Distorted olfactory perception: a systematic review

The sense of smell provides people with valuable input from the chemical environment around them. The human sense of smell generally fails in three ways; one is an intensity reduction and the other two are the quality of changes. Smell disorders can be classified into central or peripheral depending on their origin. Central causes can be related to an area of hyper-functioning brain cells generating this odor perception, thus olfactory distortions have also been observed with epilepsy and migraine. In this paper, we present a review of the current clinical understanding of olfactory distortions and discuss how they can be evaluated and therapies to treat this debilitating condition.     

Olfactory perception in children

The ability to smell is important for protection from danger and quality of life, even in children. Although smell loss is rare in children, it can be indicative of some childhood disorders and may be useful for understanding some disorders. This paper reviews the methods and results of behavioral testing olfaction in children, with an emphasis on odor identification, the most common method of assessing the sense of smell in both children and adults. The Pediatric Smell Wheel^® is described as a relatively new and powerful tool for testing olfaction in children as young as 4 years of age. An example of its use in testing children with a childhood disorders (autism spectrum disorder, ASD) is provided in addition to a review of the literature on smell function in ASD. It is possible to reliably test sense of smell in children as young as 4 years old and many studies have shown that performance improves with age and can be impacted by childhood disorders. Sex differences in children are briefly discussed. Finally, the paper suggests other methods of testing olfaction in children, such as odor discrimination, that depend less on cognitive factors, which may enhance our understanding of the olfactory capabilities of young children.     

Drug therapy for disturbances of smelling

Disorders of the sense of smell are frequent. This severely can affect the quality of live. Appropriate testing is needed to determine the nature of the patient's complaints. Following the pathogenesis, two main groups of smell disorders are discernable: The conductive-respiratory smell disorders, where the odour can not reach the receptor and the senso-neuronal disorders where perception or transduction is affected. Therefore two different therapeutical approaches are described.     

Olfactory dysfunction and its measurement in the clinic

The sense of smell is largely taken for granted by laypersons and medical professionals alike. Indeed, its role in determining the flavor of foods and beverages, as well as in warning of, or protecting against, environmental hazards, often goes unrecognized. This is exemplified, in part, by the fact that most patients presenting to medical clinics with “taste” problems are typically subjected to complex brain imaging and gastroenterological tests without the sense of smell even being tested or considered as a basis of the problem. Aside from frank deficiencies in sweet, sour, bitter, salty and savory (umami) sensations, “taste” disorders most commonly reflect inadequate stimulation of the olfactory receptors via the retronasal route; i.e., from volatiles passing to the receptors from the oral cavity through the nasal pharynx. This article describes the two most common procedures for measuring the sense of smell in the clinic and provides examples of the application of these tests to diseases and other disorders frequently associated with smell loss. Basic issues related to olfactory testing and evaluation are addressed. It is pointed out that smell loss, particularly in later life, can be a harbinger for not only a range of neurodegenerative diseases, but can be a prognostic indicator of early mortality.     

Importance of unilateral examination in olfactometry

Hyposmia, the decreased sense of smell, and anosmia, the loss of sense of smell, may be unilateral or bilateral. If the olfactory acuity examined by means of bilateral test is normal, olfactory disorders are not found; unilateral examination is therefore necessary for definite evaluation of olfactory acuity. As evidence, 7 cases out of 94 patients with chronic rhinosinusitis and 6 cases out of 12 patients who received the surgery of anterior cranial fossa showed definite different olfactory threshold between nasal cavities, and there were no patients who recognized the diminished sense of smell in spite of unilateral high olfactory threshold. Additionally, we have experienced that a patient with brain tumor was diagnosed by the help of unilateral olfactory test. We thus strongly recommend the unilateral olfactometry as a method for simple and reliable test in clinical measurement of the sense of smell.     

Design issues in chemosensory trials

Randomized clinical trials in taste and smell disorders have been infrequent, in part because of difficulties in both the design and the conduct of such trials. Hyposmia and hypogeusia, impairments of smell and taste, respectively, have a variety of causes, such as upper respiratory infection, head trauma, or laryngectomy. Once definitive diagnosis is established, eligibility and exclusion criteria may relate to etiology. Since the sense of smell is more acute at younger ages and since women can generally identify odors more accurately than men, either prestratification or poststratification should be considered. A control or comparison group is essential because, occasionally, chemosenses spontaneously return to normal. Patient recruitment may be difficult, depending to a large extent on self-referrals, with the exception of head injury cases. To enroll an adequate number of patients in a reasonable length of time usually requires participation of multiple clinical centers. Objective measurements of taste and smell must be reliably obtained before and after intervention. Design issues specific to chemosensory trials are discussed in the context of an example, a factorial design trial of surgery and steroids in patients with olfactory defects.     

