Hidden consequences of olfactory dysfunction: a patient report series

Parosmia: Pathophysiology and Management

PURPOSE OF REVIEW

Parosmia is a qualitative olfactory disorder in which there is a mismatch between the memory of an odor and the actual experience triggered by an odor. There has been a surge in parosmia-related publications since the COVID-19 pandemic. This review summarizes the latest clinical findings, theories on pathophysiology and potential treatment options.

RECENT ADVANCES

Potential models of parosmia include peripheral or central hypotheses, which refer to aberrancies in olfactory neuron regeneration or information processing in central olfactory centers respectively. This leads to an incomplete or disorganized pattern of olfactory information relay. Studies using gas chromatography and functional magnetic resonance imaging have identified molecular triggers and intracranial functional connectivity patterns in parosmia respectively. Parosmia tends to occur in a delayed fashion after virus-induced anosmia. It may run a protracted course, but typically improves over time. Currently there are no generally approved, objective ways to ascertain the presence and measure the extent of parosmia. Evidence-based treatment for parosmia remains elusive. In some people, this can lead to health and quality of life issues.

The Association of Odor Identification With Nutritional Status and Systemic Inflammation in Patients With Advanced Chronic Kidney Disease

OBJECTIVES

Anorexia is common in patients with chronic kidney disease (CKD) and could lead to protein-energy wasting (PEW). An altered sense of smell, a reflection of olfactory dysfunction, is a potential mechanism that exacerbates the impact of anorexia on PEW. In this study, we examined the extent of the altered sense of smell and its association with PEW in patients with moderate-to-advanced CKD.

METHODS

We studied 139 individuals (34 healthy subjects- controls, 50 patients with stage 3-4 CKD, and 55 patients on maintenance hemodialysis (MHD)) using the odor identification test (Sniffin' Sticks odor screening test containing 12 different smells). The odor identification test was scored as either correct or incorrect, and each participant's total odor score was calculated. Malnutrition inflammation score (MIS) was used to assess PEW.

RESULTS

Patients with CKD had higher C-reactive protein and lower serum albumin concentrations compared to healthy individuals. Total odor scores were different between groups, with controls having the highest scores and MHD patients having the lowest scores. A similar difference was observed in MIS, and MHD patients displayed the worst nutritional score (P ≤ .001). The number of participants with severe olfactory dysfunction (≤6 correct answers) was significantly higher in the CKD and MHD groups compared to the controls (P ≤ .01). There was an inverse trend between the total odor score and the MIS score for the study population. However, this relationship was not statistically significant (r = -0.124, P = .21).

CONCLUSION

This cross-sectional study suggests that olfactory dysfunction, as assessed by the odor identification test, is altered in patients with advanced CKD, most notably in ones on MHD. Although the diminished sense of smell was observed alongside development of PEW, we explicitly noted that there is no statistically significant correlation.

Humans without a sense of smell breathe differently

Olfaction may play a restricted role in human behavior, yet paradoxically, its absence in anosmia is associated with diverse deleterious outcomes, culminating in reduced life expectancy. The mammalian nose serves two purposes: olfaction and breathing. Because respiratory patterns are impacted by odors, we hypothesized that nasal respiratory airflow may be altered in anosmia. We apply a wearable device that precisely logs nasal airflow for 24-hour-long sessions in participants with isolated congenital anosmia and controls. We observe significantly altered patterns of respiratory nasal airflow in anosmia in wake and in sleep. These differences allow classification of anosmia at 83% accuracy using the respiratory trace alone. Patterns of respiratory airflow have pronounced impact on health, emotion and cognition. We therefore suggest that a portion of the deleterious outcomes associated with anosmia may be attributed to altered patterns of respiratory nasal airflow rather than a direct result of lost odor perception per se.

Multi-channel portable odor delivery device for self-administered and rapid smell testing

To improve our understanding of the perception of odors, researchers are often required to undertake experimental procedures with users exposed to multiple odors in a variety of settings, including to diagnose smell loss in clinics and care homes. Existing smell tests are typically administered using multiple sniffing pens, manually presented to patients by a highly specialized nurse using a time-consuming and complex testing paradigm. Automated odor delivery devices, such as olfactometer systems, exist but are expensive, bulky and typically lab based, making them difficult to use for on the ground odor delivery. Here we have developed a portable, affordable, odor delivery device that can deliver 24 odors through individual channels with high temporal precision and without cross-contamination. The device allows for the rapid, flexible sequencing of odors via digital control using a mobile application and has been experimentally validated in the lab, as well as tested on patients. The design provides several advantages for investigating olfactory perception and offers the possibility that users can one day self-administer smell tests in a range of settings, including at home, allowing smell healthcare services to evolve and become part of a routine practice and self-care culture.

Smell and taste disorders in childhood: Diagnostic challenges and significant impacts on a child's well-being

AIM

Smell and taste are senses that contribute to a child's overall well-being. Disorders affecting these senses can impact a child's daily life from enjoying meals to detecting potential dangers through scent. The aim of this study is to describe patient characteristics and etiological causes of olfactory (OD) and/or gustatory disorders (GD) in children referred to a smell and taste clinic. Secondly, we aim to suggest a clinical work up.

METHODS

Retrospective study where data were collected from 57 children who were referred consecutively to the University Clinic for Flavour, Balance, and Sleep; Department of Otorhinolaryngology (ORL), Head and Neck Surgery; Goedstrup Hospital, Denmark, for assessment due to OD/GD from January 2017 to May 2023.

RESULTS

Most of the children had anosmia (60 %), whereas sensation of the basic tastes was intact in all but eight children (16 %). The lowest TDI scores were in children with congenital OD. The underlying etiology was congenital followed by postinfectious mostly related to Covid-19. Picky eating including anorectic traits were seen in 16 % of patients.

CONCLUSION

The focus on smell loss in pediatric population is low, and probably does not adequately reflect either underlying prevalence in this group or the possible consequences on a child's well-being. Moreover, increased awareness of children's smell and taste loss is needed, as it may be associated with eating disturbances.

Impact of olfactory disorders on personal safety and well-being: a cross-sectional observational study

OBJECTIVES

Investigate safety perceptions, quantify hazardous events, and analyse their manifestations in individuals with olfactory dysfunction through an online cross-sectional survey.

METHODS

An online survey, available from 25th February to 28th September 2022, captured data on demographics, olfactory disorder causes, safety concerns, and experienced hazardous events. Distributed via Fifth Sense channels, it targeted individuals with self-claimed olfactory dysfunction.

RESULTS

Of 432 responses, the majority were female (79.6%), aged 41-70, with 20.6% non-UK residents from 21 countries. Leading causes of dysfunction were Covid-19 (22%), idiopathic (20.8%), and congenital (14.4%). Safety concerns were high (85.9%), with gas, smoke, and food as major worries. Over 5 years, 32.2% faced ≥ 1 food incident, 14.8% ≥ 1 gas incident, 34.5% ≥ 1 gas scare, and 18.5% ≥ 1 work incident. Preventative measures were taken by 60.2% at home. Key limitations of this study were self-reported data and sampling bias of charity members.

CONCLUSION

This study highlights the significant impact of smell loss on personal safety and emotional well-being. There is an unmet need in mitigating safety concerns/events for individuals with olfactory dysfunction. We suggest collaborate strategies such as educating the public sector and high-risk sectors (e.g. gas companies), and introducing safety 'scratch and sniff' cards as a screening method. Regular assessment of an individual's olfactory ability, similar to routine assessments for other sensory systems (sight, hearing) may allow proactive identification of at-risk people and corrective measures to take place.

Using Cooking Schools to Improve the Pleasure of Food and Cooking in Patients Experiencing Smell Loss

Smell loss affects around 15-20% of the population, with a major effect on the quality of life. The most common complaint is the impairment of the eating experience, with around 90% of patients reporting this issue. A study conducted at a specialised Taste and Smell Clinic investigated if food and cooking can positively affect the enjoyment of food, subjective cooking skills, and quality of life in patients with smell loss. The 49 participants in the study received a 5-week cooking school course that focused on emphasizing the other senses to regain the enjoyment of food. Participants gained more confidence in cooking, and their quality of life improved significantly. Positively evaluated recipes were adjusted based on feedback and published as free e-books in Danish, German, and English. Eating and cooking are multisensory experiences, and the perception of food depends on the complex interaction of senses and surroundings. If the olfactory input is reduced or absent, both the enjoyment and cooking experience can be negatively affected. Therefore, focusing on food and cooking can have a positive impact on patients with smell loss.

