Olfactory deficits in anorexia nervosa

Inflammation and olfactory loss are associated with at least 139 medical conditions

Olfactory loss accompanies at least 139 neurological, somatic, and congenital/hereditary conditions. This observation leads to the question of whether these associations are correlations or whether they are ever causal. Temporal precedence and prospective predictive power suggest that olfactory loss is causally implicated in many medical conditions. The causal relationship between olfaction with memory dysfunction deserves particular attention because this sensory system has the only direct projection to memory centers. Mechanisms that may underlie the connections between medical conditions and olfactory loss include inflammation as well as neuroanatomical and environmental factors, and all 139 of the medical conditions listed here are also associated with inflammation. Olfactory enrichment shows efficacy for both prevention and treatment, potentially mediated by decreasing inflammation.

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.

Perceptual Dysfunction in Eating Disorders

Eating disorders (EDs) are characterized by abnormal responses to food and weight-related stimuli and are associated with significant distress, impairment, and poor outcomes. Because many of the cardinal symptoms of EDs involve disturbances in perception of one's body or abnormal affective or cognitive reactions to food intake and how that affects one's size, there has been longstanding interest in characterizing alterations in sensory perception among differing ED diagnostic groups. Within the current review, we aimed to critically assess the existing research on exteroceptive and interoceptive perception and how sensory perception may influence ED behavior. Overall, existing research is most consistent regarding alterations in taste, visual, tactile, and gastric-specific interoceptive processing in EDs, with emerging work indicating elevated respiratory and cardiovascular sensitivity. However, this work is far from conclusive, with most studies unable to speak to the precise etiology of observed perceptual differences in these domains and disentangle these effects from affective and cognitive processes observed within EDs. Further, existing knowledge regarding perceptual disturbances in EDs is limited by heterogeneity in methodology, lack of multimodal assessment protocols, and inconsistent attention to different ED diagnoses. We propose several new avenues for improving neurobiology-informed research on sensory processing to generate actionable knowledge that can inform the development of innovative interventions for these serious disorders.

Olfactory Dysfunction in Children: A Scoping Review

OBJECTIVE

Olfactory disorders are well-studied in the adult population, however, there is a paucity of literature characterizing olfactory dysfunction in pediatric patients. The purpose of this scoping review was to identify known causes of olfactory loss in pediatric populations, clarify the extent of use and validity of smell tests, and summarize current therapies for olfactory loss.

DATA SOURCES

PubMed, Ovid MEDLINE, and Web of Science.

REVIEW METHODS

Databases were systematically searched in September 2020. Two independent reviewers conducted the title and abstract screen, followed by review of full-texts for inclusion based on preset inclusion and exclusion criteria. Extracted data included study type, age/age-range of participants, gender, radiological evidence of olfactory dysfunction, types and results of smell tests used, etiology of olfactory loss, and therapies employed for olfactory loss.

RESULTS

A total of 103 articles (n = 1654) were eligible for final data extraction. The University of Pennsylvania Smell Identification Test was used most frequently for smell testing (21% of studies). In total, 45 causes of olfactory dysfunction have been elucidated by this study: 22 congenital and 23 acquired. Few therapies were described, and all were specific to the etiology of olfactory loss.

CONCLUSION

Olfactory dysfunction has a wide range of etiologies in the pediatric population, and clinicians should have a diagnostic algorithm for how to identify a cause should they encounter it in practice. If no etiology can be identified, education around safety should be provided to both the patient and their caregivers.

Investigating the Link between Eating Attitudes, Taste and Odour Preferences and the Chemical Senses

OBJECTIVES

To examine if higher degrees of pathological eating attitudes in a non-clinical sample are associated with odour and taste perception and preferences based on psychophysical ratings.

PARTICIPANTS AND METHODS

A total of 80 female university students completed the eating attitudes test (EAT-26), followed by four chemosensory measures including olfactory and gustatory perception plus perceptual ratings and preferences for food odours and tastes.

RESULTS

There were no significant correlations between EAT-26 scores and measures of olfactory and gustatory perception. However, a significant interaction effect indicated higher degrees of pathological eating attitudes may be associated with differential sensitivity to sweet and fatty food odours compared to those with lower levels of pathological eating attitudes.

CONCLUSIONS

This was the first study to examine pathological eating attitudes using food stimuli with a non-clinical sample. The results remain preliminary until replication. However, the findings highlight the need for development of measures of disordered eating attitudes and behaviours that go beyond caloric restriction.

Bidirectional Mendelian randomization study of psychiatric disorders and Parkinson’s disease

Introduction

Although the relationship between psychiatric disorders and Parkinson’s disease (PD) has attracted continuous research attention, the causal linkage between them has not reached a definite conclusion.

Methods

To identify the causal relationship between psychiatric disorders and PD, we used public summary-level data from the most recent and largest genome-wide association studies (GWASs) on psychiatric disorders and PD to conduct a bidirectional two-sample Mendelian randomization (MR). We applied stringent control steps in instrumental variable selection using the Mendelian randomization pleiotropy residual sum and outlier (MR-PRESSO) method to rule out pleiotropy. The inverse-variance weighted (IVW) method was used to identify the causal relationship between psychiatric disorders and PD. Multiple MR analysis methods, including MR-Egger, weighted-median, and leave-one-out analyses, were used for sensitivity analysis, followed by heterogeneity tests. Further validation and reverse MR analyses were conducted to strengthen the results of the forward MR analysis.

Results

The lack of sufficient estimation results could suggest a causal relationship between psychiatric disorders and PD in the forward MR analysis. However, the subsequent reverse MR analysis detected a causal relationship between PD and bipolar disorder (IVW: odds ratios [OR] =1.053, 95% confidence interval [CI] =1.02–1.09, p = 0.001). Further analysis demonstrated a causal relationship between genetically predicted PD and the risk of bipolar disorder subtype. No pleiotropy or heterogeneity was detected in the analyses.

