Patterns of striatal dopamine depletion in early Parkinson disease

Baseline [18F]FP-CIT PET-based deep learning prediction of levodopa-induced dyskinesia in Parkinson's disease

We aimed to develop a convolutional neural network (CNN) model with multi-task learning to predict the onset of levodopa-induced dyskinesia (LID) in patients with Parkinson's disease (PD) using baseline [18F]FP-CIT PET images. In this retrospective, single-center study, 402 patients were classified based on whether they developed LID within 5 years after starting levodopa (within 5 years: n = 134; beyond 5 years or none: n = 268). The proposed CNN model achieved a mean AUROC ± SD of 0.666 ± 0.036. Model-derived probabilities were also incorporated into a Cox regression model, yielding a mean concordance index (C-index ± SD) of 0.643 ± 0.046, significantly outperforming the model based on specific/nonspecific binding ratios of striatal subregions (C-index = 0.392 ± 0.036) in four of five test configurations. These results suggest that model-extracted features from [18F]FP-CIT PET carry prognostic value for LID, although further performance improvements are needed for clinical application.

Salsolinol as an RNA m6A methylation inducer mediates dopaminergic neuronal death by regulating YAP1 and autophagy

JOURNAL/nrgr/04.03/01300535-202503000-00032/figure1/v/2024-06-17T092413Z/r/image-tiff Salsolinol (1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline, Sal) is a catechol isoquinoline that causes neurotoxicity and shares structural similarity with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, an environmental toxin that causes Parkinson's disease. However, the mechanism by which Sal mediates dopaminergic neuronal death remains unclear. In this study, we found that Sal significantly enhanced the global level of N6-methyladenosine (m6A) RNA methylation in PC12 cells, mainly by inducing the downregulation of the expression of m6A demethylases fat mass and obesity-associated protein (FTO) and alkB homolog 5 (ALKBH5). RNA sequencing analysis showed that Sal downregulated the Hippo signaling pathway. The m6A reader YTH domain-containing family protein 2 (YTHDF2) promoted the degradation of m6A-containing Yes-associated protein 1 (YAP1) mRNA, which is a downstream key effector in the Hippo signaling pathway. Additionally, downregulation of YAP1 promoted autophagy, indicating that the mutual regulation between YAP1 and autophagy can lead to neurotoxicity. These findings reveal the role of Sal on m6A RNA methylation and suggest that Sal may act as an RNA methylation inducer mediating dopaminergic neuronal death through YAP1 and autophagy. Our results provide greater insights into the neurotoxic effects of catechol isoquinolines compared with other studies and may be a reference for assessing the involvement of RNA methylation in the pathogenesis of Parkinson's disease.

Recent progress in the applications of presynaptic dopaminergic positron emission tomography imaging in parkinsonism

Nowadays, presynaptic dopaminergic positron emission tomography, which assesses deficiencies in dopamine synthesis, storage, and transport, is widely utilized for early diagnosis and differential diagnosis of parkinsonism. This review provides a comprehensive summary of the latest developments in the application of presynaptic dopaminergic positron emission tomography imaging in disorders that manifest parkinsonism. We conducted a thorough literature search using reputable databases such as PubMed and Web of Science. Selection criteria involved identifying peer-reviewed articles published within the last 5 years, with emphasis on their relevance to clinical applications. The findings from these studies highlight that presynaptic dopaminergic positron emission tomography has demonstrated potential not only in diagnosing and differentiating various Parkinsonian conditions but also in assessing disease severity and predicting prognosis. Moreover, when employed in conjunction with other imaging modalities and advanced analytical methods, presynaptic dopaminergic positron emission tomography has been validated as a reliable in vivo biomarker. This validation extends to screening and exploring potential neuropathological mechanisms associated with dopaminergic depletion. In summary, the insights gained from interpreting these studies are crucial for enhancing the effectiveness of preclinical investigations and clinical trials, ultimately advancing toward the goals of neuroregeneration in parkinsonian disorders.

PET, SPECT, and MRI imaging for evaluation of Parkinson's disease

This review assesses the primary neuroimaging techniques used to evaluate Parkinson's disease (PD) - a neurological condition characterized by gradual dopamine-producing nerve cell degeneration. The neuroimaging techniques explored include positron emission tomography (PET), single-photon emission computed tomography (SPECT), and magnetic resonance imaging (MRI). These modalities offer varying degrees of insights into PD pathophysiology, diagnostic accuracy, specificity by way of exclusion of other Parkinsonian syndromes, and monitoring of disease progression. Neuroimaging is thus crucial for diagnosing and managing PD, with integrated multimodal approaches and novel techniques further enhancing early detection and treatment evaluation.

