An algorithmic approach to the evaluation and treatment of olfactory disorders

Loss of smelling is an early marker of aging and is associated with inflammation and DNA damage in C57BL/6J mice

Olfactory dysfunction is a prevalent symptom and an early marker of age-related neurodegenerative diseases in humans, including Alzheimer's and Parkinson's Diseases. However, as olfactory dysfunction is also a common symptom of normal aging, it is important to identify associated behavioral and mechanistic changes that underlie olfactory dysfunction in nonpathological aging. In the present study, we systematically investigated age-related behavioral changes in four specific domains of olfaction and the molecular basis in C57BL/6J mice. Our results showed that selective loss of odor discrimination was the earliest smelling behavioral change with aging, followed by a decline in odor sensitivity and detection while odor habituation remained in old mice. Compared to behavioral changes related with cognitive and motor functions, smelling loss was among the earliest biomarkers of aging. During aging, metabolites related with oxidative stress, osmolytes, and infection became dysregulated in the olfactory bulb, and G protein coupled receptor-related signaling was significantly down regulated in olfactory bulbs of aged mice. Poly ADP-ribosylation levels, protein expression of DNA damage markers, and inflammation increased significantly in the olfactory bulb of older mice. Lower NAD⁺ levels were also detected. Supplementation of NAD⁺ through NR in water improved longevity and partially enhanced olfaction in aged mice. Our studies provide mechanistic and biological insights into the olfaction decline during aging and highlight the role of NAD⁺ for preserving smelling function and general health.

Assessment and Scientific Progresses in the Analysis of Olfactory Evoked Potentials

The human sense of smell is important for many vital functions, but with the current state of the art, there is a lack of objective and non-invasive methods for smell disorder diagnostics. In recent years, increasing attention is being paid to olfactory event-related potentials (OERPs) of the brain, as a viable tool for the objective assessment of olfactory dysfunctions. The aim of this review is to describe the main features of OERPs signals, the most widely used recording and processing techniques, and the scientific progress and relevance in the use of OERPs in many important application fields. In particular, the innovative role of OERPs is exploited in olfactory disorders that can influence emotions and personality or can be potential indicators of the onset or progression of neurological disorders. For all these reasons, this review presents and analyzes the latest scientific results and future challenges in the use of OERPs signals as an attractive solution for the objective monitoring technique of olfactory disorders.

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

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

Persistent Parosmia Caused By COVID-19 Infection: An Emerging Symptom

Objectives

Coronavirus disease 2019 (COVID-19) is associated with several known signs and symptoms, including olfactory disturbances leading to anosmia and parosmia. This study aimed to evaluate the clinical features of the emerging symptoms of post-COVID-19 parosmia and to report the outcome of commonly used intervention methods.

Methods

The study’s sample included post-COVID-19 patients who complained of parosmia, presented to otorhinolaryngology clinics at private tertiary care hospitals from December 2020 to April 2021. Patients’ data were collected from the hospital system and through direct phone interviews. The Modified Arabic 20-Items Sino-Nasal Outcome Test (MA-SNOT-20) was used to measure the severity of rhinosinusitis symptoms.

Results

Twenty-one patients were included in the study, and their ages mainly ranged between 20 and 39 years (76.2%), predominantly females 19 (90.5%). Post the COVID-19 illness course, nearly half of the patients (9; 42.9%) reported full recovery of olfaction and taste senses. Nine cases (42.9%) received treatment with intranasal and oral steroids, of which only three cases (14.3%) noticed improvement. The remaining 12 cases (57.1%) did not receive any treatment, two of which improved (9.5%). The maximum MA-SNOT score was 37 while the minimum was 3, and eight patients (38.1%) scores were between one and 10 points.

Conclusion

Olfactory and taste dysfunctions are common symptoms of COVID-19. The emerging symptom of parosmia is worth reporting in the literature to increase the awareness of this particular symptom in this pandemic era. Many management strategies have been introduced that might be effective. However, further studies are needed to establish evidence-based management protocols.

ACE2 in the Gut: The Center of the 2019-nCoV Infected Pathology

The 2019-nCoV is a rapidly contagious pneumonia caused by the recently discovered coronavirus. Although generally the most noticeable symptoms are concentrated in the lungs, the disorders in the gastrointestinal tract are of great importance in the diagnosis of 2019-nCoV. The angiotensin-converting enzyme 2 (ACE2), an important regulator of many physiological functions, including blood pressure and nutrients absorption, is recently identified as a vital entry for 2019-nCoV to enter host cells. In this review, we summarize its functions both physiologically and pathologically. We also elaborate its conflicting roles from the clews of contemporary researches, which may provide significant indications for pharmacological investigations and clinical uses.

