TDI) score (r = 0.541, P < 0.001), olfactory threshold (OT) (r = 0.440, P < 0.001), olfactory discrimination (OD) (r = 0.541, P < 0.001), and olfactory identification (OI) (r = 0.382, P = 0.001) scores. Furthermore, total MoCA scores were negatively correlated with LM-OC scores (r =  - 0.351, P = 0.002). After adjusting for patient demographics, only the OD score was an independent risk factor for MCI among patients with CRS (odds ratio = 0.792; P = 0.039). The OD scores less than 11.5 were the best predictor of MCI in patients with CRS.

CONCLUSION

Olfaction-specific clinical parameters were highly correlated with cognitive function in patients with CRS and the OD score was an independent risk factor for MCI in patients with CRS.

Practical Review of Olfactory Training and COVID-19

Olfactory disorders one of the most frequent distinctive symptoms of COVID-19 infection. COVID-19-induced olfactory disorder can be classified as post-infectious olfactory dysfunction (PIOD). The effect of drugs on olfactory disorder following upper respiratory infection, including PIOD, has not been clearly established, which adds to the difficulty with treating the disorder. However, the effect of olfactory training on PIOD has been confirmed by numerous studies. As such, olfactory training is gaining attention, and has taken on greater importance, as the sole treatment for COVID-19-induced olfactory disorder in this pandemic age. This review describes the effect of olfactory training for COVID-19-induced olfactory disorder by analyzing the relevant literature.

Two-Year Follow-Up on Chemosensory Dysfunction and Adaptive Immune Response after Infection with SARS-CoV-2 in a Cohort of 44 Healthcare Workers

Persistent chemosensory dysfunction (PCD) is a common symptom of long-COVID. Chemosensory dysfunction (CD) as well as SARS-CoV-2-specific antibody levels and CD8+ T-cell immunity were investigated in a cohort of 44 healthcare workers up to a median of 721 days after a positive PCR test. CD was assessed using questionnaires and psychophysical screening tests. After 721 days, 11 of 44 (25%) participants reported PCD, with five describing an impaired quality of life. One participant reported hyperosmia (increased sense of smell). The risk of PCD at 721 days was higher for participants reporting qualitative changes (parosmia (altered smell), dysgeusia (altered taste), or phantosmia (hallucination of smell)) during initial infection than in those with isolated quantitative losses during the first COVID-19 infection (62.5% vs. 7.1%). The main recovery rate occurred within the first 100 days and did not continue until follow-up at 2 years. No correlation was found between antibody levels and CD, but we observed a trend of a higher percentage of T-cell responders in participants with CD. In conclusion, a significant proportion of patients suffer from PCD and impaired quality of life 2 years after initial infection. Qualitative changes in smell or taste during COVID-19 pose a higher risk for PCD.

Olfactory dysfunction in type II diabetes: Therapeutic options and lessons learned from other etiologies - A scoping review

INTRODUCTION

Olfactory dysfunction (OD) is highly prevalent amongst type 2 diabetes mellitus (DM2) patients and has many associated health risks. For example, OD can lead to poor nutrition, safety issues related to diminished hazard detection, and increased mortality rates. While limited research exists about therapeutics for DM2-associated OD, recovery of olfactory function is better studied in other pathologic states. The objectives of this scoping review are to synthesize the existing data on interventions for DM2-associated OD and present the evidence for therapies that have been utilized for non-DM2-associated causes of OD. Additionally, the potential therapeutic opportunities for patients with DM2 are explored.

METHODS

A scoping review was conducted with a medical librarian to identify studies investigating treatments of DM2-related OD. 6 databases were searched (Embase, CINAHL, the Cochrane Library, Google Scholar, OVID Medline, and Web of Science). Studies were eligible if the primary discussion involved treatment of olfactory deficits in the context of DM2. All publication dates were included, and studies published in languages other than English were excluded.

RESULTS

3631 articles were identified; 3 articles met inclusion criteria and underwent full text review. Hyperbaric oxygen (HBO), the DPP-4 inhibitor Linagliptin and the GLP-1 agonists Exenatide and Liraglutide are the only therapeutics that have been used in the context of DM2. Only HBO and GLP-1 agonists produced statistically significant improvements in olfactory identification. The literature regarding non-DM2-associated OD supports interventions such as olfactory training, dietary supplements, and intranasal insulin. Specifically, olfactory training was very effective in many contexts such as post-viral and traumatic OD while being affordable and non-invasive.

CONCLUSION

This scoping review of olfactory rehabilitation options for DM2-induced OD demonstrates a paucity of prospective investigations of plausible therapeutics. Additionally, treatments for OD related to non-DM2-associated etiologies, such as olfactory training, are well-studied, efficacious, and should be investigated in the context of DM2. Future investigation has the potential to enhance the quality of clinical intervention for OD and improve short- and long-term outcomes for DM2 patients.

Tailored Approach for Persistent Olfactory Dysfunction After SARS-CoV-2 Infection: A Pilot Study

OBJECTIVE

So far, no original studies explored non-randomized, standardized protocols for COVID-19 associated olfactory dysfunction. The main objective was to determine the efficacy of a new protocol for post-COVID olfactopathy while assessing the benefit of adding adjuvant therapies to olfactory training.

METHODS

Patients suffering from long-lasting post-COVID-19 olfactory dysfunction were evaluated. A non-randomized protocol based on individual nasal endoscopy findings and patient's preferences was applied. Patients were assigned for olfactory training alone or olfactory training + adjuvant therapy. Participants performed olfactory objective and subjective evaluations at first consultation and 3 months after treatment, and results were compared.

