MRI evaluation of asymmetry of nigrostriatal damage in the early stage of early-onset Parkinson's disease

Interhemispheric reactivity of the subthalamic nucleus sustains progressive dopamine neuron loss in asymmetrical parkinsonism

Parkinson's disease (PD) is characterized by the progressive and asymmetrical degeneration of the nigrostriatal dopamine neurons and the unilateral presentation of the motor symptoms at onset, contralateral to the most impaired hemisphere. We previously developed a rat PD model that mimics these typical features, based on unilateral injection of a substrate inhibitor of excitatory amino acid transporters, L-trans-pyrrolidine-2,4-dicarboxylate (PDC), in the substantia nigra (SN). Here, we used this progressive model in a multilevel study (behavioral testing, in vivo 1H-magnetic resonance spectroscopy, slice electrophysiology, immunocytochemistry and in situ hybridization) to characterize the functional changes occurring in the cortico-basal ganglia-cortical network in an evolving asymmetrical neurodegeneration context and their possible contribution to the cell death progression. We focused on the corticostriatal input and the subthalamic nucleus (STN), two glutamate components with major implications in PD pathophysiology. In the striatum, glutamate and glutamine levels increased from presymptomatic stages in the PDC-injected hemisphere only, which also showed enhanced glutamatergic transmission and loss of plasticity at corticostriatal synapses assessed at symptomatic stage. Surprisingly, the contralateral STN showed earlier and stronger reactivity than the ipsilateral side (increased intraneuronal cytochrome oxidase subunit I mRNA levels; enhanced glutamate and glutamine concentrations). Moreover, its lesion at early presymptomatic stage halted the ongoing neurodegeneration in the PDC-injected SN and prevented the expression of motor asymmetry. These findings reveal the existence of endogenous interhemispheric processes linking the primary injured SN and the contralateral STN that could sustain progressive dopamine neuron loss, opening new perspectives for disease-modifying treatment of PD.

Imbalanced motivated behaviors according to motor sign asymmetry in drug-naïve Parkinson's disease

Few studies have considered the influence of motor sign asymmetry on motivated behaviors in de novo drug-naïve Parkinson's disease (PD). We tested whether motor sign asymmetry could be associated with different motivated behavior patterns in de novo drug-naïve PD. We performed a cross-sectional study in 128 de novo drug-naïve PD patients and used the Ardouin Scale of Behavior in Parkinson's disease (ASBPD) to assess a set of motivated behaviors. We assessed motor asymmetry based on (i) side of motor onset and (ii) MDS-UPDRS motor score, then we compared right hemibody Parkinson's disease to left hemibody Parkinson's disease. According to the MDS-UPDRS motor score, patients with de novo right hemibody PD had significantly lower frequency of approach behaviors (p = 0.031), including nocturnal hyperactivity (p = 0.040), eating behavior (p = 0.040), creativity (p = 0.040), and excess of motivation (p = 0.017) than patients with de novo left hemibody PD. Patients with de novo left hemibody PD did not significantly differ from those with de novo right hemibody PD regarding avoidance behaviors including apathy, anxiety and depression. Our findings suggest that motor sign asymmetry may be associated with an imbalance between motivated behaviors in de novo drug-naïve Parkinson's disease.

Parkinson's disease tremor prediction using EEG data analysis-A preliminary and feasibility study

PURPOSE

Tremor is one of the hallmarks of Parkinson's disease (PD) that does not respond effectively to conventional medications. In this regard, as a complementary solution, methods such as deep brain stimulation have been proposed. To apply the intervention with minimal side effects, it is necessary to predict tremor initiation. The purpose of the current study was to propose a novel methodology for predicting resting tremors using analysis of EEG time-series.

METHODS

A modified algorithm for tremor onset detection from accelerometer data was proposed. Furthermore, a machine learning methodology for predicting PD hand tremors from EEG time-series was proposed. The most discriminative features extracted from EEG data based on statistical analyses and post-hoc tests were used to train the classifier for distinguishing pre-tremor conditions.

RESULTS

Statistical analyses with post-hoc tests showed that features such as form factor and statistical features were the most discriminative features. Furthermore, limited numbers of EEG channels (F3, F7, P4, CP2, FC6, and C4) and EEG bands (Delta and Gamma) were sufficient for an accurate tremor prediction based on EEG data. Based on the selected feature set, a KNN classifier obtained the best pre-tremor prediction performance with an accuracy of 73.67%.

CONCLUSION

This feasibility study was the first attempt to show the predicting ability of EEG time-series for PD hand tremor prediction. Considering the limitations of this study, future research with longer data, and different brain dynamics are needed for clinical applications.

Dopaminergic denervation and associated MRI microstructural changes in the nigrostriatal projection in early Parkinson's disease patients

Loss of dopaminergic neurons in the substantia nigra pars compacta (SNc) and a profound reduction of striatal dopamine are two hallmarks of Parkinson's disease (PD). However, it's unclear whether degeneration starts at the neuronal soma or the striatal presynaptic terminals, and how microstructural degeneration is linked to dopaminergic loss is also uncertain. In this study, thirty de novo PD patients and twenty healthy subjects (HS) underwent 6-[18F]-fluoro-L-dopa (FDOPA) PET and MRI studies no later than 12 months from clinical diagnosis. FDOPA uptake rate (Ki), fractional volume of free-water (FW), and iron-sensitive R2* relaxometry were quantified within nigrostriatal regions. Inter-group differences (PD vs HS) were studied using non-parametric statistics and complemented with Cohen's d effect sizes and Bayesian statistics. Correlation analyses were performed exploring biomarker dependencies and their association with bradykinesia scores. PD patients exhibited a significant decline in nigrostriatal dopaminergic activity, being post-commissural putamen (-67%) and posterolateral SNc (-11.7%) the most affected subregions within striatum and SNc respectively. Microstructural alterations (FW) were restricted to the hemisphere corresponding to the most affected side and followed similar spatial gradients as FDOPA Ki (+20% in posterior putamen and +11% in posterolateral SNc). R2* revealed no relevant significant changes. FDOPA and FW were correlated within the posterolateral SNc, and clinical severity was associated with FDOPA Ki loss. The asymmetry between striatal and SNc changes for both dopaminergic depletion and microstructural degeneration biomarkers is consistent with a neurodegenerative process that begins in the striatal terminals before progressing toward the cell bodies in the SNc.

Study of the relationship between onset lateralization and hemispheric white matter asymmetry in Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is characterized by a lateralized onset, but its cause and mechanism are still unclear.

METHODS

Obtaining diffusion tensor imaging (DTI) data from the Parkinson's Progression Markers Initiative (PPMI). Tract-based spatial statistics analysis and region-of-interest-based analysis were performed to evaluate the white matter (WM) asymmetry using original DTI parameters, Z Score normalized parameters, or the asymmetry index (AI). Hierarchical cluster analysis and least absolute shrinkage and selection operator regression were performed to construct predictive models for predicting the PD onset side. DTI data from The Second Affiliated Hospital of Chongqing Medical University were obtained for external validation of the prediction model.

RESULTS

118 PD patients and 69 healthy controls (HC) from PPMI were included. Right-onset PD patients presented more asymmetric areas than left-onset PD patients. The inferior cerebellar peduncle (ICP), superior cerebellar peduncle (SCP), external capsule (EC), cingulate gyrus (CG), superior fronto-occipital fasciculus (SFO), uncinate fasciculus (UNC), and tapetum (TAP) showed significant asymmetry in left-onset and right-onset PD patients. An onset-side-specific pattern of WM alterations exists in PD patients, and a prediction model was constructed. The predicting models based on AI and ΔZ Score presented favorable efficacy in predicting PD onset side by external validation in 26 PD patients and 16 HCs from our hospital.

CONCLUSIONS

Right-onset PD patients may have more severe WM damage than left-onset PD patients. WM asymmetry in ICP, SCP, EC, CG, SFO, UNC, and TAP may predict PD onset side. Imbalances in the WM network may underlie the mechanism of lateralized onset in PD.

Exploring Asymmetric Fine Motor Impairment Trends in Early Parkinson's Disease via Keystroke Typing

Background

The nQiMechPD algorithm transforms natural typing data into a numerical index that characterizes motor impairment in people with Parkinson's Disease (PwPD).

Objectives

Use nQiMechPD to compare asymmetrical progression of PD-related impairment in dominant (D-PD) versus non-dominant side onset (ND-PD) de-novo patients.

Methods

Keystroke data were collected from 53 right-handed participants (15 D-PD, 13 ND-PD, 25 controls). We apply linear mixed effects modeling to evaluate participants' right, left, and both hands nQiMechPD relative change by group.

Results

The 6-month nQiMechPD trajectories of right (**P = 0.002) and both (*P = 0.043) hands showed a significant difference in nQiMechPD trends between D-PD and ND-PD participants. Left side trends were not significantly different between these two groups (P = 0.328).

Conclusions

Significant differences between D-PD and ND-PD groups were observed, likely driven by contrasting dominant hand trends. Our findings suggest disease onset side may influence motor impairment progression, medication response, and functional outcomes in PwPD.