Olfactory dysfunction in aging and neurodegenerative diseases

Alterations in olfactory functions are proposed to be early biomarkers for neurodegeneration. Many neurodegenerative diseases are age-related, including two of the most common, Parkinson's disease (PD) and Alzheimer's disease (AD). The establishment of biomarkers that promote early risk identification is critical for the implementation of early treatment to postpone or avert pathological development. Olfactory dysfunction (OD) is seen in 90% of early-stage PD patients and 85% of patients with early-stage AD, which makes it an attractive biomarker for early diagnosis of these diseases. Here, we systematically review widely applied smelling tests available for humans as well as olfaction assessments performed in some animal models and the relationships between OD and normal aging, PD, AD, and other conditions. The utility of OD as a biomarker for neurodegenerative disease diagnosis and future research directions are also discussed.

Pathophysiology and possible treatments for olfactory-gustatory disorders in patients affected by COVID-19

SARS-CoV-2 infects host cells mainly through the interaction between the virus's Spike protein and the viral receptors namely Angiotensin-Converting Enzyme 2 (ACE2) and transmembrane serine protease 2 (TMPRSS2). Both are highly expressed in the gastrointestinal tract, in the nasal and bronchial epithelium, as well as in the type II alveolar epithelial cells. The aim of this review is to report the evidences from the scientific literature on the pathophysiology and the available treatments for olfactory-gustatory disorders in patients with COVID-19. The mechanisms involved in these disorders are still unclear and studies on specific therapies are scarce. However, it has been hypothesized that a decrease in the sensitivity of the sensory neurons as well as the co-expression of ACE2 and TMPRSS2 in the alveolar epithelial cells are the main causes of olfactory-gustatory disorders. The possible mechanisms described in the literature for changes in taste perception in patients with COVID-19 include olfactory disorders and a competitive activity of COVID-19 on ACE2 receptors in the taste buds. In addition, SARS-CoV-2 can bind to sialic acid receptors in the taste buds. In general, evidences show that there is no specific treatment for olfactory-taste disorders induced by SARS-CoV-2, even though some treatments have been used and have shown some promising results, such as olfactory training, intranasal application of sodium citrate and vitamin A, as well as systemic use of omega-3 and zinc. Corticosteroids have also been used as a pharmacological approach to treat patients with olfactory dysfunction with some contradictory results. The knowledge of the mechanisms by which SARS-CoV-2 influences the sensory systems and how effective therapies can treat the loss of smell and taste will have important implications on the understanding and clinical management of olfactory-taste disorders.

Acupuncture is associated with a positive effect on odour discrimination in patients with postinfectious smell loss-a controlled prospective study

Introduction

Smell disorders are common in the general population and occur e.g., after infections, trauma or idiopathically Treatment strategies for smell loss range from surgery, medication to olfactory training, depending on the pathology, but they are limited This study examined the effect of acupuncture on olfactory function.

Methods

Sixty patients with smell loss following infections of the upper respiratory tract were included in this investigation Half of the study group were randomly assigned to verum acupuncture and the other half to sham acupuncture Olfaction was measured by means of the “Sniffin’ Sticks” test battery (odour threshold, discrimination and identification).

Results

Compared to sham acupuncture, verum was associated with an improvement of smell function as measured by the TDI score (p = 0.039) The improvement was largely determined by improvement in odour discrimination, and was significantly better in patients with a shorter duration of the disorder.

Conclusion

The present results suggest that acupuncture is an effective supplementary treatment option for patients with olfactory loss.

Younger adults with mild-to-moderate COVID-19 exhibited more prevalent olfactory dysfunction in Taiwan

Background

Coronavirus Disease 2019 (COVID-19) is rapidly transmitted from person to person, causing global pandemic since December 2019. Instantly detecting COVID-19 is crucial for epidemic prevention. In this study, olfactory dysfunction is a significant symptom in mild to moderate COVID-19 patients but relatively rare in other respiratory viral infections. The Taiwan smell identification test (TWSIT) is a speedy and inexpensive option for accurately distinguishing anosmia that also quantifies the degree of anosmia. Using TWSIT in the outpatient clinic for early identifying the patients with mild to moderate COVID-19 can be promising.