RESULTS

A total of 47 patients were enrolled. All groups showed significant improvement in olfactory thresholds at 3-month follow-up suggesting protocol effectiveness (olfactory training group alone showed a mean threshold difference of 2.9, P < .001; Olfactory training + Topical Corticosteroid showed a mean threshold difference of 4, P = .006; Olfactory training + Topical Corticosteroid + Vitamin B complex showed a mean threshold difference of 4.4, P = .006; Olfactory training + Intranasal Vitamin A and E showed a mean threshold difference of 4.4, P < .001). Olfactory training alone showed lower mean olfactory threshold improvement, when compared to patients undergoing olfactory training + adjuvant therapy (olfactory training alone mean improvement 2.9 ± 2.3 vs olfactory training + adjuvants mean improvement 4.3 ± 2.458, P = .03).

CONCLUSIONS

This is one of the first studies to demonstrate results in the treatment of post-COVID-19 persistent olfactory impairment. A customized approach based on endoscopy findings and patient's preferences may be a valid option for the management of persistent post-COVID-19 olfactory disorder. Adjuvant therapy could be considered in addition to olfactory training, but further studies are needed in order to confirm their effectiveness in this setting.

LEVEL OF EVIDENCE

2c (outcomes research).

Functional Connectivity of the Chemosenses: A Review

Functional connectivity approaches have long been used in cognitive neuroscience to establish pathways of communication between and among brain regions. However, the use of these analyses to better understand how the brain processes chemosensory information remains nascent. In this review, we conduct a literature search of all functional connectivity papers of olfaction, gustation, and chemesthesis, with 103 articles discovered in total. These publications largely use approaches of seed-based functional connectivity and psychophysiological interactions, as well as effective connectivity approaches such as Granger Causality, Dynamic Causal Modeling, and Structural Equation Modeling. Regardless of modality, studies largely focus on elucidating neural correlates of stimulus qualities such as identity, pleasantness, and intensity, with task-based paradigms most frequently implemented. We call for further "model free" or data-driven approaches in predictive modeling to craft brain-behavior relationships that are free from a priori hypotheses and not solely based on potentially irreproducible literature. Moreover, we note a relative dearth of resting-state literature, which could be used to better understand chemosensory networks with less influence from motion artifacts induced via gustatory or olfactory paradigms. Finally, we note a lack of genomics data, which could clarify individual and heritable differences in chemosensory perception.

Olfactory Training in Post-COVID-19 Persistent Olfactory Disorders: Value Normalization for Threshold but Not Identification

(1) Background: Persistent post-viral olfactory disorders (PPVOD) are estimated at 30% of patients one year after COVID-19 infection. No treatment is, to date, significantly effective on PPVOD with the exception of olfactory training (OT). The main objective of this work was to evaluate OT efficiency on post-COVID-19 PPVOD. (2) Methods: Consecutive patients consulting to the ENT department with post-COVID-19 PPVOD were included after completing clinical examination, the complete Sniffin’ Stick Test (TDI), the short version of the Questionnaire of olfactory disorders and the SF-36. Patients were trained to practice a self-olfactory training with a dedicated olfactory training kit twice a day for 6 months before returning to undergo the same assessments. (3) Results: Forty-three patients were included and performed 3.5 months of OT in average. We observed a significant TDI score improvement, increasing from 24.7 (±8.9) before the OT to 30.9 (±9.8) (p < 0.001). Based on normative data, a significant increase in the number of normosmic participants was observed only for the threshold values (p < 0.001). Specific and general olfaction-related quality of life improved after the OT. (4) Conclusions: Olfactory function appeared to improve only in peripheral aspects of post-COVID-19 PPVOD after OT. Future controlled studies must be performed to confirm the OT role and justify new therapeutic strategies that may focus on the central aspects of post-COVID-19 PPVOD.

Future Directions for Chemosensory Connectomes: Best Practices and Specific Challenges

Ecological chemosensory stimuli almost always evoke responses in more than one sensory system. Moreover, any sensory processing takes place along a hierarchy of brain regions. So far, the field of chemosensory neuroimaging is dominated by studies that examine the role of brain regions in isolation. However, to completely understand neural processing of chemosensation, we must also examine interactions between regions. In general, the use of connectivity methods has increased in the neuroimaging field, providing important insights to physical sensory processing, such as vision, audition, and touch. A similar trend has been observed in chemosensory neuroimaging, however, these established techniques have largely not been rigorously applied to imaging studies on the chemical senses, leaving network insights overlooked. In this article, we first highlight some recent work in chemosensory connectomics and we summarize different connectomics techniques. Then, we outline specific challenges for chemosensory connectome neuroimaging studies. Finally, we review best practices from the general connectomics and neuroimaging fields. We recommend future studies to develop or use the following methods we perceive as key to improve chemosensory connectomics: (1) optimized study designs, (2) reporting guidelines, (3) consensus on brain parcellations, (4) consortium research, and (5) data sharing.

Riech- und Schmeckstörungen

Ziel der vorliegenden Übersicht ist es, einen Überblick über die Ätiologie und Diagnostik von Riech- und Schmeckstörungen zu geben. Da etwa 5 % der Allgemeinbevölkerung betroffen sind, ist es ein häufiges Krankheitsbild. Riechen und Schmecken erhielten v. a. zuletzt Aufmerksamkeit während des Aufkommens der SARS-CoV-2-Pandemie, wobei eine plötzlich aufgetretene Riech- und/oder Schmeckstörung zu den typischen Symptomen zählt. Daneben sind Riechstörungen in der Frühdiagnostik neurodegenerativer Erkrankungen von Bedeutung. Häufig zeigen Patienten mit Riechstörungen Zeichen einer Depression. Die Auswirkungen von Riech‑/Schmeckstörungen sind also umfangreich, die Therapiemöglichkeiten aktuell begrenzt. Nach einem Einblick in die Ätiologie werden Diagnostik und Therapiemöglichkeiten auf dem aktuellen Stand der Literatur erörtert. Auch zukunftsweisende Behandlungsvorstellungen, wie z. B. autologe Schleimhauttransplantationen oder olfaktorische Implantate, werden angesprochen.