Gender may be related to the side of the motor syndrome and cognition in idiopathic Parkinson's disease

BACKGROUND

and Sex and cognitive profile may be related to the laterality of motor symptoms in idiopathic Parkinson's disease.

INTRODUCTION

Parkinson's disease (PD) is well recognised as an inherently asymmetric disease with unilateral onset of motor symptoms. The laterality of motor symptoms may be linked to sex, clinical and demographic variables, and neuropsychological disorders. However, the available data are inconsistent. This study aimed to explore the potential association between the laterality of motor symptoms and clinical and demographic variables and deficits in specific cognitive domains.

MATERIAL AND METHODS

We retrospectively recruited 97 participants with idiopathic PD without dementia; 60 presented motor symptoms on the left side and 37 on the right side. Both groups were comparable in terms of age, age at disease onset, disease duration, and severity of the neurological deficits according to the Unified Parkinson's Disease Rating Scale and the Hoehn and Yahr scale.

RESULTS

Participants with left-side motor symptoms scored lower on the Schwab and England Activities of Daily Living scale. Our sample included more men than women (67% vs. 33%). Both sexes were not equally represented in the 2 groups: there were significantly more men than women in the group of patients with left-side motor symptoms (77% vs. 23%), whereas the percentages of men and women in the group of patients with right-side motor symptoms were similar (51% vs. 49%). Both groups performed similarly in all neuropsychological tasks, but women, independently of laterality, performed better than men in the naming task.

CONCLUSION

We found a clear prevalence of men in the group of patients with left-side motor symptoms; this group also scored lower on the Schwab and England Scale. Female sex was predictive of better performance in the naming task. Sex should always be considered in disorders that cause asymmetric involvement of the brain, such as PD.

An interpretable multiparametric radiomics model of basal ganglia to predict dementia conversion in Parkinson's disease

Cognitive impairment in Parkinson's disease (PD) severely affects patients' prognosis, and early detection of patients at high risk of dementia conversion is important for establishing treatment strategies. We aimed to investigate whether multiparametric MRI radiomics from basal ganglia can improve the prediction of dementia development in PD when integrated with clinical profiles. In this retrospective study, 262 patients with newly diagnosed PD (June 2008-July 2017, follow-up >5 years) were included. MRI radiomic features (n = 1284) were extracted from bilateral caudate and putamen. Two models were developed to predict dementia development: (1) a clinical model-age, disease duration, and cognitive composite scores, and (2) a combined clinical and radiomics model. The area under the receiver operating characteristic curve (AUC) were calculated for each model. The models' interpretabilities were studied. Among total 262 PD patients (mean age, 68 years ± 8 [standard deviation]; 134 men), 51 (30.4%), and 24 (25.5%) patients developed dementia within 5 years of PD diagnosis in the training (n = 168) and test sets (n = 94), respectively. The combined model achieved superior predictive performance compared to the clinical model in training (AUCs 0.928 vs. 0.894, P = 0.284) and test set (AUCs 0.889 vs. 0.722, P = 0.016). The cognitive composite scores of the frontal/executive function domain contributed most to predicting dementia. Radiomics derived from the caudate were also highly associated with cognitive decline. Multiparametric MRI radiomics may have an incremental prognostic value when integrated with clinical profiles to predict future cognitive decline in PD.

Motor imagery vividness and symptom severity in Parkinson's disease

Motor imagery (MI), the mental simulation of movement in the absence of overt motor output, has demonstrated potential as a technique to support rehabilitation of movement in neurological conditions such as Parkinson's disease (PD). Existing evidence suggests that MI is largely preserved in PD, but previous studies have typically examined global measures of MI and have not considered the potential impact of individual differences in symptom presentation on MI. The present study investigated the influence of severity of overall motor symptoms, bradykinesia and tremor on MI vividness scores in 44 individuals with mild to moderate idiopathic PD. Linear mixed effects modelling revealed that imagery modality and the severity of left side bradykinesia significantly influenced MI vividness ratings. Consistent with previous findings, participants rated visual motor imagery (VMI) to be more vivid than kinesthetic motor imagery (KMI). Greater severity of left side bradykinesia (but not right side bradykinesia) predicted increased vividness of KMI, while tremor severity and overall motor symptom severity did not predict vividness of MI. The specificity of the effect of bradykinesia to the left side may reflect greater premorbid vividness for the dominant (right) side or increased attention to more effortful movements on the left side of the body resulting in more vivid motor imagery.

Laterality in Parkinson's disease: A neuropsychological review

Laterality of motor symptom onset in Parkinson's disease is both well-known and under-appreciated. Treatment of disorders that have asymmetric pathological features, such as stroke and epilepsy, demonstrate the importance of incorporating hemispheric lateralization and specialization into therapy and care planning. These practices could theoretically extend to Parkinson's disease, providing increased diagnostic accuracy and improved treatment outcomes. Additionally, while motor symptoms have generally received the majority of attention, non-motor features (e.g., autonomic dysfunction) also decrease quality of life and are influenced by asymmetrical neurodegeneration. Due to the laterality of cognitive and behavioral processes in the two brain hemispheres, analysis of hemibody side of onset can potentially give insight into expected symptom profile of the patient and allow for increased predictive accuracy of disease progression and outcome, thus opening the door to personalized and improved therapy in treating Parkinson's disease patients. This review discusses motor and non-motor symptoms (namely autonomic, sensory, emotional, and cognitive dysfunction) of Parkinson's disease in respect to hemispheric lateralization from a theoretical perspective in hopes of providing a framework for future research and personalized treatment.

Effective R2 relaxation rate, derived from dual-contrast fast-spin-echo MRI, enables detection of hemisphere differences in iron level and dopamine function in Parkinson's disease and healthy individuals

BACKGROUND

Clinical estimates of brain iron concentration are achievable with quantitative transverse relaxation rate R₂, via time-consuming multiple spin-echo (SE) sequences. The objective of this study was to investigate whether quantitative iron-sensitive information may be derived from 3.0 T dual-contrast fast-spin-echo (FSE) sequences (typically employed in anatomical non-quantitative evaluations), as a routinely-collected alternative to evaluate iron levels in healthy (HC) and Parkinson's disease (PD) brains.

NEW METHOD

MRI 3.0 T FSE data from the Parkinson's Progression Markers Initiative (PPMI) (12 PD, 12 age- and gender-matched HC subjects) were cross-sectionally and longitudinally evaluated. A new measure, 'effective R₂', was calculated for bilateral subcortical grey matter (caudate nucleus, putamen, globus pallidus, red nucleus, substantia nigra). Linear regression analysis was performed to correlate 'effective R₂' with models of age-dependent brain iron concentration and striatal dopamine transporter (DaT) receptor binding ratio.

RESULTS

Effective R₂ was strongly correlated with estimated brain iron concentration. In PD, putaminal effective R₂ difference was observed between the hemispheres contra-/ipsi-lateral to the predominantly symptomatic side at onset. This hemispheric difference was correlated with the putaminal DaT binding ratios in PD.

COMPARISON WITH EXISTING METHOD(S)

Effective R₂, derived from rapid dual-contrast FSE sequences, showed viability as an alternative to R₂ from SE sequences. Linear correlation of effective R₂ with estimated iron concentration was comparable to documented iron-dependent R₂. The effective R₂ correlation coefficient was consistent with theoretical R₂ iron-dependence at 3.0 T.

CONCLUSIONS

Effective R₂ has clinical potential as a fast quantitative method, as an alternative to R₂, to aid evaluation of brain iron levels and DaT function.

Multifunctional role of natural products for the treatment of Parkinson's disease: At a glance

Natural substances originating from plants have long been used to treat neurodegenerative disorders (NDs). Parkinson's disease (PD) is a ND. The deterioration and subsequent cognitive impairments of the midbrain nigral dopaminergic neurons distinguish by this characteristic. Various pathogenic mechanisms and critical components have been reported, despite the fact that the origin is unknown, such as protein aggregation, iron buildup, mitochondrial dysfunction, neuroinflammation and oxidative stress. Anti-Parkinson drugs like dopamine (DA) agonists, levodopa, carbidopa, monoamine oxidase type B inhibitors and anticholinergics are used to replace DA in the current treatment model. Surgery is advised in cases where drug therapy is ineffective. Unfortunately, the current conventional treatments for PD have a number of harmful side effects and are expensive. As a result, new therapeutic strategies that control the mechanisms that contribute to neuronal death and dysfunction must be addressed. Natural resources have long been a useful source of possible treatments. PD can be treated with a variety of natural therapies made from medicinal herbs, fruits, and vegetables. In addition to their well-known anti-oxidative and anti-inflammatory capabilities, these natural products also play inhibitory roles in iron buildup, protein misfolding, the maintenance of proteasomal breakdown, mitochondrial homeostasis, and other neuroprotective processes. The goal of this research is to systematically characterize the currently available medications for Parkinson's and their therapeutic effects, which target diverse pathways. Overall, this analysis looks at the kinds of natural things that could be used in the future to treat PD in new ways or as supplements to existing treatments. We looked at the medicinal plants that can be used to treat PD. The use of natural remedies, especially those derived from plants, to treat PD has been on the rise. This article examines the fundamental characteristics of medicinal plants and the bioactive substances found in them that may be utilized to treat PD.