Methods

Nineteen patients confirmed COVID-19 in central Taiwan were collected and divided into two groups: olfactory dysfunction and non-olfactory dysfunction. Demographic characteristics, laboratory findings, and the results of the olfactory test were compared between these two groups.

Findings

Thirteen (68.4%) of the 19 patients had olfactory dysfunction. The patients with olfactory dysfunction were younger than those without this symptom. The statistical difference in age distribution was significant between these two groups (IQR: 25.5–35.5 vs. IQR: 32.5–60.3; p-value: 0.012). There was no significant difference in gender, smoking history, comorbidities, travel history, respiratory tract infection symptoms, and laboratory findings between these two groups.

Conclusion

This study demonstrated that young adults were prone to develop olfactory dysfunctions. In the flu season, olfactory dysfunction is considered a specific screening criterion for early detecting COVID-19 in the community. TWSIT can serve as a decent test for quantifying and qualifying olfactory dysfunction.

Evaluation of the Incidence of Other Cranial Neuropathies in Patients With Postviral Olfactory Loss

Importance

Postviral olfactory loss is a common cause of olfactory impairment, affecting both quality of life as well as overall patient mortality. It is currently unclear why some patients are able to recover fully after a loss while others experience permanent deficit. There is a lack of research on the possible association between postviral olfactory loss and other cranial neuropathies.

Objective

To evaluate the incidence of other cranial nerve deficits in patients with postviral olfactory loss and determine if there is an association with neurologic injury in this group. This study also sought to determine if other known risk factors were associated with postviral olfactory loss.

Design, Setting, and Participants

A case-control study was conducted at a tertiary care rhinology clinic from January 2015 to January 2018 to review the incidence of cranial neuropathies in 2 groups of patients, those with postviral olfactory loss and those with chronic rhinosinusitis without olfactory loss used as a control group.

Exposures

The Stanford Translational Research Integrated Database Environment (STRIDE) system was used for patient identification and data extraction. Patients with a history of olfactory loss or chronic rhinosinusitis as well as incidence of cranial neuropathies were identified by using International Statistical Classification of Diseases and Related Health Problems, Tenth Revision (ICD-10) codes.

Main Outcomes and Measures

This study reviewed incidence of postviral or idiopathic cranial neuropathies in both patient groups, while also evaluating for any difference in demographic characteristics, comorbidities, or other patient-related factors.

Results

There were 91 patients in the postviral olfactory loss group and 100 patients in the control group, which were age and sex matched as closely as possible. Of the 91 patients with postviral olfactory loss, mean (SD) age was 56.8 (15.3), and 58 (64%) were women; for the control group, the mean (SD) age was 57.5 (15.6) years, and 63 (63%) were women. Racial breakdown was similar across cases and controls, with white individuals making up 59% to 65%; Asian individuals, 20% to 24%; black individuals, approximately 3%; Hispanic individuals, approximately 1%; and the remaining patients being of other race/ethnicity. The incidence of other cranial neuropathies in the postviral olfactory loss group was 11% compared with 2% within the control group (odds ratio, 6.1; 95% CI, 1.3-28.4). The study also found 2 cases of multiple cranial neuropathies within a single patient within the olfactory group. Family history of neurologic disease was associated with more than 2-fold greater odds of cranial nerve deficit (odds ratio, 3.05; 95% CI, 0.59-15.68).

Conclusions and Relevance

Postviral olfactory loss appears to be associated with a higher incidence of other cranial neuropathies. It is possible that there is an inherent vulnerability to nerve damage or decreased ability for nerve recovery in patients who experience this disease process.

Expansion of murine and human olfactory epithelium/mucosa colonies and generation of mature olfactory sensory neurons under chemically defined conditions