Levodopa-induced dyskinesia: brain iron deposition as a new hypothesis

Parkinson's disease (PD) is a common neurodegenerative disease in the older adults. The main pathological change in PD is the degenerative death of dopamine (DA) neurons in the midbrain substantia nigra, which causes a significant decrease in the DA content of the striatum. However, the exact etiology of this pathological change remains unclear. Genetic factors, environmental factors, aging, and oxidative stress may be involved in the degenerative death of dopaminergic neurons in PD. Pharmacological treatment using levodopa (L-DOPA) remains the main treatment for PD. Most patients with PD consuming L-DOPA for a long time usually develop levodopa-induced dyskinesia (LID) after 6.5 years of use, and LID seriously affects the quality of life and increases the risk of disability. Recently, studies have revealed that cerebral iron deposition may be involved in LID development and that iron deposition has neurotoxic effects and accelerates disease onset. However, the relationship between cerebral iron deposition and LID remains unclear. Herein, we reviewed the mechanisms by which iron deposition may be associated with LID development, which are mainly related to oxidative stress, neuroinflammation, and mitochondrial and lysosomal dysfunction. Using iron as an important target, the search and development of safe and effective brain iron scavengers, and thus the alleviation and treatment of LID, has a very important scientific and clinical value, as well as a good application prospect.

Modeling early phenotypes of Parkinson's disease by age-induced midbrain-striatum assembloids

Parkinson's disease, an aging-associated neurodegenerative disorder, is characterised by nigrostriatal pathway dysfunction caused by the gradual loss of dopaminergic neurons in the substantia nigra pars compacta of the midbrain. Human in vitro models are enabling the study of the dopaminergic neurons' loss, but not the dysregulation within the dopaminergic network in the nigrostriatal pathway. Additionally, these models do not incorporate aging characteristics which potentially contribute to the development of Parkinson's disease. Here we present a nigrostriatal pathway model based on midbrain-striatum assembloids with inducible aging. We show that these assembloids can develop characteristics of the nigrostriatal connectivity, with catecholamine release from the midbrain to the striatum and synapse formation between midbrain and striatal neurons. Moreover, Progerin-overexpressing assembloids acquire aging traits that lead to early neurodegenerative phenotypes. This model shall help to reveal the contribution of aging as well as nigrostriatal connectivity to the onset and progression of Parkinson's disease.

A worldwide study of subcortical shape as a marker for clinical staging in Parkinson's disease

Alterations in subcortical brain regions are linked to motor and non-motor symptoms in Parkinson's disease (PD). However, associations between clinical expression and regional morphological abnormalities of the basal ganglia, thalamus, amygdala and hippocampus are not well established. We analyzed 3D T1-weighted brain MRI and clinical data from 2525 individuals with PD and 1326 controls from 22 global sources in the ENIGMA-PD consortium. We investigated disease effects using mass univariate and multivariate models on the medial thickness of 27,120 vertices of seven bilateral subcortical structures. Shape differences were observed across all Hoehn and Yahr (HY) stages, as well as correlations with motor and cognitive symptoms. Notably, we observed incrementally thinner putamen from HY1, caudate nucleus and amygdala from HY2, hippocampus, nucleus accumbens, and thalamus from HY3, and globus pallidus from HY4-5. Subregions of the thalami were thicker in HY1 and HY2. Largely congruent patterns were associated with a longer time since diagnosis and worse motor symptoms and cognitive performance. Multivariate regression revealed patterns predictive of disease stage. These cross-sectional findings provide new insights into PD subcortical degeneration by demonstrating patterns of disease stage-specific morphology, largely consistent with ongoing degeneration.

Early detection of dopaminergic dysfunction and glymphatic system impairment in Parkinson's disease

PURPOSE

This study aimed to assess the glymphatic function and its correlation with clinical characteristics and the loss of dopaminergic neurons in Parkinson's disease (PD) using hybrid positron emission tomography (PET)-magnetic resonance imaging (MRI) combined with diffusion tensor image analysis along the perivascular space (DTI-ALPS), choroid plexus volume (CPV), and enlarged perivascular space (EPVS) volume.

METHODS

Twenty-five PD patients and thirty matched healthy controls (HC) participated in the study. All participants underwent 18F-fluorodopa (18F-DOPA) PET-MRI scanning. The striatal standardized uptake value ratio (SUVR), DTI-ALPS index, CPV, and EPVS volume were calculated. Furthermore, we also analysed the relationship between the DTI-ALPS index, CPV, EPVS volume and striatal SUVR as well as clinical characteristics of PD patients.

RESULTS

PD patients demonstrated significantly lower values in DTI-ALPS (t = 3.053, p = 0.004) and larger CPV (t = 2.743, p = 0.008) and EPVS volume (t = 2.807, p = 0.008) compared to HC. In PD group, the ALPS-index was negatively correlated with the Unified Parkinson's Disease Rating Scale III (UPDRS-III) scores (r = -0.730, p < 0.001), and positively correlated with the mean putaminal SUVR (r = 0.560, p = 0.007) and mean caudal SUVR (r = 0.459, p = 0.032). Moreover, the mean putaminal SUVR was negatively associated with the UPDRS-III scores (r = -0.544, p = 0.009).