The olfactory bulb: A neuroendocrine spotlight on feeding and metabolism

Olfaction is the most ancient sense and is needed for food-seeking, danger protection, mating and survival. It is often the first sensory modality to perceive changes in the external environment, before sight, taste or sound. Odour molecules activate olfactory sensory neurons that reside on the olfactory epithelium in the nasal cavity, which transmits this odour-specific information to the olfactory bulb (OB), where it is relayed to higher brain regions involved in olfactory perception and behaviour. Besides odour processing, recent studies suggest that the OB extends its function into the regulation of food intake and energy balance. Furthermore, numerous hormone receptors associated with appetite and metabolism are expressed within the OB, suggesting a neuroendocrine role outside the hypothalamus. Olfactory cues are important to promote food preparatory behaviours and consumption, such as enhancing appetite and salivation. In addition, altered metabolism or energy state (fasting, satiety and overnutrition) can change olfactory processing and perception. Similarly, various animal models and human pathologies indicate a strong link between olfactory impairment and metabolic dysfunction. Therefore, understanding the nature of this reciprocal relationship is critical to understand how olfactory or metabolic disorders arise. This present review elaborates on the connection between olfaction, feeding behaviour and metabolism and will shed light on the neuroendocrine role of the OB as an interface between the external and internal environments. Elucidating the specific mechanisms by which olfactory signals are integrated and translated into metabolic responses holds promise for the development of targeted therapeutic strategies and interventions aimed at modulating appetite and promoting metabolic health.

Aging and Olfactory Training: A Scoping Review

Background and Objectives

Decreased olfactory function commonly occurs alongside the aging process. Research suggests olfactory training (OT) has the potential to improve olfactory and cognitive function in individuals with and without olfactory dysfunction. The degree to which these benefits extend into older age and among those with cognitive impairment (i.e., people with dementia and mild cognitive impairment) is less clear. The purpose of the current review was to investigate the extent to which OT affects olfactory function, cognition, and well-being among older people.

Research Design and Methods

A scoping review of the literature was conducted in PubMed, Embase, EbscoHost, and SCOPUS. Articles were considered eligible for original research studies with human populations, included adults aged 55 and older, performed any type of OT, and included a form of olfactory testing. The data from the included studies were synthesized and presented narratively.

Results

A total of 23 studies were included. The results suggest that OT provides multiple benefits to older adults, including those with cognitive impairment. Particularly, OT was associated with measurable changes in olfactory function, improved cognitive function, specifically semantic verbal fluency and working memory, reduced depressive symptoms, and protection from cognitive decline.

Discussion and Implications

The findings suggest that benefits from OT extend beyond changes in olfactory function and include improved cognitive function, amelioration of depressive symptoms, and protection from cognitive decline. Future research is needed across specific participant groups, including those with differentiated types of dementia, to investigate the olfactory and cognitive benefits of OT.

Endogenous opioids in the olfactory tubercle and their roles in olfaction and quality of life

Olfactory dysfunctions decrease daily quality of life (QOL) in part by reducing the pleasure of eating. Olfaction plays an essential role in flavor sensation and palatability. The decreased QOL due to olfactory dysfunction is speculated to result from abnormal neural activities in the olfactory and limbic areas of the brain, as well as peripheral odorant receptor dysfunctions. However, the specific underlying neurobiological mechanisms remain unclear. As the olfactory tubercle (OT) is one of the brain's regions with high expression of endogenous opioids, we hypothesize that the mechanism underlying the decrease in QOL due to olfactory dysfunction involves the reduction of neural activity in the OT and subsequent endogenous opioid release in specialized subregions. In this review, we provide an overview and recent updates on the OT, the endogenous opioid system, and the pleasure systems in the brain and then discuss our hypothesis. To facilitate the effective treatment of olfactory dysfunctions and decreased QOL, elucidation of the neurobiological mechanisms underlying the pleasure of eating through flavor sensation is crucial.

Identification of the needs of individuals affected by COVID-19

BACKGROUND

The optimal management of COVID-19 symptoms and their sequelae remains an important area of clinical research. Policy makers have little scientific data regarding the effects on the daily life of affected individuals and the identification of their needs. Such data are needed to inform effective care policy.

METHODS

We studied 639 people with COVID-19 resident in France via an online questionnaire. They reported their symptoms, effects on daily life, and resulting needs, with particular focus on olfaction.

RESULTS

The results indicate that a majority of participants viewed their symptoms as disabling, with symptoms affecting their physical and mental health, social and professional lives. 60% of the individuals reported having unmet medical, psychological and socio-professional support needs. Finally, affected individuals were concerned about the risk and invasiveness of possible treatments as shown by a preference for non-invasive intervention over surgery to cure anosmia.

CONCLUSIONS

It is important that policy makers take these needs into consideration in order to assist affected individuals to regain a normal quality of life.

Comparison of the incidence of smell and taste disorders between influenza and COVID-19

OBJECTIVE

Smell and taste disorders among patients with COVID-19 has become increasingly reported in the literature, however the prevalence varies. Post-infectious respiratory dysfunction has also been linked to influenza. In this study, we aimed to compare the rates of smell and taste disorders between COVID-19 and Influenza in unvaccinated patients.

STUDY DESIGN

Retrospective cohort study.

SETTING

TriNetX research network.

METHODS

Two queries were made on 7/1/2023 to include Influenza without a diagnosis of COVID-19 and a COVID-19 without a diagnosis of Influenza. The queries included patients from January 1 to December 31, 2022 from 102 Healthcare Organizations. The resultant population of patients with ICD-10 codes for COVID-19 and Influenza were matched using demographic characteristics to evaluate the risk of smell disorders.

RESULTS

The overall 3-month incidence of smell and taste disorders was 0.73 % in the COVID-19 population and 0.1 % in the influenza population. The 3-month matched risk ratios were 11.1 [95 % CI (8.8,13.8)]; p < 0.001) times higher for disorders of the smell and taste secondary to COVID-19 compared to influenza.

CONCLUSIONS

Disorders of the smell and taste are more common among patients with COVID-19 compared to patients with Influenza. Beyond smell loss, patients experience additional nasal and sinus-related rhinological symptoms, pointing to COVID-19's and influenza's wider impact on overall rhinological health. We believe that due to the transient nature of these disorders, they might go underreported.

Experience of French patients with olfactory disorders

OBJECTIVES

To assess the experience of subjects with olfactory disorders in their daily life and medical management, and their expectations and proposals for improvement.

MATERIAL AND METHODS

A cross-sectional observational study was conducted over the period January 2020 to December 2021, with 300 subjects with olfactory disorders: 222 female, 78 male; mean age 46±15 years. In total, 126 were patients consulting in ENT, and 174 were members of the Anosmie.org patients' association. Participants filled out a questionnaire; free texts were analyzed thematically and coded for various qualitative variables.

RESULTS

Olfactory disorders considerably impacted health, safety and quality of life. Non-COVID-19 acute etiologies (non-COVID-19 viral infection, cranial trauma) showed particularly high risk of psychological, social, safety-related and nutritional consequences. Almost all patients (94%) were dissatisfied with their medical management: 28% had received little explanation, and 23% felt their dysosmia was completely neglected, with no exploration and no etiology suggested. Patients wished above all to have follow-up and accompaniment.

CONCLUSION

Despite significant impact on health and quality of life, olfactory disorders are neglected by the medical community. Patients should be given an ENT assessment with olfactometry, to establish diagnosis and prognosis. Global multidisciplinary management is necessary, including therapeutic education, and psychological, social and nutritional follow-up.

Platelet-Rich Plasma (PRP) in the Treatment of Long COVID Olfactory Disorders: A Comprehensive Review

Background: Long COVID has brought numerous challenges to healthcare, with olfactory dysfunction (OD) being a particularly distressing outcome for many patients. The persistent loss of smell significantly diminishes the affected individual's quality of life. Recent attention has been drawn to the potential of platelet-rich plasma (PRP) therapy as a treatment for OD. This comprehensive review aims to evaluate the effectiveness of PRP therapy in ameliorating OD, especially when associated with long-term COVID-19. Methods: We executed a comprehensive search of the literature, encompassing clinical trials and observational studies that utilized PRP in treating OD limited to COVID-19. We retrieved and comprehensively discussed data such as design, participant demographics, and reported outcomes, focusing on the efficacy and safety of PRP therapy for OD in COVID-19 patients. Results: Our comprehensive analysis interestingly found promising perspectives for PRP in OD following COVID-19 infection. The collective data indicate that PRP therapy contributed to a significant improvement in olfactory function after COVID-19 infection. Conclusions: The evidence amassed suggests that PRP is a promising and safe therapeutic option for OD, including cases attributable to Long COVID-19. The observed uniform enhancement of olfactory function in patients receiving PRP highlights the necessity for well-designed, controlled trials. Such studies would help to refine treatment protocols and more definitively ascertain the efficacy of PRP in a broader, more varied patient cohort.

Utilization of RNA sequencing to investigate olfactory dysfunction in chronic rhinosinusitis without nasal polyps: A pilot study

Objectives

Prior research on olfactory dysfunction in chronic rhinosinusitis (CRS) has focused on patients with polyps and suggests that direct inflammation of the olfactory cleft mucosa plays a contributory role. The purpose of this study was to evaluate gene expression in superior turbinate mucosal specimens, comparing normosmic and dysosmic CRS patients without polyps (CRSsNP).

Methods

Tissue samples were obtained from the superior turbinates of patients with CRSsNP at the time of endoscopic sinus surgery. Samples subsequently underwent RNA sequencing and functional analysis to investigate biological pathways associated with differentially expressed genes between dysosmic (n = 7) and normosmic (n = 4) patients.

