Insights into the molecular triggers of parosmia based on gas chromatography olfactometry

Comparison of Patient Characteristics and Olfactory Sensitivity for Trigger Odorants in Parosmia and Phantosmia

OBJECTIVES

This study aimed to determine the characteristics of patients with qualitative olfactory dysfunction (qualOD) and whether individuals with parosmia exhibit increased olfactory sensitivity to previously reported odorous triggers of parosmia.

METHODS

This study included individuals aged ≥18 years, divided into quantitative OD only, parosmia, and phantosmia groups. Data collected included: clinical-demographic data, "Sniffin' Sticks" scores, questionnaires (depression scale, importance of olfaction), and information about parosmia and phantosmia. A proportion of patients underwent trigger odor threshold testing for 2-Furfurylthiol [FFT] found in coffee and 2,6-nonadienal [Nonadienal] found in cucumber.

RESULTS

Those with parosmia were typically younger women, with shorter OD duration due to post-viral OD (PVOD), hyposmic/normosmic, and experienced parosmia more severely. Parosmia was 3.5 times more likely in PVOD. Those with phantosmia were older, with longer OD duration due to idiopathic OD, hyposmic/anosmic, and experienced phantosmia less severely. There were no significant differences between FFT and Nonadienal threshold scores in patients with parosmia, phantosmia, or only quantitative OD, but all groups had significantly increased olfactory sensitivity for trigger odors compared to phenyl ethyl alcohol (PEA).

CONCLUSION

Parosmia and phantosmia patients have distinct characteristics. This may provide clinicians with a better understanding of possible olfactory outcomes in these patients. The higher olfactory sensitivity of all groups to trigger odors compared to PEA raises interesting points about parosmia triggers and odors in the context of warning for danger, in relation to the pathophysiology of parosmia that may be worth exploring in future studies.

LEVEL OF EVIDENCE

3 Laryngoscope, 134:3277-3285, 2024.

Treatment of Olfactory Disorders After SARS - CoViD 2 Virus Infection

OBJECTIVE

The benefit of a nasal corticosteroid in the treatment of persistent post-infectious smell disorders is not as clear in previous studies as is assumed for olfactory training. This study would therefore like to describe the treatment strategies using the example of a persistent olfactory dysfunction as a result of a proven infection with SARS-CoViD-2-virus.

METHODS

Twenty patients (average age of 33.9 ± 11.9 years) with hyposmia were included in this study from December 2020 to July 2021. Every second patient received additionally a nasal corticosteroid. The two resulting randomized groups of equal size were screened with the TDI test, a 20-item taste powder test for the assessment of retronasal olfaction and otorhinolaryngological examination. The patients were asked to train twice daily using a standardized odor training kit and followed up after 2 months and 3 months, respectively.

RESULTS

We documented a significant overall improvement in olfactory ability over the investigation period in both groups. While the TDI score steadily increased on average under the combination therapy, the rise under olfactory training alone was initially steeper. This short-term interaction effect over mean two months was not statistically significant. According to Cohen, however, a moderate effect (eta2 = 0.055, Cohen`s d = 0.5) can still be assumed. This effect could be explained by a possibly higher compliance at the beginning of the sole olfactory training due to the lack of further drug treatment offers. When the training intensity decreases, the recovery of the sense of smell stagnates. Adjunctive therapy ultimately outweighs this short-term benefit.

CONCLUSIONS

The results reinforce the recommendation of early and consistent olfactory training on patients with dysosmia due to COVID-19. For continuous improvement of the sense of smell, an accompanying topical treatment seems at least to be worth consideration. The results should be optimized with larger cohorts and using new objective olfactometric methods.

Giving a Voice to Patients With Smell Disorders Associated With COVID-19: Cross-Sectional Longitudinal Analysis Using Natural Language Processing of Self-Reports

BACKGROUND

Smell disorders are commonly reported with COVID-19 infection. The smell-related issues associated with COVID-19 may be prolonged, even after the respiratory symptoms are resolved. These smell dysfunctions can range from anosmia (complete loss of smell) or hyposmia (reduced sense of smell) to parosmia (smells perceived differently) or phantosmia (smells perceived without an odor source being present). Similar to the difficulty that people experience when talking about their smell experiences, patients find it difficult to express or label the symptoms they experience, thereby complicating diagnosis. The complexity of these symptoms can be an additional burden for patients and health care providers and thus needs further investigation.

