A basic smell test is as sensitive as a dopamine transporter scan: comparison of olfaction, taste and DaTSCAN in the diagnosis of Parkinson's disease

The diagnostic value of dopamine transporter imaging and olfactory testing in patients with parkinsonian syndromes

The aim of the study was to compare the efficacy of olfactory testing and presynaptic dopamine imaging in diagnosing Parkinson's disease (PD) and atypical parkinsonian syndromes (APS); to evaluate if the combination of these two diagnostic tools can improve their diagnostic value. A prospective investigation of 24 PD patients, 16 APS patients and 15 patients with non-parkinsonian syndromes was performed during an 18-month period. Single photon emission computed tomography with the presynaptic radioligand (123)I-FP-CIT (DaTSCAN(®)) and olfactory testing with the Brief 12-item Smell Identification Test (B-SIT) were performed in all patients. DaTSCAN was analysed semi-quantitatively, by calculating two different striatal uptake ratios, and visually according to a predefined ranking scale. B-SIT score was significantly lower for PD patients, but not significantly different between APS and non-parkinsonism. The visual assessment of DaTSCAN had higher sensitivity, specificity and diagnostic accuracy compared to olfactory testing. Most PD patients (75%) had visually predominant dopamine depletion in putamen, while most APS patients (56%) had visually severe dopamine depletion both in putamen and in caudate nucleus. The combination of DaTSCAN and B-SIT led to a higher rate of correctly classified patients. Olfactory testing can distinguish PD from non-parkinsonism, but not PD from APS or APS from non-parkinsonism. DaTSCAN is more efficient than olfactory testing and can be valuable in differentiating PD from APS. However, combining olfactory testing and DaTSCAN imaging has a higher predictive value than these two methods separately.

Abnormal Olfaction in Parkinson's Disease Is Related to Faster Disease Progression

Introduction. A possible association between olfactory dysfunction and Parkinson's disease (PD) severity has been a topic of contention for the past 40 years. Conflicting reports may be partially explained by procedural differences in olfactory assessment and motor symptom evaluation. Methods. One hundred and sixty-six nondemented PD patients performed the Brief-Smell Identification Test and test scores below the estimated 20th percentile as a function of sex, age, and education (i.e., 80% specificity) were considered demographically abnormal. Patients underwent motor examination after 12 h without antiparkinsonian medication. Results. Eighty-two percent of PD patients had abnormal olfaction. Abnormal performance on the Brief-Smell Identification Test was associated with higher disease severity (i.e., Hoehn and Yahr, Unified Parkinson's Disease Rating Scale-III, Freezing of Gait questionnaire, and levodopa equivalent dose), even when disease duration was taken into account. Conclusions. Abnormal olfaction in PD is associated with increased severity and faster disease progression.

Body weight and food intake in Parkinson's disease. A review of the association to non-motor symptoms

Research on eating behaviours has extensively highlighted that cognitive systems interact with the metabolic system in driving food intake and in influencing body weight regulation. Parkinson's disease is a good model for studying these complex interactions since alterations in both body weight and cognitive domains have been frequently reported among these patients. Interestingly, even if different non-motor symptoms may characterize the course of the disease, their contribution to weight and food preference has been poorly investigated. This review describes body weight alterations and eating habits in patients with Parkinson's disease, including those who underwent deep brain stimulation surgery. In particular, the review considers the link between non-motor symptoms, affecting sensory perception, cognition, mood and motivation, and food intake and weight alterations. The take home message is twofold. First, we recommend a comprehensive approach in order to develop effective strategies in the management of patients' weight. Second, we also suggest that investigating this issue in patients with Parkinson's disease may provide some useful information about the mechanisms underlying food and weight regulation in healthy subjects.

Identification of odorant-receptor interactions by global mapping of the human odorome

The human olfactory system recognizes a broad spectrum of odorants using approximately 400 different olfactory receptors (hORs). Although significant improvements of heterologous expression systems used to study interactions between ORs and odorant molecules have been made, screening the olfactory repertoire of hORs remains a tremendous challenge. We therefore developed a chemical systems level approach based on protein-protein association network to investigate novel hOR-odorant relationships. Using this new approach, we proposed and validated new bioactivities for odorant molecules and OR2W1, OR51E1 and OR5P3. As it remains largely unknown how human perception of odorants influence or prevent diseases, we also developed an odorant-protein matrix to explore global relationships between chemicals, biological targets and disease susceptibilities. We successfully experimentally demonstrated interactions between odorants and the cannabinoid receptor 1 (CB1) and the peroxisome proliferator-activated receptor gamma (PPARγ). Overall, these results illustrate the potential of integrative systems chemical biology to explore the impact of odorant molecules on human health, i.e. human odorome.