Olfactory dysfunctions, including hyposmia and anosmia, affect ~100 million people around the world and the underlying causes are not fully understood. Degeneration of olfactory sensory neurons and incapacity of globose basal cells to generate olfactory sensory neurons are found in elder people and patients with smell disorders. Thus, olfactory stem cell may function as a promising tool to replace inactivated globose basal cells and to generate sensory neurons. Methods: We established clonal expansion of cells from the murine olfactory epithelium as well as colony growth from human olfactory mucosa using Matrigel-based three-dimensional system. These colonies were characterized by immunostaining against olfactory epithelium cellular markers and by calcium imaging of responses to odors. Chemical addition was optimized to promote Lgr5 expression, colony growth and sensory neuron generation, tested by quantitative PCR and immunostaining against progenitor and neuronal markers. The differential transcriptomes in multiple signaling pathways between colonies under different base media and chemical cocktails were determined by RNA-Seq. Results: In defined culture media, we found that VPA and CHIR99021 induced the highest Lgr5 expression level, while LY411575 resulted in the most abundant yield of OMP⁺ mature sensory neurons in murine colonies. Different base culture media with drug cocktails led to apparent morphological alteration from filled to cystic appearance, accompanied with massive transcriptional changes in multiple signaling pathways. Generation of sensory neurons in human colonies was affected through TGF-β signaling, while Lgr5 expression and cell proliferation was regulated by VPA. Conclusion: Our findings suggest that targeting expansion of olfactory epithelium/mucosa colonies in vitro potentially results in discovery of new source to cell replacement-based therapy against smell loss.

Self-reported course of olfactory impairment determines outcome for successful surgical intervention in nasal polyps with anosmia

BACKGROUND

Olfactory impairment is one of important symptoms of Chronic rhinosinusitis with nasal polyps (CRSwNP). However, the relationship between course of olfactory impairment and postoperative symptom improvement was still unclear.

OBJECTIVE

The aim of this study was to assess the relationship between the self-reported course of olfactory loss and the degree of improvement in olfaction to determine the timing for successful surgical intervention in improving olfaction in patients with CRSwNP.

MATERIALS AND METHODS

A total of 86 CRSwNP patients with loss of smell and undergoing functional endoscopic sinus surgery (FESS) were recruited consecutively. The self-reported course of smell lose before treatment was recorded. Olfactory function was recorded before and after FESS using T&T Olfactometry.

RESULTS

Fifty-seven patients demonstrated recovery of olfaction and 29 patients no-recovery. The average recovery time of smell loss in the study was 2.6 weeks. The course of smell loss showed moderate accuracy as a marker for determining the timing for successful FESS; with up to 4.5 years of self-reported smell loss being the cut-off point for recovery of smell following FESS.

CONCLUSION

This study suggests that FESS in CRSwNP patients with self-reported significant olfactory impairment for less than 4.5 years may lead to improvement in olfaction.

SIGNIFICANCE

FESS in CRSwNP patients with self-reported significant olfactory impairment persisting for less than 4.5 years may lead to considerable improvement in olfaction in these patients.

Subjective and Objective Assessments of Post-traumatic Olfactory Dysfunction

Introduction: Traumatic brain injuries are the most common cause of olfactory dysfunction. Deficits in olfaction may be conductive or neurosensory in nature, with varying degrees of impairment resulting in a diminished quality of life and an increased risk for personal injury among patients. The aim of this research is to evaluate the results of the subjective and objective quantitative examinations of olfactory function in a group of patients with post-traumatic anosmia in order to predict its value in identifying olfactory deficits in clinical practice.

Materials and Methods: The present study included 38 patients who reported anosmia or hyposmia caused by a traumatic head injury, and a group of 31 age- and sex-matched controls without olfactory dysfunction or prior history of head injury. The comparison of odor perception and identification of two oils (mint and anise) was assessed with the use of blast olfactometry with cortical olfactory event-related potentials.

Results: Subjective olfactory tests revealed anosmia or hyposmia in 94% of patients with head injury-related olfactory dysfunction. Objective tests revealed olfactory event-related potentials from cranial nerve I produced by the stimulation with both mint and anise in 20 patients (52.6%). Olfactory event-related potentials from cranial nerve V produced by the stimulation with mint were registered in 26 patients (68.4%). The lack of any responses, from both cranial nerve I and V, was found in 12 patients (32% of cases).

Conclusions: Findings from our study indicate the application of both subjective and objective examinations in the evaluation of patients with olfactory impairment. In the diagnosis of post-traumatic anosmia or hyposmia, objective examinations are particularly useful when the patients' level of cognition may be impaired or when subjects may be exaggerating their olfactory defects for a secondary gain. The diagnosis of damage to the olfactory system, specifically in the receptive part of the olfactory pathway, can be established in patients who showed reduced amplitudes or absent cortical responses in addition to absent odor identification and perception threshold in the subjective examination.

