Cognitive- and motor-related regions in Parkinson's disease: FDOPA and FDG PET studies

Vectorial-based analysis of dual-tracer PET imaging: A proof of concept

BACKGROUND

The diagnosis of neurological diseases is complicated since they often share similar symptoms and occur in different severity levels. Imaging techniques such as PET molecular imaging are helpful for an early and accurate diagnosis and, staging allowing a noninvasive evaluation of the disease. The combination of two radioligands in the same patient could be valuable to achieve these diagnostic goals; nevertheless, the imaging data obtained with two radioligands is commonly interpreted independently. This novel approach to combine the PET data of two radiopharmaceuticals, separately acquired in the same subject, is to obtain new quantitative metrics. PET images of patients with Parkinson's disease (PD) and healthy controls (HC) were analyzed. Voxel-by-voxel uptake is compared by combining the imaging data. Dual-tracer PET imaging analysis was tested with [11C]DTBZ-[11C]Raclopride as proof of concept.

RESULTS

The new proposed metric based on a resultant vector is capable of efficiently discriminating healthy controls from PD patients (p < 0.0001) allowing the detection of slight changes in patients undergoing therapeutic approaches. Significant differences were found between HC and PD patients for the evaluated radiotracers.

CONCLUSIONS

The resultant vector appears to deliver useful information that could be helpful to evaluate PD patients under treatment and to improve differential diagnoses.

The reconfiguration pattern of individual brain metabolic connectome for Parkinson's disease identification

¹⁸F-Fluorodeoxyglucose positron emission tomography (¹⁸F-FDG PET) is widely employed to reveal metabolic abnormalities linked to Parkinson's disease (PD) at a systemic level. However, the individual metabolic connectome details with PD based on ¹⁸F-FDG PET remain largely unknown. To alleviate this issue, we derived a novel brain network estimation method for individual metabolic connectome, that is, Jensen-Shannon Divergence Similarity Estimation (JSSE). Further, intergroup difference between the individual's metabolic brain network and its global/local graph metrics was analyzed to investigate the metabolic connectome's alterations. To further improve the PD diagnosis performance, multiple kernel support vector machine (MKSVM) is conducted for identifying PD from normal control (NC), which combines both topological metrics and connection. Resultantly, PD individuals showed higher nodal topological properties (including assortativity, modularity score, and characteristic path length) than NC individuals, whereas global efficiency and synchronization were lower. Moreover, 45 most significant connections were affected. Further, consensus connections in occipital, parietal, and frontal regions were decrease in PD while increase in subcortical, temporal, and prefrontal regions. The abnormal metabolic network measurements depicted an ideal classification in identifying PD of NC with an accuracy up to 91.84%. The JSSE method identified the individual-level metabolic connectome of ¹⁸F-FDG PET, providing more dimensional and systematic mechanism insights for PD.

Effects of average reward rate on vigor as a function of individual variation in striatal dopamine

RATIONALE

We constantly need to decide not only which actions to perform, but also how vigorously to perform them. In agreement with an earlier theoretical model, it has been shown that a significant portion of the variance in our action vigor can be explained by the average rate of rewards received for that action. Moreover, this invigorating effect of average reward rate was shown to vary with within-subject changes in dopamine, both in human individuals and experimental rodents.

OBJECTIVES

Here, we assessed whether individual differences in the effect of average reward rate on vigor are related to individual variation in a stable measure of striatal dopamine function in healthy, unmedicated participants.

METHODS

Forty-four participants performed a discrimination task to test the effect of average reward rate on response times to index vigor and completed an [¹⁸F]-DOPA PET scan to index striatal dopamine synthesis capacity.

RESULTS

We did not find an interaction between dopamine synthesis capacity and average reward rate across the entire group. However, a post hoc analysis revealed that participants with higher striatal dopamine synthesis capacity, particularly in the nucleus accumbens, exhibited a stronger invigorating effect of average reward rate among the 30 slowest participants.

CONCLUSIONS

Our findings provide converging evidence for a role of striatal dopamine in average reward rate signaling, thereby extending the current literature on the mechanistic link between average reward rate, vigor, and dopamine.

Imaging Cognitive Impairment and Impulse Control Disorders in Parkinson's Disease

Dementia and mild forms of cognitive impairment as well as neuropsychiatric symptoms (i. e., impulse control disorders) are frequent and disabling non-motor symptoms of Parkinson's disease (PD). The identification of changes in neuroimaging studies for the early diagnosis and monitoring of the cognitive and neuropsychiatric symptoms associated with Parkinson's disease, as well as their pathophysiological understanding, are critical for the development of an optimal therapeutic approach. In the current literature review, we present an update on the latest structural and functional neuroimaging findings, including high magnetic field resonance and radionuclide imaging, assessing cognitive dysfunction and impulse control disorders in PD.

Motor Cortex Stimulation Reversed Hypernociception, Increased Serotonin in Raphe Neurons, and Caused Inhibition of Spinal Astrocytes in a Parkinson's Disease Rat Model

Persistent pain is a prevalent symptom of Parkinson’s disease (PD), which is related to the loss of monoamines and neuroinflammation. Motor cortex stimulation (MCS) inhibits persistent pain by activating the descending analgesic pathways; however, its effectiveness in the control of PD-induced pain remains unclear. Here, we evaluated the analgesic efficacy of MCS together with serotonergic and spinal glial modulation in an experimental PD (ePD) rat model. Wistar rats with unilateral striatal 6-OHDA and MCS were assessed for behavioral immobility and nociceptive responses. The immunoreactivity of dopamine in the substantia nigra and serotonin in the nucleus raphe magnus (NRM) and the neuronal, astrocytic, and microglial activation in the dorsal horn of the spinal cord were evaluated. MCS, without interfering with dopamine loss, reversed ePD-induced immobility and hypernociception. This response was accompanied by an exacerbated increase in serotonin in the NRM and a decrease in neuronal and astrocytic hyperactivation in the spinal cord, without inhibiting ePD-induced microglial hypertrophy and hyperplasia. Taken together, MCS induces analgesia in the ePD model, while restores the descending serotonergic pathway with consequent inhibition of spinal neurons and astrocytes, showing the role of MCS in PD-induced pain control.

Gender Differences and Quality of Life in Parkinson's Disease

Parkinson's disease has been found to significantly affect health-related quality of life. The gender differences of the health-related quality of life of subjects with Parkinson's disease have been observed in a number of studies. These differences have been reported in terms of the age at onset, clinical manifestations, and response to therapy. In general, women with Parkinson's disease showed more positive disease outcomes with regard to emotion processing, non-motor symptoms, and cognitive functions, although women report more Parkinson's disease-related clinical manifestations. Female gender predicted poor physical functioning and socioemotional health-related quality of life, while male gender predicted the cognitive domain of health-related quality of life. Some studies reported gender differences in the association between health-related quality of life and non-motor symptoms. Depression and fatigue were the main causes of poorer health-related quality of life in women, even in the early stages of Parkinson's disease. The aim of this review was to collect the best available evidence on gender differences in the development of Parkinson's disease symptoms and health-related quality of life.

