Odour identification impairment is a trait but not a disease-specific marker for bipolar disorders: Comparisons of bipolar disorder with different episodes, major depressive disorder and schizophrenia

Association between olfactory function and metabolic syndrome in bipolar disorder patients: a cross-sectional study

BACKGROUND

Olfactory function is closely related to mood and the endocrine system. However, the role of olfactory function in bipolar disorder combined with metabolic syndrome remains unclear. The purpose of this study was to explore the associations among olfactory function, tumor necrosis factor alpha (TNF-α), and metabolic syndrome and its components in patients with bipolar disorder.

METHODS

Ninety-six bipolar disorder patients were divided into two groups with and without metabolic syndrome. We also included 46 healthy controls. Olfactory function was assessed using the Sniffin' Sticks test. Blood samples were collected to measure metabolic indicators and serum TNF-α levels.

RESULTS

Significant differences in olfactory function were found among the three groups. Compared with the healthy controls, the bipolar disorder without metabolic syndrome group showed poorer olfactory identification ability (P < 0.001) and the bipolar disorder with metabolic syndrome group showed impaired olfactory sensitivity (P = 0.003) and olfactory identification (P < 0.001). Moreover, the bipolar disorder with metabolic syndrome group had poorer olfactory identification ability than the bipolar disorder without metabolic syndrome group (P = 0.015). Both bipolar disorder groups showed lower TNF-α levels than healthy controls. However, there was no significant difference between the two patient groups. Correlation analysis showed that, in the bipolar disorder with metabolic syndrome group, olfactory identification was negatively correlated with systolic blood pressure (r = - 0.424, P = 0.031), and serum TNF-α level was negatively correlated with body mass index (BMI; r = - 0.398, P = 0.049), triglyceride (r = - 0.503, P = 0.010), total cholesterol (r = - 0.491, P = 0.013), low-density lipoprotein-cholesterol (r = - 0.491, P = 0.013), and high-density lipoprotein-cholesterol (r = - 0.454, P = 0.023).

CONCLUSIONS

The olfactory identification ability of patients with bipolar disorder is worse than that of healthy controls, and the occurrence of metabolic syndrome will further aggravate the olfactory identification impairment of those patients. Furthermore, there may be a stronger link between serum TNF-α level and multiple metabolic indicators in bipolar disorder patients with metabolic syndrome than in bipolar disorder patients without metabolic syndrome.

Significant improvements in the olfactory sensitivity of bipolar I disorder patients during euthymia versus manic episodes: a longitudinal study

Introduction

Research has indicated that individuals diagnosed with bipolar disorder (BD) might experience alterations in their olfaction or levels of serum tumor necrosis factor-α (TNF-α), but no studies have investigated olfactory function and serum TNF-α in BD patients simultaneously. Moreover, there is a lack of existing research that compares the longitudinal olfactory function between individuals with manic and euthymic BD I.

Methods

Patients with manic BD I (BDM, n=44) and healthy controls (HCs, n=32) were evaluated symptoms (measured via the Young Manic Rating Scale, YRMS), social function (measured via the Global Assessment Function, GAF), serum TNF-α, and olfactory function (via the Sniffin' Sticks test) including olfactory sensitivity (OS) and olfactory identification (OI). The BDM patients were followed up to the remission period and re-evaluated again. We compared OS, OI and serum TNF-α in manic and euthymic patients with BD I and HCs. We examined the correlation between olfactory function and symptoms, social function, and serum TNF-α in patients with BD I.

Results

The BDM patients exhibited significantly lower OS and OI compared to the HCs (Z = -2.235, P = 0.025; t = -6.005, P < 0.001), while a positive correlation was observed between OS and GAF score (r = 0.313, P = 0.039). The OS in the BD I remission group (n=25) exhibited significantly superior performance compared to the BDM group (t = -4.056, P < 0.001), and the same as that in the HCs (P = 0.503). The change in OS showed a positive correlation with the decrease in YMRS score (r = 0.445, P = 0.026), and a negative correlation with the course of disease (r = -0.594, P = 0.002). The TNF-α in BD I patients was significantly lower compared to HCs (P < 0.001), and not significantly correlated with olfactory function (all P > 0.05).

Conclusion

The findings suggest that OS and OI are impaired in BDM patients, and the impaired OS in those patients can be recovered in the remission stage. OI may serve as a potential characteristic marker of BD. OS might be useful as an index for BDM treatment efficacy and prognosis.

Comparison of olfactory function, cognitive function and serum tumor necrosis factor-α between bipolar and schizophrenic patients in the remission stage

OBJECTIVES

Olfactory function, serum tumor necrosis factor-α (TNF-α) and cognitive function were compared between bipolar disorder (BD) and schizophrenia (SP) patients in the remission stage combined with correlation analysis, with the aim of identifying new indicators for the auxiliary diagnosis of these psychiatric illnesses.