Discussion

Our study suggested that while psychiatric disorders and traits might play various roles in the risk of developing PD, PD might also be involved in the risk of developing psychiatric disorders.

Chemosensory Alterations and Impact on Quality of Life in Persistent Alcohol Drinkers

BACKGROUND

Heavy alcohol consumption-associated chemosensory dysfunction is understudied, and early detection can help predict disease-associated comorbidities, especially those related to four quality of life (QOL) domains (physical, psychological, social and environment). We examined self-reports of chemosensory ability of individuals with different alcohol drinking behaviors and their association with changes in QOL domains.

METHODS

Participants (n = 466) were recruited between June 2020 and September 2021 into the NIAAA COVID-19 Pandemic Impact on Alcohol study. Group-based trajectory modeling was used to categorize participants without any known COVID-19 infection into three groups (non-drinkers, moderate drinkers and heavy drinkers) based on their Alcohol Use Disorders Identification Test consumption scores at four different time points (at enrollment, week 4, week 8 and week 12). Linear mixed models were used to examine chemosensory differences between these groups. The associations between chemosensory abilities and QOL were determined in each group.

RESULTS

We observed significant impairment in self-reported smell ability of heavy drinking individuals compared to non-drinkers. In contrast, taste ability showed marginal impairment between these groups. There were no significant differences in smell and taste abilities between the moderate and non-drinking groups. Heavy drinkers' impairment in smell and taste abilities was significantly associated with deterioration in their physical, psychological, social and environmental QOL.

CONCLUSION

Persistent heavy drinking was associated with lower chemosensory ability. Heavy drinkers' reduced smell and taste function and association with poorer QOL indicate that early assessment of chemosensory changes may be crucial in identifying poorer well-being outcomes in heavy drinkers at risk for alcohol use disorder.

Olfactory loss is a predisposing factor for depression, while olfactory enrichment is an effective treatment for depression

The loss of olfactory stimulation correlates well with at least 68 widely differing neurological disorders, including depression, and we raise the possibility that this relationship may be causal. That is, it seems possible that olfactory loss makes the brain vulnerable to expressing the symptoms of these neurological disorders, while daily olfactory enrichment may decrease the risk of expressing these symptoms. This situation resembles the cognitive reserve that is thought to protect people with Alzheimer’s neuropathology from expressing the functional deficit in memory through the cumulative effect of intellectual stimulation. These relationships also resemble the functional response of animal models of human neurological disorders to environmental enrichment, wherein the animals continue to have the induced neuropathology, but do not express the symptoms as they do in a standard environment with restricted sensorimotor stimulation.

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.

Olfactory capacity in anorexia nervosa: correlations with set-shifting ability

PURPOSE

The purpose of this study is to examine olfactory capacity in adults with anorexia nervosa (AN), in terms of odor identification and odor threshold and search for possible correlations between odor identification and cognitive flexibility in this population.

METHODS

Thirty-nine patients diagnosed with AN and 60 healthy participants, participated. Odor identification was assessed using the University Pennsylvania Smell Identification Test and a two alternative forced choice, ascending method with n-butanol was used to assess odor threshold. Cognitive flexibility was determined using the Intra/Extra-Dimensional Set-Shift test (IED), a subtest of the Cambridge Neuropsychological Test Automated Battery (CANTAB).

RESULTS

Patients with AN presented a poorer performance in odor identification compared with controls (p = 0.001). No differences were found in odor threshold, between the two groups. Patients with AN exhibited poor cognitive flexibility compared with controls (p = 0.003). A significant correlation between odor identification and cognitive flexibility was documented in AN (p = 0.01), but not in controls.

CONCLUSION

Our findings suggest that olfactory capacity is altered in AN: Qualitative characteristics of olfaction were affected in patients with AN (lower odor identification), while there was no difference in quantitative characteristics (odor threshold) compared with controls. Furthermore, odor identification in AN was correlated to cognitive flexibility.

LEVEL OF EVIDENCE

Level III: case-control analytic study.

Psychophysical chemosensory dysfunction in eating disorders: a qualitative systematic review

PURPOSE

Patients with chemosensory dysfunction experience significant quality of life disruptions, including reduced enjoyment of eating. While chemosensory dysfunction has been associated with eating disorders, the relationship is poorly understood. This systematic review aims to characterize psychophysical gustation and olfaction in patients with eating disorders.

METHODS

Systematic review of investigations assessing psychophysical chemosensory function in patients with organic eating disorders.

RESULTS

26 studies were included. Five studies assessed both chemosenses, while 12 and 9 assessed exclusively gustation or olfaction, respectively. In total, 779 patients were included [72.4% anorexia nervosa (AN), 26.7% bulimia nervosa (BN), 0.8% combined AN/BN]. Patients with eating disorders experienced rates of hypogeusia up to 87% in AN and 84.6% in BN. There was evidence for alterations in psychophysical olfaction, but orientation of trends were less clear. Chemosensory dysfunction was more evident in AN patients. Treatment correlated with improved chemosensory function.

CONCLUSIONS

Despite heterogeneity in study methodology and results, this review demonstrates that patients with eating disorders experience some degree of chemosensory dysfunction, particularly in gustation. This symptomatology overlaps with those experienced by patients with other causes of chemosensory impairment. These findings suggest potential broad psychosocial, dietary, and mental health implications in patient populations experiencing chemosensory dysfunction.

LEVEL OF EVIDENCE

Level II.