Pretreatment brain volumes can affect the effectiveness of deep brain stimulation in Parkinson's disease patients

We aimed to assess whether brain volumes may affect the results of deep brain stimulation (DBS) in patients with Parkinson’s disease (PD). Eighty-one consecutive patients with PD (male:female 40:41), treated with DBS between June 2012 and December 2017, were enrolled. Total and regional brain volumes were measured using automated brain volumetry (NeuroQuant). The Unified Parkinson Disease Rating Scale motor score quotient was used to assess changes in clinical outcome and compare the preoperative regional brain volume in patients categorized into the higher motor improvement and lower motor improvement groups based on changes in the postoperative scores. The study groups showed significant volume differences in multiple brain areas. In the higher motor improvement group, the anterior cingulate and right thalamus showed high volumes after false discovery rate (FDR) correction. In the lower motor improvement group, the left caudate, paracentral, right primary sensory and left primary motor cortex showed high volume, but no area showed high volumes after FDR correction. Our data suggest that the effectiveness of DBS in patients with PD may be affected by decreased brain volume in different areas, including the cingulate gyrus and thalamus. Preoperative volumetry could help predict outcomes in patients with PD undergoing DBS.

Clinical and Electrophysiological Hints to TMS in De Novo Patients with Parkinson's Disease and Progressive Supranuclear Palsy

BACKGROUND

Transcranial magnetic stimulation (TMS) can non-invasively probe cortical excitability in movement disorders, although clinical significance is still controversial, especially at early stages. We compare single-pulse TMS in two prototypic synucleinopathy and tauopathy-i.e., Parkinson's disease (PD) and Progressive Supranuclear Palsy (PSP), respectively-to find neurophysiological differences and identify early measures associated with cognitive impairment.

METHODS

28 PD and 23 PSP de novo patients were age-matched with 28 healthy controls, all right-handed and drug-free. Amplitude and latency of motor evoked potentials (MEP), central motor conduction time, resting motor threshold (rMT), and cortical silent period (CSP) were recorded through a figure-of-eight coil from the First Dorsal Interosseous muscle (FDI), bilaterally.

RESULTS

Mini Mental Examination and Frontal Assessment Battery (FAB) scored worse in PSP; PD had worse FAB than controls. Higher MEP amplitude from right FDI in PD and PSP than controls was found, without difference between them. CSP was bilaterally longer in patients than controls, but similar between patient groups. A positive correlation between FAB and rMT was observed in PSP, bilaterally.

CONCLUSIONS

Despite the small sample size, PD and PSP might share, at early stage, a similar global electrocortical asset. rMT might detect and possibly predict cognitive deterioration in PSP.

Clinical and Electrophysiological Hints to TMS in De Novo Patients with Parkinson's Disease and Progressive Supranuclear Palsy

BACKGROUND

Transcranial magnetic stimulation (TMS) can non-invasively probe cortical excitability in movement disorders, although clinical significance is still controversial, especially at early stages. We compare single-pulse TMS in two prototypic synucleinopathy and tauopathy-i.e., Parkinson's disease (PD) and Progressive Supranuclear Palsy (PSP), respectively-to find neurophysiological differences and identify early measures associated with cognitive impairment.

METHODS

28 PD and 23 PSP de novo patients were age-matched with 28 healthy controls, all right-handed and drug-free. Amplitude and latency of motor evoked potentials (MEP), central motor conduction time, resting motor threshold (rMT), and cortical silent period (CSP) were recorded through a figure-of-eight coil from the First Dorsal Interosseous muscle (FDI), bilaterally.

RESULTS

Mini Mental Examination and Frontal Assessment Battery (FAB) scored worse in PSP; PD had worse FAB than controls. Higher MEP amplitude from right FDI in PD and PSP than controls was found, without difference between them. CSP was bilaterally longer in patients than controls, but similar between patient groups. A positive correlation between FAB and rMT was observed in PSP, bilaterally.

CONCLUSIONS

Despite the small sample size, PD and PSP might share, at early stage, a similar global electrocortical asset. rMT might detect and possibly predict cognitive deterioration in PSP.

Primary motor cortex in Parkinson's disease: Functional changes and opportunities for neurostimulation

Movement abnormalities of Parkinson's disease (PD) arise from disordered neural activity in multiple interconnected brain structures. The planning and execution of movement requires recruitment of a heterogeneous collection of pyramidal projection neurons in the primary motor cortex (M1). The neural representations of movement in M1 single-cell and field potential recordings are directly and indirectly influenced by the midbrain dopaminergic neurons that degenerate in PD. This review examines M1 functional alterations in PD as uncovered by electrophysiological recordings and neurostimulation studies in patients and experimental animal models. Dysfunction of the parkinsonian M1 depends on the severity and/or duration of dopamine-depletion and the species examined, and is expressed as alterations in movement-related firing dynamics; functional reorganisation of local circuits; and changes in field potential beta oscillations. Neurostimulation methods that modulate M1 activity directly (e.g., transcranial magnetic stimulation) or indirectly (subthalamic nucleus deep brain stimulation) improve motor function in PD patients, showing that targeted neuromodulation of M1 is a realistic therapy. We argue that the therapeutic profile of M1 neurostimulation is likely to be greatly enhanced with alternative technologies that permit cell-type specific control and incorporate feedback from electrophysiological biomarkers measured locally.

Parkinson Disease-Related Pattern of Glucose Metabolism Associated With the Potential for Motor Improvement After Deep Brain Stimulation

BACKGROUND

Motor dysfunctions in Parkinson disease (PD) patients are not completely normalized by deep brain stimulation (DBS), and there is an obvious difference in the degree of symptom improvement after DBS for each patient.

OBJECTIVE

To test our hypothesis that each patient has their own restoration capacity for motor improvement after DBS, and to investigate whether regional cerebral glucose metabolism in 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) scans is associated with the capacity for off-medication motor improvement (MIoff) after DBS.

METHODS

The MIoff (%) was calculated using the Unified Parkinson's Disease Rating Scale part III in 27 PD patients undergoing DBS in the globus pallidus interna. The standardized uptake value ratios (SUVRs) on FDG-PET were quantitatively measured, and the areas where the SUVR correlated with the MIoff (%) were identified. Also, the areas where the SUVR was significantly different between the 2 MIoff groups (≥60% vs <60%) were determined.

RESULTS

Ten patients achieved MIoff > 60% at 12 mo after DBS. In general, the MIoff (%) was positively correlated with preoperative SUVR in the temporo-parieto-occipital lobes, while it was inversely correlated with the metabolism in the primary motor cortex. The patients in the MIoff < 60% group showed a significant decrease in SUVR in the parieto-occipital lobes, while parieto-occipital metabolism in those with MIoff ≥ 60% was relatively preserved (Mann-Whitney U test, P = .03).

CONCLUSION

Our findings suggest that the parieto-occipital lobes may be implicated more generally in the prognosis of motor improvement after DBS in advanced PD than other regions.

Local White Matter Fiber Clustering Differentiates Parkinson's Disease Diagnoses

Scans without evidence of dopaminergic deficit (SWEDD) patients are often misdiagnosed with Parkinson's disease (PD) but have normal dopamine transporter scans. We hypothesised that white matter tracts associated with motor and cognition functions may be affected differently by SWEDD and PD. Automatically annotated fibre clustering (AAFC) is a novel clustering method based on diffusion magnetic resonance imaging (dMRI) tractography that enables highly robust reconstruction of white matter tracts that are composed of corresponding clusters. This study aimed to investigate the white matter properties in the subdivisions of white matter tracts among SWEDD and PD groups. We applied AAFC to identify white matter tracts related to motion and cognition functions in the dataset consisting of SWEDD (n = 22), PD (n = 30) and normal control (NC) (n = 30). Then, we resampled 200 nodes along fibres of cluster, and the diffusion metric values corresponding to each node were calculated and used for comparison. Compared with NC, PD showed significant difference (p < 0.05) in two clusters in thalamo-frontal (TF), one cluster in thalamo-parietal (TP) and one cluster in thalamo-occipital (TO), whereas SWEDD presented no significant difference. Three clusters in cingulum bundle (CB) commonly exhibited significant differences in PD versus SWEDD and NC versus SWEDD. The support vector machine classifier achieved high accuracies in PD-NC, PD-SWEDD and NC-SWEDD classifications. This outcome validated these local white matter differences were useful to separate the three groups. These results suggest that PD exerts more significant effects on thalamo tracts than SWEDD, and unique microstructural changes occur in CB tract in SWEDD.