OBJECTIVE

This study aims to explore the smell disorder concerns of patients and to provide an overview for each specific smell disorder by using the longitudinal survey conducted in 2020 by the Global Consortium for Chemosensory Research, an international research group that has been created ad hoc for studying chemosensory dysfunctions. We aimed to extend the existing knowledge on smell disorders related to COVID-19 by analyzing a large data set of self-reported descriptive comments by using methods from natural language processing.

METHODS

We included self-reported data on the description of changes in smell provided by 1560 participants at 2 timepoints (second survey completed between 23 and 291 days). Text data from participants who still had smell disorders at the second timepoint (long-haulers) were compared with the text data of those who did not (non-long-haulers). Specifically, 3 aims were pursued in this study. The first aim was to classify smell disorders based on the participants' self-reports. The second aim was to classify the sentiment of each self-report by using a machine learning approach, and the third aim was to find particular food and nonfood keywords that were more salient among long-haulers than those among non-long-haulers.

RESULTS

We found that parosmia (odds ratio [OR] 1.78, 95% CI 1.35-2.37; P<.001) as well as hyposmia (OR 1.74, 95% CI 1.34-2.26; P<.001) were more frequently reported in long-haulers than in non-long-haulers. Furthermore, a significant relationship was found between long-hauler status and sentiment of self-report (P<.001). Finally, we found specific keywords that were more typical for long-haulers than those for non-long-haulers, for example, fire, gas, wine, and vinegar.

CONCLUSIONS

Our work shows consistent findings with those of previous studies, which indicate that self-reports, which can easily be extracted online, may offer valuable information to health care and understanding of smell disorders. At the same time, our study on self-reports provides new insights for future studies investigating smell disorders.

Trigeminal function in patients with COVID-associated olfactory loss

PURPOSE

Olfactory dysfunction (OD) can be a long-term consequence of various viral infections, including COVID-19. Dysfunction includes hyposmia/anosmia and parosmia (odor distortions). Interactions of the virus with the olfactory nerve have been extensively researched, but little is known about the interactions of the intranasal trigeminal nerve system in modulating this sensory loss.

METHODS

We investigated intranasal trigeminal function across COVID-19 OD patients with and without parosmia compared to normosmic controls, to determine whether (1) post-viral hyposmia and/or (2) post-viral hyposmia with parosmia is associated with altered trigeminal function. OD patients (n = 27) were tested for olfactory function using the extended Sniffin' Sticks olfactory test and for trigeminal function through three methods-odor lateralization, subjective ratings of nasal patency, and ammonium vapor pain intensity ratings. This group was subsequently compared to controls, normosmic subjects (n = 15).

RESULTS

Our findings revealed that post-COVID OD patients without parosmia experienced decreased sensitivity in ammonium vapor pain intensity ratings and odor lateralization scores-but similar nasal patency ratings-compared to normosmic controls. There were no significant differences in trigeminal function between OD patients with and without parosmia.

CONCLUSIONS

Based on our results, we conclude that the trigeminal nerve dysfunction may partially explain post-viral OD, but does not seem to be a major factor in the generation of parosmia pathophysiology.

A review of post COVID syndrome pathophysiology, clinical presentation and management in children and young people

Post Covid Syndrome (PCS) is a complex multi-system disorder with a spectrum of presentations. Severity ranges from mild to very severe with variable duration of illness and recovery. This paper discusses the difficulties defining and describing PCS. We review the current understanding of PCS, epidemiology, and predisposing factors. We consider potential mechanisms including viral persistence, clotting dysfunction and immunity. We review presentation and diagnosis and finally consider management strategies including addressing symptom burden, rehabilitation, and novel therapies.

Orthonasal and retronasal odor identification in patients with parosmia

OBJECTIVE

To compare retronasal and orthonasal perception in parosmic COVID-19 patients, in order to determine whether COVID-19 has a differential effect on these functions.

METHODS

Using the Sniffin Sticks test battery orthonasal function was examined for odor threshold, discrimination and identification. Retronasal function was assessed using 20 tasteless aromatized powders. Gustatory function was measured using the Taste Strips test.