Research Progress of Olfactory Nerve Regeneration Mechanism and Olfactory Training

The olfactory nerve (ON) is the only cranial nerve exposed to the external environment. Hence, it is susceptible to damage from head trauma, viral infection, inflammatory stimulation, and chemical toxins, which can lead to olfactory dysfunction. However, compared with all other cranial nerves, the ON is unique due to its inherent ability to regenerate. This characteristic provides a theoretical basis for treatment of olfactory dysfunction. Olfactory training (OT) is one of the main treatments for olfactory dysfunction. It is easy to apply and has few side-effects, and has been shown to be efficacious for patients with olfactory dysfunction of various causes. To further understand the application value of ON regeneration and OT on olfactory dysfunction, we review the research progress on the mechanism of ON regeneration and OT.

Treatment strategies for postviral olfactory dysfunction: A systematic review

Background: The coronavirus disease 2019 (COVID-19) pandemic has been associated with a dramatic increase in postviral olfactory dysfunction (PVOD) among patients who are infected. A contemporary evidence-based review of current treatment options for PVOD is both timely and relevant to improve patient care. Objective: This review seeks to impact patient care by qualitatively reviewing available evidence in support of medical and procedural treatment options for PVOD. Systematic evaluation of data quality and of the level of evidence was completed to generate current treatment recommendations. Methods: A systematic review was conducted to identify primary studies that evaluated treatment outcomes for PVOD. A number of medical literature data bases were queried from January 1998 to May 2020, with completion of subsequent reference searches of retrieved articles to identify all relevant studies. Validated tools for the assessment of bias among both interventional and observational studies were used to complete quality assessment. The summary level of evidence and associated outcomes were used to generate treatment recommendations. Results: Twenty-two publications were identified for qualitative review. Outcomes of alpha-lipoic acid, intranasal and systemic corticosteroids, minocycline, zinc sulfate, vitamin A, sodium citrate, caroverine, intranasal insulin, theophylline, and Gingko biloba are reported. In addition, outcomes of traditional Chinese acupuncture and olfactory training are reviewed. Conclusion: Several medical and procedural treatments may expedite the return of olfactory function after PVOD. Current evidence supports olfactory training as a first-line intervention. Additional study is required to define specific treatment recommendations and expected outcomes for PVOD in the setting of COVID-19.

Olfactory dysfunction as a post-infectious symptom of SARS-CoV-2 infection

The unexpected onset smell and taste disability was being recognized as a COVID-19 related symptom. Loss of smell might occur alone or be followed by other COVID-19 symptoms, such as a dry cough, fever, headache, and shortness of breath. Other virus infections have been linked to anosmia (parainfluenza, rhinovirus, SARS, and others), affecting up to 20% of the adult population, which is much less common than SARS-CoV-2 infection. A hypothesis about the pathophysiology of post-infectious olfactory loss is that viruses could make an inflammatory response of the nasal mucosa or directly damage the olfactory neuroepithelium. However, in patients with COVID-19, loss of smell may occur without other rhino logic symptoms or suggestive nasal inflammation. According to evidence, anosmia-related SARS-CoV-2 could be a new viral syndrome unique to COVID-19. Furthermore, through experimental intranasal inoculation in mice, SARS-CoV-2 can be inoculated into the olfactory neural circuitry. This disease has not had the required focus, most likely because it is not life-threatening in and of itself. Though patients' quality of living is significantly reduced as their olfactory ability is lost, resulting in lowering and inadequate appetite, excessive or unbalanced food consumption, as well as an overall sense of insecurity. This review aims to give a quick overview of the latest epidemiological research, pathological mechanisms for the dysfunction of smell, and taste in patients infected with SARS-CoV-2. In addition, the initial diagnosis and treatment options for dysfunction are also discussed.

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The pathological mechanism of SARS-CoV-2 infection in olfactory dysfunction.

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Pathognomonic symptoms of sinonasal impairment in COVID-19 patients.

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Treatment of olfactory dysfunction after SARS-CoV-2 infection.

Olfactory training for Olfactory dysfunction in COVID-19: A promising mitigation amidst looming neurocognitive sequelae of the pandemic

Olfactory dysfunction (OD) is a recognized symptom of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and is independently associated with neurodegenerative disorders. Moreover, the central nervous system manifestations in patients infected with the coronavirus -2019 (COVID-19) have demonstrated cognitive decline and neuropsychiatric manifestations. Hence, OD in COVID -19 necessitates perusal of its' mechanism and available treatment options to avert possible development of neurocognitive sequelae of the pandemic. The article presents a literature review organized from the published information about olfactory training (OT) for OD during COVID-19. The methodology comprised retrieval of available literature from database searches and subsequent scrutinization of relevant information. Inferentially, Injury to the sustentacular cells, possessing angiotensin-converting enzyme 2 (ACE-2) receptors, is an important mechanism causing OD in COVID-19. OD may be prolonged in severe cases of anosmia predisposing to neurodegenerative and cognitive impairment in COVID-19 infection. OT demonstrates an effective treatment for OD based on human and animal-derived evidence through recent studies. It curtails the progression of OD, besides inducing neural rearrangement and changes in functional connectivity in patients receiving OT. Additionally, contemporary reports support that the administration of OT for COVID-induced anosmia is effective and encompasses no significant adverse effects. The present review highlights the prominence of olfactory training as a recommended intervention for OD in COVID-19. This review can guide the clinicians in curbing neurological repercussions of COVID besides enhancing cognitive rehabilitation through olfactory training.