CONCLUSION

DTI-ALPS has the potential to uncover glymphatic dysfunction in patients with PD, with this dysfunction correlating strongly with the severity of disease, together with the mean putaminal and caudal SUVR. PET- MRI can serve as a potential multimodal imaging biomarker for early-stage PD.

Serum phosphorus levels associated with nigrostriatal dopaminergic deficits in drug-naïve Parkinson's disease

INTRODUCTION

A major component of Lewy bodies is phosphorylated α-synuclein. This post-translational modification of α-synuclein, phosphorylation, may consume a great amount of serum phosphorus. We aimed to investigate serum phosphorus levels and their associations with clinical phenotype and the degeneration of cardiac sympathetic and nigrostriatal dopaminergic neurons in patients with Parkinson's disease (PD).

MATERIALS AND METHODS

We examined serum phosphorus levels in 127 participants (drug-naïve PD, 97; age- and sex-matched controls, 30). Associations of serum phosphorus levels with clinical features, heart-to-mediastinum (H/M) ratio on cardiac 123I-metaiodobenzylguanidine scintigraphy and striatal specific binding ratio of 123I-2-carbomethoxy-3-(4-iodophenyl)-N-(3-fluoropropyl) nortropane (123I-FP-CIT) were examined.

RESULTS

Serum phosphorus levels were 3.4 ± 0.5 mg/dL in patients with PD and were not different from those in controls after controlling for age and sex (p = 0.850). Serum phosphorus levels were significantly lower in patients with PD and decreased H/M ratio than in those with PD and normal H/M ratio (3.3 ± 0.4 mg/dL vs. 3.6 ± 0.5 mg/dL, p = 0.003). Lower serum phosphorus levels were significantly associated with more severe degeneration of nigrostriatal dopaminergic neurons in patients with PD and decreased H/M ratio. However, this association was not observed in patients with PD and normal H/M ratio.

CONCLUSIONS

Serum phosphorus levels and their association with nigrostriatal dopaminergic degeneration are different between patients with decreased H/M ratio and those with normal H/M ratio. Serum phosphorus levels may reflect the degree of nigrostriatal dopaminergic degeneration in patients with decreased H/M ratio, namely, Body-First PD.

Retinal Thickness in Essential Tremor and Early Parkinson Disease: Exploring Diagnostic Insights

BACKGROUND

Essential tremor (ET) represents a heterogeneous condition which may overlap with Parkinson disease (PD) even at early stages, by sharing some subtle clinical aspects. Longstanding ET demonstrated also higher risk of developing PD, especially with a Tremor-dominant (TD-PD) phenotype. Therefore, differential diagnosis between ET and early PD could be quite challenging. Optical coherence tomography (OCT) has been recognized as a reliable tool to assess the retina as a proxy of neurodegeneration. We aimed to explore the possible role of retinal assessment in differential diagnosis between ET and early PD.

METHODS

Macular layers and peripapillary retinal nerve fiber layer (RNFL) thickness among ET, early PD, and healthy controls (HCs) were assessed using OCT.

RESULTS

Forty-two eyes from 23 ET, 41 eyes from 21 early PD, and 33 eyes from 17 HCs were analyzed. Macular RNFL, ganglion cell layer, inner plexiform layer, and inner nuclear layer were thinner in PD as compared with ET and even more in HCs. Differences between ET and PD were more evident when considering the TD-PD subgroup, especially for RNFL. Among ET patients, thickness of the inner macular layers showed negative linear relationship with both age at onset and disease duration. Peripapillary temporal quadrant thinning was found in ET compared with HCs.

CONCLUSIONS

Macular inner retina was thinner in patients with ET and early PD compared with HCs. These findings suggest that the retinal assessment may have a utility in the differential diagnosis between ET and PD.

Pathobiology of Cognitive Impairment in Parkinson Disease: Challenges and Outlooks

Cognitive impairment (CI) is a characteristic non-motor feature of Parkinson disease (PD) that poses a severe burden on the patients and caregivers, yet relatively little is known about its pathobiology. Cognitive deficits are evident throughout the course of PD, with around 25% of subtle cognitive decline and mild CI (MCI) at the time of diagnosis and up to 83% of patients developing dementia after 20 years. The heterogeneity of cognitive phenotypes suggests that a common neuropathological process, characterized by progressive degeneration of the dopaminergic striatonigral system and of many other neuronal systems, results not only in structural deficits but also extensive changes of functional neuronal network activities and neurotransmitter dysfunctions. Modern neuroimaging studies revealed multilocular cortical and subcortical atrophies and alterations in intrinsic neuronal connectivities. The decreased functional connectivity (FC) of the default mode network (DMN) in the bilateral prefrontal cortex is affected already before the development of clinical CI and in the absence of structural changes. Longitudinal cognitive decline is associated with frontostriatal and limbic affections, white matter microlesions and changes between multiple functional neuronal networks, including thalamo-insular, frontoparietal and attention networks, the cholinergic forebrain and the noradrenergic system. Superimposed Alzheimer-related (and other concomitant) pathologies due to interactions between α-synuclein, tau-protein and β-amyloid contribute to dementia pathogenesis in both PD and dementia with Lewy bodies (DLB). To further elucidate the interaction of the pathomechanisms responsible for CI in PD, well-designed longitudinal clinico-pathological studies are warranted that are supported by fluid and sophisticated imaging biomarkers as a basis for better early diagnosis and future disease-modifying therapies.