Results

Differential gene expression analysis comparing dysosmic and normosmic CRSsNP patients showed upregulation of 563 genes and downregulation of 327 genes. Using stringent criteria for multiple comparisons, one upregulated gene (Immediate Early Response 3 [IER3]) had an false discovery rate (FDR) correction adjusted P value considered statistically significant (P < 0.001, fold change 2.69). Reactome functional analysis revealed eight biological pathways significantly different between dysosmic and normosmic patients (P < 0.05, FDR correction) including IL-4 and IL-13 signaling, IL-10 signaling, and rhodopsin-like receptors.

Conclusions

RNA sequencing of the superior turbinates in patients with CRSsNP can provide valuable information regarding biological pathways and genes involved in olfactory dysfunction. This study supports literature suggesting that Type 2 inflammation may play a role in olfactory dysfunction in at least some patients with CRSsNP. This study also prompts questions regarding the role of IL-10, rhodopsin-like receptors, and IER3 in the pathogenesis of olfactory dysfunction.

Diagnosed and subjectively perceived long-term effects of COVID-19 infection on olfactory function assessed by supervised machine learning

Loss of olfactory function is a typical acute coronavirus disease 2019 (COVID-19) symptom, at least in early variants of SARS-CoV2. The time that has elapsed since the emergence of COVID-19 now allows for assessing the long-term prognosis of its olfactory impact. Participants (n = 722) of whom n = 464 reported having had COVID-19 dating back with a mode of 174 days were approached in a museum as a relatively unbiased environment. Olfactory function was diagnosed by assessing odor threshold and odor identification performance. Subjects also rated their actual olfactory function on an 11-point numerical scale [0,…10]. Neither the frequency of olfactory diagnostic categories nor olfactory test scores showed any COVID-19-related effects. Olfactory diagnostic categories (anosmia, hyposmia, or normosmia) were similarly distributed among former patients and controls (0.86%, 18.97%, and 80.17% for former patients and 1.17%, 17.51%, and 81.32% for controls). Former COVID-19 patients, however, showed differences in their subjective perception of their own olfactory function. The impact of this effect was substantial enough that supervised machine learning algorithms detected past COVID-19 infections in new subjects, based on reduced self-awareness of olfactory performance and parosmia, while the diagnosed olfactory function did not contribute any relevant information in this context. Based on diagnosed olfactory function, results suggest a positive prognosis for COVID-19-related olfactory loss in the long term. Traces of former infection are found in self-perceptions of olfaction, highlighting the importance of investigating the long-term effects of COVID-19 using reliable and validated diagnostic measures in olfactory testing.

Mammalian odorant-binding proteins are prone to form amorphous aggregates and amyloid fibrils

Odorant-binding proteins are involved in perceiving smell by capturing odorants within the protein's β-barrel. On the example of bovine odorant-binding protein (bOBP), the structural organization of such proteins and their ability to bind ligands under various conditions in vitro were examined. We found a tendency of bOBP to form oligomers and small amorphous aggregates without disturbing the integrity of protein monomers at physiological conditions. Changes in environmental parameters (increased temperature and pH) favored the formation of larger and dense supramolecular complexes that significantly reduce the binding of ligands by bOBP. The ability of bOBP to form fibrillar aggregates with the properties of amyloids, including high cytotoxicity, was revealed at sample stirring (even at physiological temperature and pH), at medium acidification or pre-solubilization with hexafluoroisopropanol. Fibrillogenesis of bOBP was initiated by the dissociation of the protein's supramolecular complexes into monomers and the destabilization of the protein's β-barrels without a significant destruction of its native β-strands.

The Impact of Ambient and Wildfire Air Pollution on Rhinosinusitis and Olfactory Dysfunction

PURPOSE OF REVIEW

With increasing industrialization, exposure to ambient and wildfire air pollution is projected to increase, necessitating further research to elucidate the complex relationship between exposure and sinonasal disease. This review aims to summarize the role of ambient and wildfire air pollution in chronic rhinosinusitis (CRS) and olfactory dysfunction and provide a perspective on gaps in the literature.

RECENT FINDINGS

Based on an emerging body of evidence, exposure to ambient air pollutants is correlated with the development of chronic rhinosinusitis in healthy individuals and increased symptom severity in CRS patients. Studies have also found a robust relationship between long-term exposure to ambient air pollutants and olfactory dysfunction. Ambient air pollution exposure is increasingly recognized to impact the development and sequelae of sinonasal pathophysiology. Given the rising number of wildfire events and worsening impacts of climate change, further study of the impact of wildfire-related air pollution is a crucial emerging field.

Validity and Reliability of the Malay Questionnaire for Olfactory Disorders

Background

Olfactory disorders (OD) are an umbrella term for a diverse group of smell problems. Numerous tests and questionnaires have been formulated to identify and test the severity of smell impairment, which is not readily available or translated for the Malaysian population. This study aimed to translate the Questionnaire for Olfactory Disorders (QOD) and validate and test the reliability of the Malay Questionnaire for Olfactory Disorders (mQOD).

Methods

This cross-sectional study was conducted in two tertiary centres. A forward and backward translation was conducted for the QOD. The translated questionnaire was distributed to subjects with self-reported smell disorders on days 1 and 7. Internal consistency was analysed using Cronbach's alpha and test-retest reliability was tested with an intraclass correlation coefficient. Confirmatory factor analysis was performed to test construct validity.

Results

A total of 375 participants were recruited, 52 dropped out and 323 completed the questionnaire a second time. The Cronbach's alpha coefficient was 0.537 for parosmia (P), 0.892 for life quality (LQ), 0.637 for sincerity (S) and 0.865 for visual analogue score (VAS). The intraclass correlation coefficient (ICC) for domain scores was > 0.9, while the ICC for all items was good to excellent. A three-factor model for mQOD showed an acceptable fit with indices chi-square value (CMIN)/degree of freedom (DF) = 3.332, Tucker-Lewis fit index (TLI) = 0.923, comparative fit index (CFI) = 0.939, root mean square error of approximation (RMSEA) = 0.079 and standardised root mean square residual (SRMR) = 0.0574.

Conclusion

The mQOD is a valid and reliable tool for assessing OD in patients.

Experiences of living without a sense of smell: Like "Being Behind Glass"

This study addresses the paucity of research concerning the subjective experiences of those affected by anosmia. In the study, we interviewed individuals(n = 11) recruited via the charity (Fifth Sense) and used Interpretative Phenomenological Analysis (IPA) to analyse the data. Findings revealed three main themes and seven sub themes. The main themes are Living with Anosmia; Remembrance of things old and new and Resilience. The study reveals the process of becoming aware of being anosmic and the relationships with others in this process including potentially unhelpful minimisations of the impact by professionals. In addition to a sense of isolation and insecurity, living with anosmia for some participants brought with it an identification of being 'anosmic' and feeling part of a community. This was in contrast to a general lack of public knowledge and understanding of anosmia. The findings of the study demonstrated the importance of smell to time, place and relationship and the recalling of smells as bringing a sense of connectivity to loved ones, of times past and also a sense of loss of ability. Participants also described the ways in which they coped and adapted to a life with anosmia and focused on positive aspects of life. These findings provide a rich qualitative account of the experience of anosmia. The findings point towards future research which could inform us about the lives of those who are anosmic and currently unaware and of those recently diagnosed, which will create a richer understanding of the experiences of anosmia.

A double-blinded randomised controlled trial of vitamin A drops to treat post-viral olfactory loss: study protocol for a proof-of-concept study for vitamin A nasal drops in post-viral olfactory loss (APOLLO)

BACKGROUND

Smell loss is a common problem with an estimated 5% of the population having no functioning sense of smell. Viral causes of smell loss are the second most common cause and the coronavirus (COVID-19) pandemic is estimated to have caused 20,000 more people this year to have a lasting loss of smell. Isolation, depression, anxiety, and risk of danger from hazards such as toxic gas and spoiled food are all negative impacts. It also affects appetite with weight loss/gain in two-thirds of those affected. Phantosmia or smell distortion can also occur making most foods seem unpalatable. Smell training has been tried with good results in the immediate post-viral phase. Evidence behind treatment with steroids has not shown to have proven effectiveness. With this, a key problem for patients and their clinicians is the lack of proven effective therapeutic treatment options. Based on previous studies, there is some evidence supporting the regenerative potential of retinoic acid, the metabolically active form of vitamin A in the regeneration of olfactory receptor neurons. It is based on this concept that we have chosen vitamin A as our study comparator.

AIM

To undertake a two-arm randomised trial of intranasally delivered vitamin A vs no intervention to determine proof of concept.

METHODS/DESIGN

The study will compare 10,000 IU once daily Vitamin A self-administered intranasal drops versus peanut oil drops (placebo) delivered over 12 weeks in patients with post-viral olfactory loss. Potentially eligible patients will be recruited from the Smell & Taste Clinic and via the charity Fifth Sense. They will be invited to attend the Brain Imaging Centre at the University of East Anglia on two occasions, 3 months apart. If they meet the eligibility criteria, they will be consented to enter the study and randomised to receive vitamin A drops or no treatment in a 2:1 ratio. MRI scanning will enable volumetric measurement of the OB and ROS; fMRI will then be conducted using an olfactometer to deliver pulsed odours-phenethylalcohol (rose-like) and hydrogen sulphide (rotten eggs). Participants will also perform a standard smell test at both visits as well as complete a quality-of-life questionnaire. Change in OB volume will be the primary outcome measure.