Smell and taste disorders, a study of 750 patients from the University of Pennsylvania Smell and Taste Center

Smell and taste disorders are common in the general population, yet little is known about their nature or cause. This article describes a study of 750 patients with complaints of abnormal smell or taste perception from the University of Pennsylvania Smell and Taste Center, Philadelphia. Major findings suggest that: chemosensory dysfunction influences quality of life; complaints of taste loss usually reflect loss of smell function; upper respiratory infection, head trauma, and chronic nasal and paranasal sinus disease are the most common causes of the diminution of the sense of smell, with head trauma having the greatest loss; depression frequently accompanies chemosensory distortion; low body weight accompanies burning mouth syndrome; estrogens protect against loss of the sense of smell in postmenopausal women; zinc therapy may provide no benefit to patients with chemosensory dysfunction; and thyroid hormone function is associated with oral sensory distortion. The findings are discussed in relation to management of patients with chemosensory disturbances.     

Anosmia: diagnosis and management

Disorders of the sense of smell can be frustrating for both the patient and physician. Ongoing research in this field has provided insight into the possible mechanisms for smell loss; however, therapy is still limited. Commercially distributed smell testing kits and newer screening tests using material available in all clinical settings have made diagnosis and measurement of the degree of impairment available to all physicians. A detailed history and physical examination are the most powerful tools in the evaluation of smell disorders, whereas imaging studies are reserved for preoperative planning or detailed assessment of positive physical findings.     

Screening of olfaction with smell diskettes

BACKGROUND: Aim of the study was the development of a new screening test of olfaction with reusable diskettes as odorant applicators. METHODS: A screening test of olfaction was designed using 8 diskettes containing different odorants. The diskettes can be opened to release the odor and are closed after testing. The test was designed as a triple forced multiple choice test using a questionnaire, resulting in a score from 0 to 8 correct answers. Ninety-one volunteers with a normal sense of smell and 13 patients with subjective hyposmia or anosmia were tested to validate the developed test. The same volunteers were also tested with the sniffin' sticks test, another screening test of olfaction that is already validated. After testing, the volunteers were asked to compare the two tests. RESULTS: Among the 91 volunteers with normal sense of smell, 10 achieved a score of 7, and 81 a score of 8 in the smell disk test. The 13 patients with hyposmia or anosmia achieved a score between 0 and 5. Based on the test design, there is a probability of 99.74% that a person who achieves a score of 7 or 8 will have normal olfaction. In the sniffin' sticks test, 85 volunteers with normal sense of smell achieved a score in the normal range for this test (6-8) whereas 6 volunteers were below with a score of 4 or 5. The 13 patients with hyposmia or anosmia scored between 0 and 6. The smell disk test was preferred by 86 persons, the sniffin' sticks test by 5, and 12 assessed both tests as equal. CONCLUSIONS: The developed screening test is reliable for identifying patients with a normal sense of smell, and it can distinguish them from patients with hyposmia and anosmia. The diskettes proved to be reliable and comfortable applicators for odorants in clinical practice.     

An updated review of clinical olfaction

PURPOSE OF REVIEW: Disorders of the sense of smell can result through hundreds of different processes, but most commonly occur from upper-respiratory-tract infections, trauma, and chronic rhinosinusitis. RECENT DEVELOPMENTS: Research in the basic science of olfaction has progressed rapidly with powerful new molecular discoveries; however, our ability to treat these disorders remains limited. In clinical olfaction we are just realizing the broader existence of the sensory dysfunction in our population. We are discovering associations between neurodegenerative disorders and smell function that may allow us to identify these disorders earlier in the disease process. We are also challenging our previous categorization schemes and realizing that many etiologies cross the traditional conductive and neuro-sensory divisions. SUMMARY: Currently, aside from the possible therapeutic potential of systemic steroids, we have no effective treatment for the most common causes of olfactory loss. Recent advances in the basic science of olfaction provides us with an opportunity to develop new and novel clinical studies in an attempt at improving the quality of life for many of these patients.     