Hyposmia: a possible biomarker of Parkinson's disease

Hyposmia, identified as reduced sensitivity to odor, is a common non-motor symptom of Parkinson's disease (PD) that antedates the typical motor symptoms by several years. It occurs in ∼90% of early-stage cases of PD. In addition to the high prevalence, the occurrence of hyposmia may also predict a higher risk of PD. Investigations into hyposmia and its relationship with PD may help elucidate the underlying pathogenic mechanisms. This review provides an update of olfactory dysfunction in PD and its potential as a biomarker for this devastating disease.

Predictive value of the smell identification test for nigrostriatal dopaminergic depletion in Korean tremor patients

BACKGROUND

The predictive value of Cross-Cultural Smell Identification Test for nigrostriatal dopaminergic depletion in Korean tremor patients has yet to be assessed.

METHODS

Three hundred nineteen drug-naive patients who visited our clinic for the diagnosis of their tremor, and took both Cross-Cultural Smell Identification Test and dopamine transporter PET were included in the data analysis. Visual grading of each PET image was performed by two independent neurologists.

RESULTS

Smell test scores were significantly correlated to the striatal dopaminergic activity (Kendall's τb = -0.291, p < 0.001). However, smell test score alone appeared to have relatively weak power for predicting dopaminergic depletion (area under the curve = 0.693). Multivariate logistic regression model with inclusion of the patient's age and symptom duration as independent variables enhanced predictive power for dopaminergic depletion (area under the curve = 0.812).

CONCLUSIONS

These results demonstrated that Cross-Cultural Smell Identification Test measurements alone may be insufficient to predict striatal dopaminergic depletion in Korean tremor patients.

Sweet liking in patients with Parkinson's disease

Pleasant tastes and odors are considered phylogenetically old natural rewards and their hedonic evaluation is regarded as a good indicator of the reward system function. The primary aim of the present study was to compare pleasantness ratings of sucrose solutions (1-30%, w/w) and sweet liking/disliking status in 20 patients with Parkinson's disease (PD) and in 20 age-matched healthy controls. In addition, basic sensory aspects of gustatory (intensity ratings, electrogustometric thresholds) and olfactory function (identification abilities in the Sniffin' Stick test) were assessed in both groups. The number of odors rated as pleasant, unpleasant, and neutral was also compared. As expected, the PD patients showed a significant impairment in olfactory identification abilities. There were no differences between the PD patients and controls in electrogustometric thresholds. Rated intensity of higher sucrose concentrations did not differ between the groups. The PD patients tended to rate water taste as more intense in comparison with the controls. Pleasantness ratings of sucrose solutions, the proportion of subjects rating 30% sucrose as the most pleasant (sweet likers), and the number of odors rated as pleasant did not differ between the study groups. The present results suggest that PD does not lead to any obvious alterations in pleasantness ratings of chemosensory stimuli. The study requires replication in larger samples.

In vivo neurochemical imaging of olfactory dysfunction in Parkinson's disease

Olfactory dysfunction is common in Parkinson's disease (PD) and has been attributed to early deposition of α-synuclein pathology in olfactory areas. The pathophysiology of olfactory dysfunction in PD, however, remains poorly understood. Changes in odor identification suggest in part impairment in odor memory, possibly due to hippocampal dysfunction. Olfactory dysfunction occurs also in Alzheimer's disease (AD) and increases with severity of dementia. Cholinergic degeneration is not only a feature of AD but can also occur in PD, at least in a subset of patients with cognitive changes. We reported previously that impaired odor identification in early PD is more closely correlated with hippocampal dopaminergic than nigrostriatal dopaminergic denervation. Results of our multi-tracer PET studies show that odor identification deficits in PD are best predicted by cholinergic denervation and to a lesser extent by dopaminergic denervation. These results suggest that olfactory dysfunction in PD may have multiple components including hippocampal dysfunction secondary to cholinergic and dopaminergic denervations. Olfactory dysfunction in PD may be the most marked in subjects at risk of incipient dementia, and may reflect the transition of PD toward a stage with more heterogeneous multi-system neurodegenerations. Our preliminary imaging data do not support a significant contribution of amyloidopathy or serotoninergic denervation to abnormal olfactory functions in PD, at least in the absence of dementia. We outline how progressive changes in olfaction may be used as a biomarker of cholinergic denervation and cognitive decline in PD patients. We will discuss also the utility of olfactory testing as an early screening test for neurodegeneration.