RESULTS

This study included 177 patients (127 women, 50 men; mean age 45 years), of whom 127 (72%) were hyposmic and 50 (28%) normosmic. Compared to patients without parosmia, parosmic patients performed worse in odor identification for both orthonasal (F = 4.94, p = 0.03) and retronasal tests (F = 11.95, p < 0.01). However, an interaction effect between route of odor identification (orthonasal or retronasal) and parosmia status was found (F = 4.67, p = 0.03): patients with parosmia had relatively lower retronasal scores than patients without parosmia.

CONCLUSION

Our results suggest that COVID-19 may affect the olfactory mucosa differently along the anterior-posterior axis, thereby possibly contributing to the pathophysiology of parosmia. Patients with parosmia also exhibit a higher degree of impairment when odors are presented through the retronasal route during eating and drinking.

Mechanisms of SARS-CoV-2-associated anosmia

Anosmia, the loss of the sense of smell, is one of the main neurological manifestations of COVID-19. Although the SARS-CoV-2 virus targets the nasal olfactory epithelium, current evidence suggests that neuronal infection is extremely rare in both the olfactory periphery and the brain, prompting the need for mechanistic models that can explain the widespread anosmia in COVID-19 patients. Starting from work identifying the non-neuronal cell types that are infected by SARS-CoV-2 in the olfactory system, we review the effects of infection of these supportive cells in the olfactory epithelium and in the brain and posit the downstream mechanisms through which sense of smell is impaired in COVID-19 patients. We propose that indirect mechanisms contribute to altered olfactory system function in COVID-19-associated anosmia, as opposed to neuronal infection or neuroinvasion into the brain. Such indirect mechanisms include tissue damage, inflammatory responses through immune cell infiltration or systemic circulation of cytokines, and downregulation of odorant receptor genes in olfactory sensory neurons in response to local and systemic signals. We also highlight key unresolved questions raised by recent findings.

ORGANOLEPTIC AND HALITOMETRIC ASSESSMENTS DO NOT CORRELATE WELL IN INTRA-ORAL HALITOSIS: A SYSTEMATIC REVIEW AND META-ANALYSIS

BACKGROUND

The gold standard method for diagnosing oral halitosis is the subjective organoleptic measurement. Device-supported methods are also widespread worldwide. The challenges and safety concerns around performing organoleptic measurements during pandemics and the diversity of measuring device alternatives raised our clinical question: which halitometer is the most suitable for diagnosing halitosis?

METHODS

This systematic review was registered in PROSPERO (ID CRD42022320024). The search was performed on March 23, 2022 in the following electronic databases: MEDLINE, Embase, Scopus, Web of Science, and CENTRAL. Adult populations with or without halitosis were included, and patients with systemic diseases were excluded. Organoleptic (subjective) measurement and the device-supported (objective) methods were compared; the primary outcome was the correlation coefficient, and the secondary was the specificity and sensitivity of the devices. QUADAS-2 and QUADAS-C were used to evaluate the risk of bias in the studies. Random-effects meta analyses were performed on the outcomes, and the secondary outcomes were plotted on a common ROC plot.

RESULTS

A total of 1231 records were found in the 5 databases. After the selection process, 76 articles were eligible for the systematic review, and 14,635 patients were involved in the qualitative analysis. The pooled Spearman's correlation coefficient (c.c.) for sulfide monitors was 0.65; 95% CIs: [0.53-0.74]; I2 = 95%, P < .01. The pooled Spearman's c.c. for portable gas chromatographs was 0.69; 95% CIs: [0.63-0.74]; I2 = 12%, P < .01. The pooled Spearman's c.c. for gas chromatographs was 0.76; 95% CIs: [0.67-0.83]; I2 = 0%, P < .01.

DISCUSSION

None of the most commonly used halitometers proved to be significantly superior to the others. Halimeter and OralChroma measurements did not correlate well with the organoleptic level of oral halitosis in adults. Therefore, better halitometers need to be developed as an alternative to organoleptic measurements.

Characteristics of smell and taste disorders depending on etiology: a retrospective study

PURPOSE

This study investigates the impact of etiology on the epidemiologic profile, disease severity, type of treatment and therapy outcome in smell and taste disorders.