Olfaction in rhinology--methods of assessing the sense of smell

Olfactory disorders frequently occur in rhinological disease. Different subjective and objective test methods are available to assess the sense of olfaction. Among the subjective methods, screening tests and threshold measurements are commonly used to quantify hyposmia or anosmia. Qualitative methods are available using discrimination and identification tests. Objective methods are used in research and in some medicolegal situations. Objective tests include olfactory evoked potentials, functional Magnetic Resonance Imaging and functional Positron Emission Tomography. The measurement of the sense of smell helps to assess the whole spectrum of the effects of nasal disease. This is especially important before rhinological surgery, because a non-detected smell disorder in patients with rhinological disease is common. The assessment of a pre-existing hyposmia or anosmia helps to avoid a postoperative claim that this was caused by surgery. A variety of validated screening tests for olfaction is available and they are a useful tool to document whether a patient is able to smell.     

Impaired sense of smell in patients with nasal surgery

The aim of the study was to determine the incidence of olfactory disorders before and following nasal and paranasal sinus surgery. It was a prospective observational study. Over a 6-month period, all patients who had been listed for nasal and paranasal sinus surgery underwent preoperative and postoperative evaluation of their sense of smell. A questionnaire and the 'Smell Diskettes Test' were used to assess olfaction. One hundred and eighty-four patients were studied. Preoperatively, 19 patients (10.3%) had an impaired sense of smell (8.1% before septoplasty, 6.1% before rhinoplasty and 17.1% before endoscopic sinus surgery). Only 16 (84%) of these patients were aware of their impaired sense of smell. Following surgery, four patients (2.5%) who were normal preoperatively developed impaired olfaction on questioning, and this was supported by testing it. In the subgroup that had a septoplasty, no patient developed hyposmia compared to one patient (2.6%) after rhinoplasty and one patient (3%) after endoscopic sinus surgery. No patient developed anosmia. Preoperatively, 10.3% of patients had an altered sense of smell, making it desirable that this is documented in order to avoid postoperative claims that this was caused by surgery. It also helps to audit the results of surgery.     

Magnetic resonance imaging for diagnosis of congenital anosmia

Magnetic Resonance Imaging (MRI) was performed on 9 patients who lacked a sense of smell since birth. Seven of them, including two patients with Kallmann syndrome, exhibited abnormality of the olfactory bulb, olfactory tract, olfactory sulcus, or rectus gyrus, with some variation among patients in type and degree of abnormality. The other two patients exhibited normal olfactory pathway morphology, and for them the possibility of acquired sensorineural anosmia could not be ruled out. MRI is useful for determining whether patients with congenital anosmia have olfactory pathway anomalies. Many patients with congenital anosmia and hypoplasty or aplasty of the olfactory pathway nevertheless had no gonadal or endocrinological disorders.     

Prevalence and Characteristics of Altered Sense of Smell/Taste During Covid-19 first wave: A French Nationwide Cross-sectional Study

AimAltered sense of smell and/or taste is a leading symptom of SARS-CoV-2 infection, but its prevalence at a population-level is unknown.MethodsFrom a questionnaire addressed to a representative subset of the French general adult (≥ 18-year) population over a 6-week period during the first French lockdown (April 7 to May 19 2020), self-reported new cases of altered sense of smell and/or taste were collected.ResultsFrom 29,660 participants, new altered sense of smell and/or taste was 2.18% and 2.11% after direct standardization on the French population representing more than 1,110,000 subjects in France. Moreover, 0.5% of participants reported a positive SARS-CoV-2 test, among which 47.4% reported a newly altered sense of smell and/or taste. Male participants, younger ones together with those presenting with chronic condition had higher odds of reporting a newly altered sense of smell and/or taste.ConclusionThis study provides an accurate estimate of new cases of altered sense of smell and/or taste in the general population at a nationwide level during the Covid-19 first wave.     

Initial otolaryngologic assessment of patients with taste and smell disorders

Patients are often referred to otolaryngologists to evaluate dysfunctions of taste or smell. A history and physical examination focused on signs and symptoms of chemosensory disorders, in combination with screening tests for taste and smell function, can quickly and easily delineate the general type and cause of the dysfunction. Several centers for chemosensory disorders referred to in this issue are available for referral to patients who need detailed testing and evaluation. Although treatment options for most taste and smell dysfunctions are limited, by categorizing disorders, we can give the patient an idea of the probable cause and prognosis of the dysfunction.     

The close relationship between sudden loss of smell and COVID-19

IntroductionThe real number of COVID-19 cases may be underestimated since several countries have difficulty offering laboratory tests for all the population. Therefore, finding a symptom with a high predictive value would help in diagnostic and isolation strategies.ObjectiveTo correlate the sudden loss of the sense of smell in the context of the COVID-19 pandemic with results of diagnostic tests for COVID-19.MethodsThis is a cross-sectional observational study. An online questionnaire was digitally addressed to 725 outpatients in Brazil who reported partial or total sudden loss of the sense of smell from March to April 2020.ResultsTotal or partial sudden loss of the sense of smell showed high positive predictive value for COVID-19 diagnosis, during the COVID-19 pandemic in Brazil (88.8%). There were no differences between groups tested positive and negative in regard to demographic and clinical characteristics such as presence of allergy, rhinitis, neither to olfactory recovery time.ConclusionThe identification of sudden loss of the sense of smell during COVID-19 pandemic may serve as a sentinel symptom and may be a warning to establish measures to prevent the transmission of the disease.     