Imaging Mild Cognitive Impairment and Dementia in Parkinson's Disease

Cognitive dysfunction is a significant non-motor feature of Parkinson's disease, with the risk of dementia increasing with prolonged disease duration. Multiple cognitive domains are affected, and the pathophysiology cannot be explained by dopaminergic loss alone. Sophisticated neuroimaging techniques can detect the nature and extent of extra-nigral involvement by targeting neurotransmitters, abnormal protein aggregates and tissue metabolism. This review identifies the functional and anatomical imaging characteristics that predict cognitive impairment in PD, the limitations that challenge this process, and the avenues of potential research.

Why Is Aging a Risk Factor for Cognitive Impairment in Parkinson's Disease?-A Resting State fMRI Study

Using resting-state functional MRI (rsfMRI) data of younger and older healthy volunteers and patients with Parkinson's disease (PD) with and without mild cognitive impairment (MCI) and applying two different analytic approaches, we investigated the effects of age, pathology, and cognition on brain connectivity. When comparing rsfMRI connectivity strength of PD patients and older healthy volunteers, reduction between multiple brain regions in PD patients with MCI (PD-MCI) compared with PD patients without MCI (PD-non-MCI) was observed. This group difference was not affected by the number and location of clusters but was reduced when age was included as a covariate. Next, we applied a graph-theory method with a cost-threshold approach to the rsfMRI data from patients with PD with and without MCI as well as groups of younger and older healthy volunteers. We observed decreased hub function (measured by degree and betweenness centrality) mainly in the medial prefrontal cortex (mPFC) in older healthy volunteers compared with younger healthy volunteers. We also found increased hub function in the posterior medial structure (precuneus and the cingulate cortex) in PD-non-MCI patients compared with older healthy volunteers and PD-MCI patients. Hub function in these posterior medial structures was positively correlated with cognitive function in all PD patients. Together these data suggest that overlapping patterns of hub modifications could mediate the effect of age as a risk factor for cognitive decline in PD, including age-related reduction of hub function in the mPFC, and recruitment availability of the posterior medial structure, possibly to compensate for impaired basal ganglia function.

Determination of Imaging Biomarkers to Decipher Disease Trajectories and Differential Diagnosis of Neurodegenerative Diseases (DIsease TreND)

BACKGROUND

Understanding disease progression of neurodegenerative diseases (NDs) is important for better prognosis and decisions on the appropriate course of treatment to slow down the disease progression.

NEW METHOD

We present here an innovative machine learning framework capable of (1) indicating the trajectory of disease progression by identifying relevant imaging biomarkers and (2) automated disease diagnosis. Self-Organizing Maps (SOM) have been used for data dimensionality reduction and to reveal potentially useful disease-specific biomarkers, regions of interest (ROIs). These ROIs have been used for automated disease diagnosis using Least Square Support Vector Machines (LS-SVM) and to delineate disease progression.

RESULTS

A multi-site, multi-scanner dataset containing 1316 MRIs was obtained from ADNI³ and PPMI. Identified biomarkers have been used to decipher (1) trajectory of disease progression and (2) identify clinically relevant ROIs. Furthermore, we have obtained a classification accuracy of 94.29 ± 0.08% and 95.37 ± 0.02% for distinguishing AD and PD from HC subjects respectively.

COMPARISON WITH OTHER EXISTING METHODS

The goal of this study was fundamentally different from other machine learning based studies for automated disease diagnosis. We aimed to develop a method that has two-fold benefits (1) It can be used to understand pathology of neurodegenerative diseases and (2) It also achieves automated disease diagnosis.

CONCLUSIONS

In the absence of established disease biomarkers, clinical diagnosis is heavily prone to misdiagnosis. Being clinically relevant and readily adaptable in the current clinical settings, the developed framework could be a stepping stone to make machine learning based Clinical Decision Support System (CDSS) for neurodegenerative disease diagnosis a reality.

Clinical utility of FDG PET in Parkinson's disease and atypical parkinsonism associated with dementia

Purpose

There are no comprehensive guidelines for the use of FDG PET in the following three clinical scenarios: (1) diagnostic work-up of patients with idiopathic Parkinson’s disease (PD) at risk of future cognitive decline, (2) discriminating idiopathic PD from progressive supranuclear palsy, and (3) identifying the underlying neuropathology in corticobasal syndrome.

Methods

We therefore performed three literature searches and evaluated the selected studies for quality of design, risk of bias, inconsistency, imprecision, indirectness and effect size. Critical outcomes were the sensitivity, specificity, accuracy, positive/negative predictive value, area under the receiving operating characteristic curve, and positive/negative likelihood ratio of FDG PET in detecting the target condition. Using the Delphi method, a panel of seven experts voted for or against the use of FDG PET based on published evidence and expert opinion.

Results

Of 91 studies selected from the three literature searches, only four included an adequate quantitative assessment of the performance of FDG PET. The majority of studies lacked robust methodology due to lack of critical outcomes, inadequate gold standard and no head-to-head comparison with an appropriate reference standard. The panel recommended the use of FDG PET for all three clinical scenarios based on nonquantitative evidence of clinical utility.

Conclusion

Despite widespread use of FDG PET in clinical practice and extensive research, there is still very limited good quality evidence for the use of FDG PET. However, in the opinion of the majority of the panellists, FDG PET is a clinically useful imaging biomarker for idiopathic PD and atypical parkinsonism associated with dementia.

Patterns of Longitudinal Neural Activity Linked to Different Cognitive Profiles in Parkinson's Disease

Mild cognitive impairment in Parkinson's disease (PD) has been linked with functional brain changes. Previously, using functional magnetic resonance imaging (fMRI), we reported reduced cortico-striatal activity in patients with PD who also had mild cognitive impairment (MCI) vs. those who did not (non-MCI). We followed up these patients to investigate the longitudinal effect on the neural activity. Twenty-four non-demented patients with Parkinson's disease (non-MCI: 12, MCI: 12) were included in the study. Each participant underwent two fMRIs while performing the Wisconsin Card Sorting Task 20 months apart. The non-MCI patients recruited the usual cognitive corticostriatal loop at the first and second sessions (Time 1 and Time 2, respectively). However, decreased activity was observed in the cerebellum and occipital area and increased activity was observed in the medial prefrontal cortex and parietal lobe during planning set-shift at Time 2. Increased activity in the precuneus was also demonstrated while executing set-shifts at Time 2. The MCI patients revealed more activity in the frontal, parietal and occipital lobes during planning set-shifts, and in the parietal and occipital lobes, precuneus, and cerebellum, during executing set-shift at Time 2. Analysis regrouping of both groups of PD patients revealed that hippocampal and thalamic activity at Time 1 was associated with less cognitive decline over time. Our results reveal that functional alteration along the time-points differed between the non-MCI and MCI patients. They also underline the importance of preserving thalamic and hippocampal function with respect to cognitive decline over time.