Olfactory loss as a supporting feature in the diagnosis of Parkinson's disease: a pragmatic approach

There is ample evidence from a large number of clinical and pathological studies of an early involvement of olfactory bulbs and cortex in the Lewy body pathology in idiopathic Parkinson's disease (iPD), the olfactory system being one of the first targets of degeneration in this condition. The olfactory dysfunction may be measurably present at the time of initial presentation and progresses in a proportion of patients as the disease advances. Patients with iPD have a more severe olfactory loss as compared to multisystem atrophy whereas the syndromes of corticobasal degeneration and progressive supranuclear palsy have no olfactory loss. A proportion of drug induced parkinsonism may have olfactory loss indicative of primary pathology of dopaminergic degeneration in these patients. Unlike single photon emission tomography, formal measurement of olfaction would provide a supportive role in diagnosing or excluding iPD depending on the duration of an individual patient's parkinsonian symptoms. Whilst olfaction may be only minimally impaired in early stages and may thus not help to differentiate from other syndromes, an intact olfaction in patients with parkinsonism of few years' duration would indicate a non-iPD pathology. Olfactory measurement is easy, cheap and now easily available in a number of tests, and olfactory assessment at different stages of parkinsonism should be used as a diagnostic aid for idiopathic PD and would enhance the diagnostic accuracy of iPD when used in conjunction with the UK Parkinson's disease society Brain Bank supportive criteria for diagnosis of idiopathic Parkinson's disease.

Identifying prodromal Parkinson's disease: pre-motor disorders in Parkinson's disease

Increasing recognition that Parkinson's disease (PD) may start outside of the substantia nigra has led to a rapidly expanding effort to define prodromal stages of PD, before motor signs permit classical diagnosis. Many of these efforts center around the identification of clinical non-motor symptoms and signs of disease. There is now direct evidence that olfaction, rapid eye movement (REM) sleep behavior disorder (RBD), constipation, and depression can be present in prodromal PD. In addition, there is suggestive evidence that visual changes, other autonomic symptoms, and subtle cognitive changes may also be present at prodromal stages. A critical issue in utility of these prodromal markers will be assessment of sensitivity, specificity, and positive and negative predictive values. Although these have yet to be fully defined, olfactory deficits, some visual changes, and autonomic symptoms occur in the majority of PD patients at diagnosis, suggesting good potential sensitivity. However, with the exception of RBD and perhaps some specific autonomic measures, specificity, and positive predictive value of these markers may be insufficient to be used alone as identifiers of prodromal disease. The evidence for the utility of olfaction, RBD, autonomic markers, visual changes, mood disorders, and cognitive loss as markers of prodromal PD and the potential sensitivity and specificity of these markers are summarized.

Olfaction in Parkinson's disease and related disorders

Olfactory dysfunction is an early 'pre-clinical' sign of Parkinson's disease (PD). The present review is a comprehensive and up-to-date assessment of such dysfunction in PD and related disorders. The olfactory bulb is implicated in the dysfunction, since only those syndromes with olfactory bulb pathology exhibit significant smell loss. The role of dopamine in the production of olfactory system pathology is enigmatic, as overexpression of dopaminergic cells within the bulb's glomerular layer is a common feature of PD and most animal models of PD. Damage to cholinergic, serotonergic, and noradrenergic systems is likely involved, since such damage is most marked in those diseases with the most smell loss. When compromised, these systems, which regulate microglial activity, can influence the induction of localized brain inflammation, oxidative damage, and cytosolic disruption of cellular processes. In monogenetic forms of PD, olfactory dysfunction is rarely observed in asymptomatic gene carriers, but is present in many of those that exhibit the motor phenotype. This suggests that such gene-related influences on olfaction, when present, take time to develop and depend upon additional factors, such as those from aging, other genes, formation of α-synuclein- and tau-related pathology, or lowered thresholds to oxidative stress from toxic insults. The limited data available suggest that the physiological determinants of the early changes in PD-related olfactory function are likely multifactorial and may include the same determinants as those responsible for a number of other non-motor symptoms of PD, such as dysautonomia and sleep disturbances.