Clinical experience with patients with olfactory complaints, and their quality of life

CONCLUSION. A special consulting team for patients with olfactory disorders would be able to verify, describe, and explain the characteristics of the disorders, also in cases where a patient experiences a disorder, but has a normal sense of smell. OBJECTIVES. The general purpose of this paper was to present our experience with patients seeking medical attention for olfactory disorders, and to describe how quantitative and qualitative olfactory disorders are diagnosed, what the etiologies are, and how quality of life is compromised in patients with olfactory disorders. SUBJECTS AND METHODS. This investigation was performed prospectively over a 10-year period by one physician responsible for the consulting team for patients with olfactory disorders. Based on a standardized clinical examination, a structured interview, and assessment of olfactory function, its aim was to diagnose quantitative and qualitative disorders in 303 consecutive patients. Health-related quality of life was assessed with the Nottingham Health Profile (NHP) in about one-third of patients. RESULTS. In the majority of patients, a reduced sense of smell was found after testing. Often, but not always, this was combined with qualitative disorders. Dominating etiologies were infections, nasal polyposis, head trauma, and aging. Patients complaining of olfactory disorders experience a significantly reduced quality of life regarding the impact of their health problem on paid employment, household work, and social and family life.     

Assessment of Smell and Taste in Patients with Allergic Rhinitis

We examined the senses of smell and taste in 240 patients with verified hypersensitivity reactions of the respiratory tract. Olfactometry was performed according to Elsberg and Levy's method and followed by electrogustometry. The examinations revealed that the incidence of smell and taste disorders in patients with allergic rhinitis is 21.4% and 31.2%, respectively. No significant relationships between smell and taste dysfunction were found. We evaluated statistically positive correlations between the olfactory and gustatory thresholds compared with 78 qualitative and quantitative factors assessed in the study. There was a statistically significant relationship between the olfactory thresholds and levels of eosinophils in blood and in nasal discharge, acid reaction of the nasal mucosa, coexisting nasal polyps and X-ray changes in the ethmoid sinuses. There was a positive influence of pharmacotherapy as well as specific desensitization and surgery on the impairment of the sense of smell in allergic rhinitis.     

Assessment of smell and taste in patients with allergic rhinitis

We examined the senses of smell and taste in 240 patients with verified hypersensitivity reactions of the respiratory tract. Olfactometry was performed according to Elsberg and Levy's method and followed by electrogustometry. The examinations revealed that the incidence of smell and taste disorders in patients with allergic rhinitis is 21.4% and 31.2%, respectively. No significant relationships between smell and taste dysfunction were found. We evaluated statistically positive correlations between the olfactory and gustatory thresholds compared with 78 qualitative and quantitative factors assessed in the study. There was a statistically significant relationship between the olfactory thresholds and levels of eosinophils in blood and in nasal discharge. acid reaction of the nasal mucosa, coexisting nasal polyps and X-ray changes in the ethmoid sinuses. There was a positive influence of pharmacotherapy as well as specific desensitization and surgery on the impairment of the sense of smell in allergic rhinitis.     

How smell tests experience and education affect ENT specialists’ attitudes towards smell disorders? A survey study

The aim of the present study was to assess the effect of smell tests experience and education during residency or in general practice on ENT specialists’ attitudes toward smell disorders in concern of their management strategies. Methodology included a voluntary and anonymous self-administered questionnaire survey conducted in Turkey and responses from 218 questionnaires were pooled and evaluated. Results stated that only 7.3% of the respondents reported currently using smell tests in their practice, and most of those had observed a smell test during their residency (p < 0.05) and received education on the olfactory disorders (p < 0.01). Furthermore, these doctors were more likely to manage patients with no assistance from other doctors or institutions (p < 0.01). Moreover, the doctors with more knowledge of smell disorders rated the symptom of smell loss as more important. We concluded that doctors who had training in smell disorders were confident in diagnosing and treating patients with smell disorders and were more likely to perform smell tests and assume all responsibility for diagnostic and treatment procedures. These results demonstrate the importance of both the residency and continuing medical education in training doctors who are confident to treat smell disorders.