Olfactory Identification Function Research Articles

Clinical Manifestations.

Olfactory dysfunction has been reported for its association with cognitive impairment and incident dementia. However, the underlying role of neurodegeneration in this relationship is not fully understood. This prospective cohort study included participants from the Shanghai Aging Study (SAS) who were 60 years or older and diagnosed as dementia-free at baseline and completed at least one follow-up interview between 2010 and 2022. At baseline, olfactory identification function was assessed by the 12-item Sniffin' Sticks Smell test (SSST-12). Olfactory dysfunction was defined as SSST-12 < 7, 6, and 5 in three age groups of participants with (age < 70, 70 ≤ age < 80, and age ≥ 80), respectively, according to previously reported normative data of olfaction in the SAS. Baseline blood Neurofilament Light Chain (NfL) was quantified using the ultra-sensitive Single Molecular Array technology (Quanterix), and dichotomized into low and high levels according to the median concentration. Multiple cognitive function assessments were administered by the Mini-mental State Examination (MMSE) at baseline and follow-ups. We used the linear mixed-effect model to fit the MMSE trajectories in participants with and without olfactory dysfunction adjusting for baseline age, sex, education year, smoking, and APOE ε4, with person-specific MMSE intercept and slope. Stratified analysis was conducted in participants with low and high NfL. Among 1125 participants included in this study, 296 were defined as having olfactory dysfunction at baseline. Less education, higher proportion of APOE ε4 allele, and lower baseline and follow-up MMSE scores were observed in participants with olfactory dysfunction (Table 1). During the median 9.4 years follow-up, participants with olfactory dysfunction at baseline evidenced a faster MMSE decline compared with those without olfactory dysfunction (b [95% CI]: -0.08 [-0.15, -0.02], P = 0.02) (Figure 1). Such association remained statistically significant (-0.18 [-0.31, -0.06], P = 0.005) in the subgroup with high NfL, but not in the subgroup with low NfL (0.004 [-0.07, 0.07], P = 0.92) (Figure 2). Blood NfL may modify the association of olfactory dysfunction with long-term cognitive decline in community-dwelling older adults. In individuals with high potential neurodegeneration, olfactory dysfunction may be an independent indicator of future cognitive deterioration.

Poor preoperative performance at Clock Drawing Test is associated with postoperative decline in olfaction in older patients: an observational pilot study

BackgroundDecline in olfaction may occur after general anesthesia, but the exact incidence and underlying physiopathology remain scarcely investigated. Olfactory dysfunction arises with aging and is known to be linked to cognitive impairment. In this pilot study, we evaluated the incidence of immediate postoperative decline in olfaction and its association with a preoperative cognitive test, performance at Clock Drawing Test (CDT), in a group of older patients.MethodsThis pilot study is a sub-analysis of a prospective observational study. Patients ≥ 65 years old and scheduled for elective non-cardiac surgery under sevoflurane-based anesthesia were enrolled. CDT was part of the preoperative evaluation. We assessed olfaction on the day before and the day after surgery (between 16 and 26 h postoperatively) using the Sniffin’ Sticks 12-item identification test, which consists of pen-like devices displaying 12 different odors. Postoperative decline in olfaction was defined as a decrease of at least 1 standard deviation in the olfactory score.ResultsWe included a total of 93 patients, among whom 19 (20.4%) presented a postoperative decline in olfaction. The incidence of postoperative decline in olfaction was higher in the “CDT low-score” (score ≤ 5/8) group (11/34, 32.4%) than in the “CDT high-score” (score ≥ 6/8) group (8/58, 13.6%) (P = 0.030). Despite adjusting for confounding variables, CDT score remained independently associated with immediate postoperative decline in olfactory identification function (OR 0.67, 95% CI 0.48 to 0.94, P = 0.022).ConclusionsPostoperative decline in olfaction occurred in 20.4% of older patients and was associated with poor preoperative performance at CDT.Trial registrationThis study was retrospectively registered on https://clinicaltrials.gov/ under the NCT04700891 number (principal investigator: Victoria Van Regemorter), in December 2020.

Differences in olfactory dysfunction and its relationship with cognitive function in schizophrenia patients with and without auditory verbal hallucinations.