Evaluation of retina and microvascular changes in the patient with Parkinson's disease: A systematic review and meta-analysis

Background

Parkinson's disease (PD) is a multifaceted neurodegenerative disease. The optic nerve, as a window into the central nervous system (CNS), is known to be an important part of the CNS and can be detected non-invasively. With the widespread availability of optical coherence tomography (OCT) devices, an increasing number of studies have paid attention to the neuropathological disorders in the retina of PD patients in recent years. However, it is still controversial whether OCT can be used as a complementary tool for PD diagnosis.

Methods

This review is registered with PROSPERO, number CRD42022301258. The Embase, PUBMED, and The Cochrane Library databases were independently retrieved by 2 investigators to identify relevant papers published from 1 January 2017 to 24 January 2022. These studies used OCT or OCTA to evaluate the difference in the retinal nerve fiber layer (RNFL) thickness, ganglion cell layer(GCL) thickness, macula thickness, Cup and disk area superficial retinal capillary plexus (SCP), and deep retinal capillary plexus(DCP). The standard mean difference (SMD) with the 95% confidence interval (CI) was pooled for continuous outcomes.

Results

In total, 26 studies had been enrolled in this meta-analysis with a total number of 2,790 eyes, including 1,343 eyes from the PD group along with 1,447 eyes from the HC group. The results revealed that the RNFL thickness (SMD: -0.53; 95%CI, -0.71∼-0.35; P < 0.00001), GCL thickness (SMD: -0.43; 95%CI, -0.66 to -0.19; P = 0.0003), macula thickness (SMD: -0.22; 95%CI, -0.22 to -0.11; P < 0.0001) were significantly thinner in patients with PD. The SCP (SMD: -0.61; 95%CI, -1.31to -0.10; P = 0.02) was significantly lower in PD patients. The DCP (SMD: -0.48; 95%CI, -1.02 to -0.06; P = 0.08) is lower in PD patients, but the difference was statistically insignificant.

Conclusion

Retinal nerve fiber layer thickness, GCL thickness, macular thickness, and SVD of PD patients are lower than those of healthy control. OCT and OCTA could detect morphological retinal changes in PD and might be objective and reproducible auxiliary tools to assist clinician diagnosis.

Systematic review registration

[https://www.crd.york.ac.uk/prospero/], identifier [CRD42022301258].

Gray Matter Volume Loss in Proposed Brain-First and Body-First Parkinson's Disease Subtypes

BACKGROUND

α-Synuclein pathology is associated with neuronal degeneration in Parkinson's disease (PD) and considered to sequentially spread across the brain (Braak stages). According to a new hypothesis of distinct α-synuclein spreading directions based on the initial site of pathology, the "brain-first" spreading subtype would be associated with a more asymmetric cerebral and nigrostriatal pathology than the "body-first" subtype.

OBJECTIVE

Here, we tested if proposed markers of brain-first PD (ie, higher dopamine transporter [DaT] asymmetry; absence of rapid eye movement sleep behavior disorder [RBD]) are associated with a greater or more asymmetric reduction in gray matter volume (GMV) in comparison to body-first PD.

METHODS

Data of 255 de novo PD patients and 110 healthy controls (HCs) were retrieved from the Parkinson's Progression Markers Initiative. Structural magnetic resonance images were preprocessed, and GMVs and their hemispherical asymmetry were obtained for each of the neuropathologically defined Braak stages. Group and correlation comparisons were performed to assess differences in GMV and GMV asymmetry between PD subtypes.

RESULTS

PD patients demonstrated significantly smaller bilateral GMVs compared to HCs, in a pattern denoting stage-dependent disease-related brain atrophy. However, the degree of putaminal DaT asymmetry was not associated with reduced GMV or higher GMV asymmetry. Furthermore, RBD-negative and RBD-positive patients did not demonstrate a significant difference in GMV or GMV asymmetry.

CONCLUSIONS

Our findings suggest that putative brain-first and body-first patients do not present diverging brain atrophy patterns. Although certainly not disproving the brain-first/body-first spreading hypothesis, this study fails to provide evidence in support of it. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Impaired Interhemispheric Synchrony in Parkinson’s Disease with Fatigue

The characteristics of interhemispheric resting-state functional connectivity (FC) in Parkinson’s disease (PD) with fatigue remain unclear; therefore, we aimed to explore the changes in interhemispheric FC in PD patients with fatigue. Sixteen PD patients with fatigue (PDF), 16 PD patients without fatigue (PDNF) and 15 matched healthy controls (HCs) were enrolled in the retrospective cross-sectional study. We used voxel-mirrored homotopic connectivity (VMHC) to analyze the resting-state functional magnetic resonance imaging (fMRI) data of these subjects. Compared to PDNF, PDF patients had decreased VMHC values in the supramarginal gyri (SMG). Furthermore, the mean VMHC values of the SMG were negatively correlated with the mean fatigue severity scale (FSS/9) scores (r = −0.754, p = 0.001). Compared to HCs, PDF patients had decreased VMHC in the SMG and in the opercular parts of the inferior frontal gyri (IFG operc). The VMHC values in the IFG operc and middle frontal gyri (MFG) were notably decreased in PDNF patients compared with HCs. Our findings suggest that the reduced VMHC values within the bilateral SMG may be the unique imaging features of fatigue in PD, and may illuminate the neural mechanisms of fatigue in PD.

Peripheral inflammatory cytokines and motor symptoms in persons with Parkinson's disease

Background

Many of the motor symptoms of Parkinson's disease (PD) impact quality of life and are not fully ameliorated by current pharmacological and surgical treatments. A better understanding of the pathophysiology underlying these symptoms is needed. Previous research has suggested that inflammation may play a significant role in PD pathophysiology and progression, but there is limited research exploring how inflammation directly relates to motor symptoms in PD. Thus, the purpose of this study was to evaluate associations between peripheral immune inflammatory markers and motor symptoms of PD, specifically, tremor, bradykinesia, and postural and gait instability. We hypothesized that peripheral inflammatory cytokines would predict the severity of motor symptoms in persons with PD, and that there will be higher levels of peripheral inflammatory cytokine markers in persons with PD when compared to age-matched healthy older adults.

Methods

Twenty-six participants with PD and fourteen healthy older adults completed the study. For participants with PD, the motor section of the Unified Parkinson's Disease Rating Scale (UPDRS) was recorded and scored by two Movement Disorders Neurologists masked to the study. A blood sample was collected from both participants with PD and the healthy older adults. Through the MILLIPLEX® map High Sensitivity Human Cytokine Kit, key inflammation-related markers were analyzed (TNF-α, IFN-γ, IL-1β, IL-8, IL-2, IL-7, IL-5, IL-13, IL, 4, IL-10 IL-12p70, GM-CSF, and IL-6).

Results

Results revealed significantly higher levels of IL-6 in persons with PD when compared to healthy older adults (p ​= ​0.005). Moreover, results revealed that higher levels of IL-4 (p ​= ​0.011) and lower levels of IFNγ (p ​= ​0.003) significantly predicted more severe tremor in persons with PD. No other associations between the peripheral inflammation markers and other motor symptoms were observed.

Conclusions

Overall, these results are consistent with a growing body of literature that implicates inflammatory cytokines in the PD, and further suggests that inflammatory cytokines, or lack thereof, may be associated with tremor in persons with PD.

Striatal synaptic bioenergetic and autophagic decline in premotor experimental parkinsonism

Synaptic impairment might precede neuronal degeneration in Parkinson’s disease. However, the intimate mechanisms altering synaptic function by the accumulation of presynaptic α-synuclein in striatal dopaminergic terminals before dopaminergic death occurs, have not been elucidated. Our aim is to unravel the sequence of synaptic functional and structural changes preceding symptomatic dopaminergic cell death. As such, we evaluated the temporal sequence of functional and structural changes at striatal synapses before parkinsonian motor features appear in a rat model of progressive dopaminergic death induced by overexpression of the human mutated A53T α-synuclein in the substantia nigra pars compacta, a protein transported to these synapses. Sequential window acquisition of all theoretical mass spectra proteomics identified deregulated proteins involved first in energy metabolism and later, in vesicle cycling and autophagy. After protein deregulation and when α-synuclein accumulated at striatal synapses, alterations to mitochondrial bioenergetics were observed using a Seahorse XF96 analyser. Sustained dysfunctional mitochondrial bioenergetics was followed by a decrease in the number of dopaminergic terminals, morphological and ultrastructural alterations, and an abnormal accumulation of autophagic/endocytic vesicles inside the remaining dopaminergic fibres was evident by electron microscopy. The total mitochondrial population remained unchanged whereas the number of ultrastructurally damaged mitochondria increases as the pathological process evolved. We also observed ultrastructural signs of plasticity within glutamatergic synapses before the expression of motor abnormalities, such as a reduction in axospinous synapses and an increase in perforated postsynaptic densities. Overall, we found that a synaptic energetic failure and accumulation of dysfunctional organelles occur sequentially at the dopaminergic terminals as the earliest events preceding structural changes and cell death. We also identify key proteins involved in these earliest functional abnormalities that may be modulated and serve as therapeutic targets to counterbalance the degeneration of dopaminergic cells to delay or prevent the development of Parkinson’s disease.