Premotor biomarkers for Parkinson's disease - a promising direction of research

The second most serious neurodegenerative disease is Parkinson’s disease (PD). Over the past several decades, a strong body of evidence suggests that PD can begin years before the hallmark clinical motor symptoms appear. Biomarkers for PD are urgently needed to differentiate between neurodegenerative disorders, screen novel therapeutics, and predict eventual clinical PD before the onset of symptoms. Some clinical evaluations and neuroimaging techniques have been developed in the last several years with some success in this area. Moreover, other strategies have been utilized to identify biochemical and genetic markers associated with PD leading to the examination of PD progression and pathogenesis in cerebrospinal fluid, blood, or saliva. Finally, interesting results are surfacing from preliminary studies using known PD-associated genetic mutations to assess potential premotor PD biomarkers. The current review highlights recent advances and underscores areas of potential advancement.

Olfactory dysfunction in Parkinson disease

Olfactory dysfunction is among the earliest nonmotor features of Parkinson disease (PD). Such dysfunction is present in approximately 90% of early-stage PD cases and can precede the onset of motor symptoms by years. The mechanisms responsible for olfactory dysfunction are currently unknown. As equivalent deficits are observed in Alzheimer disease, Down syndrome, and the Parkinson-dementia complex of Guam, a common pathological substrate may be involved. Given that olfactory loss occurs to a lesser extent or is absent in disorders such as multiple system atrophy, corticobasal degeneration, and progressive supranuclear palsy, olfactory testing can be useful in differential diagnosis. The olfactory dysfunction in PD and a number of related diseases with smell loss correlates with decreased numbers of neurons in structures such as the locus coeruleus, the raphe nuclei, and the nucleus basalis of Meynart. These neuroanatomical findings, together with evidence for involvement of the autonomic nervous system in numerous PD-related symptoms, suggest that deficits in cholinergic, noradrenergic and serotonergic function may contribute to the olfactory loss. This Review discusses the current understanding of olfactory dysfunction in PD, including factors that may be related to its cause.

Diagnostic markers for Parkinson's disease

PURPOSE OF REVIEW

This review enumerates recent developments in the early diagnosis of Parkinson's disease, with an emphasis on detection of preclinical Parkinson's disease.

RECENT FINDINGS

Several clinical, laboratory, and imaging tests are now being investigated as potential early markers of Parkinson's disease. These include various nonmotor features that predate the motor manifestations of Parkinson's disease, including sleep abnormalities, neurobehavioral symptoms, and olfactory dysfunction. Tests of the autonomic nervous system, such as cardiac functional imaging, allow for a measure of cardiac sympathetic denervation. Cerebrospinal fluid and serum tests, including α-synuclein and DJ-1, are being developed and refined. Various imaging modalities have contributed to the diagnostic armamentarium in Parkinson's disease, including transcranial Doppler ultrasonography, radiolabeled tracer imaging, and magnetic resonance imaging. Early Parkinson's disease detection will pave the way for major advances in disease modifying therapies.

SUMMARY

Various diagnostic modalities hold promise for the early and preclinical diagnosis of Parkinson's disease. It is likely that the future diagnosis of Parkinson's disease will rely on a combination of clinical, laboratory, imaging, and genetic data.

Olfactory loss in Parkinson's disease

Impairment of olfaction is a characteristic and early feature of Parkinson's disease. Recent data indicate that >95% of patients with Parkinson's disease present with significant olfactory loss. Deficits in the sense of smell may precede clinical motor symptoms by years and can be used to assess the risk for developing Parkinson's disease in otherwise asymptomatic individuals. This paper summarizes the available information about olfactory function in Parkinson's disease, indicating the advantageous use of olfactory probes in early and differential diagnosis.