Olfactory discrimination dysfunction has been observed in patients with schizophrenia (SCZ), but its relationship with cognitive function has not been clarified. The purpose of this study was to examine the differences in olfactory identification function in SCZ patients with and without auditory verbal hallucinations (AVHs) and its relationship with cognitive function. Olfactory identification function was measured in 80 SCZ patients with AVHs, 57 SCZ patients without AVHs, and 87 healthy controls (HC). Clinical symptom scores and neuropsychological measures were also administered to all corresponding subjects. Compared to HC, SCZ patients showed significant deficits in olfactory identification and cognitive function, but there were no differences in olfactory identification dysfunction and cognitive dysfunction between the two subgroups. In the non-AVHs subgroup only, poorer Olfactory Stick Identification Test for Japanese (OSIT-J) scores were significantly and positively correlated with total and delayed recall (Bonferroni correction, p < 0.002). Stepwise regression analysis revealed that factors affecting olfactory identification impairment differed in the two SCZ patient subgroups. In conclusion, this study highlights the commonality of olfactory identification dysfunction in SCZ patients and the importance of olfactory assessment of different subtypes of SCZ patients.

Olfactory function changes and the predictive performance of the Chinese Smell Identification Test in patients with mild cognitive impairment and Alzheimer's disease.

Olfactory disorder is one of the sensory features that reflects a decline in cognitive function. However, olfactory changes and the discernibility of smell testing in the aging population have yet to be fully elucidated. Therefore, this study aimed to examine the effectiveness of the Chinese Smell Identification Test (CSIT) in distinguishing individuals with cognitive decline from those with normal aging and to determine whether the patients with MCI and AD show changes in their olfactory identification abilities. This cross-sectional study included eligible participants aged over 50 years between October 2019 and December 2021. The participants were divided into three groups: individuals with mild cognitive impairment (MCI), individuals with Alzheimer's disease (AD), and cognitively normal controls (NCs). All participants were assessed using neuropsychiatric scales, the Activity of Daily Living scale, and the 16-odor cognitive state test (CSIT) test. The test scores and the severity of olfactory impairment were also recorded for each participant. In total, 366 eligible participants were recruited, including 188 participants with MCI, 42 patients with AD, and 136 NCs. Patients with MCI achieved a mean CSIT score of 13.06 ± 2.05, while patients with AD achieved a mean score of 11.38 ± 3.25. These scores were significantly lower than those of the NC group (14.6 ± 1.57; P < 0.001). An analysis showed that 19.9% of NCs exhibited mild olfactory impairment, while 52.7% of patients with MCI and 69% of patients with AD exhibited mild to severe olfactory impairment. The CSIT score was positively correlated with the MoCA and MMSE scores. The CIST score and the severity of olfactory impairment were identified as robust indicators for MCI and AD, even after adjusting for age, gender, and level of education. Age and educational level were identified as two important confounding factors that influence cognitive function. However, no significant interactive effects were observed between these confounders and CIST scores in determining the risk of MCI. The area under the ROC curve (AUC) generated from the ROC analysis was 0.738 and 0.813 in distinguishing patients with MCI and patients with AD from NCs based on the CIST scores, respectively. The optimal cutoff for distinguishing MCI from NCs was 13, and for distinguishing AD from NCs was 11. The AUC for distinguishing AD from MCI was 0.62. The olfactory identification function is frequently affected in patients with MCI and patients with AD. CSIT is a beneficial tool for the early screening of cognitive impairment among elderly patients with cognitive or memory issues.