Electromyographic measures of asymmetric muscle control of swallowing in Parkinson’s disease

Introduction

During the early stages, Parkinson’s disease (PD) is well recognized as an asymmetric disease with unilateral onset of resting tremor with varying degrees of rigidity, and bradykinesia. However, it remains unknown if other impairments, such as swallowing impairment (i.e., dysphagia), also present asymmetrically.

Purpose

The primary aim of this study was to examine muscle activity associated with swallow on the most affected side (MAS) and least affected side (LAS) in persons with PD. A secondary aim was to explore the relationship between differences in muscle activity associated with swallow and subjective reports of swallowing impairment and disease severity.

Methods

Function of muscles associated with swallowing was assessed using surface electromyography placed over the right and left submental and laryngeal regions during three swallows for a THIN and THICK condition. The Swallowing Quality of Life (SWAL-QOL) questionnaire and the Unified Parkinson’s Disease Rating Scale (UPDRS) were collected as measures of subjective swallow impairment and disease severity, respectively.

Results

Thirty-five participants diagnosed with idiopathic PD and on a stable antiparkinsonian medication regimen completed this study. Results revealed no significant mean difference in muscle activity during swallow between the more and less affected side. For the laryngeal muscle region, a significant difference in coefficient of variation between the MAS and LAS was revealed for peak amplitude for the THIN swallow condition. For the laryngeal muscle region, a significant association was revealed between muscle activity and disease severity but not subjective reports of swallowing impairment.

Conclusion

Superficially it appears that swallowing impairment present symmetrical during the early stages of PD, however, our variability data indicates otherwise. These results will be used to inform future studies in specific types of swallowing impairment (i.e., oral dysphagia, pharyngeal dysphagia, and esophageal dysphagia), disease progression, and overall asymmetry.

Mapping Motor Pathways in Parkinson’s Disease Patients with Subthalamic Deep Brain Stimulator: A Diffusion MRI Tractography Study

Introduction

This study assessed the safety of postoperative diffusion tensor imaging (DTI) with on-state deep brain stimulation (DBS) and the feasibility of reconstruction of the white matter tracts in the vicinity of the stimulation site of the subthalamic nucleus (STN). The association between the impact of DBS on the nigrostriatal pathway (NSP) and the treatment effect on motor symptoms in Parkinson’s disease (PD) was then evaluated.

Methods

Thirty-one PD patients implanted with STN-DBS (mean age: 66 years; 25 male) were scanned on a 1.5-T magnetic resonance imaging (MRI) scanner using the DTI sequence with DBS on. Twenty-three of them were scanned a second time with DBS off. The NSP, dentato-rubro-thalamic tract (DRTT), and hyperdirect pathway (HDP) were generated using both deterministic and probabilistic tractography methods. The DBS-on-state and off-state tractography results were validated and compared. Afterward, the relationships between the characteristics of the reconstructed white matter tracts and the clinical assessment of PD symptoms and the DBS effect were further examined.

Results

No adverse events related to DTI were identified in either the DBS-on-state or off-state. Overall, the NSP was best reconstructed, followed by the DRTT and HDP, using the probabilistic tractography method. The connection probability of the left NSP was significantly lower than that of the right side (p < 0.05), and a negative correlation (r = −0.39, p = 0.042) was identified between the preoperative symptom severity in the medication-on state and the connection probability of the left NSP in the DBS-on-state images. Furthermore, the distance from the estimated left-side volume of tissue activated (VTA) by STN-DBS to the ipsilateral NSP was significantly shorter in the DBS-responsive group compared to the DBS-non-responsive group (p = 0.046).

Conclusions

DTI scanning is safe and delineation of white matter pathway is feasible for PD patients implanted with the DBS device. Postoperative DTI is a useful technique to strengthen our current understanding of the therapeutic effect of DBS for PD and has the potential to refine target selection strategies for brain stimulation.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40120-022-00331-1.

For some more seriously affected Parkinson’s disease (PD) patients, drugs are no longer effective in treating their symptoms. An alternate treatment is to use deep brain stimulation (DBS), a commonly used neurosurgical therapy for PD patients. For those DBS treatments targeting the subthalamic nucleus (STN), the electrical stimulation used may impact nearby white matter tracts and alter the effectiveness of the DBS treatment. The nigrostriatal pathway (NSP), dentato-rubro-thalamic tract, and hyperdirect pathway are three white matter tracts near the STN. They are all relevant to motor symptoms in PD. This study examined whether imaging these tracts using magnetic resonance imaging (MRI) is safe and feasible in the presence of DBS leads. The relationships between the fiber-tracking characteristics and distance to the DBS leads were then evaluated. For this purpose, 31 PD patients with stimulation-on were scanned on a 1.5 T MRI scanner using a diffusion tensor imaging sequence. A total of 23 subjects underwent another scan using the same sequence with stimulation-off. No adverse events related to diffusion tensor imaging were found. Among the white matter tracts near the STN, the NSP was best delineated, followed by the dentato-rubro-thalamic tract and the hyperdirect pathway. The connection probability of the left NSP was significantly lower than that of the right side as were the subject’s motor symptoms. The closer the distance between the NSP and the stimulation location, the better the DBS outcome. These findings indicate that imaging white matter tracts with DBS on is safe and useful in mapping DBS outcomes.

Evidence That Methylphenidate Treatment Evokes Anxiety-Like Behavior Through Glucose Hypometabolism and Disruption of the Orbitofrontal Cortex Metabolic Networks

Methylphenidate (MPH) has been widely misused by children and adolescents who do not meet all diagnostic criteria for attention-deficit/hyperactivity disorder without a consensus about the consequences. Here, we evaluate the effect of MPH treatment on glucose metabolism and metabolic network in the rat brain, as well as on performance in behavioral tests. Wistar male rats received intraperitoneal injections of MPH (2.0 mg/kg) or an equivalent volume of 0.9% saline solution (controls), once a day, from the 15th to the 44th postnatal day. Fluorodeoxyglucose-18 was used to investigate cerebral metabolism, and a cross-correlation matrix was used to examine the brain metabolic network in MPH-treated rats using micro-positron emission tomography imaging. Performance in the light-dark transition box, eating-related depression, and sucrose preference tests was also evaluated. While MPH provoked glucose hypermetabolism in the auditory, parietal, retrosplenial, somatosensory, and visual cortices, hypometabolism was identified in the left orbitofrontal cortex. MPH-treated rats show a brain metabolic network more efficient and connected, but careful analyses reveal that the MPH interrupts the communication of the orbitofrontal cortex with other brain areas. Anxiety-like behavior was also observed in MPH-treated rats. This study shows that glucose metabolism evaluated by micro-positron emission tomography in the brain can be affected by MPH in different ways according to the region of the brain studied. It may be related, at least in part, to a rewiring in the brain the metabolic network and behavioral changes observed, representing an important step in exploring the mechanisms and consequences of MPH treatment.

The cross-hemispheric nigrostriatal pathway prevents the expression of levodopa-induced dyskinesias

Parkinson's disease (PD) is a neurodegenerative movement disorder that is routinely treated with levodopa. Unfortunately, long-term dopamine replacement therapy using levodopa leads to levodopa-induced dyskinesias (LID), a significant and disabling side-effect. Clinical findings indicate that LID typically only occurs following the progression of PD motor symptoms from the unilateral (Hoehn and Yahr (HY) Stage I) to the bilateral stage (HY Stage II). This suggests the presence of some compensatory interhemispheric mechanisms that delay the occurrence of LID. We therefore investigated the role of interhemispheric connections of the nigrostriatal pathway on LID expression in a rat model of PD. The striatum of one hemisphere of rats was first injected with a retrograde tracer to label the ipsi- and cross-hemispheric nigrostriatal pathways. Rats were then split into groups and unilaterally lesioned in the striatum or medial forebrain bundle of the tracer-injected hemisphere to induce varying levels of hemiparkinsonism. Finally, rats were treated with levodopa and tested for the expression of LID. Distinct subsets emerged from rats that underwent the same lesioning paradigm based on LID. Strikingly, non-dyskinetic rats had significant sparing of their cross-hemispheric nigrostriatal pathway projecting from the unlesioned hemisphere. In contrast, dyskinetic rats only had a small proportion of this cross-hemispheric nigrostriatal pathway survive lesioning. Crucially, both non-dyskinetic and dyskinetic rats had nearly identical levels of ipsi-hemispheric nigrostriatal pathway survival and parkinsonian motor deficits. Our data suggest that the survival of the cross-hemispheric nigrostriatal pathway plays a crucial role in preventing the expression of LID and represents a potentially novel target to halt the progression of this devastating side-effect of a common anti-PD therapeutic.

Gender may be related to the side of the motor syndrome and cognition in idiopathic Parkinson's disease

BACKGROUND

and Sex and cognitive profile may be related to the laterality of motor symptoms in idiopathic Parkinson's disease.

INTRODUCTION

Parkinson's disease (PD) is well recognised as an inherently asymmetric disease with unilateral onset of motor symptoms. The laterality of motor symptoms may be linked to sex, clinical and demographic variables, and neuropsychological disorders. However, the available data are inconsistent. This study aimed to explore the potential association between the laterality of motor symptoms and clinical and demographic variables and deficits in specific cognitive domains.