Association between choroid plexus volume and cognition in Parkinson disease

BACKGROUND AND PURPOSE

The choroid plexus (CP) clears harmful metabolites from the central nervous system as part of the glymphatic system. We investigated the association of CP volume (CPV) with baseline and longitudinal cognitive decline in patients with Parkinson disease (PD).

METHODS

We retrospectively reviewed the medical records of 240 patients with newly diagnosed PD who had undergone detailed neuropsychological tests and high-resolution T1-weighted structural magnetic resonance imaging during the initial assessment. The CPV of each patient was automatically segmented, and the intracranial volume ratio was used in subsequent analyses. The relationship between CPV and baseline composite scores of each cognitive domain was assessed using multivariate linear regression analyses. A Cox proportional hazards model was used to compare the risk of dementia conversion with CPV.

RESULTS

CPV negatively correlated with composite scores of the frontal/executive function domain (β = -0.375, p = 0.002) after adjusting for age, sex, years of education, and parkinsonian symptom duration. The Cox regression model revealed that a larger CPV was associated with a higher risk of dementia conversion (hazard ratio [HR] = 1.509, p = 0.038), which was no longer significant after adjusting for the composite scores of the frontal/executive function domain. A mediation analysis demonstrated that the effect of CPV on the risk of dementia conversion was completely mediated by frontal/executive function (direct effect: HR = 1.203, p = 0.396; indirect effect: HR = 1.400, p = 0.015).

CONCLUSIONS

Baseline CPV is associated with baseline frontal/executive function, which subsequently influences dementia conversion risk in patients with PD.

The Role of Cellular Defense Systems of Ferroptosis in Parkinson's Disease and Alzheimer's Disease

Parkinson's disease (PD) and Alzheimer's disease (AD) are the most common rapidly developing neurodegenerative diseases that lead to serious health and socio-economic consequences. Ferroptosis is a non-apoptotic form of cell death; there is growing evidence to support the notion that ferroptosis is involved in a variety of pathophysiological contexts, and there is increasing interest in the role of ferroptosis in PD and AD. Simultaneously, cells may have evolved four defense systems to counteract the toxic effects of ferroptosis occasioned by lipid peroxidation. This review, which focuses on the analysis of ferroptosis in the PD and AD context, outlines four cellular defense systems against ferroptosis and how each of them is involved in PD and AD.

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.

Suitability of visual cues for freezing of gait in patients with idiopathic Parkinson's disease: a case-control pilot study

BACKGROUND

Freezing of gait (FOG) is one of the most debilitating symptoms in patients with idiopathic Parkinson's disease (IPD). Visual cues can relieve FOG symptoms. However, there is no consensus on patient characteristics that can benefit from visual cues. Therefore, we examined the differences in IPD patient characteristics according to the effectiveness of visual cueing.

METHODS

Through gait experiments, we investigated the number of FOG occurrences, average FOG period per episode, proportion of FOG duration in the total gait cycles, and FOG-free period gait spatiotemporal parameters in ten participants diagnosed with FOG due to IPD. Subsequently, the differences between their clinical characteristics and striatal dopamine active transporter availability from six subregions of the striatum were compared by dividing them into two groups based on the three reduction rates: occurrence numbers, mean durations per episode, and proportion of FOG duration in the total gait cycles improved by visual cueing using laser shoes. The relationships among these three reduction rates and other FOG-related parameters were also investigated using Spearman correlation analyses.

RESULTS

According to the three FOG-related reduction rates, the group assignments were the same, which was also related to the baseline self-reported FOG severity score (New Freezing of Gait Questionnaire): the more severe the FOG, the poorer the response to the visual cueing. By visual cueing, the better response group demonstrated the characteristics of lower new FOG questionnaire total scores, higher dopamine active transporter availability of the anterior and posterior putamen, and shorter mean duration of FOG per episode in the absence of cueing. These results were replicated using Spearman correlation analyses.