DISCUSSION

We expect the outputs of this study to enable a subsequent randomised controlled trial of Vitamin A versus placebo. With PPI input we will make the outputs publicly available using journals, conferences, and social media via Fifth Sense. We have already prepared a draft RCT proposal in partnership with the Norwich Clinical Trials Unit and plan to develop this further in light of the findings.

TRIAL REGISTRATION

ISRCTN registry 39523. Date of registration in the primary registry: 23rd February 2021.

Incidence of Olfactory Dysfunction and Associated Factors: A Nationwide Cohort Study From South Korea

OBJECTIVES

Olfactory dysfunction, a reduced or complete loss of the ability to smell, is gaining attention because of its substantial impact on an individual's quality of life and the possibility that it is an important sign of underlying disease. However, olfactory dysfunction is underdiagnosed in the general population due to diagnostic difficulty and unpredictable prognosis. This study aimed to evaluate the prevalence of clinically diagnosed olfactory dysfunction in South Korea by using well-organized, nationwide, population-based cohort data, and the associations between olfactory dysfunction and risk of neurodegenerative disorders.

METHODS

We investigated the Korean National Health Insurance Service-National Sample Cohort for patients diagnosed with olfactory dysfunction according to the International Classification of Diseases. Annual and overall incidence and prevalence of olfactory dysfunction during 2003 to 2013 and patient characteristics were analyzed. Based on those identified patients who were later diagnosed with neurodegenerative disorder, hazard ratios (HRs) of sociodemographic factors and comorbidities associated with neurodegenerative disorder were evaluated using a Cox proportional hazard regression model.

RESULTS

In total, 6296 patients were clinically diagnosed with olfactory dysfunction during the study period (524.67 patients/year). The prevalence increased annually and was higher in female patients. The incidence of neurodegenerative disorders among patients with olfactory dysfunction was 4.2% within the study period. Multivariate cox regression analysis of the patients (n = 249) revealed that diabetes mellitus (HR = 1.976) and depression (HR = 2.758) were significant risk factors.

CONCLUSIONS

Olfactory dysfunction is underdiagnosed in South Korea, but it is clinically important considering the possibility of presymptom of neurodegenerative disorders. In clinical practice, we should consider its association with neurodegenerative disorders and possibly other systemic conditions.

Outcome and Safety of Insulin in the Management of Smell Loss: A Systematic Review

Background: Olfactory dysfunction can negatively impact the quality of life and increase the risk of danger from warning odors. Various factors can cause olfactory dysfunction, including COVID-19 infection, which has increased anosmia cases. No medications are approved; however, recent studies have suggested that intranasal insulin could effectively treat olfactory dysfunction. Aim: To comprehensively evaluate the effectiveness and safety of intranasal insulin in treating olfactory dysfunction. Materials and Methods: PubMed, Google Scholar, and CENTRAL databases were searched using specific keywords, and the outputs were screened using the Rayyan AI system. Original research articles published without time frame limitations that reported the relevant outcomes were included. The reviewers performed the screening and data extraction, and any disagreements were resolved by a third senior author. Results: This systematic review identified 66 references from 3 databases, with 45 articles meeting the criteria for review after duplicates were removed. Six articles met the inclusion criteria and were selected, including 177 subjects. The selected studies consisted of various study designs, including pilot studies, placebo-controlled trials, crossover studies, and randomized clinical trials. The findings showed that intranasal insulin therapy had beneficial effects on olfactory function. Specifically, improvements were observed in olfactory detection and discrimination in patients with post-COVID-19 anosmia, olfactory threshold performance in healthy participants, and odor identification in hyposmic patients. However, there were variations in the observed effects based on different doses of insulin administered and gender differences. It also shows that using insulin provides good outcomes. Using it intranasally was safe and did not cause any complications. Conclusion: Intranasal insulin has shown promising results as a potentially safe treatment for olfactory dysfunction. Studies suggest that it can improve olfactory thresholds. Further studies are needed to investigate optimal doses and potential gender differences in response.

Exploring Olfactory Dysfunction as a Marker of Frailty and Postoperative Outcomes in Head and Neck Cancer

Importance

Olfactory dysfunction (OD) is increasingly recognized as a robust marker of frailty and mortality. Despite broad recognition of frailty as a critical component of head and neck cancer (HNC) care, there is no standardized frailty assessment.

Objective

To assess the prevalence of OD and its association with frailty and postoperative outcomes in HNC.

Design, Setting, and Participants

In this prospective cohort study with enrollment between February 17, 2021, to September 29, 2021, at a tertiary academic medical center, 85 eligible adult patients with primary, treatment-naive HNC of mucosal or cutaneous origin were included. Patients with a history of COVID-19, neurocognitive, or primary smell/taste disorders were excluded.

Exposures

Prospective olfactory assessments (self-reported, visual analog scale [VAS] and psychophysical, University of Pennsylvania Smell Identification Test [UPSIT]) with concurrent frailty assessment (Risk Analysis Index [RAI]) were used. Olfactory-specific quality of life (QOL) was examined with brief Questionnaire of Olfactory Disorders-Negative Statements (QOD-NS).

Main Outcome(s) and Measure(s)

The primary outcome was the prevalence of OD as assessed by VAS (0-10, no to normal smell) and UPSIT (0-40, higher scores reflect better olfaction) and its association with frailty (RAI, 0-81, higher scores indicate greater frailty). For surgical patients, secondary outcomes were associations between OD and postoperative length of stay (LOS), 30-day postoperative outcomes, and QOD-NS (0-21, higher scores indicate worse QOL).

Results

Among 51 patients with HNC (mean [SD] age, 63 [10] years; 39 [77%] male participants; 41 [80%] White participants), 24 (47%) were frail, and 4 (8%) were very frail. Despite median (IQR) self-reported olfaction by VAS of 9 (8-10), 30 (59%) patients demonstrated measured OD with psychophysical testing. No meaningful association was found between self-reported and psychophysical testing (Hodges-Lehmann, <0.001; 95% CI, -2 to 1); a total of 46 (90%) patients did not report decreased olfaction-specific QOL. Median UPSIT scores were lower in frail patients (Hodges-Lehmann, 6; 95% CI, 2-12). Multivariate modeling demonstrated severe microsmia/anosmia was associated with 1.75 (95% CI, 1.09-2.80) times odds of being frail/very frail and approximately 3 days increased LOS (β, 2.96; 95% CI, 0.29-5.62).

Conclusions and Relevance

Although patients with HNC are unaware of olfactory changes, OD is common and may serve as a bellwether of frailty. In this prospective cohort study, a dose-dependent association was demonstrated between increasing degrees of OD and frailty, and the potential utility of olfaction was highlighted as a touchstone in the assessment of HNC frailty.

Axonal Regrowth of Olfactory Sensory Neurons In Vitro

One of the most prevalent causes of olfactory loss includes traumatic brain injury with subsequent shearing of olfactory axons at the level of the cribriform plate (anterior skull base). Scar tissue at this level may prevent axonal regrowth toward the olfactory bulb. Currently, there is no cure for this debilitating and often permanent condition. One promising therapeutic concept is to implant a synthetic scaffold with growth factors through the cribriform plate/scar tissue to induce neuroregeneration. The first step toward this goal is to investigate the optimum conditions (growth factors, extracellular matrix proteins) to boost this regeneration. However, the lack of a specifically tailored in vitro model and an automated procedure for quantifying axonal length limits our ability to address this issue. The aim of this study is to create an automated quantification tool to measure axonal length and to determine the ideal growth factors and extracellular proteins to enhance axonal regrowth of olfactory sensory neurons in a mouse organotypic 2D model. We harvested olfactory epithelium (OE) of C57BL/6 mice and cultured them during 15 days on coverslips coated with various extracellular matrix proteins (Fibronectin, Collagen IV, Laminin, none) and different growth factors: fibroblast growth factor 2 (FGF2), brain-derived neurotrophic factor (BDNF), glial cell-derived neurotrophic factor (GDNF), nerve growth factor (NGF), retinoic acid (RA), transforming growth factor β (TGFβ), and none. We measured the attachment rate on coverslips, the presence of cellular and axonal outgrowth, and finally, the total axonal length with a newly developed automated high-throughput quantification tool. Whereas the coatings did not influence attachment and neuronal outgrowth rates, the total axonal length was enhanced on fibronectin and collagen IV (p = 0.001). The optimum growth factor supplementation media to culture OE compared to the control condition were as follows: FGF2 alone and FGF2 from day 0 to 7 followed by FGF2 in combination with NGF from day 7 to 15 (p < 0.0001). The automated quantification tool to measure axonal length outperformed the standard Neuron J application by reducing the average analysis time from 22 to 3 min per specimen. In conclusion, robust regeneration of murine olfactory neurons in vitro can be induced, controlled, and efficiently measured using an automated quantification tool. These results will help advance the therapeutic concept closer toward preclinical studies.

Effect of any form of steroids in comparison with that of other medications on the duration of olfactory dysfunction in patients with COVID-19: A systematic review of randomized trials and quasi-experimental studies

BACKGROUND

The life quality of about two-thirds of patients with COVID-19 is affected by related olfactory dysfunctions. The negative impact of olfactory dysfunction ranged from the decreased pleasure of eating to impaired quality of life. This research aimed to provide a comprehensive understanding of the effects of corticosteroid treatments by comparing that to other currently available treatments and interventions.