MATERIAL AND METHODS

We retrospectively recruited 97 participants with idiopathic PD without dementia; 60 presented motor symptoms on the left side and 37 on the right side. Both groups were comparable in terms of age, age at disease onset, disease duration, and severity of the neurological deficits according to the Unified Parkinson's Disease Rating Scale and the Hoehn and Yahr scale.

RESULTS

Participants with left-side motor symptoms scored lower on the Schwab and England Activities of Daily Living scale. Our sample included more men than women (67% vs. 33%). Both sexes were not equally represented in the 2 groups: there were significantly more men than women in the group of patients with left-side motor symptoms (77% vs. 23%), whereas the percentages of men and women in the group of patients with right-side motor symptoms were similar (51% vs. 49%). Both groups performed similarly in all neuropsychological tasks, but women, independently of laterality, performed better than men in the naming task.

CONCLUSION

We found a clear prevalence of men in the group of patients with left-side motor symptoms; this group also scored lower on the Schwab and England Scale. Female sex was predictive of better performance in the naming task. Sex should always be considered in disorders that cause asymmetric involvement of the brain, such as PD.

Substantia nigra micro-haemorrhage causing ipsilateral unilateral Parkinsonism and abnormal dopamine transporter scan uptake

Parkinsonism is a commonly seen movement disorder syndrome with neurodegenerative and non-neurodegenerative causes. Presynaptic dopamine transporter (DaT) single-photon emission computed tomography (SPECT) imaging is the most commonly used imaging technique in clinical practice to differentiate degenerative Parkinson's disease (PD) and PD plus syndromes from other causes such as essential tremor and drug-induced parkinsonism. This can help identify the patients who would benefit from medical therapy due to underlying pre-synaptic dopaminergic deficits. We report a case of unilateral parkinsonism caused by ipsilateral substantia nigra micro-haemorrhage resulting in disruption of the nigrostriatal pathway. This is an unusual case of a 55-year-old male patient who presented with unilateral Parkinsonism a decade after significant head trauma where MRI plays a critical and complementary role in diagnosing complete interruption of the nigrostriatal pathway due to cerebral micro-haemorrhage. The case also beautifully demonstrates the anatomy of the nigrostriatal pathway where a small lesion in the substantia nigra caused complete loss of radioligand uptake in the ipsilateral corpus striatum. Physicians should be aware of the importance of structural imaging in atypical movement disorder cases and, in particular, the routine use of susceptibility-weighted sequences (SWI).

Gait Progression Over 6 Years in Parkinson's Disease: Effects of Age, Medication, and Pathology

Background: Gait disturbance is an early, cardinal feature of Parkinson's disease (PD) associated with falls and reduced physical activity. Progression of gait impairment in Parkinson's disease is not well characterized and a better understanding is imperative to mitigate impairment. Subtle gait impairments progress in early disease despite optimal dopaminergic medication. Evaluating gait disturbances over longer periods, accounting for typical aging and dopaminergic medication changes, will enable a better understanding of gait changes and inform targeted therapies for early disease. This study aimed to describe gait progression over the first 6 years of PD by delineating changes associated with aging, medication, and pathology. Methods: One-hundred and nine newly diagnosed PD participants and 130 controls completed at least two gait assessments. Gait was assessed at 18-month intervals for up to 6 years using an instrumented walkway to measure sixteen spatiotemporal gait characteristics. Linear mixed-effects models assessed progression. Results: Ten gait characteristics significantly progressed in PD, with changes in four of these characteristics attributable to disease progression. Age-related changes also contributed to gait progression; changes in another two characteristics reflected both aging and disease progression. Gait impairment progressed irrespective of dopaminergic medication change for all characteristics except step width variability. Conclusions: Discrete gait impairments continue to progress in PD over 6 years, reflecting a combination of, and potential interaction between, disease-specific progression and age-related change. Gait changes were mostly unrelated to dopaminergic medication adjustments, highlighting limitations of current dopaminergic therapy and the need to improve interventions targeting gait decline.

Asymmetrical nigral iron accumulation in Parkinson's disease with motor asymmetry: an explorative, longitudinal and test-retest study

Parkinson's disease (PD) is commonly characterized by asymmetrical motor impairment. This study aimed to clarify the iron distributions in PD patients with significant motor asymmetry and their longitudinal alterations. This study included 123 PD patients and 121 normal controls. Thirty-eight PD patients were revisited. PD patients with significant motor asymmetry were identified by using an objective criterion. Inter-group, inter-hemisphere and inter-visit differences of regional tissue susceptibility were analyzed. Iron accumulation in dominantly and non-dominantly affected substantia nigra (SN) were observed in PD patients with motor asymmetry compared with normal controls (p < 0.005, Bonferroni corrected). Iron accumulation in the dominantly affected SN was significantly higher than that in the non-dominantly affected SN (p < 0.01, Bonferroni corrected). After follow-up, time effect on the iron content in SN was observed, directing to decrease in PD patients with motor asymmetry without hemispherical difference (p < 0.05). In conclusion, asymmetrical iron accumulation in SN was associated with the motor asymmetry in PD at baseline, while along the disease evolution iron content in SN became longitudinally decreased. All these findings provide new evidence for PD pathogenesis that the abnormal iron metabolism in SN is complicated and not always unidirectional.

Diffusion Tensor Imaging in Parkinson's Disease and Parkinsonian Syndrome: A Systematic Review

Diffusion tensor imaging (DTI) allows measuring fractional anisotropy and similar microstructural indices of the brain white matter. Lower than normal fractional anisotropy as well as higher than normal diffusivity is associated with loss of microstructural integrity and neurodegeneration. Previous DTI studies in Parkinson's disease (PD) have demonstrated abnormal fractional anisotropy in multiple white matter regions, particularly in the dopaminergic nuclei and dopaminergic pathways. However, DTI is not considered a diagnostic marker for the earliest Parkinson's disease since anisotropic alterations present a temporally divergent pattern during the earliest Parkinson's course. This article reviews a majority of clinically employed DTI studies in PD, and it aims to prove the utilities of DTI as a marker of diagnosing PD, correlating clinical symptomatology, tracking disease progression, and treatment effects. To address the challenge of DTI being a diagnostic marker for early PD, this article also provides a comparison of the results from a longitudinal, early stage, multicenter clinical cohort of Parkinson's research with previous publications. This review provides evidences of DTI as a promising marker for monitoring PD progression and classifying atypical PD types, and it also interprets the possible pathophysiologic processes under the complex pattern of fractional anisotropic changes in the first few years of PD. Recent technical advantages, limitations, and further research strategies of clinical DTI in PD are additionally discussed.

Assessing White Matter Pathology in Early-Stage Parkinson Disease Using Diffusion MRI: A Systematic Review

Structural brain white matter (WM) changes such as axonal caliber, density, myelination, and orientation, along with WM-dependent structural connectivity, may be impacted early in Parkinson disease (PD). Diffusion magnetic resonance imaging (dMRI) has been used extensively to understand such pathological WM changes, and the focus of this systematic review is to understand both the methods utilized and their corresponding results in the context of early-stage PD. Diffusion tensor imaging (DTI) is the most commonly utilized method to probe WM pathological changes. Previous studies have suggested that DTI metrics are sensitive in capturing early disease-associated WM changes in preclinical symptomatic regions such as olfactory regions and the substantia nigra, which is considered to be a hallmark of PD pathology and progression. Postprocessing analytic approaches include region of interest-based analysis, voxel-based analysis, skeletonized approaches, and connectome analysis, each with unique advantages and challenges. While DTI has been used extensively to study WM disorganization in early-stage PD, it has several limitations, including an inability to resolve multiple fiber orientations within each voxel and sensitivity to partial volume effects. Given the subtle changes associated with early-stage PD, these limitations result in inaccuracies that severely impact the reliability of DTI-based metrics as potential biomarkers. To overcome these limitations, advanced dMRI acquisition and analysis methods have been employed, including diffusion kurtosis imaging and q-space diffeomorphic reconstruction. The combination of improved acquisition and analysis in DTI may yield novel and accurate information related to WM-associated changes in early-stage PD. In the current article, we present a systematic and critical review of dMRI studies in early-stage PD, with a focus on recent advances in DTI methodology. Yielding novel metrics, these advanced methods have been shown to detect diffuse WM changes in early-stage PD. These findings support the notion of early axonal damage in PD and suggest that WM pathology may go unrecognized until symptoms appear. Finally, the advantages and disadvantages of different dMRI techniques, analysis methods, and software employed are discussed in the context of PD-related pathology.

Hemispheric asymmetry in the human brain and in Parkinson's disease is linked to divergent epigenetic patterns in neurons

BACKGROUND

Hemispheric asymmetry in neuronal processes is a fundamental feature of the human brain and drives symptom lateralization in Parkinson's disease (PD), but its molecular determinants are unknown. Here, we identify divergent epigenetic patterns involved in hemispheric asymmetry by profiling DNA methylation in isolated prefrontal cortex neurons from control and PD brain hemispheres. DNA methylation is fine-mapped at enhancers and promoters, genome-wide, by targeted bisulfite sequencing in two independent sample cohorts.