Evaluation of olfactory bulb volume and olfactory sulcus depth in patients with panic disorder and depressive disorder: An MRI study

BACKGROUND

Although some studies have shown decreases in the olfactory bulb (OB) volume and olfactory function in depressive disorder, there are no studies investigating OB volume in patients with panic disorder.

AIM

The aim of this study was to investigate whether there was a change in OB volume and olfactory sulcus (OS) depth in patients with panic and depressive disorder when compared with the control group, and which group was more affected by comparing the two disease groups.

METHODS

Data of 51 patients with panic disorder and 56 patients with depressive disorder were obtained by scanning the database of the hospital retrospectively. The control group consisted of 56 subjects without panic and depressive disorder. OB volume and OS depth measurements were performed on cranial magnetic resonance imaging (MRI).

RESULTS

Bilateral OB volume of the panic and depressive disorder groups were significantly lower than those of the control group. The lowest volume was found in depressive patients. There was no significant difference between the groups with respect to OS measurements. When OB volume and OS depth differences between the genders were evaluated, a statistically significant difference was not determined.

CONCLUSION

Reduced OB volume was determined in both panic and depressive disorder patients, and clarification of these preliminary findings may contribute to the pathophysiology of panic and depressive disorders.

Gustatory Function and Salivary Flow Rate in Healthy Adults

OBJECTIVES/HYPOTHESIS

In this study, we assessed gustatory function and whole-mouth saliva in healthy adults and investigated the association between gustatory function, salivary flow rate (SFR), and dry mouth.

STUDY DESIGN

Descriptive clinical study.

METHODS

We recruited 413 participants who reported a normal sense of smell-taste, comprising 206 females and 207 males with an age range of 19 to 80 years. Taste scores were obtained using whole-mouth tests to evaluate the gustatory function, SFR was assessed using the spitting method, and dry mouth was measured with the visual analog scale.

RESULTS

The total taste score (TTS) and SFR were significantly negatively correlated with age (r_taste  = -0.522, P < .001; r_SFR  = -0.200, P < .001): TTS was significantly lower after the age of 50 and SFR decreased significantly after age 65. Women exhibited a significantly higher TTS than men (P < .001). However, there was no effect of sex on SFR. Dry mouth was negatively correlated with TTS (r = -0.223, P < .01) and SFR (r = -0.218, P < .01). Multiple regression analysis showed the independent variables of age, sex, and dry mouth predicted 34% of the variation in taste, while the independent variables of age and dry mouth predicted 6.1% of the variation in whole-mouth saliva. TTS was not significantly correlated with the SFR in healthy adults (r = 0.094, P = .056).

CONCLUSIONS

Age and dry mouth are important factors affecting gustatory function and whole-mouth saliva, with women exhibiting better taste sensitivity than men. Furthermore, there is no direct correlation between SFR and gustatory function in healthy adults.

LEVEL OF EVIDENCE

3 Laryngoscope, 2021.

Persistent olfactory complaints after COVID-19: a new interpretation of the psychophysical olfactory scores

Background: Sudden olfactory loss is a major symptom of SARS-CoV-2 infection and has a negative impact on daily life quality. Almost 80% of disorders regress spontaneously. No precise characterization of the medium- and long-term olfactory symptoms has been carried out yet, apart from self-assessments. The main objective of this work was to characterize persistent smell disorders in this population. Methodology: Consecutive patients consulting to the ENT department with post-Covid19 olfactory loss were included. The clinical examination included an analog scale for the self-assessment of olfactory recovery), a nasofibroscopy, the Sniffin’ Stick Test and the short version of the Questionnaire of olfactory disorders. Results: Among the 34 patients included, based on the Sniffin’ Sticks Test, 29.4% (n=10) could be classified as normosmic, 55.9% (n=19) as hyposmic and 14.7% (n=5) as functional anosmic). Only olfactory identification impairment was significantly correlated with olfactory complaint and daily anxiety and annoyance related to lack of olfaction recovery. This identification disorder seemed to worsen over time. Conclusions: It is crucial to assess odor identification disorders in case of persistent olfactory complaints after COVID-19. It is fundamental to target this disorder, as it does not improve spontaneously and negatively impact quality of life.

Arousal influences olfactory abilities in adults with different degree of food neophobia

Food neophobia, i.e., the aversion to novel foods, and olfaction are both factors strongly affecting food choices. Mounting evidence suggests a higher arousal towards food as a key factor underlying the reluctance to eat what is unfamiliar to us. As the role of olfaction behind this phenomenon is poorly understood, we explored the associations between food neophobia and trait anxiety, olfactory functions (odor threshold, discrimination and identification) and retronasal aroma release from a reference food in a healthy cohort of 83 adult volunteers. We grouped participants in Low-Neophobics or neophilics (n = 35), Medium-Neophobics (n = 32) and High-Neophobics (n = 16) according to the widely recognized Food Neophobia Scale. Participants with higher neophobic tendencies were found to have marginally higher trait anxiety levels than neophilics (p = 0.10). A lower global olfactory functioning and odor discrimination abilities characterized High-Neophobics, while Medium-Neophobics showed a higher odor sensitiveness than Low-Neophobics. Lastly, High-Neophobics showed a lower extent of retronasal aroma release, likely due to a shorter duration of oral processing and higher anxiety-related physiological responses (such as breathing rate). In summary, this study supports the assumption that the conflicting relationship that neophobics have with food may be led by higher levels of arousal toward foods, rather than different chemosensory functions.

Influence of Olfactory Function on Appetite and Nutritional Status in the Elderly Requiring Nursing Care

OBJECTIVE

To investigate olfactory function in elderly subjects requiring nursing care to clarify its association with appetite and nutritional status.

SETTING

Facility for the elderly requiring nursing care.