CONCLUSIONS

For FOG symptoms following IPD, gait assistance by visual cueing may be more effective when the total NFOGQ score is lower and the DAT of putamen is higher. Through this study, we demonstrated clinical and striatal dopaminergic conditions to select patients who may be more likely to benefit from visual cueing with laser shoes, and these findings lead to the need for early diagnosis of FOG in patients with IPD.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT05080413. Registered on September 14, 2021.

Astrocytes and Alpha-Synuclein: Friend or Foe?

Despite its devastating disease burden and alarming prevalence, the etiology of Parkinson's disease (PD) remains to be completely elucidated. PD is characterized by the degeneration of dopaminergic neurons in the substantia nigra pars compacta and this correlates with the accumulation of misfolded α-synuclein. While the aggregation of α-synuclein in the form of Lewy bodies or Lewy neurites is a well-established intraneuronal hallmark of the disease process, our understanding of the glial contribution to aberrant α-synuclein proteostasis is lacking. In this regard, restoring astrocyte function during early PD could offer a promising therapeutic avenue and understanding the involvement of astrocytes in handling/mishandling of α-synuclein is of particular interest. Here, we explore the growing body of scientific literature implicating aberrant astrocytic α-synuclein proteostasis with the seemingly inexorable pathological sequelae typifying PD. We also provide a perspective on how heterogeneity in the morphological relationship between astrocytes and neurons will need to be considered in the context of PD pathogenesis.

Association Between White Matter Networks and the Pattern of Striatal Dopamine Depletion in Patients With Parkinson Disease

OBJECTIVES

Individual variability in nigrostriatal dopaminergic denervation is an important factor underlying clinical heterogeneity in Parkinson disease (PD). This study aimed to explore whether the pattern of striatal dopamine depletion was associated with white matter (WM) networks in PD.

METHODS

A total of 240 newly diagnosed patients with PD who underwent 18F-FP-CIT PET scans and brain diffusion tensor imaging at initial assessment were enrolled in this study. We measured 18F-FP-CIT tracer uptake as an indirect marker for striatal dopamine depletion. Factor analysis-derived striatal dopamine loss patterns were estimated in each patient to calculate the composite scores of 4 striatal subregion factors (caudate, more-affected and less-affected sensorimotor striata, and anterior putamen) based on the availability of striatal dopamine transporter. The WM structural networks that were correlated with the composite scores of each striatal subregion factor were identified using a network-based statistical analysis.

RESULTS

A higher composite score of caudate (i.e., relatively preserved dopaminergic innervation in the caudate) was associated with a strong structural connectivity in a single subnetwork comprising the left caudate and left frontal gyri. Selective dopamine loss in the caudate was associated with strong connectivity in the structural subnetwork whose hub nodes were bilateral thalami and left insula, which were connected to the anterior cingulum. However, no subnetworks were correlated with the composite scores of other striatal subregion factors. The connectivity strength of the network with a positive correlation with the composite score of caudate affected the frontal/executive function either directly or indirectly through the mediation of dopamine depletion in the caudate.

CONCLUSIONS

Our findings indicate that different patterns of striatal dopamine depletion are closely associated with WM structural alterations, which may contribute to heterogeneous cognitive profiles in individuals with PD.

Predicting the onset of freezing of gait in Parkinson's disease

BACKGROUND

Freezing of gait is a debilitating symptom of Parkinson's disease associated with high risks of falls and poor quality of life. While productive therapy for FoG is still underway, early prediction of FoG could help high-risk PD patients to take preventive measures. In this study, we predicted the onset of FoG in de novo PD patients using a battery of risk factors from patients enrolled in PPMI cohort.

METHODS

Baseline characteristics were compared between subjects who developed FoG (68 patients, 37.2%, pre-FoG group) during the five-year follow up and subjects who did not (115 patients, 62.8%, non-FoG group). A multivariate logistic regression model was built based on backward stepwise selection of factors that were associated with FoG onset in the univariate analysis. ROC curves were used to assess sensitivity and specificity of the predictive model.

RESULTS

At baseline, age, PIGD score, cognitive functions, autonomic functions, sleep behavior, fatigue and striatal DAT uptake were significantly different in the pre-FoG group relative to the non-FoG group. However, there was no difference in genetic characteristics between the two patient sets. Univariate analysis showed several motor and non-motor factors that correlated with FoG, including PIGD score, MDS-UPDRS part II score, SDMT score, HVLT Immediate/Total Recall, MOCA, Epworth Sleepiness Scale, fatigue, SCOPA-AUT gastrointestinal score, SCOPA-AUT urinary score and CSF biomarker Abeta42. Multivariate logistic analysis stressed that high PIGD score, fatigue, worse SDMT performance and low levels of Abeta42 were independent risk factors for FoG onset in PD patients.

CONCLUSIONS

Combining motor and non-motor features including PIGD score, poor cognitive functions and CSF Abeta can identify PD patients with high risk of FoG onset.