[Olfactory and gustatory disorders]

Ziel der vorliegenden Übersicht ist es, einen Überblick über die Ätiologie und Diagnostik von Riech- und Schmeckstörungen zu geben. Da etwa 5 % der Allgemeinbevölkerung betroffen sind, ist es ein häufiges Krankheitsbild. Riechen und Schmecken erhielten v. a. zuletzt Aufmerksamkeit während des Aufkommens der SARS-CoV-2-Pandemie, wobei eine plötzlich aufgetretene Riech- und/oder Schmeckstörung zu den typischen Symptomen zählt. Daneben sind Riechstörungen in der Frühdiagnostik neurodegenerativer Erkrankungen von Bedeutung. Häufig zeigen Patienten mit Riechstörungen Zeichen einer Depression. Die Auswirkungen von Riech‑/Schmeckstörungen sind also umfangreich, die Therapiemöglichkeiten aktuell begrenzt. Nach einem Einblick in die Ätiologie werden Diagnostik und Therapiemöglichkeiten auf dem aktuellen Stand der Literatur erörtert. Auch zukunftsweisende Behandlungsvorstellungen, wie z. B. autologe Schleimhauttransplantationen oder olfaktorische Implantate, werden angesprochen.

Restoration of olfactory dysfunctions by nanomaterials and stem cells-based therapies: Current status and future perspectives

Dysfunction in the olfactory system of a person can have adverse effects on their health and quality of life. It can even increase mortality among individuals. Olfactory dysfunction is related to many factors, including post-viral upper respiratory infection, head trauma, and neurodegenerative disorders. Although some clinical therapies such as steroids and olfactory training are already available, their effectiveness is limited and controversial. Recent research in the field of therapeutic nanoparticles and stem cells has shown the regeneration of dysfunctional olfactory systems. Thus, we are motivated to highlight these regenerative approaches. For this, we first introduce the anatomical characteristics of the olfactory pathway, then detail various pathological factors related to olfactory dysfunctions and current treatments, and then finally discuss the recent regenerative endeavors, with particular focus on nanoparticle-based drug delivery systems and stem cells. This review offers insights into the development of future therapeutic approaches to restore and regenerate dysfunctional olfactory systems.

Association of Sinonasal Inflammation With Functional Brain Connectivity

Importance

In recent years, there have been several meaningful advances in the understanding of the cognitive effects of chronic rhinosinusitis. However, an investigation exploring the potential link between the underlying inflammatory disease and higher-order neural processing has not yet been performed.

Objective

To describe the association of sinonasal inflammation with functional brain connectivity (Fc), which may underlie chronic rhinosinusitis-related cognitive changes.

Design, Setting, and Participants

This is a case-control study using the Human Connectome Project (Washington University-University of Minnesota Consortium of the Human Connectome Project 1200 release), an open-access and publicly available data set that includes demographic, imaging, and behavioral data for 1206 healthy adults aged 22 to 35 years. Twenty-two participants demonstrated sinonasal inflammation (Lund-Mackay score [LMS] ≥ 10) and were compared with age-matched and sex-matched healthy controls (LMS = 0). These participants were further stratified into moderate (LMS < 14, n = 13) and severe (LMS ≥ 14, n = 9) inflammation groups. Participants were screened and excluded if they had a history of psychiatric disorder and/or neurological or genetic diseases. Participants with diabetes or cardiovascular disease were also excluded, as these conditions may affect neuroimaging quality. The data were accessed between October 2019 and August 2020. Data analysis was performed between May 2020 and August 2020.

Main Outcomes and Measures

The primary outcome was the difference in resting state Fc within and between the default mode, frontoparietal, salience, and dorsal attention brain networks. Secondary outcomes included assessments of cognitive function using the National Institutes of Health Toolbox Cognition Battery.

Results

A total of 22 patients with chronic rhinosinusitis and 22 healthy controls (2 [5%] were aged 22-25 years, 26 [59%] were aged 26-30 years, and 16 [36%] were aged 31-35 years; 30 [68%] were men) were included in the analysis. Participants with sinonasal inflammation showed decreased Fc within the frontoparietal network, in a region involving bilateral frontal medial cortices. This region demonstrated increased Fc to 2 nodes within the default-mode network and decreased Fc to 1 node within the salience network. The magnitude of these differences increased with inflammation severity (dose dependent). There were no significant associations seen on cognitive testing.

Conclusions and Relevance

In this case-control study, participants with sinonasal inflammation showed decreased brain connectivity within a major functional hub with a central role in modulating cognition. This region also shows increased connectivity to areas that are activated during introspective and self-referential processing and decreased connectivity to areas involved in detection and response to stimuli. Future prospective studies are warranted to determine the applicability of these findings to a clinical chronic rhinosinusitis population.

Steroids and Olfactory Training for Postviral Olfactory Dysfunction: A Systematic Review

Background: Postviral olfactory dysfunction (PVOD) is a clinical challenge due to limited therapeutic options and poor prognosis. Both steroids and olfactory training have been proved to be effective for olfactory dysfunction with varied etiologies. We sought to perform a systematic review to summarize the evidence of steroids or olfactory training for patients with PVOD.

Methods: A systematic literature review using PubMed, Embase, Cochrane Library, and Web of Science was conducted to identify studies assessing olfactory change in patients with PVOD receiving steroid or olfactory training.