PARTICIPANTS

The subjects were 158 elderly people requiring nursing care and 37 elderly people not requiring nursing care.

MEASUREMENTS

Experiment I: Olfactory function and factors (cognitive function, appetite, and nutritional status) that may be associated with it were compared between the elderly subjects requiring nursing care and those not requiring nursing care using covariance analysis in consideration of age. For evaluation, the OSIT-J was used for olfactory function, the HDS-R for cognitive function, the CNAQ for appetite, and BMI for nutritional status. Experiment II: The subjects were the same elderly subjects requiring nursing care in Experiment I, and food intake was surveyed in addition to the OSIT-J, HDS-R, CNAQ, and BMI. A univariate linear regression analysis was performed with OSIT-J as the response variable, and age, HDS-R, CNAQ, BMI, and food intake as the explanatory variables.

RESULTS

Experiment I: On covariance analysis, the OSIT-J score was significantly lower for the elderly subjects requiring nursing care than for those not requiring nursing care (p<0.01). The mean score was 8 or lower in both groups, demonstrating lower olfactory function in both groups. Regarding factors that may be associated with olfactory function, a significant difference was noted in the HDS-R (p<0.01), confirming significantly lower cognitive function in the elderly subjects requiring nursing care. No significant difference was noted in the CNAQ or BMI. Experiment II: On a univariate linear regression analysis, an association with the OSIT-J was noted for age and HDS-R. Age was inversely correlated and the HDS-R was positively correlated. Factors associated with lower olfactory function in the elderly subjects requiring nursing were age and cognitive function, whereas appetite, nutritional status, and food intake were not associated.

CONCLUSION

Olfactory function in elderly subjects requiring nursing care was poorer than that in those not requiring nursing care, suggesting that aging and cognitive decline are associated with lower olfactory function. In addition, no association of lower olfactory function with appetite, nutritional status, or food intake was noted in the elderly subjects requiring nursing care.

Caloric restriction reduces basal cell proliferation and results in the deterioration of neuroepithelial regeneration following olfactotoxic mucosal damage in mouse olfactory mucosa

The effects of caloric restriction (CR) on cell dynamics and gene expression in the mouse olfactory neuroepithelium are evaluated. Eight-week-old male C57BL/6 mice were fed either control pellets (104 kcal/week) or CR pellets (67 kcal/week). The cytoarchitecture of the olfactory neuroepithelium in the uninjured condition and its regeneration after injury by an olfactotoxic chemical, methimazole, were compared between mice fed with the control and CR diets. In the uninjured condition, there were significantly fewer olfactory marker protein (OMP)-positive olfactory receptor neurons and Ki67-positive proliferating basal cells at 3 months in the CR group than in the control group. The number of Ki67-positive basal cells increased after methimazole-induced mucosal injury in both the control and the CR groups, but the increase was less robust in the CR group. The recovery of the neuroepithelium at 2 months after methimazole administration was less complete in the CR group than in the control group. These histological changes were region-specific. The decrease in the OMP-positive neurons was prominent in the anterior region of the olfactory mucosa. Gene expression analysis using a DNA microarray and quantitative real-time polymerase chain reaction demonstrated that the expression levels of two inflammatory cytokines, interleukin-6 and chemokine ligand 1, were elevated in the olfactory mucosa of the CR group compared with the control group. These findings suggest that CR may be disadvantageous to the maintenance of the olfactory neuroepithelium, especially when it is injured.

Autistic traits impact on olfactory processing in adolescent girls with Anorexia Nervosa restricting type

The correct functioning of the chemosensory pathway is pivotal for the attitude towards feeding. In some neuropsychiatric disorders, abnormalities of the sensory processing dramatically affect feeding behavior; however, evidences for an olfactory involvement in Anorexia Nervosa (AN) are still controversial. We administered a complete olfactory testing battery, the Sniffin' Sticks Extended Test, to a cohort of 19 girls with Restrictive Anorexia Nervosa (AN-R) and 19 healthy controls. A battery of questionnaires aiming to evaluate eating attitude, psychopathologic disorders and autistic traits was also administered. No difference was found between the two groups in any of the olfactory tasks. Despite the lack of correlation between olfaction and disease severity, however, olfactory performances were related to autistic traits in anorectic girls (r = -0.489, p = 0.039). Girls with AN-R do not appear to have an impaired olfactory function with respect to controls. However, a possible correlation between olfactory ability and autistic traits was discovered. In light of such findings, the role of possible relations between social functioning-related features and olfactory processing in AN-R is discussed.

Heightened Olfactory Sensitivity in Young Females with Recent-Onset Anorexia Nervosa and Recovered Individuals

Introduction

Olfaction may be related to food restriction and weight loss. However, reports regarding olfactory function in individuals with anorexia nervosa (AN) have been inconclusive.

Objective

Characterize olfactory sensitivity and identification in female adolescents and young adults with first-episode AN and young females recovered from AN.

Methods

We used the Sniffin’ Sticks Odor Threshold Test and Odor Identification Test to assess 43 participants with first-episode AN, 27 recovered participants, and 39 control participants. Participants completed the Importance of Olfaction questionnaire, the Beck Youth Inventory and the Eating Disorder Inventory. We also conducted a psychiatric diagnostic interview and the Autism Diagnostic Observation Schedule with participants.

Results

Both clinical groups showed heightened olfactory sensitivity. After excluding participants with depression, participants with first-episode AN identified more odors than recovered participants.

Conclusion

Heightened olfactory sensitivity in AN may be independent of clinical status, whereas only individuals with current AN and without depression show more accurate odor identification.