METHODS

The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) checklist's 27-point checklist was used to conduct this review. PubMed (Public/Publisher MEDLINE), PubMed Central and EMBASE (Excerpta Medica Database) databases were conveniently selected and Boolean search commands were used for a comprehensive literature search. Five core search terms were "effects of treatments", " COVID-19-related olfactory dysfunction", "corticosteroids", "treatments" and "interventions". The reporting qualities of the included studies were appraised using JBI (Joanna Briggs Institute) appraisal tools. The characteristics of the 21 experimental studies with a total sample (of 130,550) were aggregated using frequencies and percentages and presented descriptively. The main interventions and their effects on the duration of the COVID-19-related olfactory dysfunction were narratively analyzed.

RESULTS

Among patients with COVID-19, the normal functions of the olfactory lobe were about 23 days earlier to gain with the treatments of fluticasone and triamcinolone acetonide nasal spray compared with that of mometasone furoate nasal spray and oral corticosteroid. The smell loss duration was reduced by fluticasone and triamcinolone acetonide nasal spray 9 days earlier than the inflawell syrup and 16 days earlier than the lavender syrup. The nasal spray of corticosteroids ended the COVID-19-related smell loss symptoms 2 days earlier than the zinc supplementation, about 47 days earlier than carbamazepine treatment and was more effective than palmitoylethanolamide (PEA) and luteolin and omega-3 supplementations and olfactory training. Treatment with oral corticosteroid plus olfactory training significantly improved Threshold, Discrimination and Identification (TDI) scores compared with olfactory training alone. A full dose of the COVID-19 vaccination was not uncertain to reduce the COVID-19-related smell loss duration.

CONCLUSION

Corticosteroid treatment is effective in reducing the duration of COVID-19-related smell loss and olfactory training, the basic, essential and effective intervention, should be used as a combination therapy.

Olfactory Function and Olfactory Disorders

The sense of smell is important. This became especially clear to patients with infection-related olfactory loss during the SARS-CoV-2 pandemic. We react, for example, to the body odors of other humans. The sense of smell warns us of danger, and it allows us to perceive flavors when eating and drinking. In essence, this means quality of life. Therefore, anosmia must be taken seriously. Although olfactory receptor neurons are characterized by regenerative capacity, anosmia is relatively common with about 5 % of anosmic people in the general population. Olfactory disorders are classified according to their causes (e. g., infections of the upper respiratory tract, traumatic brain injury, chronic rhinosinusitis, age) with the resulting different therapeutic options and prognoses. Thorough history taking is therefore important. A wide variety of tools are available for diagnosis, ranging from short screening tests and detailed multidimensional test procedures to electrophysiological and imaging methods. Thus, quantitative olfactory disorders are easily assessable and traceable. For qualitative olfactory disorders such as parosmia, however, no objectifying diagnostic procedures are currently available. Therapeutic options for olfactory disorders are limited. Nevertheless, there are effective options consisting of olfactory training as well as various additive drug therapies. The consultation and the competent discussion with the patients are of major importance.

Momentary gustative-olfactory sensitivity and tonic heart rate variability are independently associated with motivational behavior

Deficits in motivational functioning including impairments in reward learning or reward sensitivity are common in psychiatric disorders characterized by anhedonia. Recently, anhedonic symptoms have been exacerbated by the pandemic caused by the Coronavirus disease 2019 (COVID-19) in the general population. The present study examined the putative associations between loss of smell (anosmia) and taste (ageusia) sensitivity, irrespective of COVID-19 infection, and anhedonia, measured by a signal-detection task probing the ability to modify behavior as a function of rewards (Probabilistic Reward Task; PRT). Tonic heart rate variability (HRV) was included in the model, due to its association with both smell and taste sensitivity as well as motivational functioning. The sample included 114 healthy individuals (81 females; mean age 22.2 years), who underwent a laboratory session in which dispositional traits, resting HRV and PRT performance were assessed, followed by a 4-days ecological momentary assessment to obtain daily measures of anosmia and ageusia. Lower levels of tonic HRV and lower momentary levels of smell and taste sensitivity were associated with impaired reward responsiveness and ability to shape future behavioral choices based on prior reinforcement experiences. Overall, the current results provide initial correlational evidence that could be fruitfully used to inform future experimental investigations aimed at elucidating the disruptive worldwide mental health consequences triggered by the pandemic.

Qualitative Olfactory Dysfunction and COVID-19: An Evidence-Based Review with Recommendations for the Clinician

BACKGROUND

Nearly 40% of patients who experience smell loss during SARS-CoV-2 infection may develop qualitative olfactory dysfunction, most commonly parosmia. Our evidence-based review summarizes the evolving literature and offers recommendations for the clinician on the management of patients experiencing parosmia associated with COVID-19.

METHODS

We performed a systematic search using independent queries in PubMed, Embase, Ovid, and Cochrane databases, then categorized articles according to themes that emerged regarding epidemiology, effect on quality of life, disease progression, prognosis, pathophysiology, diagnosis, and treatment of parosmia.

RESULTS

We identified 123 unique references meeting eligibility and performed title and abstract review with 2 independent reviewers, with 74 articles undergoing full-text review. An inductive approach to thematic development provided 7 central themes regarding qualitative olfactory dysfunction following COVID-19.

CONCLUSIONS

While other respiratory viruses are known to cause qualitative olfactory disturbances, the incidence of parosmia following COVID-19 is notable, and correlates negatively with age. The presence of parosmia predicts persistent quantitative olfactory dysfunction. Onset can occur months after infection, and symptoms may persist for well over 7 months. Affected patients report increased anxiety and decreased quality of life. Structured olfactory training with essential oils is the preferred treatment, where parosmia predicts recovery of aspects of quantitative smell loss when undergoing training. There is limited evidence that nasal corticosteroids may accelerate recovery of olfactory function. Patients should be prepared for the possibility that symptoms may persist for years, and providers should guide them to resources for coping with their psychosocial burden.

Establishing UK research priorities in smell and taste disorders: A James Lind alliance priority setting partnership

OBJECTIVES

To determine the top 10 research priorities in Smell and Taste Disorders (SATD).

DESIGN

After steering group was established, an electronic survey was disseminated to determine the list of questions. After removing out-of-scope responses, the remainder were consolidated to create summary questions. A literature search was conducted to remove already answered questions. A second survey was used to determine the top questions that formed the subject of final debate at a workshop attended by clinicians and patients to determine the top 10 priorities.

SETTING

A James Lind Alliance Priority Setting Partnership (JLAPSP) was established by FifthSense to identify the top 10 research questions in SATDs in the United Kingdom.

PARTICIPANT

All stakeholders in SATDs (patients, healthcare professionals, family, carers, researchers).

MAIN OUTCOME MEASURES

Final 10 research priorities.

RESULTS

The 665 respondents to the initial survey provided 1698 research questions. Thirteen were out-of-scope and removed; remaining 1685 were then consolidated to form 147 summary questions. Following literature search and discussion with the steering group, 37 questions remained for the second survey, which 235 people responded. The top ten priorities agreed upon in the workshop covered themes of improved understanding of pathophysiologlogy, improving health services, and managing long-term effects of smell/taste disorders. The most important research question agreed was "How can we further our understanding of the mechanism of disease in the nerve pathways that affect smell and taste disorders, including where parosmia and phantosmia exist."

CONCLUSION

We report the top 10 research priorities in smell and taste disorders. These priorities will now empower researchers to secure research funding and provide the basis of the FifthSense research hub.

Proof-of-concept: SCENTinel 1.1 rapidly discriminates COVID-19-related olfactory disorders

It is estimated that 20%-67% of those with COVID-19 develop olfactory disorders, depending on the SARS-CoV-2 variant. However, there is an absence of quick, population-wide olfactory tests to screen for olfactory disorders. The purpose of this study was to provide a proof-of-concept that SCENTinel 1.1, a rapid, inexpensive, population-wide olfactory test, can discriminate between anosmia (total smell loss), hyposmia (reduced sense of smell), parosmia (distorted odor perception), and phantosmia (odor sensation without a source). Participants were mailed a SCENTinel 1.1 test, which measures odor detection, intensity, identification, and pleasantness, using one of 4 possible odors. Those who completed the test (N = 287) were divided into groups based on their self-reported olfactory function: quantitative olfactory disorder only (anosmia or hyposmia, N = 135), qualitative olfactory disorder only (parosmia and/or phantosmia; N = 86), and normosmia (normal sense of smell; N = 66). SCENTinel 1.1 accurately discriminates quantitative olfactory disorders, qualitative olfactory disorders, and normosmia groups. When olfactory disorders were assessed individually, SCENTinel 1.1 discriminates between hyposmia, parosmia, and anosmia. Participants with parosmia rated common odors less pleasant than those without parosmia. We provide proof-of-concept that SCENTinel 1.1, a rapid smell test, can discriminate quantitative and qualitative olfactory disorders, and is the only direct test to rapidly discriminate parosmia.