Biomarkers for dementia and mild cognitive impairment in Parkinson's disease

Cognitive decline is one of the most frequent and disabling nonmotor features of Parkinson's disease. Around 30% of patients with Parkinson's disease experience mild cognitive impairment, a well-established risk factor for the development of dementia. However, mild cognitive impairment in patients with Parkinson's disease is a heterogeneous entity that involves different types and extents of cognitive deficits. Because it is not currently known which type of mild cognitive impairment confers a higher risk of progression to dementia, it would be useful to define biomarkers that could identify these patients to better study disease progression and possible interventions. In this sense, the identification among patients with Parkinson's disease and mild cognitive impairment of biomarkers associated with dementia would allow the early detection of this process. This review summarizes studies from the past 25 years that have assessed the potential biomarkers of dementia and mild cognitive impairment in Parkinson's disease patients. Despite the potential importance, no biomarker has as yet been validated. However, features such as low levels of epidermal and insulin-like growth factors or uric acid in plasma/serum and of Aß in CSF, reduction of cerebral cholinergic innervation and metabolism measured by PET mainly in posterior areas, and hippocampal atrophy in MRI might be indicative of distinct deficits with a distinct risk of dementia in subgroups of patients. Longitudinal studies combining the existing techniques and new approaches are needed to identify patients at higher risk of dementia. © 2016 International Parkinson and Movement Disorder Society.

Profiling cognitive and neuropsychiatric heterogeneity in Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is a highly heterogeneous disease, in which motor symptom subtypes are often-described. While it is recognized that motor, cognitive and affective neuropsychiatric symptoms negatively influence the patients' quality of life, it is currently unknown how these symptoms contribute to phenotypic subtypes. The objective of this study was to assess subtypes of motor, cognitive and affective symptoms in PD.

METHODS

A hierarchical cluster analysis was conducted on clinical data of 226 PD patients screened at the VU University Medical Center using comprehensive assessment of cognitive, affective and motor symptoms. Subsequent linear discriminant analyses were conducted to investigate discriminating constructs between clusters.

RESULTS

The cluster analysis yielded four clusters: (1) a young-age (59.9 years), mildly affected cluster (N = 86), (2) an old-age (72.3 years) cluster with severe motor and non-motor symptoms (N = 15), (3) a cluster (age 64.7 years) with mild motor symptoms, below-average executive functioning and affective symptoms (N = 46) and (4) a cluster (age 64.8 years) with severe motor symptoms, affective symptoms and below-average verbal memory (N = 79).

CONCLUSIONS

Cluster 1 and 2 seem to represent opposite ends of the PD disease stages. Patients in clusters 3 and 4 had similar age, educational level and disease duration but different symptom profiles - we therefore suggest that these clusters represent different pathways of disease progression, presumably with distinct underlying pathology localization. Future research on the neuropathophysiological characteristics of these two clusters and monitoring of disease progression is required.

Apathy and noradrenaline: silent partners to mild cognitive impairment in Parkinson's disease?

PURPOSE OF REVIEW

Mild cognitive impairment (MCI) is a comorbid factor in Parkinson's disease. The aim of this review is to examine the recent neuroimaging findings in the search for Parkinson's disease MCI (PD-MCI) biomarkers to gain insight on whether MCI and specific cognitive deficits in Parkinson's disease implicate striatal dopamine or another system.

RECENT FINDINGS

The evidence implicates a diffuse pathophysiology in PD-MCI rather than acute dopaminergic involvement. On the one hand, performance in specific cognitive domains, notably in set-shifting and learning, appears to vary with dopaminergic status. On the other hand, motivational states in Parkinson's disease along with their behavioral and physiological indices suggest a noradrenergic contribution to cognitive deficits in Parkinson's disease. Finally, Parkinson's disease's pattern of neurodegeneration offers an avenue for continued research in nigrostriatal dopamine's role in distinct behaviors, as well as the specification of dorsal and ventral striatal functions.

SUMMARY

The search for PD-MCI biomarkers has employed an array of neuroimaging techniques, but still yields divergent findings. This may be due in part to MCI's broad definition, encompassing heterogeneous cognitive domains, only some of which are affected in Parkinson's disease. Most domains falling under the MCI umbrella include fronto-dependent executive functions, whereas others, notably learning, rely on the basal ganglia. Given the deterioration of the nigrostriatal dopaminergic system in Parkinson's disease, it has been the prime target of PD-MCI investigation. By testing well defined cognitive deficits in Parkinson's disease, distinct functions can be attributed to specific neural systems, overcoming conflicting results on PD-MCI. Apart from dopamine, other systems such as the neurovascular or noradrenergic systems are affected in Parkinson's disease. These factors may be at the basis of specific facets of PD-MCI for which dopaminergic involvement has not been conclusive. Finally, the impact of both dopaminergic and noradrenergic deficiency on motivational states in Parkinson's disease is examined in light of a plausible link between apathy and cognitive deficits.

Unsupervised learning based feature extraction for differential diagnosis of neurodegenerative diseases: A case study on early-stage diagnosis of Parkinson disease

BACKGROUND

The development of MRI based methods could prove extremely valuable for identification of reliable biomarkers to aid diagnosis of neurodegenerative diseases (NDs). A great deal of current research has been aimed at identification biomarkers for both diagnosis at early stage and evaluation of the progression of NDs.

NEW METHOD

We present here a novel synergetic paradigm integrating Kohonen self organizing map (KSOM) and least squares support vector machine (LS-SVM) for individual-level clinical diagnosis of NDs. Feature are extracted in an unsupervised manner using KSOM on preprocessed brain MRIs. Thereafter, these features are fed as input to LSSVM for subject classification.

RESULTS

The applicability of the proposed methodology has been demonstrated using 831 T1-weighted MRIs obtained from Parkinson's Progression Markers Initiative (PPMI) database. We have achieved classification accuracy of up to 99% for differential diagnosis of Parkinson disease with confidence interval of 99.9%.

COMPARISON WITH OTHER EXISTING METHODS

The potential for translation of similar research findings to clinical application is greatly dependent upon two factors (1) accuracy of subject classification achieved and (2) size of the dataset used. Here, we report very high accuracy achieved on one of the largest MRI datasets using multivariate analysis tools.

CONCLUSIONS

In this paper, we describe a methodology that has the potential to be translated into first-line diagnostic tool for NDs. We also demonstrate the applicability of this methodology for diagnosing PD subjects in early stages of the disease, i.e., subjects in age of 31-60 years.

Decreased Resting-State Interhemispheric Functional Connectivity in Parkinson's Disease

BACKGROUND

Abnormalities in white matter integrity and specific functional network alterations have been increasingly reported in patients with Parkinson's disease (PD). However, little is known about the inter-hemispheric interaction in PD.

METHODS

Fifty-one drug naive patients with PD and 51 age- and gender-matched healthy subjects underwent resting-state functional magnetic resonance imaging (rs-fMRI) scans. We compared the inter-hemispheric resting-state functional connectivity between patients with PD and healthy controls, using the voxel-mirrored homotopic connectivity (VMHC) approach. Then, we correlated the results from VMHC and clinical features in PD patients.