METHODS

This is a retrospective analysis of 270 patients that presented with a smell or taste disorder in a specialized, tertiary care center. An established questionnaire was used to collect data from patients and physicians. Olfactometry was performed with the Sniffin' Sticks test kit, while gustometry was performed by taste strips.

RESULTS

Post-traumatic etiology was associated with young age (median 46 years) and male sex, and showed the most severe degrees of smell loss compared to other etiologies (64.3% anosmia). Postinfectious causes occurred more frequently in females (77.3%) and correlated with a history of pharyngeal surgery, suggesting a vulnerability for virally mediated sensory dysfunction following adenoid/tonsil removal. Parosmia also correlated with both postinfectious etiology (62.5%) and female sex. In sinunasal etiology, the presence of nasal polyps worsened the overall olfactory test score by approximately 50%. In particular, smell threshold and discrimination were reduced, while smell identification was not significantly impacted by nasal polyp obstruction. Sinunasal dysfunction was the only etiology to show significant improvement after therapy (73.9% improved). Finally, we could establish good correlations between the subjective impairment and objective dysfunction for each sensory modality.

CONCLUSION

Each etiology of chemosensory dysfunction shows particular distributions of variables like sex, age, comorbidities and operations, disease severity, sensory threshold, discrimination and identification. This paper offers a detailed account of the correlations between the cause and the characteristics of smell and taste loss.

A parosmia severity index based on word-classification predicts olfactory abilities and impairment

Parosmia is an olfactory disorder that involves distortions of specific odors that may co-occur with anosmia, loss of smell of other odors. Little is known about which odors frequently trigger parosmia, and measures of parosmia severity are lacking. Here, we present an approach to understand and diagnose parosmia that is based on semantic properties (e.g., valence) of words describing odor sources ("fish", "coffee", etc.). Using a data-driven method based on natural language data, we identified 38 odor descriptors. Descriptors were evenly dispersed across an olfactory-semantic space, which was based on key odor dimensions. Parosmia patients (n = 48) classified the corresponding odors in terms of whether they trigger parosmic or anosmic sensations. We investigated whether these classifications are related to semantic properties of the descriptors. Parosmic sensations were most often reported for words describing unpleasant odors of inedibles that are highly associated to olfaction (e.g., "excrement"). Based on PCA modeling, we derived the Parosmia Severity Index-a measure of parosmia severity that can be determined solely from our non-olfactory behavioral task. This index predicts olfactory-perceptual abilities, self-reported olfactory impairment, and depression. We thus provide a novel approach for investigating parosmia and establishing its severity that does not require odor exposure. Our work may enhance our understanding of how parosmia changes over time and how it is expressed differently across individuals.

Post-viral olfactory loss and parosmia

The emergence of SARS-CoV-2 has brought olfactory dysfunction to the forefront of public awareness, because up to half of infected individuals could develop olfactory dysfunction. Loss of smell-which can be partial or total-in itself is debilitating, but the distortion of sense of smell (parosmia) that can occur as a consequence of a viral upper respiratory tract infection (either alongside a reduction in sense of smell or as a solo symptom) can be very distressing for patients. Incidence of olfactory loss after SARS-CoV-2 infection has been estimated by meta-analysis to be around 50%, with more than one in three who will subsequently report parosmia. While early loss of sense of smell is thought to be due to infection of the supporting cells of the olfactory epithelium, the underlying mechanisms of persistant loss and parosmia remain less clear. Depletion of olfactory sensory neurones, chronic inflammatory infiltrates, and downregulation of receptor expression are thought to contribute. There are few effective therapeutic options, so support and olfactory training are essential. Further research is required before strong recommendations can be made to support treatment with steroids, supplements, or interventions applied topically or injected into the olfactory epithelium in terms of improving recovery of quantitative olfactory function. It is not yet known whether these treatments will also achieve comparable improvements in parosmia. This article aims to contextualise parosmia in the setting of post-viral olfactory dysfunction, explore some of the putative molecular mechanisms, and review some of the treatment options available.