METHODS

A total of 46 euthymic BD patients, 42 clinically stable SP patients and 42 healthy controls (HC) were included in this study. Olfactory sensitivity (OS) and olfactory identification (OI) were assessed using Sniffin' Sticks test, and serum TNF-α levels were measured by ELISA. Clinical symptoms were evaluated with the Hamilton Rating Scale for Depression, Young Mania Rating Scale, Hamilton anxiety scale, and the Positive and Negative Syndrome Scale (PANSS). Social function was evaluated with the Global Assessment Function (GAF) scale. Cognitive function was evaluated using the Trail Making Test-A (TMT-A) and Digit Cancellation Test (DCT).

RESULTS

OI and cognitive function scores and serum TNF-α levels were significantly lower in the BD and SP patients compared with the HC participants. There was no significant difference between the BD and SP groups, and there were no significant differences in OS among the three groups. OI score was positively correlated with years of education in both the BD and SP groups. OI score in the SP group was negatively correlated with age and PANSS score, and positively correlated with GAF score. In the BD group, OS was positively correlated with DCT II and DCT III. In the SP group, OS and OI scores were positively correlated with DCT III, and negatively correlated with TMT-A time. Furthermore, there was a positive correlation between TNF-α and DCT II in the BD group. There was no significant linear correlation between olfactory function and TNF-α in the BD or SP group.

CONCLUSION

OI may be a trait marker for BD and SP. Some cognitive functions may be correlated not only with TNF-α in BD patients in remission, but also with olfactory function in BD and SP patients in remission.

Impaired olfactory function in bipolar disorder patients during acute episodes regardless of psychotic symptoms

Background

The aim of this study was to analyze whether the presence of psychotic symptoms affects olfactory function in patients with bipolar disorder (BD). We also compared olfactory function between the period of episode and remission in patients with BD.

Methods

BD patients in the acute phase were tracked to the remission stage. The psychiatric symptoms and social function of the enrolled subjects were assessed using the Hamilton Rating Scale for Depression (HAMD), the Young Mania Rating Scale (YMRS), the Hamilton Rating Scale for Anxiety (HAMA), the Positive and Negative Syndrome Scale (PANSS) and the Global Assessment Function (GAF). Olfactory sensitivity (OS) and olfactory identification (OI) was assessed using the Sniffin' Sticks test. Differences in OS and OI among the episodic group, the euthymic group, and the healthy control (HC) group were compared. According to whether BD is accompanied by psychotic symptoms, the OS and OI in the BD with psychotic symptoms group (P-BD), the BD without psychotic symptoms group (NP-BD), and the HC group were compared.

Results

The P-BD and NP-BD groups exhibited impaired OI compared with the HC group, but there was no significant difference in OI between the P-BD and NP-BD groups, or in OS among all three groups. All patients with episodic BD had significantly lower OS and OI compared with the HC group. OI in euthymic BD patients was still impaired; however, OS recovered, showing no significant difference compared with that in the HC group.

Conclusion

The results indicate that patients with episodic BD have impaired OS and OI, regardless of psychotic symptoms. OI may be a characteristic marker of BD, and OS may be a state marker that can be used to distinguish between episodic and euthymic BD.

Olfactory Dysfunction in Mental Illness

PURPOSE OF REVIEW

Olfactory dysfunction contributes to the psychopathology of mental illness. In this review, we describe the neurobiology of olfaction, and the most common olfactory alterations in several mental illnesses. We also highlight the role, hitherto underestimated, that the olfactory pathways play in the regulation of higher brain functions and its involvement in the pathophysiology of psychiatric disorders, as well as the effect of inflammation on neurogenesis as a possible mechanism involved in olfactory dysfunction in psychiatric conditions.

RECENT FINDINGS

The olfactory deficits present in anxiety, depression, schizophrenia or bipolar disorder consist of specific alterations of different components of the sense of smell, mainly the identification of odours, as well as the qualifications of their hedonic valence (pleasant or unpleasant). Epidemiological findings have shown that both environmental factors, such as air pollutants, and inflammatory disease of the upper respiratory tract, can contribute to an increased risk of mental illness, at least in part, due to peripheral inflammatory mechanisms of the olfactory system. In this review, we describe the neurobiology of olfaction, and the most common olfactory function alterations in several psychiatric conditions and its role as a useful symptom for the differential diagnosis. We also highlight the effect of inflammation on neurogenesis as a possible mechanism involved in olfactory dysfunction in these psychiatric conditions.