RESULTS

We find that neurons of the human prefrontal cortex exhibit hemispheric differences in DNA methylation. Hemispheric asymmetry in neuronal DNA methylation patterns is largely mediated by differential CpH methylation, and chromatin conformation analysis finds that it targets thousands of genes. With aging, there is a loss of hemispheric asymmetry in neuronal epigenomes, such that hemispheres epigenetically converge in late life. In neurons of PD patients, hemispheric asymmetry in DNA methylation is greater than in controls and involves many PD risk genes. Epigenetic, transcriptomic, and proteomic differences between PD hemispheres correspond to the lateralization of PD symptoms, with abnormalities being most prevalent in the hemisphere matched to side of symptom predominance. Hemispheric asymmetry and symptom lateralization in PD is linked to genes affecting neurodevelopment, immune activation, and synaptic transmission. PD patients with a long disease course have greater hemispheric asymmetry in neuronal epigenomes than those with a short disease course.

CONCLUSIONS

Hemispheric differences in DNA methylation patterns are prevalent in neurons and may affect the progression and symptoms of PD.

Unilateral accumbal dopamine depletion affects decision-making in a side-specific manner

Mechanisms underlying affective and cognitive deficits in Parkinson's disease (PD) remain less studied than motor symptoms. Nucleus accumbens (NAc) is affected in PD and due to its well-known involvement in motivation is an interesting target in this context. Furthermore, PD is frequently asymmetrical, with side-specific deficits aligning with evidences of accumbal laterality. We therefore used a 6-hydroxydopamine (6-OHDA) model to study the role of left and right NAc dopamine depletion in a battery of behavioral tasks. 2 months old male rats were used in all experiments. Habitual-based and goal-directed decision-making, impulsivity, anxiety- and depressive-like behavior and motor performance were tested 3 weeks after left (6-OHDA L) or right (6-OHDA R) NAc lesion was induced. Upon contingency degradation, 6-OHDA R decrease their lever press rate less than Sham and 6-OHDA L, indicating an impairment in the shift from habit-based to goal-directed strategies. On the other hand, 6-OHDA L lesions lead to increased rates of premature responding when delays where increased in the variable delay-to-signal test. Importantly, in both paradigms task acquisition was similar between groups. In the same line we found no differences in the amount of sugared pellets eaten when freely available as well as in both general and fine motor behaviors. In conclusion, left and right NAc play distinct roles in the contingency degradation and impulsivity. More studies are needed to understand the mechanisms behind this functional lateralization and its implications for PD patients.

Predicting severity and prognosis in Parkinson's disease from brain microstructure and connectivity

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White matter disruption occurs in Parkinson's disease across several brain regions.

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DTI properties could identify clinically distinct subtypes of Parkinson's disease.

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Structural neural disruption can predict clinical outcomes in Parkinson's disease.

Objectives: Investigating biomarkers to demonstrate progression of Parkinson's disease (PD) is of high priority. We investigated the association of brain structural properties with progression of clinical outcomes and their ability to differentiate clinical subtypes of PD.

Methods: A comprehensive set of clinical features was evaluated at baseline and 4.5-year follow-up for 144 de-novo PD patients from the Parkinson's Progression Markers Initiative. We created a global composite outcome (GCO) by combining z-scores of non-motor and motor symptoms, motor signs, overall activities of daily living and global cognition, as a single numeric indicator of prognosis. We classified patients into three subtypes based on multi-domain clinical criteria: ‘mild motor-predominant’, ‘intermediate’ and ‘diffuse-malignant’. We analyzed diffusion-weighted scans at the early drug-naïve stage and extracted fractional anisotropy and mean diffusivity (MD) of basal ganglia and cortical sub-regions. Then, we employed graph theory to calculate network properties and used network-based statistic to investigate our primary hypothesis.

Results: Baseline MD of globus pallidus was associated with worsening of motor severity, cognition, and GCO after 4.5 years of follow-up. Connectivity disruption at baseline was correlated with decline in cognition, and increase in GCO. Baseline MD of nucleus accumbens, globus pallidus and basal-ganglia were linked to clinical subtypes at 4.5-year of follow-up. Disruption in sub-cortical networks associated with being subtyped as ‘diffuse-malignant’ versus ‘mild motor-predominant’ after 4.5 years.

Conclusions: Diffusion imaging analysis at the early de-novo stage of PD was able to differentiate clinical sub-types of PD after 4.5 years and was highly associated with future clinical outcomes of PD.

Impaired Fine Motor Function of the Asymptomatic Hand in Unilateral Parkinson's Disease

The early detection of Parkinson's disease (PD) still remains a challenge to date. Although studies have previously reported subtle motor function abnormalities in early PD patients, it is unclear whether such clinical signs can be better detected while patients are concurrently performing a cognitive task, and whether they can be useful in predicting patients' clinical conversion state. Seventy-two right-handed participants (40 drug-naive patients with idiopathic unilateral PD and 32 age-matched healthy controls) were enrolled in this study. All participants were asked to perform the Purdue Pegboard test (PPT) either alone (single-task condition) or during a concurrent mental subtraction-by-3 task (dual-task condition). A 4-year telephone follow-up was later conducted to determine whether PD patients converted to bilateral signs. We found that PD patients showed a significant reduction in dexterity on the PPT compared to the controls in both single- and dual-task conditions. Yet patients' performance in the dual-task condition revealed a greater interference effect when patients performed the task with their right hand than with their left hand. PPT also revealed reasonable discriminative ability for prediagnosing PD. However, dual-tasking did not have added value in differentiating early patients and controls. At follow-up, the baseline PPT performance of the asymptomatic hands was positively correlated with time to convert from unilaterally to bilaterally affected states (r = 0.62, P = 0.031). Together, these findings suggest that PPT can serve as a useful auxiliary tool in evaluating early PD, and shed light on the neuroplasticity mechanism of fine motor deficit at this very early stage.

Manganese promotes the aggregation and prion-like cell-to-cell exosomal transmission of α-synuclein

The aggregation of α-synuclein (αSyn) is considered a key pathophysiological feature of certain neurodegenerative disorders, collectively termed synucleinopathies. Given that a prion-like, cell-to-cell transfer of misfolded αSyn has been recognized in the spreading of αSyn pathology in synucleinopathies, we investigated the biological mechanisms underlying the propagation of the disease with respect to environmental neurotoxic stress. Considering the potential role of the divalent metal manganese (Mn2+) in protein aggregation, we characterized its effect on αSyn misfolding and transmission in experimental models of Parkinson's disease. In cultured dopaminergic neuronal cells stably expressing wild-type human αSyn, misfolded αSyn was secreted through exosomes into the extracellular medium upon Mn2+ exposure. These exosomes were endocytosed through caveolae into primary microglial cells, thereby mounting neuroinflammatory responses. Furthermore, Mn2+-elicited exosomes exerted a neurotoxic effect in a human dopaminergic neuronal model (LUHMES cells). Moreover, bimolecular fluorescence complementation (BiFC) analysis revealed that Mn2+ accelerated the cell-to-cell transmission of αSyn, resulting in dopaminergic neurotoxicity in a mouse model of Mn2+ exposure. Welders exposed to Mn2+ had increased misfolded αSyn content in their serum exosomes. Stereotaxically delivering αSyn-containing exosomes, isolated from Mn2+-treated αSyn-expressing cells, into the striatum initiated Parkinsonian-like pathological features in mice. Together, these results indicate that Mn2+ exposure promotes αSyn secretion in exosomal vesicles, which subsequently evokes proinflammatory and neurodegenerative responses in both cell culture and animal models.

Identifying mild-moderate Parkinson's disease using whole-brain functional connectivity

OBJECTIVE

Our study aims to extract significant disorder-associated patterns from whole brain functional connectivity to distinguish mild-moderate Parkinson's disease (PD) patients from controls.

METHODS

Resting-state fMRI data were measured from thirty-six PD individuals and thirty-five healthy controls. Multivariate pattern analysis was applied to investigate whole-brain functional connectivity patterns in individuals with 'mild-moderate' PD. Additionally, the relationship between the asymmetry of functional connectivity and the side of the initial symptoms was also analyzed.

RESULTS

In a leave-one-out cross-validation, we got the generalization rate of 80.28% for distinguishing PD patients from controls. The most discriminative functional connectivity was found in cortical networks that included the default mode, sensorimotor and attention networks. Compared to patients with the left side initially affected, an increased abnormal functional connectivity was found in patients in whom the right side was initially affected.

CONCLUSIONS

Our results indicated that discriminative functional connectivity is likely associated with disturbances of cortical networks involved in sensorimotor control and attention. The spatiotemporal patterns of motor asymmetry may be related to the lateralized dysfunction on the early stages of PD.

SIGNIFICANCE

This study identifies discriminative functional connectivity that is associated with disturbances of cortical networks. Our results demonstrated new evidence regarding the functional brain changes related to the unilateral motor symptoms of early PD.