RESULTS

Relative to healthy subject, patients exhibited significantly lower VMHC in putamen and cortical regions associated with sensory processing and motor control (involving sensorimotor and supramarginal cortex), which have been verified to play a critical role in PD. In addition, there were inverse relationships between the UPDRS motor scores and VMHC in the sensorimotor, and between the illness duration and VMHC in the supramarginal gyrus in PD patients.

CONCLUSIONS

Our results suggest that the functional coordination between homotopic brain regions is impaired in PD patients, extending previous notions about the disconnection of corticostriatal circuit by providing new evidence supporting a disturbance in inter-hemispheric connections in PD.

Brain (18)F-DOPA PET and cognition in de novo Parkinson's disease

PURPOSE

The role of mesocortical dopaminergic pathways in the cognitive function of patients with early Parkinson's disease (PD) needs to be further clarified.

METHODS

The study groups comprised 15 drug-naive patients with de novo PD and 10 patients with essential tremor (controls) who underwent (18)F-DOPA PET (static acquisition, normalization on mean cerebellar counts) and an extended neuropsychological test battery. Factor analysis with varimax rotation was applied to the neuropsychological test scores, to yield five factors from 16 original scores, which explained 82 % of the total variance. Correlations between cognitive factors and (18)F-DOPA uptake were assessed with SPM8, taking age and gender as nuisance variables.

RESULTS

(18)F-DOPA uptake was significantly lower in PD patients than in controls in the bilateral striatum, mainly in the more affected (right) hemisphere, and in a small right temporal region. Significant positive correlations were found only in PD patients between the executive factor and (18)F-DOPA uptake in the bilateral anterior cingulate cortex (ACC) and the middle frontal gyrus, between the verbal fluency factor and (18)F-DOPA uptake in left BA 46 and the bilateral striatum, and between the visuospatial factor and (18)F-DOPA uptake in the left ACC and bilateral striatum. No correlations were found between (18)F-DOPA uptake and either the verbal memory factor or the abstraction-working memory factor.

CONCLUSION

These data clarify the role of the mesocortical dopaminergic pathways in cognitive function in early PD, highlighting the medial frontal lobe, anterior cingulate, and left BA 46 as the main sites of cortical correlation with executive and language functions.

Alterations in cerebral white matter and neuropsychology in patients with cirrhosis and falls

Background & Aim

Falls are frequent in patients with cirrhosis but underlying mechanisms are unknown. The aim was to determine the neuropsychological, neurological and brain alterations using magnetic resonance-diffusion tensor imaging (MR-DTI) in cirrhotic patients with falls.

Patients and methods

Twelve patients with cirrhosis and falls in the previous year were compared to 9 cirrhotic patients without falls. A comprehensive neuropsychological and neurological evaluation of variables that may predispose to falls included: the Mini-Mental State Examination, Psychometric Hepatic Encephalopathy Score (PHES), Parkinson’s Disease-Cognitive Rating Scale, specific tests to explore various cognitive domains, Unified Parkinson’s Disease Rating Scale to evaluate parkinsonism, scales for ataxia and muscular strength, and electroneurography. High-field MR (3T) including DTI and structural sequences was performed in all patients.

Results

The main neuropsychological findings were impairment in PHES (p = 0.03), Parkinson’s Disease-Cognitive Rating Scale (p = 0.04) and in executive (p<0.05) and visuospatial-visuoconstructive functions (p<0.05) in patients with falls compared to those without. There were no statistical differences between the two groups in the neurological evaluation or in the visual assessment of MRI. MR-DTI showed alterations in white matter integrity in patients with falls compared to those without falls (p<0.05), with local maxima in the superior longitudinal fasciculus and corticospinal tract. These alterations were independent of PHES as a covariate and correlated with executive dysfunction (p<0.05).

Conclusions

With the limitation of the small sample size, our results suggest that patients with cirrhosis and falls present alterations in brain white matter tracts related to executive dysfunction. These alterations are independent of PHES impairment.

Evaluation of selective positron emission tomography template method for spatial normalization of amyloid imaging with 11C-Pittsburgh Compound B

OBJECTIVE

Spatial normalization of C-Pittsburgh Compound B (PiB) images is challenging for an automatic quantitative analysis without magnetic resonance imaging (MRI) because of different distribution patterns between amyloid positive and negative images. To overcome this issue, we evaluated a selective positron emission tomography template (SPT) method.

MATERIALS AND METHODS

Three sets of single positron emission tomography templates were created: PiB negative template, PiB positive template, and mixed template. Sixty-one patients with dementia were enrolled as the validation cohort. Magnetic resonance imaging-aided normalization method was used as a reference. The SPT method was based on visual classification (positive, negative, and equivocal). The optimal templates for each visual group were determined by correlation values and average percent errors (APEs) with MRI-aided normalization. The results of the SPT and the single template methods were compared with those of MRI-aided normalization in terms of correlation values, APEs, and concordance rates.

RESULTS

The SPT (PiB negative template for the negative and equivocal groups and PiB positive template for the positive group) showed higher correlations and concordance rate and lower APEs with MRI-aided normalization than did the single template.

CONCLUSIONS

Use of the SPT provides accurate normalization of amyloid images without MRI.

Fibrofog and fibromyalgia: a narrative review and implications for clinical practice

Patients with fibromyalgia often report forgetfulness as well as declines in cognitive function, memory, and mental alertness-symptoms that have been termed "fibrofog" in popular and electronic media as well as in professional literature. "Fibrofog" is the subjectively experienced cognitive dysfunction associated with fibromyalgia and is a clinically important yet comparatively less well-studied aspect of the disorder; it includes loss of mental clarity (mental fogginess) as well as attention and memory impairment. Although until recently cognitive symptoms have been largely ignored, these symptoms can be more disturbing than the widespread pain and can change these patients' lives, sometimes dramatically so. Whereas widespread musculoskeletal pain, tenderness, and fatigue may be the hallmark symptoms of fibromyalgia, patients rank cognitive dysfunction highly in terms of disease impact. This review addresses (1) the prevalence of self-reported cognitive disturbances in fibromyalgia, (2) the clinical presentation of fibrofog, (3) neuropsychological test performance, with particular attention to discrepancies between self-report and test results, (3) clinical correlates of impaired cognitive function in fibromyalgia, (4) neurobiology relevant to cognitive disturbances in fibromyalgia, and (5) clinical management of fibrofog. Although the pathophysiology of fibromyalgia remains an enigma, evidence suggests that it may be a brain disorder, with cognitive deficits ("fibrofog") reflecting disturbed centrally mediated processes.

Recent progress of imaging agents for Parkinson's disease

Parkinson's disease (PD) is a common progressive, neurodegenerative brain disease that is promoted by mitochondrial dysfunction, oxidative stress, protein aggregation and proteasome dysfunction in the brain. Compared with computer tomography (CT) or magnetic resonance imaging (MRI), non-invasive nuclear radiopharmaceuticals have great significance for the early diagnosis of PD due to their high sensitivity and specificity in atypical and preclinical cases. Based on the development of coordination chemistry and chelator design, radionuclides may be delivered to lesions by attaching to PD-related transporters and receptors, such as dopamine, serotonin, and others. In this review, we comprehensively detailed the current achievements in radionuclide imaging in Parkinson's disease.