The assessment of qualitative olfactory dysfunction in COVID-19 patients: a systematic review of tools and their content validity

Background

There is a lack of overview of the tools used to assess qualitative olfactory dysfunction, including parosmia and phantosmia, following COVID-19 illness. This could have an impact on the diagnosis and treatment offered to patients. Additionally, the formulations of symptoms are inconsistent and often unclear, and consensus around the wording of questions and responses is needed.

Aim of study

The aim of this systematic review is to provide an overview of tools used to assess qualitative olfactory dysfunction after COVID-19, in addition to addressing the content validity (i.e., item and response formulations) of these tools.

Methods

MEDLINE, Web of Science, and EMBASE were searched 5th of August 2022 and updated on the 25th of April 2023 to identify studies that assess qualitative olfactory dysfunction in COVID-19 patients. Primary outcomes were the tool used (i.e., questionnaire or objective test) and item and response formulations. Secondary outcomes included psychometric properties, study design, and demographic variables.

Results

The assessment of qualitative olfactory dysfunction is characterized by heterogeneity, inconsistency, and lack of validated tools to determine the presence and degree of symptoms. Several tools with overlapping and distinct features were identified in this review, of which some were thorough and detailed, while others were merely assessing the presence of symptoms as a binary measure. Item and response formulations are also inconsistent and often used interchangeably, which may lead to confusion, incorrect diagnoses, and inappropriate methods for solving the problem.

Conclusions

There is an unmet need for a reliable and validated tool for assessing qualitative olfactory dysfunction, preferably one that also captures quantitative olfactory issues (i.e., loss of smell), to ensure time-effective and specific assessment of the ability to smell. A consensus around the formulation of items and response options is also important to increase the understanding of the problem, both for clinicians, researchers, and the patient, and ultimately to provide the appropriate diagnosis and treatment.

Registration and protocol

The URL is https://www.crd.york.ac.uk/PROSPERO/display_record.php?RecordID=351621. A preregistered protocol was submitted and accepted (12.09.22) in the International prospective register of systematic reviews (PROSPERO) with the registration number CRD42022351621.

Olfactory Nomenclature: An Orchestrated Effort to Clarify Terms and Definitions of Dysosmia, Anosmia, Hyposmia, Normosmia, Hyperosmia, Olfactory Intolerance, Parosmia, and Phantosmia/Olfactory Hallucination

BACKGROUND

Definitions are essential for effective communication and discourse, particularly in science. They allow the shared understanding of a thought or idea, generalization of knowledge, and comparison across scientific investigation. The current terms describing olfactory dysfunction are vague and overlapping.

SUMMARY

As a group of clinical olfactory researchers, we propose the standardization of the terms "dysosmia," "anosmia," "hyposmia," "normosmia," "hyperosmia," "olfactory intolerance," "parosmia," and "phantosmia" (or "olfactory hallucination") in olfaction-related communication, with specific definitions in this text.

KEY MESSAGES

The words included in this paper were determined as those which are most frequently used in the context of olfactory function and dysfunction, in both clinical and research settings. Despite widespread use in publications, however, there still exists some disagreement in the literature regarding the definitions of terms related to olfaction. Multiple overlapping and imprecise terms that are currently in use are confusing and hinder clarity and universal understanding of these concepts. There is a pressing need to have a unified agreement on the definitions of these olfactory terms by researchers working in the field of chemosensory sciences. With the increased interest in olfaction, precise use of these terms will improve the ability to integrate and advance knowledge in this field.

Parosmia and altered taste in patients recovering from Covid 19

Parosmia is a well-documented consequence of smell loss associated with Covid 19. Those who experience this qualitative olfactory disorder during recovery find that the odour of common foods and household items is distorted, and the experience can range from merely altered to profoundly disgusting. This can lead to a greatly altered relationship with food, including the physical symptoms of loss of appetite, nausea, vomiting, as well as wider reaching issues such as withdrawal from social situations, emotional distancing from others in their close social circles, and anhedonia. There is at present no known cure or intervention to mitigate the condition. The AbScent Parosmia and Phantosmia support group on Facebook became an important resource for patients with this condition during the early part of the pandemic, and the crowd-sourcing of experiences, tips and peer-to-peer advice became a valuable source of information for the community as well as researchers trying to understand the condition. Using protocols described in earlier literature on the use of social media for qualitative research, this paper provides information on the management of parosmia based on the experiences of over 30k patients in the AbScent Parosmia and Phantosmia group on Facebook and 6k member of the AbScent Network.