Changes in olfactory identification function in total laryngectomy patients - A retrospective study focusing on nasal airflow-inducing maneuver usage, Open Essence misreactions, and odor cluster

PurposeWe aimed to examine how the olfactory identification function of laryngectomy patients is altered by nasal airflow-inducing maneuver (NAIM), a method of olfactory rehabilitation, by analyzing incorrect and correct responses to olfactory identification tests to achieve odor classification. MethodsOlfactory identification test (Open Essence [OE]) was administered to 46 patients who had undergone a total laryngectomy [Start group (NAIM was initiated from this study) = 17; (already) Using group = 19; and Nonuse group = 10]. The tests were immediately performed after the NAIM and after a mean duration of 8 months. ResultsIn the Start group, changes in OE correct and incorrect responses showed a significant increase and decrease in the number of correct (p < 0.01) and “detectable but not recognizable” responses (p < 0.05), respectively. In the Using group, errors related to “same cluster” and “detectable but not recognizable” increased and decreased significantly (p < 0.05), respectively. The Nonuse group showed a trend of demonstrating a relatively lower number of correct responses (p < 0.1). Results of odor classification showed that only “putrefaction and sulfur” did not have any significant positive responses in the Start group. DiscussionEvidently, the possibility of capturing changes in olfactory identification function by performing a false response analysis was observed, even if recovery appears to have stalled after long-term use of NAIM. Furthermore, including the “putrefaction and sulfur” cluster in the olfactory rehabilitation of laryngectomy patients and teaching them to consciously sniff “putrefaction and sulfur” in their daily lives is necessary.

Effects of Nasal Airflow-Inducing Maneuver in Total Laryngectomy Patients Based on Changes to Olfactory Test Results: A Retrospective Study

Introduction: This study aims to retrospectively examine temporal changes in three aspects, i.e., olfactory threshold test, olfactory identification test, and olfactory perception on daily living test, caused by the use of the nasal airflow-inducing maneuver (NAIM). Methods: The olfactory threshold test (Sniffin’ Sticks test), olfactory identification test (Open Essence [OE]), and olfactory perception on daily living test (self-administered odor question; SAOQ) were administered to 46 patients who had undergone a total laryngectomy (NAIM Start group: 17; Using group: 19; and Nonuse group: 10). The tests were immediately performed after the NAIM and again after an average of 8 months. Results: In the NAIM Start group, all olfactory functions significantly improved in the second test compared with the first test (Sniffin’ Sticks test and OE, p < 0.01 for both; self-administered, p < 0.05). Additionally, in terms of the intergroup changes among scores for the Sniffin’ Sticks test and OE, the NAIM Start group showed a significant difference compared with all of the other groups (Start group > Using and Nonuse group, p < 0.01). The NAIM Using group did not exhibit any significant changes. In the NAIM Nonuse group, olfactory identification function was lower in the second test compared with the first test and showed a trend toward a significant difference (OE, p < 0.1). Temporal changes in SAOQ showed a significant increase in all intragroup comparisons. However, there were no significant differences observed in terms of the changes between the groups. Conclusion: The results demonstrated that even in those who were not using NAIM and undergoing olfactory rehabilitation after laryngectomy (NAIM Start group), the subsequent daily use of NAIM and voluntary rehabilitation aided in the recovery of olfactory function to the same level as that in the already using NAIM group. SAOQ results were considered because of the experimenter effect and they appeared to be unrelated to use NAIM. This study showed that in total laryngectomy patients who did not receive olfactory rehabilitation, olfactory identification was reduced.

Dementia screening in rural-dwelling Chinese older adults: The utility of a smell test and the self-rated AD8.

Olfactory impairment is associated with dementia in clinical settings. We examined the relationship of olfactory identification function with all-cause dementia, Alzheimer's disease (AD), and vascular dementia (VaD) and assessed the discriminative ability of the Sniffin' Sticks Identification Test (SSIT), the self-rated Ascertain Dementia 8-item Questionnaire (AD8), and their combination for dementia detection among rural-dwelling older adults in China. This population-based cross-sectional study included 4481 participants (age ≥ 65 years; 56.8% women; 38.1% illiteracy) living in rural communities. The 16-item SSIT was performed to assess olfactory identification function. The self-rated AD8 was administered to participants for cognitive status. We diagnosed dementia, AD, and VaD following the international criteria. Data were analyzed with logistic regression models and receiver operating characteristic curve. Of the 4481 participants, dementia was diagnosed in 139 persons (3.1%), including 92 with AD and 42 with VaD. The SSIT score (range, 0-16) was associated with multiadjusted odds ratios of 0.83 (95% CI: 0.79-0.88) for dementia, 0.84 (0.79-0.90) for AD, and 0.79 (0.71-0.87) for VaD. The area under the curve for the discrimination between participants with and without dementia was 0.73 (95% CI: 0.69-0.77) for SSIT score ≤ 8 alone, 0.86 (0.82-0.89) for self-rated AD8 score ≥ 3 alone, and 0.89 (0.86-0.92) for their combination using a logistic model. Olfactory impairment is a clinical marker for all-cause dementia, AD, and VaD. The smell identification test, in combination with the brief self-rated cognitive screening tool, is accurate for screening dementia among rural-dwelling Chinese older adults with no or limited education.