Neuroimaging in Parkinson disease: from research setting to clinical practice

Over the past three decades, neuroimaging studies-including structural, functional and molecular modalities-have provided invaluable insights into the mechanisms underlying Parkinson disease (PD). Observations from multimodal neuroimaging techniques have indicated changes in brain structure and metabolic activity, and an array of neurochemical changes that affect receptor sites and neurotransmitter systems. Characterization of the neurobiological alterations that lead to phenotypic heterogeneity in patients with PD has considerably aided the in vivo investigation of aetiology and pathophysiology, and the identification of novel targets for pharmacological or surgical treatments, including cell therapy. Although PD is now considered to be very complex, no neuroimaging modalities are specifically recommended for routine use in clinical practice. However, conventional MRI and dopamine transporter imaging are commonly used as adjuvant tools in the differential diagnosis between PD and nondegenerative causes of parkinsonism. First-line neuroimaging tools that could have an impact on patient prognosis and treatment strategies remain elusive. This Review discusses the lessons learnt from decades of neuroimaging research in PD, and the promising new approaches with potential applicability to clinical practice.

Brain 18F-FDG PET imaging in the differential diagnosis of parkinsonism

AIM

The aims in this study were to evaluate the role of brain F-FDG PET imaging in differential diagnosis of parkinsonism and to correlate brain metabolism findings with patients' clinical findings.

METHODS

Brain F-FDG PET images were evaluated both visually and quantitatively using the NeuroQ software in 21 parkinsonism patients in whom final clinical diagnoses were established.

RESULTS

Final clinical diagnoses were idiopathic Parkinson disease in 7, multisystem atrophy (MSA) in 7, progressive supranuclear palsy (PSP) in 4, corticobasal degeneration in 2, and Lewy body disease in 1 patient. Asymmetrical cortical hypometabolism was observed in most of the patients in frontal and parietotemporal regions. Fifteen of 21 patients had basal ganglia involvement, which was bilateral in patients with MSA and more frequently unilateral in patients with idiopathic Parkinson disease and PSP. Four patients with PSP and 1 patient with corticobasal degeneration had thalamic hypometabolism. Cerebellar hypometabolism was observed in 4 patients with MSA. The Unified Parkinson Disease Rating Scale motor and bradykinesia scores were higher in patients with basal ganglia involvement.

CONCLUSIONS

Brain F-FDG PET findings in subcortical nuclei and cerebellum were found to be useful in differential diagnosis of patients with parkinsonism. The extent of cerebral cortical and basal ganglia hypometabolism showed correlation with the presentation and severity of clinical findings.

Increased turnover of dopamine in caudate nucleus of detoxified alcoholic patients

A previous study of the DOPA decarboxylase substrate 6-[¹⁸F]fluoro-L-DOPA (FDOPA) with positron emission tomography (PET) detected no difference of the net blood-brain transfer rate (K_in^app) between detoxified alcoholic patients and healthy controls. Instead, the study revealed an inverse correlation between K_in^app in left ventral striatum and alcohol craving scores. To resolve the influx and efflux phases of radiolabeled molecules, we independently estimated the unidirectional blood-brain FDOPA clearance rate (K) and the washout rate of [¹⁸F]fluorodopamine and its deaminated metabolites (k_loss), and we also calculated the total distribution volume of decarboxylated metabolites and unmetabolized FDOPA as a steady-state index of the dopamine storage capacity (V_d) in brain. The craving scores in the 12 alcoholics correlated positively with the rate of loss (k_loss) in the left ventral striatum. We conclude that craving is most pronounced in the individuals with relatively rapid dopamine turnover in the left ventral striatum. The blood-brain clearance rate (K), corrected for subsequent loss of radiolabeled molecules from brain, was completely normal throughout the brain of the alcoholics, in whom the volume of distribution (V_d) was found to be significantly lower in the left caudate nucleus. The magnitude of V_d in the left caudate head was reduced by 43% relative to the 16 controls, consistent with a 58% increase of k_loss. We interpret the findings as indicating that a trait for rapid dopamine turnover in the ventral striatum subserves craving and reward-dependence, leading to an acquired state of increased dopamine turnover in the dorsal striatum of detoxified alcoholic patients.

The cerebellum in Parkinson's disease

Parkinson's disease is a chronic progressive neurodegenerative disorder characterized by resting tremor, slowness of movements, rigidity, gait disturbance and postural instability. Most investigations on Parkinson's disease focused on the basal ganglia, whereas the cerebellum has often been overlooked. However, increasing evidence suggests that the cerebellum may have certain roles in the pathophysiology of Parkinson's disease. Anatomical studies identified reciprocal connections between the basal ganglia and cerebellum. There are Parkinson's disease-related pathological changes in the cerebellum. Functional or morphological modulations in the cerebellum were detected related to akinesia/rigidity, tremor, gait disturbance, dyskinesia and some non-motor symptoms. It is likely that the major roles of the cerebellum in Parkinson's disease include pathological and compensatory effects. Pathological changes in the cerebellum might be induced by dopaminergic degeneration, abnormal drives from the basal ganglia and dopaminergic treatment, and may account for some clinical symptoms in Parkinson's disease. The compensatory effect may help maintain better motor and non-motor functions. The cerebellum is also a potential target for some parkinsonian symptoms. Our knowledge about the roles of the cerebellum in Parkinson's disease remains limited, and further attention to the cerebellum is warranted.

Characterizing dementia with Lewy bodies by means of diffusion tensor imaging

OBJECTIVE

To investigate patterns of in vivo white matter tract change using diffusion tensor imaging (DTI), we conducted a cross-sectional study of dementia with Lewy bodies (DLB) in comparison with Alzheimer disease (AD) and normal aging.

METHODS

The study included 106 subjects (35 with DLB, 36 with AD, and 35 elderly controls) who underwent clinical and neuropsychological assessment and diffusion tensor MRI. We used tract-based spatial statistics to investigate patterns of reduced fractional anisotropy (FA) and increased mean diffusivity (MD) across the entire white matter tract skeleton and also investigated correlations with clinical features.

RESULTS

Areas of reduced FA in subjects with DLB vs controls were found primarily in parieto-occipital white matter tracts; in AD, the changes were much more diffuse. DLB was also associated with reduced FA in the pons and left thalamus, in comparison with AD. The pattern of MD increase was diffuse in AD and DLB. We found an association between DTI parameters and impaired episodic memory, letter fluency, and severity of motor parkinsonism in DLB.

CONCLUSIONS

Despite a similar level of dementia severity, patterns of DTI changes in AD and DLB differed significantly. The selective involvement of the visual association areas and subcortical structures and the significant clinical correlations highlight the potential importance of white matter tract change in the pathogenesis of DLB. DTI may be a useful technique to investigate early and possible preclinical changes in DLB and warrants further investigation.

Glucose metabolism in small subcortical structures in Parkinson's disease

OBJECTIVES

Evidence from experimental animal models of Parkinson's disease (PD) suggests a characteristic pattern of metabolic perturbation in discrete, very small basal ganglia structures. These structures are generally too small to allow valid investigation by conventional positron emission tomography (PET) cameras. However, the high-resolution research tomograph (HRRT) PET system has a resolution of 2 mm, sufficient for the investigation of important structures such as the pallidum and thalamic subnuclei.

MATERIALS AND METHODS

Using the HRRT, we performed [(18)F]-fluorodeoxyglucose (FDG) scans on 21 patients with PD and 11 age-matched controls. We employed three types of normalization: white matter, global mean, and data-driven normalization. We performed volume-of-interest analyses of small subcortical gray matter structures. Voxel-based comparisons were performed to investigate the extent of cortical hypometabolism.

