Pallidal dopaminergic denervation and rest tremor in early Parkinson's disease: PPMI cohort analysis

Differentiating patterns of neuro-circuitry abnormalities in tremor dominant parkinson's disease and multiple system atrophy: a resting-state fMRI study

This study aimed to elucidate distinctive patterns of brain functional activity in tremor-dominant Multiple System Atrophy (MSA) and Parkinson's Disease (PD) patients and develop a diagnostic model distinguishing between the two conditions based on these changes. Resting-state fMRI data from 45 MSA patients, 55 PD patients, and 48 healthy controls were analyzed using Percent Amplitude of Fluctuation (PerAF), Functional (FC) and Effective Connectivity (EC) analyses. The Support Vector Machine (SVM) was used to create the diagnostic model from the identified functional alterations. Partial correlation analyses explored the relationship between functional abnormalities and tremors. Both MSA and PD patients with tremors exhibited similar activity changes in bilateral Orbital part of the superior frontal gyrus (ORBsup), Cerebellum VIII (CRBL8), left Cerebellum IV-V (CRBL45.L), right rectus (REC), and FC based on the seeds of PUT.L, CRBL8.R, and REC.R. These changes were more pronounced in MSA patients. However, MSA patients exhibited heightened putamen activity and enhanced EC from caudate (CAU) to putamen, whereas these activity and connectivity were decreased in PD patients. The SVM model achieved strong performance, with the putamen exerting the most significant influence on classification. In summary, dysfunction within the cerebello-cortical and basal ganglia network circuits is implicated in the tremors of both MSA and PD patients. The alteration in cerebellar-cortical regions were similar, with MSA displaying more pronounced changes, contrasting changes were observed in the basal ganglia region. The putamen may serve as crucial neurobiological indicators for the precise differentiation of MSA and PD patients.

Striatal dopaminergic depletion was associated with motor subtype conversion in Parkinson's disease

BACKGROUND

The instability of classical Parkinson's disease (PD) motor subtypes over the disease course suggests that motor subtype is influenced by disease severity. Tremor-dominant (TD) PD is susceptible to conversion to non-tremor-dominant (NTD) PD, with the risk increasing over time. This study investigates whether presynaptic striatal dopaminergic loss can predict the conversion from TD-PD to NTD-PD.

METHODS

A total of 220 early TD-PD patients with baseline Dopamine Transporter Single-Photon Emission Computed Tomography (DAT-SPECT) data from the Parkinson's Progression Markers Initiative (PPMI) database were included. Patients were divided into high and low DAT uptake groups based on the median baseline striatal DAT uptake value. The Kaplan-Meier survival curve was used to compare the conversion rates of TD-PD subtype between the two groups. Multivariable Cox regression was used to further analyze the relationship between baseline striatal DAT uptake and TD-PD subtype conversion.

RESULTS

The risk of conversion from TD to NTD was higher in the low striatal DAT group. In the multivariable Cox regression analysis, after adjusting for age, sex, baseline disease duration, MDS-UPDRS-II score and GDS score, the baseline striatal DAT uptake value was significantly associated with the conversion of TD-PD (HR = 0.39; 95 % CI 0.22-0.68; P = 0.001). In the stratified analysis, this association was not influenced by baseline TD or PIGD score.

CONCLUSIONS

In early-stage TD-PD, a high baseline presynaptic striatal dopaminergic reserve reduces the risk of future conversion to NTD-PD. This supports the notion that classical motor subtypes may reflect the disease stage or severity.

Changes in Action Tremor in Parkinson's Disease over Time: Clinical and Neuroimaging Correlates

BACKGROUND

The various symptoms of Parkinson's disease (PD) may change differently over time as the disease progresses. Tremor usually manifests early in the disease, but unlike other motor symptoms, its severity may diminish over time. The cerebral mechanisms underlying these symptom-specific longitudinal trajectories are unclear. Previous magnetic resonance imaging (MRI) studies have shown structural changes in brain regions associated with PD tremor, suggesting that structural changes over time may define clinical trajectories.

OBJECTIVES

The aims were to investigate the longitudinal trajectory of PD tremor in relation to bradykinesia and rigidity, and assess whether tremor progression is related to structural changes in tremor-related areas.

METHODS

We used data from the Personalized Parkinson Project: a two-year longitudinal study involving 520 PD patients and 60 healthy controls, who were measured twice clinically and with MRI. Mixed-effects models were used to compare tremor, bradykinesia, and rigidity progression; investigate gray matter changes in tremor-related regions (cerebello-thalamo-cortical circuit and pallidum); and calculate associations between symptom severity and brain structure. Associations across the whole brain were included to assess anatomical specificity.

RESULTS

Bradykinesia and rigidity worsened over 2 years, whereas tremor behaved differently: resting tremor severity remained stable, whereas postural and kinetic tremor severity decreased. Attenuation of postural and kinetic tremor was associated with, but not restricted to, atrophy in tremor-related areas. Opposite relationships were observed for bradykinesia and rigidity.