Results: Of the initial 273 abstracts reviewed, 20 articles with data from 2,415 patients with PVOD were included. Treatments including topical steroids, systemic steroids, classical olfactory training (COT), modified olfactory training (MOT), and olfactory training with steroid were analyzed. Both psychophysical olfactory testing and subjective symptom scores were utilized to assess the olfactory function. The routine use of nasal steroid spray alone during the management of PVOD seems to have no positive effect on olfactory dysfunction. Direct injection of steroid or nasal steroid spray into the olfactory cleft significantly improved the olfactory function in patients with PVOD. Olfactory improvement is greater than that of the natural course of the disease with short-term COT. Patients with PVOD would benefit more from long-term COT (>12 weeks). Treatment duration, various odorants, olfactory training devices, changing the types of odors periodically, different molecular odorants, and different concentrations of odorants tended to increase the efficiency of MOT. Clinically significant improvement after olfactory training was defined as an increase of threshold, discrimination, and identification (TDI) score ≥6. From week 24 to week 36, both COT and MOT groups reached the maximum therapeutic effect regarding the number of participants achieving clinically significant improvement. A combination of local or oral steroids with olfactory training is more efficient than COT only.

Conclusion: Olfactory function in patients with PVOD was effectively improved through direct steroid administration in the olfactory cleft, COT, or modification of COT. The addition of topical steroids to COT therapy showed a tendency for greater olfactory improvement in patients with PVOD.

Investigating morphological changes in the brain in relation to etiology and duration of olfactory dysfunction with voxel-based morphometry

Olfactory loss (OL) affects up to 20% of the general population and is related to changes in olfaction-related brain regions. This study investigated the effect of etiology and duration of OL on gray matter volume (GMV) of these regions in 257 patients. Voxel-based morphometry was applied to measure GMV in brain regions of interest to test the effects of etiology and duration on regional GMV and the relation between olfactory function and regional GMV. Etiology of OL had a significant effect on GMV in clusters representing the gyrus rectus and orbitofrontal cortex (OFC), bilaterally. Patients with congenital anosmia had reduced GMV in the gyrus rectus and an increased OFC volume compared to patients with acquired OL. There was a significant association between volume of the left OFC and olfactory function. This implies that changes in GMV in patients with acquired OL are mainly reflected in the OFC and depend on olfactory function. Morphology of olfactory areas in the brain therefore seems to relate to olfactory function and the subsequent degree of exposure to olfactory input in patients with acquired OL. Differences in GMV in congenital anosmia are most likely due to the fact that patients were never able to smell.

Association of Olfactory Training With Neural Connectivity in Adults With Postviral Olfactory Dysfunction

Importance

Viral upper respiratory tract infections are a major cause of olfactory loss. Olfactory training (OT) is a promising intervention for smell restoration; however, a mechanistic understanding of the changes in neural plasticity induced by OT is absent.

Objective

To evaluate functional brain connectivity in adults with postviral olfactory dysfunction (PVOD) before and after OT using resting-state functional magnetic resonance imaging.

Design, Setting, and Participants

This prospective cohort study, conducted from September 1, 2017, to November 30, 2019, recruited adults with clinically diagnosed or self-reported PVOD of 3 months or longer. Baseline olfaction was measured using the University of Pennsylvania Smell Identification Test (UPSIT) and the Sniffin' Sticks test. Analysis was performed between December 1, 2020, and July 1, 2020.

Interventions

Participants completed 12 weeks of OT using 4 essential oils: rose, eucalyptus, lemon, and clove. The resting-state functional magnetic resonance imaging measurements were obtained before and after intervention.

Main Outcome and Measures

The primary outcome measure was the change in functional brain connectivity before and after OT. Secondary outcome measures included changes in UPSIT and Sniffin' Sticks test scores, as well as patient-reported changes in treatment response as measured by subjective changes in smell and quality-of-life measures.

Results

A total of 16 participants with PVOD (11 female [69%] and 14 White [88%]; mean [SD] age, 60.0 [10.5] years; median duration of smell loss, 12 months [range, 3-240 months]) and 20 control participants (15 [75%] female; 17 [85%] White; mean [SD] age, 55.0 [9.2] years; median UPSIT score, 37 [range, 34-39]) completed the study. At baseline, participants had increased connectivity within the visual cortex when compared with normosmic control participants, a connection that subsequently decreased after OT. Furthermore, 4 other network connectivity values were observed to change after OT, including an increase in connectivity between the left parietal occipital junction, a region of interest associated with olfactory processing, and the cerebellum.

Conclusions and Relevance

The use of OT is associated with connectivity changes within the visual cortex. This case-control cohort study suggests that there is a visual connection to smell that has not been previously explored with OT and that further studies examining the efficacy of a bimodal visual and OT program are needed.

Neurosensory Rehabilitation and Olfactory Network Recovery in Covid-19-related Olfactory Dysfunction

Non-conductive olfactory dysfunction (OD) is an important extra-pulmonary manifestation of coronavirus disease 2019 (COVID-19). Olfactory bulb (OB) volume loss and olfactory network functional connectivity (FC) defects were identified in two patients suffering from prolonged COVID-19-related OD. One patient received olfactory treatment (OT) by the combination of oral vitamin A and smell training via the novel electronic portable aromatic rehabilitation (EPAR) diffusers. After four-weeks of OT, clinical recuperation of smell was correlated with interval increase of bilateral OB volumes [right: 22.5 mm³ to 49.5 mm³ (120%), left: 37.5 mm³ to 42 mm³ (12%)] and improvement of mean olfactory FC [0.09 to 0.15 (66.6%)].

Reorganizing brain structure through olfactory training in post-traumatic smell impairment: An MRI study

PURPOSE AND BACKGROUND

Post-traumatic olfactory dysfunction (PTOD), mostly caused by head injury, is thought to be associated with changes in the structure and function of the brain olfactory processing areas. Training and repeated exposure to odorants lead to enhanced olfactory capability. This study investigated the effects of a 16-weeks olfactory training (OT) on olfactory function and brain structure.