Spatial normalization and quantification approaches of PET imaging for neurological disorders

Quantification approaches of positron emission tomography (PET) imaging provide user-independent evaluation of pathophysiological processes in living brains, which have been strongly recommended in clinical diagnosis of neurological disorders. Most PET quantification approaches depend on spatial normalization of PET images to brain template; however, the spatial normalization and quantification approaches have not been comprehensively reviewed. In this review, we introduced and compared PET template-based and magnetic resonance imaging (MRI)-aided spatial normalization approaches. Tracer-specific and age-specific PET brain templates were surveyed between 1999 and 2021 for ¹⁸F-FDG, ¹¹C-PIB, ¹⁸F-Florbetapir, ¹⁸F-THK5317, and etc., as well as adaptive PET template methods. Spatial normalization-based PET quantification approaches were reviewed, including region-of-interest (ROI)-based and voxel-wise quantitative methods. Spatial normalization-based ROI segmentation approaches were introduced, including manual delineation on template, atlas-based segmentation, and multi-atlas approach. Voxel-wise quantification approaches were reviewed, including voxel-wise statistics and principal component analysis. Certain concerns and representative examples of clinical applications were provided for both ROI-based and voxel-wise quantification approaches. At last, a recipe for PET spatial normalization and quantification approaches was concluded to improve diagnosis accuracy of neurological disorders in clinical practice.

Association Between White Matter Connectivity and Early Dementia in Patients With Parkinson Disease

OBJECTIVES

Several clinical and neuroimaging biomarkers have been proposed to identify individuals with Parkinson's disease (PD) who are at risk for ongoing cognitive decline. This study aimed to explore whether white matter (WM) connectivity disruption is associated with dementia conversion in patients with newly diagnosed PD with mild cognitive impairment (PD-MCI).

METHODS

Seventy-five patients with drug-naïve PD-MCI who underwent serial cognitive assessments during the follow-up period (>5 years) were enrolled for the neuroimaging analyses. The patients were classified into either the PD with dementia (PDD) high-risk group (PDD-H, n = 38) or low-risk group (PDD-L, n = 37), depending on whether they converted to dementia within 5 years of PD diagnosis. We conducted degree-based statistic analyses based on a graph-theoretical concept to identify the subnetworks whose WM connectivity was disrupted in the PDD-H group compared with the PDD-L group.

RESULTS

The PDD-H group showed poorer cognitive performance on frontal/executive, visual memory/visuospatial, and attention/working memory/language function than the PDD-L group at baseline assessment. The PDD-H group exhibited more severely disrupted WM connectivity in both frontal and posterior cortical regions with eight hub nodes in the degree-based statistic analysis. The strength of structural connectivity within the identified subnetworks was correlated with the composite scores of frontal/executive function domain (γ = 0.393) and the risk score of PDD conversion within 5 years (γ = -0.480).

CONCLUSIONS

This study demonstrated that disrupted WM connectivity in frontal and posterior cortical regions, which correlated with frontal/executive dysfunction, is associated with early dementia conversion in PD-MCI.

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.

Dopamine Transporter Imaging, Current Status of a Potential Biomarker: A Comprehensive Review

A major goal of current clinical research in Parkinson's disease (PD) is the validation and standardization of biomarkers enabling early diagnosis, predicting outcomes, understanding PD pathophysiology, and demonstrating target engagement in clinical trials. Molecular imaging with specific dopamine-related tracers offers a practical indirect imaging biomarker of PD, serving as a powerful tool to assess the status of presynaptic nigrostriatal terminals. In this review we provide an update on the dopamine transporter (DAT) imaging in PD and translate recent findings to potentially valuable clinical practice applications. The role of DAT imaging as diagnostic, preclinical and predictive biomarker is discussed, especially in view of recent evidence questioning the incontrovertible correlation between striatal DAT binding and nigral cell or axon counts.

Hybrid PET-MRI for early detection of dopaminergic dysfunction and microstructural degradation involved in Parkinson's disease

Dopamine depletion and microstructural degradation underlie the neurodegenerative processes in Parkinson’s disease (PD). To explore early alterations and underlying associations of dopamine and microstructure in PD patients utilizing the hybrid positron emission tomography (PET)-magnetic resonance imaging (MRI). Twenty-five PD patients in early stages and twenty-four matched healthy controls underwent hybrid ¹⁸F-fluorodopa (DOPA) PET-diffusion tensor imaging (DTI) scanning. The striatal standardized uptake value ratio (SUVR), DTI maps (fractional anisotropy, FA; mean diffusivity, MD) in subcortical grey matter, and deterministic tractography of the nigrostriatal pathway were processed. Values in more affected (MA) side, less affected (LA) side and mean were analysed. Correlations and mediations among PET, DTI and clinical characteristics were further analysed. PD groups exhibited asymmetric pattern of dopaminergic dysfunction in putamen, impaired integrity in the microstructures (nigral FA, putaminal MD, and FA of nigrostriatal projection). On MA side, significant associations between DTI metrics (nigral FA, putaminal MD, and FA of nigrostriatal projection) and motor performance were significantly mediated by putaminal SUVR, respectively. Early asymmetric disruptions in putaminal dopamine concentrations and nigrostriatal pathway microstructure were detected using hybrid PET-MRI. The findings further implied that molecular degeneration mediates the modulation of microstructural disorganization on motor dysfunction in the early stages of PD.