Back on the scent: the olfactory system in CNS demyelinating diseases

Olfactory dysfunction is recognised across an ever broadening spectrum of neuropsychiatric conditions including central nervous system (CNS) demyelinating diseases such as multiple sclerosis (MS) and neuromyelitis optica (NMO). In this review, we unravel the striking evidence highlighting how olfactory loss is a common clinical feature in MS and NMO. We provide an overview of the supportive psychophysical, electrophysiological, radiological and pathological data that point to the anatomical substrate of olfactory deficits in these diseases. The pattern of underlying pathology affecting the olfactory system is shown to be complex, involving multiple structures that are affected in different ways throughout the course of the disease. This review is the first to synthesise the expanding body of literature on the topic, provides novel insight into the way in which the olfactory system is affected in CNS demyelinating diseases, and raises intriguing questions about the role of this system in the pathogenesis of these diseases.

Impact of short-term refeeding on appetite and meal experiences in new onset adolescent eating disorders

Restrictive eating disorders (ED) are increasing and represent a serious risk to the health of adolescent females. Restrictive ED in youth are often treated through aggressive short-term refeeding. Although evidence supports that this intervention is the "gold standard" for improving ED outcomes in youth, little research has specifically probed appetite and meal-related responses to this type of intensive, short-term refeeding in newly diagnosed individuals. Information about appetite and meal-related dysfunction could provide valuable insights regarding treatment-interfering features of ED in both acute inpatient and longer-term outpatient treatment. The purpose of this study was to evaluate the hunger, fullness, olfactory, and gustatory responses of adolescents with newly-diagnosed restrictive ED and to probe how and when these responses are altered by refeeding. Using a quasi-experimental ecologically valid methodology, this study described and compared profiles of hunger, fullness, olfactory, and gustatory responses in adolescent females (n = 15) with newly diagnosed restrictive ED at hospital admission (i.e., severe malnutrition) and after medical refeeding, in comparison to healthy controls (n = 15). Results showed that newly diagnosed (i.e., malnourished) adolescents with ED showed significantly different meal-related experiences than controls. Refeeding improved some of these differences, but not all. Following refeeding, females with ED continued to show lower hunger, greater fullness, and lower pleasantness of smell ratings compared to controls. Unpleasantness of taste ratings maladaptively increased, such that females who were re-fed reported more aversive scents than pre-treatment. Profiles of meal-related responses were also identified and compared between groups. The applicability of these findings are discussed within the context of critical periods of change during refeeding treatment and potentially promising intervention targets that might enhance treatment outcomes for adolescents with newly onset, restrictive ED.

The "Sniffin' Kids" test--a 14-item odor identification test for children

Tools for measuring olfactory function in adults have been well established. Although studies have shown that olfactory impairment in children may occur as a consequence of a number of diseases or head trauma, until today no consensus on how to evaluate the sense of smell in children exists in Europe. Aim of the study was to develop a modified "Sniffin' Sticks" odor identification test, the "Sniffin' Kids" test for the use in children. In this study 537 children between 6-17 years of age were included. Fourteen odors, which were identified at a high rate by children, were selected from the "Sniffin' Sticks" 16-item odor identification test. Normative date for the 14-item "Sniffin' Kids" odor identification test was obtained. The test was validated by including a group of congenital anosmic children. Results show that the "Sniffin' Kids" test is able to discriminate between normosmia and anosmia with a cutoff value of >7 points on the odor identification test. In addition the test-retest reliability was investigated in a group of 31 healthy children and shown to be ρ = 0.44. With the 14-item odor identification "Sniffin' Kids" test we present a valid and reliable test for measuring olfactory function in children between ages 6-17 years.

Chemosensory rehabilitation and malnutrition in the newborn: how far, how close?

Olfaction is critical to the hedonic appreciation of foods, caloric regulation of food intake, quality of life and taste preferences since birth. However, malnutrition in newborns down-regulates chemosensory function. Thus, olfactory measures might be used as early markers of chemosensory dysfunction in malnutrition, and may also be useful in assessing feeding adjustments during nutritional rehabilitation. Olfactory anomalies originated by malnutrition would be reversed by nutritional rehabilitation following flavor-enhancing odorants.

Brain structural imaging correlates of olfactory dysfunction in obsessive-compulsive disorder

Olfactory dysfunction has been described in obsessive-compulsive disorder (OCD). Brain regions involved in smell processing partially overlap with structures included in the neurobiological models of OCD, although no previous studies have analyzed the neuroanatomical correlates of olfactory dysfunction in this disorder. The aim of our study was to examine the association between regional gray matter volume, as assessed by a voxel-based morphometry analysis of magnetic resonance images (MRI), and olfactory function, as assessed by the Sniffin' Sticks test (SST). Olfactory function was assessed in 19 OCD patients and 19 healthy volunteers. All participants were also scanned in a 1.5-T magnet to obtain T1-weighted anatomical MRIs, which were pre-processed and analyzed with SPM8. Three different correlation models were used to study the association between regional gray matter volumes and olfactory function in the domains assessed by the SST: detection threshold, discrimination, and identification. OCD patients showed a significant impairment in all the domains assessed by the SST. Voxel-based mapping revealed a positive association in healthy controls between detection threshold and the gray matter content of a left anterior cingulate cortex cluster. In OCD patients, a positive correlation was observed between identification errors and the gray matter volume of the left medial orbital gyrus. In a post hoc analysis, these two gray matter regions were shown to be enlarged in OCD patients. Our findings support the idea that olfactory dysfunction in OCD is associated with volumetric changes in brain areas typically implicated in the neurobiology of the disorder.