METHODS

Twenty-five patients with PTOD were randomly divided in three groups: (1) 9 control patients who did not receive any training, (2) 9 patients underwent classical OT by 4 fixed odors, and (3) 7 patients underwent modified OT coming across 4 sets of 4 different odors sequentially. Before and after the training period, all patients performed olfactory function tests and structural magnetic resonance imaging (MRI). Sniffin' Sticks test was used to assess olfactory function. MRI data were analyzed using voxel-based morphometry and surface-based morphometry.

RESULTS

Both trained groups showed a considerable recovery of olfactory function, especially in odor identification. MRI data analysis revealed that the classical OT leads to increases in cortical thickness/density of several brain regions, including the right superior and middle frontal gyrus, and bilateral cerebellums. In addition, the modified OT yielded a lower extent of cortical measures in the right orbital frontal cortex and right insular. Following modified OT, a positive correlation was observed between the odor identification and the right orbital frontal cortex.

CONCLUSION

Both olfactory training methods can improve olfactory function and that the improvement is associated with changes in the structure of olfactory processing areas of the brain.

Comparative Effects of Repetitive Odor Identification and Odor Memory Tasks on Olfactory Engagement in Older Populations - A Pilot fMRI Study

OBJECTIVE

This study evaluated human Blood Oxygen Level-Dependent (BOLD) responses in primary and higher-order olfactory regions of older adults, using odor memory and odor identification tasks. The goal was to determine which olfactory and memory regions of interest are more strongly engaged in older populations comparing these two odor training tasks.

METHODS

Twelve adults 55-75 years old (75% females) without intranasal or major neurological disorders performed repetitive odor memory and identification tasks using a 3-tesla magnetic resonance scanner. Odors were presented intermittently at 10-second bursts separated by 20-second intervals of odorless air. Paired t-tests were used to compare differences in the degree of activation between odor identification and odor memory tasks within individuals. An FDR cluster-level correction of p<0.05 was used for multiplicity of tests (with a cluster-defining threshold set at p<0.01 and 10 voxels).

RESULTS

Odor identification compared to memory (ie, odor identification > odor memory) contrasts had several areas of significant activation, including many of the classical olfactory brain regions as well as the hippocampus. The opposite contrast (odor memory > odor identification) included the piriform cortex, though this was not significant. Both tasks equally activated the piriform cortex, and thus when the two tasks are compared to each other this area of activation appears to be either absent (OI > OM) or only weakly observed (OM > OI).

CONCLUSION

These findings from a predominantly African American sample suggest that odor identification tasks may be more potent than memory tasks in targeted olfactory engagement in older populations. Furthermore, repetitive odor identification significantly engaged the hippocampus - a region relevant to Alzheimer's disease - more significantly than did the odor memory task. If validated in larger studies, this result could have important implications in the design of olfactory training paradigms.

[Research progress in the treatment of sensorineural olfactory dysfunction]

Sensorineural olfactory dysfunction refers to the reduction or distortion of sensory intensity due to insufficient reception or processing of stimulation by olfactory receptors, olfactory sensory neurons or central nervous system. As olfactory dysfunction can affect patients' physical and mental health and even safety of life and the etiology of sensorineural olfactory dysfunction is complicated, it has great clinical significance for understanding the development of olfactory dysfunction's treatment. This article summarizes the current promising treatment for sensorineural olfactory dysfunction, including drug therapy, cell therapy, gene therapy and olfactory training.

Clinical Olfactory Working Group consensus statement on the treatment of postinfectious olfactory dysfunction

BACKGROUND

Respiratory tract viruses are the second most common cause of olfactory dysfunction. As we learn more about the effects of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), with the recognition that olfactory dysfunction is a key symptom of this disease process, there is a greater need than ever for evidence-based management of postinfectious olfactory dysfunction (PIOD).

OBJECTIVE

Our aim was to provide an evidence-based practical guide to the management of PIOD (including post-coronavirus 2019 cases) for both primary care practitioners and hospital specialists.

METHODS

A systematic review of the treatment options available for the management of PIOD was performed. The written systematic review was then circulated among the members of the Clinical Olfactory Working Group for their perusal before roundtable expert discussion of the treatment options. The group also undertook a survey to determine their current clinical practice with regard to treatment of PIOD.

RESULTS

The search resulted in 467 citations, of which 107 articles were fully reviewed and analyzed for eligibility; 40 citations fulfilled the inclusion criteria, 11 of which were randomized controlled trials. In total, 15 of the articles specifically looked at PIOD whereas the other 25 included other etiologies for olfactory dysfunction.

CONCLUSIONS

The Clinical Olfactory Working Group members made an overwhelming recommendation for olfactory training; none recommended monocycline antibiotics. The diagnostic role of oral steroids was discussed; some group members were in favor of vitamin A drops. Further research is needed to confirm the place of other therapeutic options.

Factors associated with relevant olfactory recovery after olfactory training: a retrospective study including 601 participants

BACKGROUND

Olfactory training (OT) represents a therapeutic option for multiple etiologies of olfactory dysfunction (OD) that also benefits normosmic subjects. In this retrospective study, we report the effectiveness of OT and factors associated with relevant changes in olfactory function (OF) in large groups of normosmic participants and patients with OD, including a control group that performed no training.

METHODS

This was a retrospective pooled analysis including 2 treatment cohorts of 8 previously published studies. Adult partici- pants that either presented with the major complaint of quantitative OD or normosmic volunteers were recruited at various ENT clinics and received OT or no training. The outcome was based on changes in objective olfactory test scores after OT.