RESULTS

The most significant level of relative subcortical hypermetabolism was detected in the external pallidum (GPe), irrespective of normalization strategy. Hypermetabolism was suggested also in the internal pallidum, thalamic subnuclei, and the putamen. Widespread cortical hypometabolism was seen in a pattern very similar to previously reported patterns in patients with PD.

CONCLUSION

The presence and extent of subcortical hypermetabolism in PD is dependent on type of normalization. However, the present findings suggest that PD, in addition to widespread cortical hypometabolism, is probably characterized by true hypermetabolism in the GPe. This finding was predicted by the animal 2-deoxyglucose autoradiography literature, in which high-magnitude hypermetabolism was also most robustly detected in the GPe.

Efficacy of tailored computer-based neurorehabilitation for improvement of movement initiation in Parkinson's disease

While Parkinson's disease (PD) is considered a motor disorder, motor signs of PD can be exacerbated by cognitive dysfunction. We evaluated the efficacy of a computer-based cognitive rehabilitation training program designed to improve motor-related executive function. Thirty people with PD and 21 controls participated in the 10-day training. Training consisted of a two-phase button press task. First, subjects produced an externally cued (EC) digit sequence, typing numbers displayed on the computer screen. Second, subjects were prompted to generate the same sequence in the absence of the number display (internally represented sequence, IR). Sequence length was automatically adjusted to maintain 87% correct performance. Participants were evaluated before and after training using a fixed version of the training task, and generalization of training was assessed using measures involving IR motor sequencing, switching and activities of daily living. PD participants were divided into two groups, those who showed impairment in IR motor sequence production prior to training (N=14) and those whose performance was similar to controls (N=16). Following training the impaired PD group showed significantly greater reduction in sequence initiation and completion time and in error rate for IR conditions compared to the unimpaired PD and control groups. All groups improved on Trails B-A, and pre-training Trails B was identified as a predictor of training-based improvement in IR sequence completion time and error rate. Our findings highlight the importance of neurorehabilitation tailored to the specific cognitive deficits of the PD patient.

Neurotransmitter receptors and cognitive dysfunction in Alzheimer's disease and Parkinson's disease

Cognitive dysfunction is one of the most typical characteristics in various neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease (advanced stage). Although several mechanisms like neuronal apoptosis and inflammatory responses have been recognized to be involved in the pathogenesis of cognitive dysfunction in these diseases, recent studies on neurodegeneration and cognitive dysfunction have demonstrated a significant impact of receptor modulation on cognitive changes. The pathological alterations in various receptors appear to contribute to cognitive impairment and/or deterioration with correlation to diversified mechanisms. This article recapitulates the present understandings and concepts underlying the modulation of different receptors in human beings and various experimental models of Alzheimer's disease and Parkinson's disease as well as a conceptual update on the underlying mechanisms. Specific roles of serotonin, adrenaline, acetylcholine, dopamine receptors, and N-methyl-D-aspartate receptors in Alzheimer's disease and Parkinson's disease will be interactively discussed. Complex mechanisms involved in their signaling pathways in the cognitive dysfunction associated with the neurodegenerative diseases will also be addressed. Substantial evidence has suggested that those receptors are crucial neuroregulators contributing to cognitive pathology and complicated correlations exist between those receptors and the expression of cognitive capacities. The pathological alterations in the receptors would, therefore, contribute to cognitive impairments and/or deterioration in Alzheimer's disease and Parkinson's disease. Future research may shed light on new clues for the treatment of cognitive dysfunction in neurodegenerative diseases by targeting specific alterations in these receptors and their signal transduction pathways in the frontal-striatal, fronto-striato-thalamic, and mesolimbic circuitries.

A multicenter brain perfusion SPECT study evaluating idiopathic normal-pressure hydrocephalus on neurological improvement

PURPOSE

This study was designed to investigate the specific cerebral blood flow (CBF) pattern in patients with idiopathic normal-pressure hydrocephalus (iNPH) and a predictive value for shunt responsiveness in a multicenter study (Study of Idiopathic Normal-Pressure Hydrocephalus on Neurological Improvement: SINPHONI).

METHODS

Eighty-four iNPH patients underwent shunt operations using MRI selection criteria from the SINPHONI and were subjected to CBF single photon emission computed tomography (SPECT). The perfusion patterns on SPECT were classified: anterior-dominant CBF reduction type (A type), posterior-dominant CBF reduction type (P type), and mixed or diffuse CBF reduction type (M type). The predictive value of the CBF pattern for favorable shunt outcome was evaluated.

RESULTS

Favorable outcomes were obtained in 76% (64/84) of patients, and shunt responsiveness was achieved in 85% (71/84) of patients. Areas of severely reduced relative CBF were demonstrated around the corpus callosum and in the sylvian fissure area, which included the effects of dilatations of the ventricles and sylvian fissures and relatively increased perfusion in the medial and lateral frontal, parietal, and occipital areas at high convexity. Forty-nine (58%) cases were A type, 25 (30%) cases were M type, and 10 (12%) cases were P type. A, M, and P type cases exhibited 83, 84, and 90% positive predictive values for shunt responsiveness, respectively. Mean modified Rankin scale and Mini-Mental State Examination scores of the A type group were significantly better than those of other groups.

CONCLUSION

The iNPH patients showed various patterns of CBF reduction, but there was no significant difference in the predictive value among the three patterns, though CBF reduction patterns may suggest a severe condition of iNPH.

PET/CT in diagnosis of movement disorders

Molecular imaging with PET offers a broad variety of tools supporting the diagnosis of movement disorders. The more widely applied PET imaging techniques have focused on the assessment of neurotransmitter systems, predominantly the pre- and postsynaptic dopaminergic system. Additionally, PET imaging with [(18) F]fluorodeoxyglucose has been extensively used to assess local synaptic activity in the resting state and to highlight local changes in brain metabolism accompanying changes in neural activity in movement disorders. PET imaging has provided us with diagnostic agents as well as tools for evaluation of novel therapeutics, and has served as a powerful means for revealing in vivo changes at different stages of movement disorders and within the course of an individual patient's illness.

Radionuclide brain imaging correlates of cognitive impairment in Parkinson's disease (PD)

A subtle cognitive impairment can be detected early in the course of Parkinson's disease (PD). Executive, memory and visuospatial functions are specifically affected, but the underlying pathophysiological basis is not well elucidated yet and may be heterogeneous. The recent identification of a PD-related cognitive metabolic pattern (PDCP), including hypometabolism in associative frontal, parietal and posterior limbic structures, has integrated the classical notion of a striato-frontal syndrome at the basis of cognitive dys-function. Recent evidence suggests that whilst executive dys-function is seen in virtually all PD patients, visuospatial and memory impairment may share a higher risk for the subsequent development of dementia. By means of perfusion SPECT and [18F]FDG-PET, cortical dys-function may be highlighted since the early stages, it is more evident in PD patients with Mild Cognitive Impairment (MCI), and reaches the maximum in PD dementia (PDD). Posterior temporo-parieto-occipital dys-function in associative and limbic cortex, closely resembling that found in Alzheimer's disease patients, is found in PDD, with a more severe occipital hypometabolism and a relatively milder hypometabolism in medial temporal lobe structures. Furthermore, deficit of acetylcholinesterase (AchE) can be found by means of [11C]MP4A-PET already in early stage of PD, especially in posterior regions, then becoming more severe in PDD and in dementia with Lewy bodies (DLB). Administration of AchE inhibitors to PDD patients increased brain metabolism in bilateral frontal and left parietal regions, and left posterior cingulate. Finally, the recent availability of radiopharmaceuticals able to disclose amyloid brain deposition has allowed to demonstrate amyloid load in a part of patients with PDD, possibly due to diffuse rather than neuritic plaques. Brain PET and SPECT have strongly contributed to the understanding of the pathophysiology of cognitive impairment in PD and may serve as probes to monitor the effects of therapeutic interventions.