Lateralisation in Parkinson disease

Asymmetry of dopaminergic neurodegeneration and subsequent lateralisation of motor symptoms are distinctive features of Parkinson's disease compared to other forms of neurodegenerative or symptomatic parkinsonism. Even 200 years after the first description of the disease, the underlying causes for this striking clinicopathological feature are not yet fully understood. There is increasing evidence that lateralisation of disease is due to a complex interplay of hereditary and environmental factors that are reflected not only in the concept of dominant hemispheres and handedness but also in specific susceptibilities of neuronal subpopulations within the substantia nigra. As a consequence, not only the obvious lateralisation of motor symptoms occurs but also patterns of associated non-motor signs are defined, which include cognitive functions, sleep behaviour or olfaction. Better understanding of the mechanisms contributing to lateralisation of neurodegeneration and the resulting patterns of clinical phenotypes based on bilateral post-mortem brain analyses and clinical studies focusing on right/left hemispheric symptom origin will help to develop more targeted therapeutic approaches, taking into account subtypes of PD as a heterogeneous disorder.

Evidence for cross-hemispheric preconditioning in experimental Parkinson's disease

Dopamine loss and motor deficits in Parkinson's disease typically commence unilaterally and remain asymmetric for many years, raising the possibility that endogenous defenses slow the cross-hemispheric transmission of pathology. It is well-established that the biological response to subtoxic stress prepares cells to survive subsequent toxic challenges, a phenomenon known as preconditioning, tolerance, or stress adaptation. Here we demonstrate that unilateral striatal infusions of the oxidative toxicant 6-hydroxydopamine (6-OHDA) precondition the contralateral nigrostriatal pathway against the toxicity of a second 6-OHDA infusion in the opposite hemisphere. 6-OHDA-induced loss of dopaminergic terminals in the contralateral striatum was ablated by cross-hemispheric preconditioning, as shown by two independent markers of the dopaminergic phenotype, each measured by two blinded observers. Similarly, loss of dopaminergic somata in the contralateral substantia nigra was also abolished, according to two blinded measurements. Motor asymmetries in floor landings, forelimb contacts with a wall, and spontaneous turning behavior were consistent with these histological observations. Unilateral 6-OHDA infusions increased phosphorylation of the kinase ERK2 and expression of the antioxidant enzyme CuZn superoxide dismutase in both striata, consistent with our previous mechanistic work showing that these two proteins mediate preconditioning in dopaminergic cells. These findings support the existence of cross-hemispheric preconditioning in Parkinson's disease and suggest that dopaminergic neurons mount impressive natural defenses, despite their reputation as being vulnerable to oxidative injury. If these results generalize to humans, Parkinson's pathology may progress slowly and asymmetrically because exposure to a disease-precipitating insult induces bilateral upregulation of endogenous defenses and elicits cross-hemispheric preconditioning.

Deviation of Spatial Representation and Asymmetric Saccadic Reaction Time in Hemi-Parkinson's Disease

Background: Patients with Parkinson's disease (PD) commonly show spatially asymmetric behaviors, such as veering while attempting to walk in a straight line. While there is general agreement that the lateral motor dysfunction contributes to asymmetric behaviors in PD, it is dispute regarding whether the spatial perception is also biased. In addition, it is not clear whether PD impairs the speed of spatial information process, i.e., the efficiency of information process. Objectives: To assess the visuospatial representation and efficiency of spatial information processing in hemi-PD. Methods: Two saccadic tasks were employed: non-spatial cue evoked saccade and spatial cue evoked saccade. In the former task, an identical visual stimulus (appeared on the body mid-sagittal plane) was artificially associated with a fixed saccadic target (left or right) in a given session. In the latter task, subjects were instructed to make a rightward or leftward saccade based on the perceived location of a visual cue (left vs. right side of the body mid-sagittal plane). We estimated the location of subjective straight ahead (SSA) for each subject by using a psychometric fitting function to fit the location judgment results, enabling evaluation of the symmetry of representation between the left and right hemifields. In addition, since the locations of saccadic targets were same in these two tasks, thus, for each individual subject, the elongated saccadic reaction time (SRT) in the latter task, comparing with the former one, mainly reflects the time spent on judgment of the spatial location of visual cue, i.e., spatial perception. We also assessed the efficiency of spatial perception between two hemispheres, through comparing the normalized SRT (i.e., SRT difference between two tasks) between trials with leftward and rightward judgments. Results: Compared with healthy control subjects (HCs), the SSA was shifted to the contralesional side in both left onset PD (LPD, lesion of right substantia nigra) and right onset PD (RPD, lesion of left substantia nigra) patients. The process of spatial information was significantly longer when a spatial cue appeared in the contralesional hemifield. Conclusions: Patients with hemi-PD showed biased visuospatial representation between left and right hemifields and decreased the efficiency of spatial information processing in the contralesional side. Such results indicate that the hemi-PD impairs both spatial representation and the efficiency of spatial information process, which might contribute to asymmetric behaviors.

Asymmetric neuromodulation of motor circuits in Parkinson's disease: The role of subthalamic deep brain stimulation

Whereas hemispheric dominance is well-established for appendicular motor control in humans, the evidence for dominance in axial motor control is still scarce. In Parkinson's disease (PD), unilateral (UL) onset of appendicular motor symptoms corresponds with asymmetric neurodegeneration predominantly affecting contralateral nigrostriatal circuits. Disease progression yields bilateral and axial motor symptoms but the initial appendicular asymmetry usually persists. Furthermore, there is evidence for hemispheric dominance for axial motor dysfunction in some of these patients. Dopaminergic medications improve appendicular symptoms but can also produce motor complications over time. Once these complications develop, bilateral (BL) deep brain stimulation (DBS) of the subthalamic nuclei (STN) can significantly improve appendicular symptoms while reducing medication doses and motor complications. Conversely, axial motor symptoms remain a significant source of disability, morbidity, and mortality for patients with PD. These axial symptoms do not necessarily improve with dopaminergic therapy, might not respond, and could even worsen after BL-DBS. In contrast to medications, DBS provides the opportunity to modify stimulation parameters for each cerebral hemisphere. Identical, BL-DBS of motor circuits with hemispheric dominance in PD might produce overstimulation on one side and/or understimulation on the other side, which could contribute to motor dysfunction. Several studies based on asymmetry of appendicular motor symptoms already support an initial UL rather than BL approach to DBS in some patients. The response of axial motor symptoms to UL versus BL-DBS remains unclear. Nonetheless, UL-DBS, staged BL-DBS, or asymmetric programming of BL-DBS could also be considered in patients with PD.

The End Is the Beginning: Parkinson's Disease in the Light of Brain Imaging

Parkinson's disease (PD), the most common neurodegenerative disorder, is characterized by abnormal accumulation of α-synuclein aggregates known as Lewy bodies (LB) and loss of nigrostriatal dopaminergic neurons. Recent neuroimaging studies suggest that in the early phases of PD, synaptic and axonal damage anticipate the onset of a frank neuronal death. Paralleling, even post mortem studies on the brain of affected patients and on animal models support that synapses might represent the primary sites of functional and pathological changes. Indeed, α-synuclein microaggregation and spreading at terminals, by dysregulating the synaptic junction, would block neurotransmitter release, thus triggering a retrograde neurodegenerative process ending with neuronal cell loss by proceeding through the axons. Rather than neurodegeneration, loss of dopaminergic neuronal endings and axons could thus underlie the onset of connectome dysfunction and symptoms in PD and parkinsonisms. However, the manifold biases deriving from the interpretation of human brain imaging data hinder the validation of this hypothesis. Here, we present pivotal evidence supporting that novel comparative brain imaging studies, in patients and experimental models of PD in preliminary stages of disease, could be instrumental for proving whether synaptic endings are the sites where degeneration begins and initiating the factual achievement of disease modifying approaches. The need for such investigations is timely to define an early therapeutic window of intervention to attempt disease halting by terminal and/or axonal healing.

Lateralized microstructural changes in early-stage Parkinson's disease in anterior olfactory structures, but not in substantia nigra

Parkinson's disease (PD) is a progressive neurological disorder characterized by motor symptoms as well as severe deficits in olfactory function and microstructural changes in olfactory brain regions. Because of the evidence of asymmetric neuropathological features in early-stage PD, we examined whether lateralized microstructural changes occur in olfactory brain regions and the substantia nigra in a group of early-stage PD patients. Using diffusion tensor imaging (DTI) and the University of Pennsylvania Smell Identification Test (UPSIT), we assessed 24 early-stage PD patients (Hoehn and Yahr stage 1 or 2) and 26 healthy controls (HC). We used DTI and a region of interest (ROI) approach to study the microstructure of the left and right anterior olfactory structures (AOS; comprising the olfactory bulbs and anterior end of the olfactory tracts) and the substantia nigra (SN). PD patients had reduced UPSIT scores relative to HC and showed increased mean diffusivity (MD) in the SN, with no lateralized differences. Significant group differences in fractional anisotropy (FA) and MD were seen in the AOS, but these differences were restricted to the right side and were not associated with the primary side of motor symptoms amongst PD patients. No associations were observed between lateralized motor impairment and lateralized microstructural changes in AOS. Impaired olfaction and microstructural changes in AOS are useful for early identification of PD but asymmetries in AOS microstructure seem unrelated to the laterality of PD motor symptoms.