Food neophobia and its relation with olfaction

Food neophobia, that is the reluctance to try novel foods, is an attitude that dramatically affects human feeding behavior in many different aspects among which food preferences and food choices appear to be the most thoroughly considered. This attitude has an important evolutionary meaning since it protects the individual from ingesting potentially dangerous substances. On the other hand, it fosters an avoidance behavior that can extend even toward useful food elements. A strong link exists between food neophobia and both the variety in one person’s diet and previous exposures to different foods. In this review, the more recent findings about food neophobia will be concisely described. Given the suggested connection between the exposure to different foods and food neophobia, this review will focus on the relation between this attitude and human chemosensory abilities. Olfaction, in particular, is a sensory modality that has a central role in flavor perception and in food preference acquisition. Therefore, the latest evidences about its relation with food neophobia will be discussed along with the applied and cognitive implications.

Olfaction in alcohol-dependence: a neglected yet promising research field

Olfaction research deeply renewed the knowledge of the pathophysiological mechanisms involved in various psychopathological states and showed that olfactory deficits might constitute an onset or trait marker in psychiatry. However, while alcohol-dependence is the most wide spread psychiatric disorder and while olfaction might be involved in its development and maintenance, olfactory abilities have been little explored in this population. The central aim of this paper is thus to underline the usefulness of olfaction research in alcohol-dependence. After reviewing the few olfaction studies available, a research agenda will be proposed, identifying the major challenges for future research, and particularly: (1) the identification of the origin, extent and cerebral correlates of olfaction deficits; (2) the links between olfaction and emotional-cognitive deficits, and the use of olfaction to understand the pathomechanisms of alcohol-dependence; (3) the interactions between olfaction and other sensory modalities; (4) the use of olfaction to predict the appearance and intensity of cognitive impairments; (5) the impact of olfaction deficits on everyday life in alcohol-dependence.

Alterations of the olfactory-gustatory functions in patients with eating disorders

OBJECTIVE

The purpose of this study was to assess olfactory-gustatory function impairment in patients with eating disorders.

METHODS

Nineteen patients with a diagnosis of bulimia nervosa, 18 patients with a diagnosis of anorexia nervosa and a control sample of 19 healthy subjects were recruited from the day hospital service of the Complex Operative Unit for Alimentary Conduct Disorders of the Policlinico Umberto I in Rome. Evaluation of olfactory and gustatory functions was performed on patients through the 'Sniffin' Sticks' method in order to assess the olfactory threshold, the capacity for discriminating and identifying olfactory stimuli, and the overall olfactory function, and through the 'taste strip' kit method in order to assess the gustatory function. The results were processed statistically to assess differences between patients with anorexia nervosa, patients with bulimia nervosa and healthy controls.

RESULTS

The two groups of patients with bulimia nervosa and anorexia nervosa showed a poorer olfactory and gustatory function compared with the healthy controls; discrimination of olfactory stimuli and overall olfactory function were reduced in both samples, as well as the overall gustatory function and the perception of bitter stimuli, whereas olfactory threshold was altered only in patients with bulimia nervosa. In both samples, scores for olfactory function fell within the range of hyposmia.

DISCUSSION

Our data suggest that patients with eating disorders have an altered perception of olfactory and gustatory stimuli. The alterations observed are worth further investigation.

Olfaction under metabolic influences

Recently published work and emerging research efforts have suggested that the olfactory system is intimately linked with the endocrine systems that regulate or modify energy balance. Although much attention has been focused on the parallels between taste transduction and neuroendocrine controls of digestion due to the novel discovery of taste receptors and molecular components shared by the tongue and gut, the equivalent body of knowledge that has accumulated for the olfactory system, has largely been overlooked. During regular cycles of food intake or disorders of endocrine function, olfaction is modulated in response to changing levels of various molecules, such as ghrelin, orexins, neuropeptide Y, insulin, leptin, and cholecystokinin. In view of the worldwide health concern regarding the rising incidence of diabetes, obesity, and related metabolic disorders, we present a comprehensive review that addresses the current knowledge of hormonal modulation of olfactory perception and how disruption of hormonal signaling in the olfactory system can affect energy homeostasis.

Olfactory function and alternation learning in eating disorders

Orbitofrontal dysfunction is a prominent feature of obsessive compulsive disorder (OCD). In the present study we assessed orbitofrontal functioning in eating disorders (EDs) which share many features with OCD. For this purpose we studied female adolescent inpatients with anorexia nervosa restricting type (n=40), anorexia nervosa binge/purge type (n=23), a normal weight group including patients with either bulimia nervosa or eating disorder not otherwise specified-purging type (n=33), and 20 non-ED control females. Patients were assessed at admission, and when achieving weight restoration and symptom stabilization at discharge, for depression, non-ED, and ED-related OC symptoms. Orbitofrontal functioning was assessed with an alternation learning task, and with a battery assessing olfactory threshold and discrimination. Control females were assessed once. ED patients of all subtypes performed better on olfactory threshold and discrimination, but not on alternation learning, in comparison to healthy controls. More favorable orbitofrontal functioning was associated with greater ED-related obsessionality. No changes were found in olfactory threshold and discrimination between acutely-ill and symptomatically-stabilized patients. The improvement shown in alternation learning from admission to discharge was suggested to reflect a learning effect rather than being an actual change. Our findings suggest that the better orbitofrontal functioning of ED patients in comparison to healthy controls may represent a core feature of the ED that is independent of malnutrition and deranged eating behaviors, but is associated with ED-related obsessionality.

Intact sensory function in anorexia nervosa

BACKGROUND

In anorexia nervosa (AN), taste and smell are believed to be anhedonic, hunger and pain are muted, and body-image distortion obscures wasting, which together facilitate self-starvation. However, the emphasis on these deficits may be biased because other sensory systems have been sparsely investigated.