Parosmia as a predictor of a better olfactory function in COVID-19: a multicentric longitudinal study for upper respiratory tract infections

PURPOSE

This study aimed to evaluate the course of olfactory dysfunction [OD] due to upper respiratory tract infections [URTI] especially for COVID-19 [C19] in a multicentric design and to investigate possible predictors for the outcome.

METHODS

In a multicentric study, patients (n = 147, of which 96 were women) with OD due to URTI, including C19 and non-C19 were evaluated at two visits with a standardized medical history and "Sniffin' Sticks" extended psychophysical testing to examine the course and possible predictors for improvement of olfactory function.

RESULTS

C19 patients showed better overall olfactory function (p < 0.001) compared to non-C19. Olfactory function (p < 0.001) improved over 3.5 ± 1.2 months in a comparable fashion for C19 and non-C19 comparable over time (p = 0.20) except for a more pronounced improvement of odour threshold (p = 0.03) in C19. C19 patients with parosmia exhibited a higher probability of clinically relevant improvement of odour threshold, a better threshold in the second visit, and tended to have a better TDI-score at the second visit. Further possible predictors for an improving olfactory function were younger age, female gender, and had lower scores in olfactory tests at the first visit.

CONCLUSIONS

Patients with C19 and non-C19 URTI exhibit a similar improvement over 3-4 months except for the odour threshold, with a better TDI in both visits for C19. For C19 a better prognosis in terms of olfactory recovery was found for younger patients with parosmia and lower olfactory scores at the first visit. Still, for many patients with olfactory loss, an improvement that is experienced as complete may only occur over months and possibly years.

Impaired olfaction post-coronavirus disease 2019: a systematic review of smell recovery predictive factors

Background

The devastating coronavirus disease (COVID-19) pandemic seemed not yet to cease. Numerous studies regarding its typical sign and symptoms have been done, presenting one of the most promising predictors of the infection: olfactory dysfunction. Although not life-threatening, the symptom could decrease one’s quality of life, especially if persistent throughout their entire life. Among the countless literature regarding loss of smell, only limited studies denote predictors of smell recovery. This systematic review aimed to bridge the knowledge gap of olfactory impairment prevalence and recovery predictors in people with COVID-19.

Methods

This review was carried out through journal databases, including PubMed, Science Direct, Google Scholar, and medRxiv. Literature published from 2020 to 2022 that complied with the inclusion and exclusion criteria was retrieved, scanned for duplicates with Zotero, and reported using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols 2020 (PRISMA) guidelines.

Results

Of the 2243 studies, seven were assessed with the Prediction model Risk Of Bias ASsessment Tool (PROBAST) to analyze the risk of bias, which five cohort studies deemed relevant. Olfactory dysfunction, olfactory recovery, and its predictive factors are noted. This review is registered in PROSPERO (Registration Number CRD42022318412).

Conclusions

No clinical markers predicted the recovery of olfactory dysfunction, but patients who are more likely to recover are associated with younger age, female sex, and having COVID-19-related symptoms such as nasal congestion and trigeminal sensation. Modifiable factors are still dubious in predicting the olfaction recovery.

Development and Psychometric Validation of the Olfactory Dysfunction Outcomes Rating

Importance

Olfactory dysfunction (OD) is an increasingly common and morbid condition, especially given the ongoing COVID-19 pandemic. Thus, the ability to reproducibly measure smell loss-associated quality of life (QOL) and its response to treatment is paramount.

Objective

To develop and validate a concise and visually appealing smell loss-associated QOL patient-reported outcome measure for OD.

Design, Setting, and Participants

A secondary analysis of comments to an online survey by 1000 patients with olfactory dysfunction published in 2013 was used as the primary source to generate items of the Olfactory Dysfunction Outcomes Rating (ODOR). In addition, 30 patients with OD enrolled in 2 clinical studies at a tertiary care medical center (Washington University) were asked to identify their main concerns associated with smell loss. And finally, 4 otolaryngologists reviewed the items generated from the online survey and the patients' interviews to identify any additional items. Prospective study design was used for data collection from the 30 patients and 4 otolaryngologists. Prospective study design was used for survey validation. Validation of the ODOR was performed with 283 patients enrolled in several prospective studies at a single institution that completed the ODOR as an outcome measure.

Main Outcomes and Measures

Item generation and selection were the outcomes of ODOR development. The psychometric and clinimetric measures evaluated for validation were internal consistency, test-retest reliability, face and content validity, concurrent validity, and discriminant validity. Minimal clinically important difference was also determined.

Results

The ODOR is a 28-item instrument with each item scored as either no difficulty or very rarely bothered (0) to complete difficulty or very frequently bothered (4) with a total instrument score range of 0 to 112 points. Higher scores indicate higher degree of dysfunction and limitation. Validation in the cohort of 283 patients (mean [SD] age, 47.0 [14.4] years; 198 female participants [73%]; 179 White participants [80%]) revealed that the instrument has high internal consistency (Cronbach α = 0.968), test-retest reliability (r = 0.90 [95% CI, 0.81-0.95]), face validity, content validity, concurrent validity (r = 0.87 [95% CI, 0.80-0.91] compared with the Questionnaire of Olfactory Disorders-Negative Statements; ρ = -0.76 [95% CI, -0.81 to -0.71] compared with a patient-reported symptom severity scale), and divergent validity (mean score difference, -33.9 [95% CI, -38.3 to -29.6] between normosmic patients and hyposmic/anosmic patients). The minimal clinically important difference was 15 points. The estimated time for survey completion was approximately 5 minutes.

Conclusions and Relevance

In this survey creation and validation study, the ODOR was shown to be a novel, concise, reliable, and valid patient-reported outcome measure of OD-associated QOL. It can be used to measure physical problems, functional limitations, and emotional consequences associated with OD and how they change after a given intervention, which is clinically applicable and particularly pertinent given the growing burden of OD associated with COVID-19.

Proof-of-concept: SCENTinel 1.1 rapidly discriminates COVID-19 related olfactory disorders

It is estimated that 20-67% of those with COVID-19 develop olfactory disorders, depending on the SARS-CoV-2 variant. However, there is an absence of quick, population-wide olfactory tests to screen for olfactory disorders. The purpose of this study was to provide a proof-of-concept that SCENTinel 1.1, a rapid, inexpensive, population-wide olfactory test, can discriminate between anosmia (total smell loss), hyposmia (reduced sense of smell), parosmia (distorted odor perception), and phantosmia (odor sensation without a source). Participants were mailed a SCENTinel 1.1 test, which measures odor detection, intensity, identification, and pleasantness, using one of four possible odors. Those who completed the test (N = 381) were divided into groups based on their self-reported olfactory function: quantitative olfactory disorder (anosmia or hyposmia, N = 135), qualitative olfactory disorder (parosmia and/or phantosmia; N = 86), and normosmia (normal sense of smell; N = 66). SCENTinel 1.1 accurately discriminates quantitative olfactory disorders, qualitative olfactory disorders, and normosmia groups. When olfactory disorders were assessed individually, SCENTinel 1.1 discriminates between hyposmia, parosmia and anosmia. Participants with parosmia rated common odors less pleasant than those without parosmia. We provide proof-of-concept that SCENTinel 1.1, a rapid smell test, can discriminate quantitative and qualitative olfactory disorders, and is the only direct test to rapidly discriminate parosmia.

Incidence of Anosmia among Covid 19 patients in India

The pandemic COVID-19 has relentlessly caused havoc to human life since its outbreak in December 2019. The disease has been a challenge for all. The clinical manifestations of Covid-19 ranges from no symptoms at all to severe acute respiratory distress syndrome. Anosmia being one of the important clinical features of COVID-19 has always been overlooked by the Indian population. This formed the background for this study. Aim To identify the incidence of anosmia reported in COVID- 19 patients in India. Materials and Methods Literature search was carried out from January 2020 to March 2021 in databases like PUBMED and Google Scholar using the key words "ANOSMIA", "HYPOSMIA" and "OLFACTORY DYSFUNCTION" in conjunction with "COVID-19", "SARS-COV-2", and "CORONAVIRUS". Boolean operators were used to narrow and broaden the search. The search yielded sixteen eligible articles. Result The scrutiny of the 16 articles revealed an incidence range of anosmia from 9.2% to 82% and an average anosmia incidence rate of 30.19%. The cumulative incidence rate of anosmia in those studies where objective analysis was done is 52.2% and 16.4% for subjective analysis. Discussion The prevalence of anosmia in Indian population is found to be much lesser than that reported by European countries due to ethnicity or negligence. Objective evaluation of anosmia in COVID-19 patients increases the incidence of anosmia drastically. Hence objective evaluations such as UPIST, SNIFFING STICK test, etc. is to be promoted. This study also Emphasises the lack of common gold standard testing for olfaction like vision and hearing.

Associations of Prior Head Injury With Olfaction in Older Adults: Results From the Atherosclerosis Risk in Communities (ARIC) Study

Importance

Traumatic brain injury has been associated with short-term olfactory dysfunction, but the association of number of prior head injuries and head injury severity with both subjective and objective long-term olfactory function is less clear.

Objective

To investigate the associations of prior head injury, number of prior head injuries, and head injury severity with subjective and psychophysical (objective) olfactory function in older adults and to examine concordance between subjective and objective olfactory function among individuals with and without head injury.