The cortical signature of symptom laterality in Parkinson's disease

Patients with Parkinson's disease (PD) often present with unilateral motor symptoms that eventually spread to the other side. This symptom lateralization is diagnostically important, as it serves to distinguish PD from other motor disorders with overlapping symptom profiles. Further, recent studies have shown that the side of symptom onset is important for prognosis, as there are differences in the rate of disease progression and the incidence of secondary symptoms between right- and left-dominant (RD, LD) patients. Physiologically, previous studies have shown asymmetrical decline in structure and metabolism throughout the basal ganglia, although connecting this directly to motor function has been difficult. To identify the neurophysiological basis of symptom laterality in PD, we recorded magnetoencephalography (MEG) during left- and right-hand movement paradigms in patients with PD who exhibited either RD or LD symptomatology. The beta oscillations serving these movements were then imaged using beamforming methods, and we extracted the time series of the peak voxel in the left and right primary motor cortices for each movement. In addition, each patient's symptom asymmetry was quantitated using the Unified Parkinson's Disease Rating Scale (UPDRS), which allowed the relationship between symptom asymmetry and neural asymmetry to be assessed. We found that LD patients had stronger beta suppression during movement, as well as greater post-movement beta rebound compared to patients with RD symptoms, independent of the hand that was moved. Interestingly, the asymmetry of beta activity during right-hand movement uniquely correlated with symptom asymmetry, such that the more LD the symptom profile, the more left-lateralized (i.e., contralateral to movement) the beta response; conversely, the more RD the symptom profile, the more right-lateralized (i.e., ipsilateral to movement) the beta response. This study is the first to directly probe the relationship between symptom asymmetry and the laterality of neural activity during movement in patients with PD, and suggests that LD patients have a fundamentally different and more “healthy” oscillatory pattern relative to RD patients.

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Right-dominant expression of Parkinson's has been connected to faster progression.

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Linkage between symptom asymmetry and cortical physiology remains unknown.

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Cortical motor activity was measured in patients with left/right-dominant symptoms.

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Patients with left-dominant symptoms had “healthier” pattern of motor responses.

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Laterality of cortical activity during movement was related to symptom laterality.

Review: Parkinson's disease: from synaptic loss to connectome dysfunction

Parkinson's disease (PD) is a common neurodegenerative disorder with prominent loss of nigro-striatal dopaminergic neurons. The resultant dopamine (DA) deficiency underlies the onset of typical motor symptoms (MS). Nonetheless, individuals affected by PD usually show a plethora of nonmotor symptoms (NMS), part of which may precede the onset of motor signs. Besides DA neuron degeneration, a key neuropathological alteration in the PD brain is Lewy pathology. This is characterized by abnormal intraneuronal (Lewy bodies) and intraneuritic (Lewy neurites) deposits of fibrillary aggregates mainly composed of α-synuclein. Lewy pathology has been hypothesized to progress in a stereotypical pattern over the course of PD and α-synuclein mutations and multiplications have been found to cause monogenic forms of the disease, thus raising the question as to whether this protein is pathogenic in this disorder. Findings showing that the majority of α-synuclein aggregates in PD are located at presynapses and this underlies the onset of synaptic and axonal degeneration, coupled to the fact that functional connectivity changes correlate with disease progression, strengthen this idea. Indeed, by altering the proper action of key molecules involved in the control of neurotransmitter release and re-cycling as well as synaptic and structural plasticity, α-synuclein deposition may crucially impair axonal trafficking, resulting in a series of noxious events, whose pressure may inevitably degenerate into neuronal damage and death. Here, we provide a timely overview of the molecular features of synaptic loss in PD and disclose their possible translation into clinical symptoms through functional disconnection.

Cortical asymmetry in Parkinson's disease: early susceptibility of the left hemisphere

BACKGROUND AND PURPOSE

Clinically, Parkinson's disease (PD) presents with asymmetric motor symptoms. The left nigrostriatal system appears more susceptible to early degeneration than the right, and a left-lateralized pattern of early neuropathological changes is also described in several neurodegenerative conditions, including Alzheimer's disease, frontotemporal dementia, and Huntington's disease. In this study, we evaluated hemispheric differences in estimated rates of atrophy in a large, well-characterized cohort of PD patients.

METHODS

Our cohort included 205 PD patients who underwent clinical assessments and T1-weighted brain MRI's. Patients were classified into Early (n = 109) and Late stage (n = 96) based on disease duration, defined as greater than or less than 10 years of motor symptoms. Cortical thickness was determined using FreeSurfer, and a bootstrapped linear regression model was used to estimate differences in rates of atrophy between Early and Late patients.

RESULTS

Our results show that patients classified as Early stage exhibit a greater estimated rate of cortical atrophy in left frontal regions, especially the left insula and olfactory sulcus. This pattern was replicated in left-handed patients, and was not influenced by the degree of motor symptom asymmetry (i.e., left-sided predominant motor symptoms). Patients classified as Late stage exhibited greater atrophy in the bilateral occipital, and right hemisphere-predominant cortical areas.

CONCLUSIONS

We show that cortical degeneration in PD differs between cerebral hemispheres, and findings suggest a pattern of early left, and late right hemisphere with posterior cortical atrophy. Further investigation is warranted to elucidate the underlying mechanisms of this asymmetry and pathologic implications.

Combined Diffusion Tensor Imaging and Arterial Spin Labeling as Markers of Early Parkinson's disease

This study aimed to identify a PD-specific MRI pattern using combined diffusion tensor imaging (DTI) and arterial spin labeling (ASL) to discriminate patients with early PD from healthy subjects and evaluate disease status. Twenty-one early and 22 mid-late PD patients, and 22 healthy, age/gender-matched controls underwent 3-T MRI with apparent diffusion coefficient (ADC), fractional anisotropy (FA), fiber number (FN) and cerebral blood flow (CBF) measurements. We found that compared with healthy subjects, there was a profound reduction in FN passing through the SN in PD. FA in the SN and CBF in the caudate nucleus were inversely correlated with motor dysfunction. A negative correlation was observed between FA in the hippocampus (Hip) and the NMSS-Mood score, whereas CBF in the Hip and the prefrontal cortex(PFC) correlated with declined cognition. Stratified five-fold cross-validation identified FA in the SN(FA-SN_Av), CBF in the PFC(CBF-PFC_Av) and FA in the parietal white matter(FA-PWM_Av), and the combination of these measurements offered relatively high accuracy (AUC 0.975, 90% sensitivity and 100% specificity) in distinguishing those with early PD from healthy subjects. We demonstrate that the decreased FNs through SN in combination with changes in FA-SN_Av, CBF-PFC_Av and FA-PWM_Av values might serve as potential markers of early-stage PD.

Does Side of Onset Influence the Pattern of Cerebral Atrophy in Parkinson's Disease?

Background

Imaging studies have revealed widespread neurodegeneration in Parkinson’s disease (PD), but only a few considered the issue of asymmetrical clinical presentations.

Objective

To investigate if the side of onset influences the pattern of gray matter (GM) atrophy in PD.

Methods

Sixty patients (57.87 ± 10.27 years) diagnosed with idiopathic PD according to the U.K. Brain Bank criteria, 26 with right-sided disease onset (RDO) and 34 with left-sided disease onset (LDO), were compared to 80 healthy controls (HC) (57.1 ± 9.47 years). We acquired T1-weighted images on a 3 T scanner. Images were processed and analyzed with VBM8 (SPM8/Dartel) on Matlab R2012b platform. Statistic assessments included a two-sample test (family-wise error p < 0.05) with extent threshold of 20 voxels.

Results

Compared to HC, LDO patients had GM atrophy in the insula, putamen, anterior cingulate, frontotemporal cortex, and right caudate, while the RDO group showed atrophy at the anterior cingulate, insula, frontotemporal, and occipital cortex.

Conclusion

This study revealed widespread GM atrophy in PD, predominantly in the left hemisphere, regardless of the side of onset. Future investigations should also consider handedness and side of onset to better characterize cerebral involvement and its progression in PD.

Impaired interhemispheric synchrony in Parkinson's disease with depression

The alterations of interhemispheric resting-state functional connectivity (FC) in Parkinson’s disease (PD) with depression remain unclear, so we aimed to explore the differences of interhemispheric FC between PD with and without depression. Twenty-one depressed PD (DPD) patients, 49 non-depressed PD (NDPD) patients and 50 matched healthy controls (HC) participated in this study. Resting-state functional magnetic resonance imaging (fMRI) data were analyzed with the voxel-mirrored homotopic connectivity (VMHC) approach. The DPD patients showed lower VMHC values in the bilateral dorsolateral prefrontal cortex (DLPFC) and calcarine cortex compared to both NDPD and HC groups, and further receiver operating characteristic curves (ROC) analyses revealed that the VMHC in these two brain areas could be used as biomarkers to distinguish DPD from NDPD and from HC. The pooled PD patients (both DPD and NDPD) exhibited decreased VMHC in the bilateral putamen, middle occipital gyrus (MOG), postcentral gyrus (PoCG), paracentral lobule (PCL) and cerebellum posterior lobe when compared with HC. Decreased VMHC values within the DLPFC and calcarine cortex appeared to be unique features for DPD and might be used as potential neuroimaging markers to distinguish DPD patients from NDPD and HC groups. These findings may underlie the neural mechanisms of depression in PD.