Olfactory Dysfunction in Schizophrenia: Evaluating Olfactory Abilities Across Species

Though understudied relative to perturbations in the auditory and visual domains, olfactory dysfunction is a common symptom of schizophrenia. Over the past two decades, the availability of standardized assessments to quantify human olfactory abilities, and enhance understanding of the neurophysiology supporting olfaction, has increased, enabling a more thorough characterization of these deficits. In contrast to other psychiatric conditions for which olfactory dysfunction has been observed (e.g., major depressive disorder, bipolar disorder, Alzheimer's disease), the impairments observed in schizophrenia are particularly global and profound. At this level, such deficits in olfactory abilities likely impact the enjoyment of food, detection of environmental hazards, and influence social relationships. More broadly, the study of olfactory phenotypes in schizophrenia presents new avenues for detection of those at-risk for the condition, identification of therapeutic targets for treatment development, and for the characterization of novel animal models relevant to schizophrenia and psychosis. This review will consider the olfactory performance of individuals with schizophrenia in domains for which standardized assessments are available (odor sensitivity, discrimination, identification, and memory). Paradigms available for assessing these abilities in rodents will also be discussed with the aim of facilitating translation. Thus, future studies will be able to include cross-species translation of mechanisms relevant to olfactory function and cognition, what has gone awry in the disease state, and test potential therapeutics.

Variations in olfactory function among bipolar disorder patients with different episodes and subtypes

Purpose

Most studies on olfactory function in individuals with bipolar disorder (BD) have not distinguished between the different subtypes or between the acute phase (mania or depression) and euthymic state. In this study, we compared olfactory function among BD patients with different subtypes and episodes to explore the potential use of olfactory function as a biomarker for the early identification of BD.

Patients and methods

The study sample consisted of 117 BD patients who were hospitalized between April 2019 and June 2019, and 47 healthy volunteers as controls. The BD patients were divided into a bipolar I disorder (BD I) (n = 86) and bipolar II disorder (BD II) group (n = 31) according to the different subtypes, and divided into depressive BD (n = 36), manic BD (n = 44), or euthymic BD (n = 37) groups according to the types of episodes they experienced. We assessed olfactory sensitivity (OS) and olfactory identification (OI) via the Sniffin' Sticks test and used the Hamilton Depression Rating Scale (HAMD) and Young Manic Rating Scale (YMRS) to evaluate BD characteristics among all subjects.

Results

Compared with controls, the participants with BD showed decreased OS and OI. We found statistically significant differences in OS and OI between the BD I group and controls, as well as differences in OS between the BD I and BD II group. Least-significant difference multiple comparisons revealed statistically significant differences in OS between the depressive BD group, manic BD group and controls and also between the manic BD and euthymic BD group. OI was positively correlated with the YMRS score in the BD I group and OS was negatively correlated with the HAMD score in the BD II group.

Conclusion

This may be the first study to compare olfactory function in patients with BD I vs. BD II via pairwise comparisons. Our findings suggest that OS may have potential as a biomarker for distinguishing the different subtypes of BD and as a state-related biomarker for differentiating the acute phase from the euthymic state of BD. However, further prospective research is warranted.

Interactive Effects of Agitation and Cognitive Impairment on Odor Identification in Patients With Late-Life Depression

BACKGROUND

Late-life depression (LLD) is a risk factor for cognitive decline in older adults, and odor identification (OI) deficits are an early indicator of cognitive decline with LLD. However, neuropsychiatric symptoms (NPSs) are common in LLD and are associated with OI deficits. In subjects with LLD, when OI deficits forecast cognitive decline, whether and how NPS affects the relationship between OI and cognition still must be further explored.

OBJECTIVE

To comprehensively explore the potential effects of various NPSs on the relationship between OI and cognition in participants with LLD.

METHODS

There were 167 patients with LLD and 105 normal elderly (NE) participants. The odor identification test (Sniffin' Sticks), cognitive function assessments (global cognition, memory, executive function, attention, language, visual space), and an NPS assessment (the neuropsychiatric inventory questionnaire) were performed on the subjects. In patients with LLD, the relationship among OI, cognition and NPSs was examined using correlation analysis and moderation analysis.

RESULTS

In patients with LLD, OI was positively correlated with cognition (global cognition, memory, executive function, attention, language) and negatively associated with NPSs (agitation and aberrant motor behavior). In NE group, OI was correlated with executive function. Moderation analysis showed that there was an interactive effect of agitation and cognitive impairment (language deficit or attention deficit) on OI in patients with LLD.

CONCLUSION

The coexistence of agitation and language or attention deficit was associated with worse OI in subjects with LLD. Agitation should be considered since OI predicts cognitive decline in patients with LLD.

Sex Differences in Odor Hedonic Perception: An Overview

Odor hedonic evaluation (pleasant/unpleasant) is considered as the first and one of the most prominent dimension in odor perception. While sex differences in human olfaction have been extensively explored, gender effect in hedonic perception appears to be less considered. However, a number of studies have included comparisons between men and women, using different types of measurements (psychophysical, psychophysiological,…). This overview presents experimental works with non-specific and body odors separately presented as well as experimental studies comparing healthy participants vs patients with psychiatric disorders. Contrary to sensitivity, identification or discrimination, the overall literature tends to prove that no so clear differences occur in odor hedonic judgment between men and women. On the whole, gender effect appears more marked for body than non-specific odors and is almost never reported in psychiatric diseases. These findings are discussed in relation to the processes classically implied in pleasantness rating and emotional processes.