Associations between probable REM sleep behavior disorder, olfactory disturbance, and clinical symptoms in Parkinson’s disease: A multicenter cross-sectional study

Rapid eye movement sleep behavior disorder (RBD) and olfactory dysfunction are useful for early diagnosis of Parkinson's disease (PD). RBD and severe olfactory dysfunction are also regarded as risk factors for cognitive impairment in PD. This study aimed to assess the associations between RBD, olfactory function, and clinical symptoms in patients with PD. The participants were 404 patients with non-demented PD. Probable RBD (pRBD) was determined using the Japanese version of the RBD screening questionnaire (RBDSQ-J) and the RBD Single-Question Screen (RBD1Q). Olfactory function was evaluated using the odor identification test for Japanese. Clinical symptoms were evaluated using the Movement Disorder Society Revision of the Unified PD Rating Scale (MDS-UPDRS) parts I-IV. In total, 134 (33.2%) patients indicated a history of pRBD as determined by the RBD1Q and 136 (33.7%) by the RBDSQ-J based on a cutoff value of 6 points. Moreover, 101 patients were diagnosed as pRBD by both questionnaires, 35 by the RBDSQ-J only, and 33 by the RBD1Q only. The MDS-UPDRS parts I-III scores were significantly higher and disease duration significantly longer in the pRBD group. pRBD was significantly associated with male gender and the MDS-UPDRS part I score. The olfactory identification function was significantly reduced in the pRBD group. About 33% of the patients with PD had pRBD based on the questionnaires, and both motor and non-motor functions were significantly decreased in these patients. These results suggest that more extensive degeneration occurred in patients with non-demented PD with RBD.

Smell identification function in early-onset Alzheimer's disease and mild cognitive impairment.

Little is known about olfactory identification (OI) function in early-onset Alzheimer's disease (EOAD) and early-onset mild cognitive impairment (eoMCI) with age of onset <65 years. We aimed to study OI in EOAD compared with eoMCI and age-matched healthy controls (HC). Nineteen EOAD subjects with mild to moderate dementia, 17 with eoMCI, and 21 HC recruited as a convenience sample from memory services were assessed for cognition, behavioral symptoms, and activities for daily living. The OI was tested using the University of Pennsylvania smell identification test (UPSIT). EOAD participants performed worse compared with eoMCI and HC on cognitive tests and OI (p < 0.001). Although eoMCI had poorer cognitive scores compared to HC, they were similar in their OI function. OI correlated with attention (r = 0.494, p = 0.031), executive functions (r = 0.508, p = 0.026), and praxis (r = 0.455, p = 0.05) within the EOAD group. OI impairment was significantly associated with the diagnosis of EOAD versus eoMCI, but not with eoMCI when compared with HC. OI could potentially be useful in differentiating EOAD from eoMCI. Studies with late-life MCI patients showing OI impairment relative to HC may be attributed to a different disease process. Independent replication in a larger sample is needed to validate these findings.

Smell identification function and Alzheimer's disease: a selective review.

To provide an update of the recent studies on the olfactory function in Alzheimer's disease, with a focus on the olfactory identification function. The studies reviewed here confirm previous reports on the poor olfactory function in Alzheimer's disease compared to health normal controls and also as a marker for conversion from mild cognitive impairment to Alzheimer's disease. Olfactory identification function has been associated with severity of illness, non-cognitive neuropsychiatric symptoms, and structural and functional MRI measures. There is a possible interaction of apolipoprotein E genotype with olfactory performance in Alzheimer's disease patients and those at risk for Alzheimer's disease. Usefulness of smell identification function in differentiating Alzheimer's disease patients from other types of dementia needs to be established. The need for simple, inexpensive and non-invasive procedures for aiding in the diagnosis and understanding of Alzheimer's disease has led to theories and procedures examining the role of olfactory functions in Alzheimer's disease. Although there is increasing evidence for olfactory dysfunction in general and impaired odour identification in particular in Alzheimer's disease, additional larger and methodologically sound research is needed for testing its clinical utility in day-to-day clinical practice for early, accurate and differential diagnosis of Alzheimer's disease.