Design, Setting, and Participants

This prospective cohort study included 5951 participants who attended Atherosclerosis Risk in Communities (ARIC) Study visit 5 (2011 through 2013). Data analysis was performed between November 2021 and May 2022.

Exposures

Head injury was defined by self-report and International Classification of Diseases codes.

Main Outcomes and Measures

Self-reported subjective olfactory dysfunction was assessed by the question, "Do you suffer from smell loss or a significantly decreased sense of smell?" Objective olfactory performance was assessed using the 12-item Sniffin' Sticks odor identification test.

Results

Overall, the 5951 participants were a mean (SD) age of 75.6 (5.2) years, 3501 (58.8%) were female, 1356 (22.8%) were of Black race, and 1666 (28.0%) had a history of head injury. Participants with prior head injury were more likely than individuals without prior head injury to report subjective olfactory dysfunction (24% vs 20%; difference, 4%; 95% CI, 1% to 6%) and have objective anosmia (15% vs 13%; difference, 2%; 95% CI, 0.1% to 4%) but had lower concordance between subjective and objective assessment (72% vs 77%; difference, -5%; 95% CI, -8% to -3%). In logistic regression models adjusted for sociodemographics and medical comorbidities including cognitive status, participants with a history of prior head injury, particularly individuals with 2 or more prior head injuries and more severe head injuries, were more likely to self-report subjective olfactory dysfunction and were more likely to be found to have objective anosmia compared with participants with no history of head injury.

Conclusions and Relevance

Findings of this cohort study provide evidence supporting the association between head injury and olfactory dysfunction, particularly among individuals who experienced multiple prior head injuries and among individuals with more severe head injury. The findings also suggest that individuals with prior head injury were more likely to both under-self-report and over-self-report deficits compared with objective olfactory testing; therefore, it may be important to consider objective olfactory testing in this patient population.

Sociodemographic Characteristics and Comorbidities of Patients With Long COVID and Persistent Olfactory Dysfunction

IMPORTANCE

Determining the characteristics, type, and severity of olfactory dysfunction in patients with long COVID is important for the prognosis and potential treatment of the affected population.

OBJECTIVE

To describe the sociodemographic and clinical features of patients with long COVID who develop persistent olfactory dysfunction.

DESIGN, SETTING, AND PARTICIPANTS

This cross-sectional study, conducted at a rehabilitation center at a public university in the Amazon region of Brazil between September 9, 2020, and October 20, 2021, comprised 219 patients with long COVID and self-reported neurologic symptoms. Of these 219 patients, 139 received a diagnosis of chronic olfactory dysfunction, as confirmed by the Connecticut Chemosensory Clinical Research Center (CCCRC) test.

EXPOSURE

Clinical diagnosis of long COVID.

MAIN OUTCOMES AND MEASURES

Electronic case report forms were prepared for the collection of sociodemographic and clinical data. Patients' sense of smell was evaluated via a CCCRC test, and the association of olfactory dysfunction with aspects of daily life was recorded using a questionnaire.

RESULTS

Of the 219 patients included in the study, 164 (74.9%) were women, 194 (88.6%) were between 18 and 59 years of age (mean [SD] age, 43.2 [12.9] years), 206 (94.1%) had more than 9 years of education, and 115 (52.5%) had a monthly income of up to US $192.00. In the study group, 139 patients (63.5%) had some degree of olfactory dysfunction, whereas 80 patients (36.5%) had normosmia. Patients with olfactory dysfunction had a significantly longer duration of long COVID symptoms than those in the normosmia group (mean [SD], 242.7 [101.9] vs 221.0 [97.5] days; P = .01). Among patients with anosmia, there was a significant association between olfactory dysfunction and daily activities, especially in terms of impairment in hazard detection (21 of 31 patients [67.7%]), personal hygiene (21 of 31 patients [67.7%]), and food intake (21 of 31 patients [67.7%]). Univariable logistic regression analyses found that ageusia symptoms were associated with the occurrence of olfactory dysfunction (odds ratio [OR], 11.14 [95% CI, 4.76-26.07]; P < .001), whereas headache (OR, 0.41 [95% CI, 0.22-0.76]; P < .001) and sleep disorders (OR, 0.48 [95% CI, 0.26-0.92]; P = .02) showed an inverse association with the occurrence of olfactory dysfunction.

CONCLUSIONS AND RELEVANCE

Olfactory dysfunction is one of the most important long-term neurologic symptoms of COVID-19, with the highest prevalence seen among women, adults, and outpatients. Patients with olfactory dysfunction may experience persistent severe hyposmia or anosmia more than 1 year from the onset of symptoms, suggesting the possibility of the condition becoming a permanent sequela.

COVID-19, Anosmia, and Allergies: Is There a Relationship? A Pediatric Perspective

Background: Between June and July 2020, we evaluated children and adolescents concerning post-infection surveillance after a COVID-19 positivity during the lockdown. We aimed to assess whether the anamnestic presence of allergies could correlate with the presence of SARS-CoV-2 symptoms, and in particular with anosmia. Material and methods: For each patient, we collected anamnestic data, the presence of allergies documented by performing skin prick tests, and COVID-19 symptoms. Then, if over six years of age, each patient underwent an active anterior rhinomanometry. Results: A total of 296 patients were enrolled, of whom 105 (35.4%) reported allergies. Considering COVID-19 symptoms, 74 subjects (25%) presented an asymptomatic form, 222 (75%) reported symptoms, and anosmia recurred in 60 subjects (27.03%). A statistically significant relationship was found between allergies and symptomatic COVID-19 (p = 0.042), allergies, and anosmia (p = 0.05), and allergies and anosmia in males (p = 0.007). Moreover, anosmic patients presented a higher body mass index, older age, and a longer COVID-19 duration with statistical significance (p = 0.001, 0.001, 0.006, respectively). Conclusions: Allergic subjects seem to develop symptomatic COVID-19 more frequently and allergies appear to be a protective factor from anosmia’s onset in males.

Could melatonin have a potential adjuvant role in the treatment of the lasting anosmia associated with COVID-19? A review

INTRODUCTION

Anosmia, the loss of the sense of smell, is usually associated with rhinopathies and has been reported as a common symptom of COVID-19. There is no specific drug to treat this condition, although some evidence suggests that melatonin could promote the recovery of olfactory sensory neurons.

METHODS

We set out to perform a narrative review to synthesize the current evidence in this area in respect of our hypothesis that melatonin may be linked with anosmia and play a part in oxidative stress and the regulation of inflammation. The main electronic databases (MEDLINE/PubMed, Embase, and Cochrane) were searched.

RESULTS

The search produced 26 articles related to our hypothesis. Some studies examined issues related to melatonin's effects and its use as adjuvant therapy for COVID-19. Despite some studies suggesting that melatonin may have potential in the treatment of COVID-19, to the best of our knowledge, there have been no trials that have used it to treat anosmia associated with the disease. Few articles identified proposed that melatonin might have an effect on olfactory cells.

DISCUSSION

Further experimental and clinical research on the role of circadian melatonin in the olfactory system is warranted. This will provide evidence of the use of melatonin in the management of anosmia. A number of identified studies suggest that the imbalanced release of melatonin by the pineal gland associated with sleep disturbance may play a role in anosmia, although the specific pathway is not yet entirely clear. This may be a base for further research into the potential role of melatonin as adjuvant treatment of anosmia.

Long-Lasting Olfactory Dysfunction in Hospital Workers Due to COVID-19: Prevalence, Clinical Characteristics, and Most Affected Odorants

Hospital workers have increased exposure risk of healthcare-associated infections due to the frontline nature of their work. Olfactory dysfunction is highly prevalent. The objectives for this investigation are to study the prevalence of long-lasting olfactory dysfunction associated with COVID-19 infection in hospital workers during the first pandemic wave, to identify clinical characteristics and associated symptomatology, and to analyze how many patients with COVID-19 infection had developed olfactory dysfunction during infection and maintained a reduced olfactory function for approximately 10 weeks after diagnosis. Between June and July of 2020, a cross-sectional study was carried out at the Hospital Central de la Cruz Roja San José and Santa Adela in Madrid, Spain. One hundred sixty-four participants were included, of which 110 were patient-facing healthcare staff and 54 were non-patient-facing healthcare staff. Participants were split into three groups, according to COVID-19 diagnosis and presence of COVID-19 related olfactory symptomatology. Participants were asked to complete a structured online questionnaire along with Sniffin' Stick Olfactory Test measurements. In this study, 88 participants were confirmed for COVID-19 infection, 59 of those participants also reported olfactory symptomatology. The prevalence of COVID-19 infection was 11.35%, and the prevalence for olfactory dysfunction was 67.05%. Olfactory dysfunction associated with COVID-19 infection leads to long-lasting olfactory loss. Objective assessment with Sniffin' Stick Olfactory Test points to odor identification as the most affected process. Lemon, liquorice, solvent, and rose are the odors that are worst recognized. Mint, banana, solvent, garlic, coffee, and pineapple, although they are identified, are perceived with less intensity. The findings of this study confirmed a high prevalence of SARS-CoV-2 infection among the hospital workers.