RESULTS

A total of 601 patients with OD or normosmic subjects were included. OT was more effective compared to no training. No interaction was found between OT and OF. In multivariate analysis, higher baseline OF (adjusted odds ratio, aOR, 0.93) and posttraumatic (aOR, 0.29) or idiopathic OD (aOR, 0.18) compared to postinfectious causes were significantly associated with lower odds of relevant improvements in patients with OD receiving OT. Subgroup analysis of normosmic participants receiving OT further revealed a significant association of age and baseline olfactory function with improvements of overall OF.

CONCLUSIONS

This study demonstrated that OT was more effective than no training in patients with various causes of OD. Additi- onally, baseline olfactory performance and etiology of OD were identified as important factors associated with relevant improve- ments after OT.

Treatment of post-viral olfactory dysfunction: an evidence-based review with recommendations

Background

Post‐viral olfactory dysfunction (PVOD) is one of the most common causes of olfactory loss. Despite its prevalence, optimal treatment strategies remain unclear. This article provides a comprehensive review of PVOD treatment options and provides evidence‐based recommendations for their use.

Methods

A systematic review of the Medline, Embase, Cochrane, Web of Science, Scopus, and Google Scholar databases was completed according to the Preferred Reporting Items for Systematic Reviews and Meta‐Analyses (PRISMA) guidelines. Studies with defined olfactory outcomes of patients treated for PVOD following medical, surgical, acupuncture, or olfactory training interventions were included. The Clinical Practice Guideline Development Manual and Conference on Guideline Standardization (COGS) instrument recommendations were followed in accordance with a previously described, rigorous, iterative process to create an evidence‐based review with recommendations.

Results

From 552 initial candidate articles, 36 studies with data for 2183 patients with PVOD were ultimately included. The most common method to assess olfactory outcomes was Sniffin’ Sticks. Broad treatment categories included: olfactory training, systemic steroids, topical therapies, a variety of heterogeneous non‐steroidal oral medications, and acupuncture.

Conclusion

Based on the available evidence, olfactory training is a recommendation for the treatment of PVOD. The use of short‐term systemic and/or topical steroids is an option in select patients after careful consideration of potential risks of oral steroids. Though some pharmacological investigations offer promising preliminary results for systemic and topical medications alike, a paucity of high‐quality studies limits the ability to make meaningful evidence‐based recommendations for the use of these therapies for the treatment of PVOD.

Null Effect of Olfactory Training With Patients Suffering From Depressive Disorders-An Exploratory Randomized Controlled Clinical Trial

Due to a close functional relation between brain areas processing emotion and those processing olfaction, major depression is often accompanied by reduced olfactory function. Such hyposmia can be improved by regular olfactory training (OT) over several months. As this training furthermore improves subjective well-being, we explored whether OT is a useful complementary strategy for depression treatment. A total of 102 depressive outpatients were randomly assigned to OT or a control training condition, which were performed twice a day for 16 weeks. Compliance was continuously monitored. Before and after training we measured depression severity and olfactory function. About half of the patients of both groups did not complete the training. Among the remaining patients, depression severity decreased significantly in both groups. The absence of an interaction effect indicated no selective impact of OT and the variance of depression improvement explained by OT was as little as 0.1%. The low compliance suggests that OT is not feasible for large parts of our sample of depressive outpatients, most likely due to a disease-immanent lack of motivation. In those patients who completed the training, lack of specific effects suggest that OT is not more useful then unspecific activation or attention training.

CLINICAL TRIAL REGISTRATION

This clinical trial was registered at German Registry for Clinical Trials (DRKS), main ID: DRKS00016350, URL: http://www.drks.de/DRKS00016350.

Altered Functional Brain Networks in Patients with Traumatic Anosmia: Resting-State Functional MRI Based on Graph Theoretical Analysis

OBJECTIVE

Traumatic anosmia is a common disorder following head injury; however, little is known regarding its neural basis and influence on the functional networks. Therefore, we aimed to investigate the functional connectivity changes in patients with traumatic anosmia compared to healthy controls using resting-state functional magnetic resonance imaging (rs-fMRI).

MATERIALS AND METHODS

Sixteen patients with traumatic anosmia and 12 healthy controls underwent rs-fMRI. Differences in the connectivity of the olfactory and whole brain networks were compared between the two groups. Graph theoretical parameters, such as modularity and global efficiency of the whole brain or olfactory networks, were calculated and compared. Correlation analyses were performed between the parameters and disease severity.

RESULTS

Patients with traumatic anosmia showed decreased intra-network connectivity in the olfactory network (false discovery rate [FDR]-corrected p < 0.05) compared with that in healthy controls. Furthermore, the inter-network connectivity was increased in both the olfactory (FDR-corrected p < 0.05) and whole brain networks (degree-based statistic-corrected p < 0.05) in the anosmia group. The whole brain networks showed decreased modularity (p < 0.001) and increased global efficiency (p = 0.019) in patients with traumatic anosmia. The modularity and global efficiency were correlated with disease severity in patients with anosmia (p < 0.001 and p = 0.002, respectively).

CONCLUSION

Traumatic anosmia increased the inter-network connectivity observed with rs-fMRI in the olfactory and global brain functional networks. rs-fMRI parameters may serve as potential biomarkers for traumatic anosmia by revealing a more widespread functional damage than previously expected.

Differences in Mechanisms of Steroid Therapy and Olfactory Training for Olfactory Loss in Mice

Objective

Steroid therapy and olfactory training are common treatments for olfactory loss. Systemic steroid treatment is the most effective approach for treating sinonasal olfactory loss. Olfactory training is typically effective for treating sensorineural olfactory loss. However, the differences in mechanisms of steroid therapy and olfactory training for olfactory dysfunction are unclear. The aim of this study was thus to evaluate the differences in mechanisms of olfactory training and steroid therapy.