[Olfaction and respiratory viruses… A relationship revealed by Covid-19]

The sense of smell has been underestimated for a long time in humans. It has been brought to the fore by its sudden disappearance during the Covid-19 pandemic of which anosmia (complete loss of smell) is one of the major symptoms. However, respiratory viruses have long been associated with smell disorders, 25% of which are linked to a viral infection. Olfaction begins in the nose within the olfactory epithelium which has the particularity of containing neurons in direct contact with the environment. Several respiratory viruses are known for their replicative capacity within this epithelium. This is particularly the case for the flu virus (influenza) and bronchiolitis (respiratory syncytial virus) but their tropism for this tissue is much lower than SARS-CoV-2. The understanding of the SARS-CoV-2 pathophysiology in the nasal cavity makes it possible to reveal part of the links between viral infection and olfactory disorders.

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.

Parosmia and Phantosmia: Managing Quality Disorders

Purpose of Review

The purpose of this review was to summarize the current knowledge on parosmia and phantosmia and introduce support and treatment algorithms for the two qualitative olfactory disorders.

Recent Findings

Recent literature regarding parosmia has revealed that patients with the disorder are mainly triggered by certain substances, including thiols and pyrazines. In 2015, the existing "olfactory training" regimen was improved to more effectively treat post-infectious olfactory loss and was named "modified olfactory training" (MOT). It was also found in 2022 that MOT is also effective against COVID-19-induced parosmia.

Summary

Parosmia, the distortion of smells, is a symptom in qualitative olfactory disorders that severely affects patients' mental well-being and enjoyment of their everyday lives. The condition was first documented in 1895 and can affect up to 5% of the general population. Etiologies of parosmia include sinonasal diseases, viruses, surgeries, traumatic brain injury, neurological and psychiatric conditions, toxic chemicals, and medications. Parosmia has seen a surge in cases since the onset of the COVID-19 pandemic and is linked to changes in brain structure following an infection. The evaluation of the symptom is done using surveys, smell identification tests, fMRI, MRI, PET/CT, and gas chromatography. Treatment for parosmia can vary in duration, which makes it essential to focus not only on helping the patients regain normosmia, but also on supporting the patient through the recovery journey. Parosmia should not be confused with phantosmia, in which the distortion of smells occurs in the absence of olfactory stimuli. The etiology of phantosmia can vary from infections and traumatic brain injury to psychiatric disorders like schizophrenia. Unlike parosmia, the treatment of phantosmia is less straightforward, with an emphasis on determining the etiology and providing symptomatic relief.

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.

Olfactory dysfunction in COVID-19: new insights into the underlying mechanisms

The mechanisms of olfactory dysfunction in COVID-19 are still unclear. In this review, we examine potential mechanisms that may explain why the sense of smell is lost or altered. Among the current hypotheses, the most plausible is that death of infected support cells in the olfactory epithelium causes, besides altered composition of the mucus, retraction of the cilia on olfactory receptor neurons, possibly because of the lack of support cell-derived glucose in the mucus, which powers olfactory signal transduction within the cilia. This mechanism is consistent with the rapid loss of smell with COVID-19, and its rapid recovery after the regeneration of support cells. Host immune responses that cause downregulation of genes involved in olfactory signal transduction occur too late to trigger anosmia, but may contribute to the duration of the olfactory dysfunction.

Insight into the mechanisms of olfactory dysfunction by COVID-19

One of the unique symptoms of COVID-19 is chemosensory dysfunction. Almost three years since the beginning of the pandemic of COVID-19, there have been many studies on the symptoms, progress, and possible causes, and also studies on methods that may facilitate recovery of the senses. Studies have shown that some people recover their senses even within a couple of weeks whereas there are other patients that fail to recover chemosensory functions fully for several months and some never fully recover. Here we summarize the symptoms and the progress, and then review the papers on the causation as well as the treatments that may help facilitate the recovery of the symptoms. Depending on the differences in the levels of severity and the locations where the main pathological venues are, what is most effective in facilitating recovery can vary largely across patients and thus may require individualized strategies for each patient. The goal of this paper is to provide some thoughts on these choices depending on the differences in the causes and severity.