The Adaptive Olfactory Measure of Threshold (ArOMa-T): A rapid test of olfactory function

PURPOSE

Many widely-used psychophysical tests of olfaction have limitations that can create barriers to adoption outside research settings. For example, tests that measure the ability to identify odors may confound sensory performance with memory recall, verbal ability, and past experience with the odor. Conversely, threshold-based tests typically avoid these issues, but are labor intensive. Additionally, many commercially available olfactory tests are slow and may require a trained administrator, making them impractical for use in a short wellness visit or other broad clinical assessment.

METHODS

We tested the performance of the Adaptive Olfactory Measure of Threshold (ArOMa-T) -- a novel odor detection threshold test that employs an adaptive Bayesian algorithm paired with a disposable odor-delivery card -- in a non-clinical sample of individuals (n=534) at the 2021 Twins Day Festival in Twinsburg, OH.

RESULTS

Participants successfully completed the test in under 3 min with a false alarm rate of 9.6% and a test-retest reliability of 0.61. Odor detection thresholds differed by sex (~3.2-fold) and between the youngest and oldest age groups (~8.7-fold), consistent with prior work. In an exploratory analysis, we failed to observe evidence of detection threshold differences between participants who reported a history of COVID-19 and matched controls who did not. We also found evidence for broad-sense heritability of odor detection thresholds.

CONCLUSION

Together, these data indicate the ArOMa-T can determine odor detection thresholds. The ArOMa-T may be particularly valuable in clinical or field settings where rapid and portable assessment of olfactory function is needed.

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.

Dedicated Olfaction and Taste Items do not Improve Psychometric Performance of the SNOT-22

Objective

Previous work has shown the chemosensory dysfunction item of the 22‐item Sinonasal Outcome Test (SNOT‐22) that assesses problems with “taste/smell” has poor psychometric performance compared with other items on the SNOT‐22, which we have hypothesized is due to the simultaneous assessment of two different senses. Our aim was to determine whether distinct smell and taste items in the SNOT‐22 would improve psychometric performance.

Methods

One hundred and eighty‐one CRS patients were recruited and completed the SNOT‐22. Additional items querying problems with the senses of “smell” and “taste,” using the same response scale and recall period were given to study participants. Item response theory (IRT) was used to determine IRT parameters, including item discrimination, difficulty, and information provided by each SNOT‐22 item.

Results

Confirming previous studies, the chemosensory item of the SNOT‐22 (reflecting “taste/smell”) had poor psychometric performance. Use of a distinct smell or taste item instead of the combined “taste/smell” item did not improve psychometric performance. However, a dedicated smell question resulted in a left shift of threshold parameters, showing that the dedicated smell item better captures moderate CRS disease burden than the original taste/smell item of the SNOT‐22, which by virtue of near‐identical IRT parameters appears to more greatly reflect problems with taste.

Conclusions

A dedicated smell‐ or taste‐specific item, rather than the combined “taste/smell” item currently in the SNOT‐22 does not provide significantly greater psychometric performance. However, a dedicated smell item may better capture moderate CRS disease burden compared with the current chemosensory item on the SNOT‐22. Laryngoscope, 132:1644–1651, 2022

Emerging Pattern of Post-COVID-19 Parosmia and Its Effect on Food Perception

Olfactory dysfunction is amongst the many symptoms of Long COVID. Whilst most people that experience smell loss post COVID-19 recover their sense of smell and taste within a few weeks, about 10% of cases experience long-term problems, and their smell recovery journey often begins a few months later when everyday items start to smell distorted. This is known as parosmia. The aim of this study was to identify the key food triggers of parosmic distortions and investigate the relationship between distortion and disgust in order to establish the impact of parosmia on diet and quality of life. In this cross-sectional study (n = 727), respondents experiencing smell distortions completed a questionnaire covering aspects of smell loss, parosmia and the associated change in valence of everyday items. There was a significant correlation between strength and disgust (p < 0.0001), and when the selected items were reported as distorted, they were described as either unpleasant or gag-inducing 84% of the time. This change in valence associated with loss of expected pleasure and the presence of strange tastes and burning sensations must certainly lead to changes in eating behaviours and serious longer-term consequences for mental health and quality of life.

Smell Changes and Efficacy of Nasal Theophylline (SCENT) irrigation: A randomized controlled trial for treatment of post-viral olfactory dysfunction

OBJECTIVE

To evaluate the efficacy and safety of intranasal theophylline saline irrigation on olfactory recovery in patients with post-viral olfactory dysfunction (PVOD).

METHODS

Between May 2019 and April 2020, we conducted a double-blinded, placebo-controlled randomized clinical trial of adults with 6-36 months of PVOD. Patients were randomized to nasal theophylline saline irrigation or placebo saline irrigation twice a day for 6 weeks. The primary outcome was the Global Rating of Smell Change. Secondary outcomes were changes in the University of Pennsylvania Smell Identification Test (UPSIT) and Questionnaire of Olfactory Disorders-Negative Statements (QOD-NS).

RESULTS

Twenty-two patients (n = 12, theophylline; n = 10, placebo) completed the study. Slightly more patients in the theophylline group (33%) reported improved smell compared to the placebo group (30%, difference 3.3%, 95% CI -35.6% to 42.3%). The median differences in pre- and post-treatment UPSIT and QOD-NS change between the two groups were 1 (95% CI -3 to 5) and -10 (95% CI -15 to -4), respectively in favor of theophylline. Three patients receiving theophylline and 2 receiving placebo had clinically meaningful improvements on the UPSIT (difference 5%, 95% CI -30% to 40%). There were no adverse events, and serum theophylline levels were undetectable in 10/10 patients.

CONCLUSIONS

While safe, there were no clinically meaningful differences in olfactory change between the two groups except for olfaction-related quality of life, which was better with theophylline. The imprecise estimates suggest future trials will need substantially larger sample sizes or treatment modifications, such as increasing the theophylline dose, to observe larger treatment effects.

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.

The Adaptive Olfactory Measure of Threshold (ArOMa-T): a rapid test of olfactory function

Many widely used psychophysical olfactory tests have limitations that can create barriers to adoption. For example, tests that measure the ability to identify odors may confound sensory performance with memory recall, verbal ability, and prior experience with the odor. Conversely, classic threshold-based tests avoid these issues, but are labor intensive. Additionally, many commercially available tests are slow and may require a trained administrator, making them impractical for use in situations where time is at a premium or self-administration is required. We tested the performance of the Adaptive Olfactory Measure of Threshold (ArOMa-T)-a novel odor detection threshold test that employs an adaptive Bayesian algorithm paired with a disposable odorant delivery card-in a non-clinical sample of individuals (n = 534) at the 2021 Twins Day Festival in Twinsburg, OH. Participants successfully completed the test in under 3 min with a false alarm rate of 7.5% and a test-retest reliability of 0.61. Odor detection thresholds differed by sex (~3.2-fold lower for females) and age (~8.7-fold lower for the youngest versus the oldest age group), consistent with prior studies. In an exploratory analysis, we failed to observe evidence of detection threshold differences between participants who reported a history of COVID-19 and matched controls who did not. We also found evidence for broad-sense heritability of odor detection thresholds. Together, this study suggests the ArOMa-T can determine odor detection thresholds. Additional validation studies are needed to confirm the value of ArOMa-T in clinical or field settings where rapid and portable assessment of olfactory function is needed.

Electrical stimulation of the trigeminal nerve improves olfaction in healthy individuals: A randomized, double-blind, sham-controlled trial

BACKGROUND

Both activated by environmental odorants, there is a clear role for the intranasal trigeminal and olfactory nerves in smell function. Unfortunately, our ability to perceive odorants decreases with age or with injury, and limited interventions are available to treat smell loss.

OBJECTIVE

We investigated whether electrical stimulation of the trigeminal nerve via trigeminal nerve stimulation (TNS) or transcranial direct current stimulation (tDCS) modulates odor sensitivity in healthy individuals.

METHODS

We recruited 20 healthy adults (12 Female, mean age = 27) to participate in this three-visit, randomized, double-blind, sham-controlled trial. Participants were randomized to receive one of three stimulation modalities (TNS, tDCS, or sham) during each of their visits. Odor detection thresholds were obtained at baseline, immediately post-intervention, and 30-min post-intervention. Furthermore, participants were asked to complete a sustained attention task and mood assessments before odor detection testing.

RESULTS

Findings reveal a timeXcondition interaction for guaiacol (GUA) odorant detection thresholds (F (3.188, 60.57) = 3.833, P = 0.0125), but not phenyl ethyl alcohol (PEA) odorant thresholds. At 30-min post-stimulation, both active TNS and active tDCS showed significantly increased sensitivity to GUA compared to sham TNS (Sham TNS = -8.30% vs. Active TNS = 9.11%, mean difference 17.43%, 95% CI 5.674 to 29.18, p = 0.0044; Sham TNS = -8.30% vs. Active tDCS = 13.58%, mean difference 21.89%, 95% CI 10.47 to 33.32, p = 0.0004).

CONCLUSION

TNS is a safe, simple, noninvasive method for boosting olfaction. Future studies should investigate the use of TNS on smell function across different stimulation parameters, odorants, and patient populations.