OBJECTIVES

Objectives of the study were to clarify whether these dysfunctions are specific or part of a pattern of sensory-perceptual deficits in AN patients and to test the gustatory senses dissociated from ingestion to clarify whether any deficit is sensory or affective.

DESIGN

In 15 adolescent, first-episode, hospitalized, restrictive AN patients and 15 matched healthy controls who responded to gustatory stimuli (intensity and hedonics of 5 basic tastes and tastes and odors of foods and nonfoods), size estimation (manual and oral judgment of size and shape, kinesthesia, and body size and esthetics), cold pain, and auditory and visual processing were compared.

RESULTS

AN patients did not differ on most tests, were better at odor recognition, were less successful in central auditory processing and oral assessment of size and shape, and may have been more sensitive to cold. Body-image dissatisfaction in AN patients was not related to dysfunctional size estimation.

CONCLUSIONS

There is no systematic sensory-perceptual deficit in AN patients, and specifically, not in gustatory function. The few differences shown might be due to fear of food-related stimuli or comorbidity.

Gustatory and olfactory dysfunction in older adults: a national probability study

BACKGROUND

Olfactory and gustatory functions have not been well characterized in older adults in the US. Consequently, their relationships to sociodemographic characteristics, as well as physical and mental health, were studied in a large national probability sample using brief validated tests of chemosensory function.

METHODS

A five-odour identification test and taste-impregnated strips of filter paper (sweet, sour, bitter, and salty) assessed the ability to identify chemosensory stimuli.

RESULTS

Severe gustatory dysfunction was more prevalent than severe olfactory dysfunction. Age, education and sex were independently associated with performance on both the olfactory and gustatory identification tasks. Higher scores were associated with female sex, higher level of education, and lower age. Odour identification scores exhibited a positive, albeit weak, correlation with BMI, and food-related odours were better identified than non-food odours. In addition, odour identification performance was also negatively associated with depressive symptoms.

CONCLUSIONS

These data demonstrate a high prevalence of severe gustatory and, to a somewhat lesser extent, olfactory dysfunction in a population-based sample and demonstrate that even brief tests are capable of detecting correlations between both chemical senses and relevant health measures outside a clinical setting.

Olfactory impairment is correlated with confabulation in alcoholism: towards a multimodal testing of orbitofrontal cortex

BACKGROUND

Olfactory abilities are now a flourishing field in psychiatry research. As the orbitofrontal cortex appears to be simultaneously implicated in odour processing and executive impairments, it has been proposed that olfaction could constitute a cognitive marker of psychiatric states. While this assumption appears promising, very few studies have been conducted on this topic among psychopathological populations. The present study thus aimed at exploring the links between olfaction and executive functions. These links were evaluated using two tasks of comparable difficulty, one known to rely on orbitofrontal cortex processing (i.e., a confabulation task), and one not associated with this area (i.e., Stop-Signal task).

METHODOLOGY/PRINCIPAL FINDINGS

Twenty recently detoxified alcoholic individuals and twenty paired controls took part in an experiment evaluating olfactory abilities and executive functioning (i.e., Stop-Signal task and confabulation task). Comorbidities and potential biasing variables were also controlled for. Alcoholic individuals exhibited impaired performance for high-level olfactory processing and significant confabulation problems as compared to controls (but no deficit in Stop-Signal task), even when the influence of comorbidities was taken into account. Most importantly, olfactory abilities and confabulation rates were significantly correlated in both groups.

CONCLUSIONS/SIGNIFICANCE

Alcoholism jointly leads to olfactory and memory source impairments, and these two categories of deficits are associated. These results strongly support the proposition that olfactory and confabulation measures both index orbitofrontal functioning, and suggest that olfaction could become a reliable cognitive marker in psychiatric disorders. Moreover, it underlines the need to take into account these olfactory and source memory impairments in a clinical context.

Role of the evolutionarily conserved starvation response in anorexia nervosa

This review will summarize recent findings concerning the biological regulation of starvation as it relates to anorexia nervosa (AN), a serious eating disorder that mainly affects female adolescents and young adults. AN is generally viewed as a psychosomatic disorder mediated by obsessive concerns about weight, perfectionism and an overwhelming desire to be thin. By contrast, the thesis that will be developed here is that, AN is primarily a metabolic disorder caused by defective regulation of the starvation response, which leads to ambivalence towards food, decreased food consumption and characteristic psychopathology. We will trace the starvation response from yeast to man and describe the central role of insulin (and insulin-like growth factor-1 (IGF-1))/Akt/ F-box transcription factor (FOXO) signaling in this response. Akt is a serine/threonine kinase downstream of the insulin and IGF-1 receptors, whereas FOXO refers to the subfamily of Forkhead box O transcription factors, which are regulated by Akt. We will also discuss how initial bouts of caloric restriction may alter the production of neurotransmitters that regulate appetite and food-seeking behavior and thus, set in motion a vicious cycle. Finally, an integrated approach to treatment will be outlined that addresses the biological aspects of AN.

Acute, short-term hyperinsulinemia increases olfactory threshold in healthy subjects

OBJECTIVE

Smell plays an important role in feeding behavior. We therefore tested whether insulin as a postprandial signal is involved in the regulation of olfactory function.

RESEARCH DESIGN AND METHODS

We assessed olfactory thresholds in eight lean subjects (age: 34 ± 7 years, M/F: 5/3) before and during a 2-h hyperinsulinemic (1 mU kg(-1) min(-1)) euglycemic clamp and in eight lean fasted subjects (age: 36 ± 6 years, M/F: 5/3) without insulin infusion at the same time of the day. To define odor thresholds, standardized 'sniffing sticks' were used.