CONCLUSIONS

Action tremor (postural and kinetic) is an early symptom of PD, which reduces with disease progression. Longitudinal brain atrophy correlates with tremor and other motor symptoms in opposite ways. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Association of motor subtype and tremor type with Parkinson's disease progression: An exploratory longitudinal analysis

BackgroundParkinson's disease (PD) is a neurodegenerative disorder with heterogenous symptoms and progression rates. Some studies have classifying PD into tremor-dominant and non-tremor-dominant PD (TD-PD and Non-TD-PD), finding that TD-PD tend to have a better prognosis, slower disease progression, and lower pathological burden compared to Non-TD-PD. However, this classification does not consider the specific types of tremors, even though recent studies have shown that different types of tremors in PD might have distinct underlying mechanism.ObjectiveData from 517 de novo drug-naïve PD patients was analyzed.MethodsSurvival analysis was carried out including motor subtypes, rest tremor presence, kinetic tremor presence, postural tremor presence, as well as the instability of tremor presence or motor subtypes as predictors. Occurrence of 6 outcomes, including motor and non-motor milestones at follow-up, were used as the time-to-event.ResultsBoth TD-PD subtype and rest tremor presence was associated with slower PD progression, while kinetic tremor presence and postural tremor presence, especially kinetic tremor presence, was associated with a faster one.ConclusionsOur study suggests different types of tremors are associated with distinct PD prognoses, indicating potential differences in underlying mechanisms. Further investigation is warranted to elucidate the specific mechanisms underlying different types of tremors in PD and to explain their relationship to disease prognosis.

Relative sparing of dopaminergic terminals in the caudate nucleus is a feature of rest tremor in Parkinson's disease

Resting tremor (RT) is a Parkinson's disease (PD) symptom with an unclear relationship to the dopaminergic system. We analysed data from 432 subjects from the Parkinson's Progression Markers Initiative, 57 additional PD patients and controls and 86 subjects referred for dopamine transporter single-photon emission computed tomography (DaT-SPECT). Caudate binding ratio (CBR), but not putamen binding ratio, was higher in RT patients. Furthermore, higher baseline CBR was linked to RT development. In the smaller cohorts, a 4-6 Hz oscillation-based metric from inertial sensors correlated with RT amplitude, distinguished controls from patients with reduced DaT binding and correlated with CBR in the latter group. In silico modelling uncovered that higher CBR in RT patients explained correlations between RT and DaT-SPECT found in several datasets, supporting a spurious origin for ipsilateral correlations between CBR and RT. These results suggest that caudate dopaminergic terminals integrity is a feature of RT with potential pathophysiological implications.

Rest Tremor in Parkinson's Disease Is Associated with Ipsilateral Striatal Dopamine Transporter Binding

BACKGROUND

The cardinal motor symptoms of Parkinson's disease (PD) include rigidity, bradykinesia, and rest tremor. Rigidity and bradykinesia correlate with contralateral nigrostriatal degeneration and striatal dopamine deficit, but association between striatal dopamine function and rest tremor has remained unclear.

OBJECTIVE

The aim of this study was to investigate the possible link between dopamine function and rest tremor using Parkinson's Progression Markers Initiative dataset, the largest prospective neuroimaging cohort of patients with PD.

METHODS

Clinical, [123I]N-ω-fluoropropyl-2β-carbomethoxy-3β-(4-iodophenyl)nortropane ([123I]FP-CIT) single photon emission computed tomography (SPECT), and structural magnetic resonance imaging data from 354 early PD patients and 166 healthy controls were included in this study. We employed a novel approach allowing nonlinear registration of individual scans accurately to a standard space and voxelwise analyses of the association between motor symptoms and striatal dopamine transporter (DAT) binding.

RESULTS

Severity of both rigidity and bradykinesia was negatively associated with contralateral striatal DAT binding (PFWE < 0.05 [FWE, family-wise error corrected]). However, rest tremor amplitude was positively associated with increased ipsilateral DAT binding (PFWE < 0.05). The association between rest tremor and binding remained the same controlling for Hoehn & Yahr stage, Movement Disorder Society Unified Parkinson's Disease Rating Scale (MDS-UPDRS) part III score, bradykinesia-rigidity score, or motor phenotype. The association between rest tremor and binding was independent of bradykinesia-rigidity and replicated using 2-year follow-up data (PFWE < 0.05).

CONCLUSION

In agreement with the existing literature, we did not find a consistent association between rest tremor and contralateral dopamine defect. However, our results demonstrate a link between rest tremor and increased or less decreased ipsilateral DAT binding. Our findings provide novel information about the association between dopaminergic function and parkinsonian rest tremor. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Dopaminergic versus anticholinergic treatment effects on physiologic complexity of hand tremor in Parkinson's disease: A randomized crossover study

AIMS

Parkinsonian tremor (PT) is regulated by numerous neurophysiological components across multiple temporospatial scales. The dynamics of tremor fluctuation are thus highly complex. This study aimed to explore the effects of different medications on tremor complexity, and how the underlying factors contribute to such tremor complexity.