Cross-Cultural Application of the “Sniffin’ Sticks” Odor Identification Test

Odor identification tasks are an important tool for the clinical assessment of olfactory function. However, cultural differences prevent odor identification tests from being used in different countries, because odor identification is strongly dependent on familiarity with these odors. The "Sniffin' Sticks" olfactory test has been developed in Europe and is used for assessment of olfactory function in many European countries. The aim of this study was to investigate the applicability of the "Sniffin' Sticks" odor identification test in an area with a different culture compared with its place of origin. The 16 odors in the ''Sniffin' Stick'' odor identification test were kept the same but some descriptors were changed compared with the original version. One odor was presented for 3 seconds. Then, subjects chose an item from a list of four descriptors. Two hundred two subjectively normosmic subjects were tested. Forty-two subjects were retested 1 week after the first test. Mean odor identification scores of age groups 18-35 years, 36-55 years, and >55 years were 14.8, 14.7, and 13.3, respectively. The score at the 10th percentile was 13.0 in the youngest group of subjects. Age-related decrease of odor identification scores was clearly established. The decrease of the odor identification score was most obvious in subjects aged 63-67 years. The coefficient of correlation between test and retest was 0.76. After revision of the descriptors, the ''Sniffin' Sticks'' odor identification test appears to be suited for assessment of olfactory identification function in an Asian region.

Olfactory screening test in mild cognitive impairment

Mild cognitive impairment (MCI) is a transient status between physiologic ageing and dementia. Each year more than 12% of subjects with MCI develop Alzheimer's disease. This study evaluated the presence of an olfactory deficit in amnesic MCI (aMCI) patients. Twenty-nine patients diagnosed with aMCI and a homogeneous control group of 29 subjects were enrolled in the study. Olfactory function was assessed by the Sniffin' Sticks Screening Test (SSST) and the Mini Mental State Examination, the Clinical Dementia Rating, the Geriatric Depression Scale and the Mental Deterioration Battery were used to evaluate the neurocognitive status. aMCI patients showed a significant impairment of their olfactory identification compared to controls (SSST score: 8.3+/-2.1 vs. 10.8+/-0.9; p<0.001). These results suggest that olfactory tests should be part of the diagnostic armamentarium of pre-clinical dementia. A long-term follow up might confirm the olfactory identification function as an early and reliable marker in the diagnosis of pre-clinical dementia.

Olfactory identification deficit in relation to schizotypy

Past studies have shown that schizophrenic men tend to be impaired on the olfactory identification task. We examined individual differences in the olfactory function in relation to schizotypy. Healthy individuals who might carry latent liability for schizophrenia participated in olfactory identification and acuity tasks. Psychometrically ascertained schizotypic men showed deficits on the olfactory identification task but not on the olfactory acuity task. The olfactory identification function partly depended on the menstrual cycle in women. But further systematic research is needed to clarify the possible role of estrogen.

Olfactory Dysfunction in Patients with Minamata Disease

We studied the olfactory functions of organic mercury poisoning (Minamata disease) by using both the smell identification test and the olfactory detection threshold test (with phenyl ethyl alcohol). The subjects were 19 patients with Minamata disease who were treated in Meisuien, Minamata, Kumamoto, Japan and include cases that developed the disease in utero. The mean age was 78.7 ± 14.3 years old. Both smell identification and olfactory detection tests in the majority of patients decreased significantly compared with those of healthy elder subjects. A few cases showed normal olfactory identification and detection functions. The olfactory identification function deceased with advancing age. Correlation existed between detection threshold and background factors such as age and duration after documented Minamata disease was found. No significant relationship was identified between olfactory function and the typical symptoms of Minamata disease.