RESULTS

Odor thresholds decreased from 7.8 ± 1.2 to 6.2 ± 1.1 during euglycemic hyperinsulinemia (P=0.0173), representing an increase in odor threshold. In the control group, odor thresholds were 8.3 ± 1.6 and did not change after 120 min of fasting (8.9 ± 2.2, P=0.6).

CONCLUSIONS

Increased insulin levels lead to a reduced smelling capacity, potentially reducing the pleasantness of eating. Therefore, insulin action in the olfactory bulb may be involved in the process of satiation and may thus be of interest in the pathogenesis of obesity.

Eating without a nose: olfactory dysfunction and sensory-specific satiety

Odor stimuli play an important role in the perception of food flavor. Olfactory dysfunction is thus likely to affect eating behavior. In the present study, we hypothesized that dysfunctional olfactory perception promotes sensory-specific satiety, a decrease in pleasure derived from a certain test food during and shortly after its consumption relative to other unconsumed control foods. A total of 34 hyposmic/anosmic participants were compared with 29 normosmic control participants. All participants repeatedly consumed a fixed portion of one and the same food item, a procedure known to induce sensory satiation. We found evidence for sensory-specific satiety (SSS) regardless of olfactory function. It thus appears that olfactory deficits have no major effect on SSS.

Odor perception in alexithymic patients

Alexithymia is characterized by a marked inability to identify feelings and emotional states and some studies have documented sensorial perception in response to visual or auditory cues in this disease. Although olfaction is well known for its emotional correlates, the perception of olfactory stimulations has not been previously investigated. This study compares with standard psychophysical methods the olfactory sensitivity and the self-ratings of intensity and hedonic valence of a panel of odorants in alexithymic patients, non-alexithymic patients and control subjects. Results show that alexithymics over-evaluate intensity and pleasantness of odorants compared to non-alexithymics or control subjects. This could be interpreted in the framework of a lack of inhibitory control including this particular sense.

Gustatory and olfactory sensitivity in patients with anorexia and bulimia in the course of treatment

BACKGROUND

The majority of studies on taste and smell in eating disorders have revealed several alterations of olfactory or gustatory functions. Aim of this prospective study was to employ detailed olfactory and gustatory testing in female subjects of three homogenous groups - anorexia nervosa, bulimia nervosa and healthy controls - and to look at the effects of treatment on these measures.

METHODS

Sixteen hospitalized female patients with anorexia (restricting type, mean age [M]=24.5 years), 24 female patients with bulimia (purging type, M=24.3 years) as well as 23 healthy controls (M=24.5 years) received olfactory ("Sniffin' Sticks") and gustatory testing ("Taste Strips"). Group differences in olfactory and gustatory sensitivity, body mass index (BMI), the Beck depression inventory, the eating attitudes test (EAT), and the influence of therapy on gustatory and olfactory function were investigated.

RESULTS

(1) Group differences were present for odor discrimination and overall olfactory function with anorexic patients having the lowest scores. (2) Regarding taste function, controls scored higher than patients with anorexia. (3) At admission small but significant correlations were found between overall olfactory function and body weight (r(63)=0.35), BMI (r(63) = 0.37), and EAT score (r(63) = -0.27). Similarly, (4) the taste test score correlated significantly with body weight (r(63)= 0.48), and BMI (r(63) = 0.45). Finally, (5) at discharge overall olfactory and gustatory function were significantly higher compared to admission in anorexic patients.

CONCLUSIONS

As compared to healthy controls and bulimic patients our results show lowered olfactory and gustatory sensitivities in anorexic patients that improved with increasing BMI and decreasing eating pathology in the course of treatment.

[Changed taste perception in patients with eating disorders]

OBJECTIVE

Taste is a hereditary trait and affects eating and dietary behavior. The tongue's papillae represent the first line of the gustatory apparatus to provide information about taste. The aim of the present investigation was to evaluate the number of fungiform papillae (fPap) in relationship with 6-n-propylthiouracil (PROP) sensitivity and body mass index (BMI) in patients with eating disorders.

METHODS

18 female patients with eating disorders (anorexia or bulimia nervosa; age 14-20 yrs.) and 15 age-matched female controls were included. The number of fPap was quantified. Bitter taste was probed with PROP. Different BMIs (e.g. minimal BMI, maximal BMI) were calculated.

RESULTS

As regards non-tasters (PROP negative), anorectic patients showed a significant reduction in the number of fPap compared to both PROP negative healthy controls and also bulimic patients. The number of fPap did not differ significantly between tasters and non-tasters within controls and eating disorder groups. There was a trend of higher BMI's in bulimic and healthy non-tasters.

CONCLUSIONS

In anorectic patients a reduced number of fPap was associated with a decreased PROP sensitivity, which is a new finding. The data of the present study support the notion that the variation of fPap number and PROP sensitivity influences the pathophysiology of eating behavior and taste perception, and following this are involved in the development of eating disorders.

Olfaction: a potential cognitive marker of psychiatric disorders

Cognitive deficits are well documented in psychiatric disorders, particularly in schizophrenia and depression. Cognitive activity roots in perceptions. However, research on sensorial alterations in psychiatric conditions has mainly focused on visual or auditory processes and less on olfaction. Here, we examine data on olfactory deficits in psychiatric patients using a systematic review of recent publications. Schizophrenic patients are mainly characterized by no reliable change in odour sensitivity and by a deficit in odour identification, recognition and discrimination. Depressed patients principally exhibit a deficit in the hedonic aspects of this perception, even if, in some case, alterations in sensitivity or identification are also found. Changes in odour perception are also found in dementia and in some neurodegenerative disease, but in this case alterations concern all aspects of the sensorial experience (detection threshold, identification and recognition). Taken together, these data indicate that olfactory abnormalities might be a marker of psychiatric conditions, with a specific pattern for each disease.