To explore early alterations and underlying associations of dopamine levels and microstructure in Parkinson’s Disease (PD), Shang et al use a hybrid positron emission tomography (PET)-magnetic resonance imaging (MRI) approach in early stage patients and age-matched controls. Their data implies that molecular degeneration mediates the effects of microstructural disorganization on motor dysfunction in the early stages of PD.

Association between heart rate variability and striatal dopamine depletion in Parkinson's disease

Striatal dopamine depletion is associated with not only motor symptom but also non-motor symptoms in patients with Parkinson's disease (PD). The purpose is to elucidate the relation between heart rate variability (HRV) and dopaminergic depletion in specific striatal subregions. The subjects were 84 patients with newly diagnosed untreated PD. All patients underwent striatal ¹²³I-2β-carbomethoxy-3β-(4-iodophenyl)-N-(3-fluoropropyl) nortropane (¹²³I-FP-CIT) dopamine transporter single-photon emission computed tomography (DAT-SPECT). DaTQUANT software (GE Healthcare) was used as a semi-quantitative tool to analyze DAT-SPECT data. Association of HRV with dopaminergic depletion in specific striatal subregions was examined. HRV was related to dopamine depletion in the caudate and anterior putamen, especially the left side, after controlling for age, hemoglobin A1c level, disease duration, motor severity and global cognition on multiple regression analysis (left caudate p = 0.012). HRV was closely related to striatal dopamine depletion, especially in the left associative striatum, in patients with PD.

Neuropsychiatric Burden Is a Predictor of Early Freezing and Motor Progression in Drug-Naïve Parkinson's Disease

BACKGROUND

Neuropsychiatric symptoms (NPS) are the most common non-motor symptom in Parkinson's disease (PD).

OBJECTIVE

To investigate the association between the burden of NPS and motor prognosis in patients with PD.

METHODS

We enrolled 329 drug-naïve patients with PD, who was non-demented and followed-up≥2 years after their first visit to the clinic with baseline dopamine transporter (DAT) imaging and neuropsychiatric inventory (NPI) scores. We performed a survival analysis and a linear mixed model analysis to assess longitudinal motor outcomes according to the NPI total score.

RESULTS

The Kaplan-Meier analysis showed no difference in the development of levodopa-induced dyskinesia and wearing-off according to the NPI total score. However, higher burden of NPI total score was associated with earlier freezing of gait (FOG) development in the time-dependent Cox regression models after adjusting for age at symptom onset, sex, disease duration, Unified PD Rating Scale motor score, baseline Mini-Mental State Examination score, DAT activity in the posterior putamen and levodopa-equivalent daily dose (LEDD) (Hazard ratio 1.047, p = 0.002). A linear mixed model analysis revealed that patients with a higher NPI total score had a more rapid LEDD increment (NPI×time, p = 0.003). Among 52 patients with PD who eventually developed FOG during the follow-up period, there was a significant correlation between the NPI total score and time with FOG development (γ= -0.472; p = 0.001) after adjusting for confounding factors.

CONCLUSION

The present study demonstrated that the severity of NPS is a predictor of early freezing and motor progression in patients with PD.

Perivascular Spaces in the Basal Ganglia and Long-term Motor Prognosis in Newly Diagnosed Parkinson Disease

OBJECTIVE

To investigate the association between enlarged perivascular spaces (PVS) in the basal ganglia (BG-PVS) and long-term motor outcomes in Parkinson disease (PD).

METHODS

We reviewed the medical records of 248 patients with drug-naive early-stage PD (follow-up >3 years, mean age 67.44 ± 8.46 years, 130 female) who underwent brain MRI and dopamine transporter (DAT) scans at initial assessment. The number of baseline enlarged BG-PVS was counted on axial T2-weighted images. Then, patients were divided into 2 groups: a PD group with a low number (0-10) of enlarged PVS (PD-EPVS-; n = 156) and a PD group with a high number (>10) of enlarged PVS (PD-EPVS+; n = 92). We used Cox regression models to compare the levodopa-induced dyskinesia (LID)-, wearing-off-, and freezing of gait (FOG)-free times between groups. We also compared longitudinal increases in levodopa-equivalent dose per body weight between groups using a linear mixed model.