Subjects and Methods

Mice in each group were administered 3-methylindole at a dose of 300 mg/kg. Olfactory function was evaluated with a food-finding test once a week. The olfactory neuroepithelium was harvested for histologic examination and protein analysis. Subsequently, data analysis, gene ontology and pathway analysis, quantitative real-time polymerase chain reaction of mRNA, and western blot analysis were conducted.

Results

Mice were divided into four groups according to treatment. Control, anosmia, training, and steroid groups resumed food-finding. MMP27, CCL22 and IL18rap mRNA expression were significantly increased in the training group compared to that in the steroid group. IL1R2 mRNA expression was significantly higher in the olfactory neuroepithelium of steroid-treated mice than in that of the training group mice.

Conclusions

Steroid therapy improved olfactory function via anti-inflammatory effects, unlike olfactory training which involved cell regeneration and tissue remodeling. Protein and gene analyses revealed that steroid therapy and olfactory training are underpinned by distinct mechanisms. Selection of the most appropriate treatment will be dependent on the cause of olfactory loss.

Exposure to Odors Increases Pain Threshold in Chronic Low Back Pain Patients

Objectives

Structured exposure to odors is an acknowledged therapy in patients with smell loss but has also been shown to be effective in depression. The latter might rely on connections between olfactory and emotional structures, suggesting possible effects of a similar approach in pain patients. Based on neuroanatomy, there are several interfaces between the “pain matrix” and olfactory system, such as the limbic system, hypothalamus, and mediodorsal thalamus. We aimed to investigate whether structured exposure to odors may impact perceived pain in patients with chronic low back pain.

Design

Randomized controlled parallel-group design. Subjects were tested on two occasions, at baseline and after four weeks.

Setting

Ambulatory.

Subjects

Forty-two patients with chronic low back pain

Methods

For all patients, olfactory function (using the “Sniffin’Sticks” test kit), detection, and pain thresholds for cutaneous electrical stimuli (applied to the forearm) were tested at baseline and after four weeks. Twenty-eight patients exposed themselves to four odors (rose, vanilla, chocolate, peach) every two hours over a period of four weeks (training group). Control patients (N = 14) underwent no such “olfactory training” (nontraining group).

Results

Pain thresholds were significantly increased in patients who performed olfactory training compared with patients who did not train with odors. Detection thresholds and olfactory function remained unchanged.

Conclusions

The present results indicate that regular exposure to odors increases pain thresholds in patients with chronic back pain and could be useful for general pain control in these patients. Furthermore, olfactory training in chronic pain patients might help to reduce chronification of pain by desensitization.

Different Food Odors Control Brain Connectivity in Impulsive Children

BACKGROUND

Impulsivity is a complex multi-dimensional combination of behaviors which include: ineffective impulse control, premature decision-making and inability to delay gratification.

OBJECTIVE

The aim of this work was to explore how food odor perception and its emotional value is affected in impulsive children.

METHODS

Here we compared two cohorts of impulsive and control children with ages between 10 and 16 years. Both groups underwent a functional magnetic resonance imaging experiment, in which foodrelated odor-cues were presented to all of them.

RESULTS

Differences in regions of blood oxygen level dependent activation, as well as connectivity, were calculated. Activations were significant for all odors in the impulsive group in the temporal lobe, cerebellum, supplementary motor area, frontal cortex, medial cingulate cortex, insula, precuneus, precentral, para-hippocampal and calcarine cortices.

CONCLUSION

Connectivity results showed that the expected emotional reward, based on odor perceived and processed in temporal lobes, was the main cue driving responses of impulsive children. This was followed by self-consciousness, the sensation of interaction with the surroundings and feelings of comfort and happiness, modulated by the precuneus together with somatosensory cortex and cingulum. Furthermore, reduced connectivity to frontal areas as well as to other sensory integration areas (piriform cortex), combined to show different sensory processing strategies for olfactory emotional cues in impulsive children. Finally, we hypothesize that the cerebellum plays a pivotal role in modulating decision-making for impulsive children.

Clinical effects of two combinations of olfactory agents on olfactory dysfunction after upper respiratory tract infection during olfactory training

OBJECTIVE

To compare two combinations of olfactory agents for olfactory training therapy of olfactory dysfunction after upper respiratory tract infection (URTI) and investigate the influencing factors on clinical effects.

METHODS

125 patients with olfactory dysfunction were randomly divided into two groups: test and control. During the olfactory training, four odors were used in both groups. The olfactory training lasted for 24 weeks. Then, participants were tested using Sniffin' Sticks and threshold-discrimination-identification (TDI) composite scoring before treatment and at 1, 3, and 6 months after treatment. The TDI scores were compared at different time points between the groups and within them, and influence factors were analyzed.

RESULTS

There was no significant difference in TDI scores between both groups. Furthermore, TDI scores did not significantly change after one month of treatment in either of the groups. After 3 and 6 months of treatment, TDI scores both significantly increased, and the odor discrimination and identification abilities significantly strengthened in both groups; however, the odor thresholds did not improve. The course of the disease was a significant influencing factor on the therapeutic effect of olfactory training for both groups.

CONCLUSION

The combination of essential balm, vinegar, alcohol, and rose perfume for olfactory training, which are scents commonly found in daily life, can effectively cure URTI-induced olfactory dysfunction, and significantly improve the odor discrimination and identification abilities. Furthermore, prolonging the treatment time can help with the recovery of olfactory functions, and earlier olfactory training can improve the therapeutic effect.