The neural substrates of script knowledge deficits as revealed by a PET study in Huntington's disease

INTRODUCTION

Previous neuropsychological investigations have suggested that both the prefrontal cortex and the basal ganglia are involved in the management of script event knowledge required in planning behavior.

METHODS

This study was designated to map, the correlations between resting-state brain glucose utilization as measured by FDG-PET (positron emission tomography) and scores obtained by means of a series of script generation and script sorting tasks in 8 patients with early Huntington's disease.

RESULTS

These patients exhibited a selectively greater impairment for the organizational aspects of scripts compared to the semantic aspects of scripts. We showed significant negative correlations between the number of sequencing, boundary, perseverative and intrusion errors and the metabolism of several cortical regions, not only including frontal, but also posterior regions.

CONCLUSION

Our findings suggest that, within the fronto-striatal system, the cortical frontal regions are more crucial in script retrieval and script sequencing than the basal ganglia.

Gender differences in Parkinson's disease: clinical characteristics and cognition

More men than women are diagnosed with Parkinson's disease (PD), and a number of gender differences have been documented in this disorder. Examples of clinical characteristics that appear in men more often than women include rigidity and rapid eye movement behavior disorder, whereas more women than men exhibit dyskinesias and depression. Differences between men and women in cognition have not been extensively examined, though there are reports of deficits in men in aspects of cognition that contribute to activities of daily living, in verbal fluency, and in the recognition of facial emotion, and deficits in women in visuospatial cognition. Side of disease onset may interact with gender to affect cognitive abilities. One possible source of male-female differences in the clinical and cognitive characteristics of PD is the effect of estrogen on dopaminergic neurons and pathways in the brain. This effect is not yet understood, as insight into how the fluctuation of estrogen over the lifetime affects the brain is currently limited. Further attention to this area of research will be important for accurate assessment and better management of PD. Attention should also be directed to multiple covariates that may affect clinical characteristics and cognition. Knowledge about differences in the presentation of PD symptoms in men and women and about the pathophysiology underlying those differences may enhance the accuracy and effectiveness of clinical assessment and treatment of the disease.

Molecular imaging and the neuropathologies of Parkinson's disease

The main motor symptoms of Parkinson's disease (PD) are linked to degeneration of the nigrostriatal dopamine (DA) fibers, especially those innervating the putamen. This degeneration can be assessed in molecular imaging studies with presynaptic tracers such as [(18)F]-fluoro-L-DOPA (FDOPA) and ligands for DA transporter ligands. However, the pathologies of PD are by no means limited to nigrostriatal loss. Results of post mortem and molecular imaging studies reveal parallel degenerations of cortical noradrenaline (NA) and serotonin (5-HT) innervations, which may contribute to affective and cognitive changes of PD. Especially in advanced PD, cognitive impairment can come to resemble that seen in Alzheimer's dementia, as can the degeneration of acetylcholine innervations arising in the basal forebrain. The density of striatal DA D(2) receptors increases in early untreated PD, consistent with denervation upregulation, but there is an accelerated rate of DA receptor loss as the disease advances. Animal studies and post mortem investigations reveal changes in brain opioid peptide systems, but these are poorly documented in imaging studies of PD. Relatively minor changes in the binding sites for GABA are reported in cortex and striatum of PD patients. There remains some controversy about the expression of the 18 kDa translocator protein (TSPO) in activated microglia as an indicator of an active inflammatory component of neurodegeneration in PD. A wide variety of autonomic disturbances contribute to the clinical syndrome of PD; the degeneration of myocardial sympathetic innervation can be revealed in SPECT studies of PD patients with autonomic failure. Considerable emphasis has been placed on investigations of cerebral blood flow and energy metabolism in PD. Due to the high variance of these physiological estimates, researchers have often employed normalization procedures for the sensitive detection of perturbations in relatively small patient groups. However, a widely used normalization to the global mean must be used with caution, as it can result in spurious findings of relative hypermetabolic changes in subcortical structures. A meta-analysis of the quantitative studies to date shows that there is in fact widespread hypometabolism and cerebral blood flow in the cerebral cortex, especially in frontal cortex and parietal association areas. These changes can bias the use of global mean normalization, and probably represent the pathophysiological basis of the cognitive impairment of PD.

Functional imaging of cognitive impairment in Parkinson's disease

Parkinson's disease (PD) is known by most persons to be a neurodegenerative disorder that affects one's motor skills. However, the disease is also characterized by the less recognized cognitive symptoms, including deficits in executive functioning, as well as mood and behavioral problems, which are just as disabling and distressing as the motor symptoms. Imaging methods such as positron emission tomography (PET) have recently enhanced our understanding of cognitive disturbances in PD, and are reviewed in the current article. Furthermore, insights gained from the use of specific radiotracers in the dopaminergic and cholinergic neurotransmitter systems are discussed, as well as findings from in vivo detection of amyloid-beta. We will also discuss the potential use of a metabolic covariance network as a biomarker in clinical trials for the objective assessment of cognitive dysfunction in PD.

Chronic therapy with citalopram decreases regional cerebral glucose utilization in OBX, and not sham-operated, rats: an autoradiographic study

RATIONALE

Chronic treatment with the selective serotonin reuptake inhibitor, citalopram, normalizes several behavioral and neurochemical abnormalities in the olfactory bulbectomized (OBX) rat model of depression.

OBJECTIVE

To assess the changes in regional cerebral glucose utilization (rCGU) following chronic treatment with citalopram in OBX and sham-operated rats.

METHODS

Male Sprague Dawley rats (160-190 g) were used. Two weeks following the surgeries, the rats were implanted with osmotic minipumps which delivered 10 mg/kg/day of citalopram (the sham-CTP and OBX-CTP groups) or saline (to the sham-SAL and OBX-SAL groups) for 2 weeks. Following the treatment, the rates of rCGU were determined in 43 brain regions using 2-[(14)C]deoxyglucose (2-[(14)C]DG) autoradiography.

RESULTS

The general linear model statistical analysis revealed significantly lower rCGU in the OBX-SAL group compared to the sham-SAL group in the medial prefrontal cortex and the median forebrain bundle. The sham-CTP group had significantly lower rCGU relative to the sham-SAL group in the medial prefrontal cortex. The OBX-CTP group had significantly lower rCGU than the OBX-SAL group in the anterior olfactory nucleus, orbitofrontal cortex, frontal cortex, anterior cingulate cortex, visual cortex, and substantia nigra--pars reticulata. The rCGU in the OBX-CTP group was significantly lower than that in the sham-CTP group in the anterior olfactory nucleus, orbitofrontal cortex, visual cortex, and substantia nigra--pars reticulata.

CONCLUSION

The results imply that chronic citalopram treatment, shown previously to result in behavioral normalization in OBX rats, establishes a new pattern of rCGU, rather than normalizing it to the pattern of the sham-CTP rats.