Diseases of the nasal cavity

Despite garnering minimal attention from the medical community overall, olfaction is indisputably critical in the manner in which we as humans interact with our surrounding environment. As the initial anatomical structure in the olfactory pathway, the nasal airway plays a crucial role in the transmission and perception of olfactory stimuli. The goal of this chapter is to provide a comprehensive overview of olfactory disturbances as it pertains to the sinonasal airway. This comprises an in-depth discussion of clinically relevant nasal olfactory anatomy and physiology, classification systems of olfactory disturbance, as well as the various etiologies and pathophysiologic mechanisms giving rise to this important disease entity. A systematic clinical approach to the diagnosis and clinical workup of olfactory disturbances is also provided in addition to an extensive review of the medical and surgical therapeutic modalities currently available.

Management of long-lasting phantosmia: a systematic review

BACKGROUND

Interest in the pathophysiology and management of phantom smells has increased rapidly over the last decade. A PubMed search for the term "phantosmia" demonstrated a near-doubling of articles published on phantosmia within the past 7 years. We aimed to systematically review the literature on the management of phantosmia.

METHODS

The PubMed, EMBASE, and Cochrane databases were searched for articles published since January 1990, using terms combined with pertinent Boolean search operators. We included articles evaluating management of phantosmia written in the English language, with original data and a minimum of 6 months of follow-up, on at least 2 patients and with well-defined and measurable outcomes.

RESULTS

A total of 2151 unique titles were returned upon the initial search. Of these, 146 abstracts were examined, yielding 7 articles meeting the inclusion criteria. All articles were predominantly level 4 evidence. One prospective level 3 study was included. The studies included a total of 96 patients, with follow-up ranging from 6 months to 11 years. Endpoints were primarily based on subjective patient responses. Management options included observation and medical and surgical therapy. Olfactory mucosa excision was the only surgical intervention studied, with short-term symptomatic improvement in 10 of 11 patients. Forty-one patients were treated medically, which included antipsychotic, antimigraine, and antiseizure medications, transcranial stimulation, and topical cocaine application.

CONCLUSION

Despite increasing interest in the treatment of phantosmia and reports of successful therapies, there remains a paucity of data and lack of consensus regarding optimal management of this difficult condition.

Anosmia: Differential diagnosis, evaluation, and management

The ability to scrutinize our surroundings remains heavily dependent on the sense of smell. From the ability to detect dangerous situations such as fires to the recollection of a fond memory triggered by an odor, the advantages of an intact olfactory system cannot be overstated. Outcomes studies have highlighted the profound negative impact of anosmia and parosmia on the overall quality of life. The National Institute on Deafness and Other Communication Disorders estimates that ∼1.4% of the United States population experiences chronic olfactory dysfunction and smell loss. Efforts have focused on improving both the diagnosis of olfactory dysfunction through olfactory testing and improved reporting of treatment outcomes of olfactory training. The purpose of this article was to review the differential diagnosis, workup, and current treatment strategies of anosmia and smell disorders.

Prognosis of Olfactory Dysfunction according to Etiology and Timing of Treatment

Objective We evaluated the severity of olfactory impairment according to risk factors, compared responses with risk factors and treatment timing, and investigated prognosis according to treatments. Study design Case series with chart review. Setting Tertiary referral center. Subjects and Methods We retrospectively reviewed medical records of patients complaining of loss of their sense of smell between January 2006 and May 2016. In total, 491 patients were included. We evaluated olfactory function using the Connecticut Chemosensory Clinical Research Center test (threshold test) and Cross-cultural Smell Identification Test. Results Post-upper respiratory infection patients showed better results than those with other risk factors (59.6% recovered). Patients with head trauma (12.5% recovered) and congenital olfactory dysfunction (0% recovered) showed poorer results. Earlier treatment showed better olfactory recovery outcomes for post-upper respiratory infection ( P = .001), head trauma ( P = .022), and nasal/sinus surgery ( P = .009). Xerostomia ( P = .73) and idiopathy ( P = .365) showed no significant difference in terms of treatment timing. The threshold test better reflected subjective recovery than the identification test. The systemic + topical steroid group and the systemic steroid treatment group both showed better smell recovery outcomes than the group with topical treatment alone (both, P < .001). However, there was no significant difference between the systemic treatment group and the systemic + topical treatment group ( P = .978). Conclusions Our findings suggest that the duration of smell loss is important for better olfactory outcomes with most etiologies. Also, the effects of systemic steroids were better than those of topical steroids, regardless of combined treatment.