RESULTS

Patients in the PD-EPVS+ group were older (72.28 ± 6.07 years) and had greater small vessel disease burden than those in the PD-EPVS- group (64.58 ± 8.38 years). The PD-EPVS+ group exhibited more severely decreased DAT availability in all striatal subregions except the ventral striatum. The risk of FOG was higher in the PD-EPVS+ group, but the risk of LID or wearing-off was comparable between groups. The PD-EPVS+ group required higher doses of dopaminergic medications for effective symptom control compared to the PD-EPVS- group.

CONCLUSION

This study suggests that baseline enlarged BG-PVS can be an indicator of the progression of motor disability in PD.

A simple-to-use web-based calculator for survival prediction in Parkinson's disease

Background: To establish and validate a nomogram and corresponding web-based calculator to predict the survival of patients with Parkinson’s disease (PD).

Methods: In this cohort study, we retrospectively evaluated patients (n=497) with PD using a two-stage design, from March 2004 to November 2007 and from July 2005 to July 2015. Predictive variables included in the model were identified by univariate and multiple Cox proportional hazard analyses in the training set.

Results: Independent prognostic factors including age, PD duration, and Hoehn and Yahr stage were determined and included in the model. The model showed good discrimination power with the area under the curve (AUC) values generated to predict 4-, 6-, and 8-year survival in the training set being 0.716, 0.783, and 0.814, respectively. In the validation set, the AUCs of 4- and 6-year survival predictions were 0.85 and 0.924, respectively. Calibration plots and decision curve analysis showed good model performance both in the training and validation sets. For convenient application, we established a web-based calculator (https://tangyl.shinyapps.io/PDprognosis/).

Conclusions: We developed a satisfactory, simple-to-use nomogram and corresponding web-based calculator based on three relevant factors to predict prognosis and survival of patients with PD. This model can aid personalized treatment and clinical decision-making.

Dopaminergic Correlates of Orthostatic Hypotension in de novo Parkinson's Disease

BACKGROUND

Orthostatic hypotension (OH) at an early stage of Parkinson's disease (PD) predicts poor prognosis, which may suggest degeneration of dopaminergic neurons affects sympathetic function, causing OH.

OBJECTIVE

We tested the hypothesis that striatal dopaminergic depletion is associated with OH in PD.

METHODS

Out of 99 patients with newly diagnosed untreated PD, 81 patients were enrolled according to our selection criteria. All patients underwent head-up tilt-table testing and striatal 123I-2β-carbomethoxy-3β-(4-iodophenyl)-N-(3-fluoropropyl) nortropane (123I-FP-CIT) dopamine transporter single photon emission computed tomography (DAT-SPECT). DaTQUANT software (GE Healthcare) was used as a semi-quantitative tool to analyze DAT-SPECT data. The association between hemodynamic changes and 123I-FP-CIT uptake was examined.

RESULTS

123I-FP-CIT uptake in the putamen, especially the anterior part and left side, was related not only to motor severity but also to OH. Change in systolic blood pressure correlated negatively with 123I-FP-CIT uptake in bilateral anterior putamen (left: p < 0.01, right: p < 0.05) and left posterior putamen (p < 0.05). Patients with OH had more severe dopamine depletion in left anterior (p = 0.008) and posterior (p = 0.007) putamen at a similar motor severity than did patients without OH even though both groups have similar baseline characteristics. An analysis of asymmetry index showed patients with OH had symmetrically decreased dopamine levels in anterior putamen when compared to those without OH (p = 0.024).

CONCLUSION

OH is closely related to striatal dopamine depletion in PD. This relation may help to account for the prognostic value of OH.

Can adenosine A2A receptor antagonists modify motor behavior and dyskinesia in experimental models of Parkinson's disease?

Current treatment of the motor symptoms of Parkinson's disease (PD) focuses on dopamine replacement therapies. While these treatments are initially highly effective, with long-term use and disease progression, the therapeutic response is often limited by the development of motor complications, dopaminergic side effects, and residual unresponsive motor and non-motor symptoms. An alternative or additive treatment approach may be to target non-dopaminergic receptors within the motor control pathways, which function to modulate basal ganglia output. Adenosine A_2A receptors are one potential non-dopaminergic target as they are selectively localized to the basal ganglia and to the indirect output pathway known to modulate the striato-thalamo-cortical loops critical to the expression of the motor symptoms of PD. This paper reviews the preclinical evidence base for the ability of adenosine A_2A receptor blockade to influence motor function and modulate dyskinesia expression. There is consensus that adenosine A_2A receptor antagonists - administered either as a monotherapy or in combination with l-DOPA or dopamine agonists - improve motor function in both rodent and primate models of PD, and should be effective for treating the motor symptoms of PD in humans. Importantly, the improvements in motor function were seen in the absence of dyskinesia. The introduction of a non-dopaminergic approach to modifying basal ganglia function provides a useful addition to the range of available therapies for treating PD, and there is a rational basis for a drug that focuses on modifying basal ganglia output.