METHODS

In this study, 66 participants received a 2-mg dose of benzhexol or a pre-determined dose of levodopa at two study visits in a randomized order. Before and after taking the medications, tremor fluctuation was recorded using surface electromyography electrodes and accelerometers in resting, posture, and weighting conditions with and without a concurrent cognitive task. Tremor complexity was quantified using multiscale entropy.

RESULTS

Tremor complexity in resting (p = 0.002) and postural condition (p < 0.0001) was lower when participants were performing a cognitive task compared to a task-free condition. After taking levodopa and benzhexol, participants had increased (p = 0.02-0.03) and decreased (p = 0.03) tremor complexity compared to pre-medication state, respectively. Tremor complexity and its changes as induced by medications were significantly correlated with clinical ratings and their changes (β = -0.23 to -0.39; p = 0.002-0.04), respectively.

CONCLUSION

Tremor complexity may be a promising marker to capture the pathophysiology underlying the development of PT, aiding the characterization of the effects medications have on PT regulation.

18F-FP-DTBZ PET/CT detectable associations between monoaminergic depletion in the putamen with rigidity and the pallidus with tremor in Parkinson's disease

INTRODUCTION

The motor subtypes of Parkinson's disease (PD) are widely accepted and implemented. However, the motor subtypes have been thought to represent different stages of PD recently because some patients experience tremor-dominant (TD) conversion to the non-tremor-dominant subtype, such as postural instability-gait difficulty (PIGD). In this study, we explore the monoaminergic denervation features of the striatal and extra-striatal areas in patients with different subtypes of PD with 18F-9-fluoropropyl-(+)-dihydrotetrabenazine (18F-FP-DTBZ) PET/CT.

METHODS

Sixty-five patients diagnosed with PD were included and classified as TD (n = 25) and PIGD (n = 40). We evaluated the difference of monoaminergic features of each subregion of brain between motor subtypes of PD, as well as associations between these features and Parkinsonian motor symptoms.

RESULTS

The striatal standardized uptake value ratios (SUVR) showed that dopaminergic disruption of patients with PIGD was more symmetrical in the posterior ventral putamen (p < 0.001) and more severe in the ipsilateral posterior dorsal putamen (p < 0.001 corrected) compared with that of patients with TD. The severity of PIGD scores was associated with striatal dopaminergic depletion, while tremor was associated with monoaminergic changes in extra-striatal areas, including pallidus, thalamus, and raphe nuclie.

CONCLUSION

These results indicate that patients with different motor subtypes may have different underlying mechanisms of PD pathogenesis. Therefore, accurate diagnosis of PD subtypes can aid prognosis evaluation and treatment decision-making.

Brain connectivity for subtypes of parkinson's disease using structural MRI

Objective. Delineating Parkinson's disease (PD) into distinct subtypes is a major challenge. Most studies use clinical symptoms to label PD subtypes while our work uses an imaging-based data-mining approach to subtype PD. Our study comprises two major objectives - firstly, subtyping Parkinson's patients based on grey matter information from structural magnetic resonance imaging scans of human brains; secondly, comparative structural brain connectivity analysis of PD subtypes derived from the former step.Approach. Source-based-morphometry decomposition was performed on 131 Parkinson's patients and 78 healthy controls from PPMI dataset, to derive at components (regions) with significance in disease and high effect size. The loading coefficients of significant components were thresholded for arriving at subtypes. Further, regional grey matter maps of subtype-specific subjects were separately parcellated and employed for construction of subtype-specific association matrices using Pearson correlation. These association matrices were binarized using sparsity threshold and leveraged for structural brain connectivity analysis using network metrics.Main results. Two distinct Parkinson's subtypes (namely A and B) were detected employing loadings of two components satisfying the selection criteria, and a third subtype (AB) was detected, common to these two components. Subtype A subjects were highly weighted in inferior, middle and superior frontal gyri while subtype B subjects in inferior, middle and superior temporal gyri. Network metrics analyses through permutation test revealed significant inter-subtype differences (p < 0.05) in clustering coefficient, local efficiency, participation coefficient and betweenness centrality. Moreover, hubs were obtained using betweenness centrality and mean network degree.Significance. MRI-based data-driven subtypes show frontal and temporal lobes playing a key role in PD. Graph theory-driven brain network analyses could untangle subtype-specific differences in structural brain connections showing differential network architecture. Replication of these initial results in other Parkinson's datasets may be explored in future. Clinical Relevance- Investigating structural brain connections in Parkinson's disease may provide subtype-specific treatment.

[Neurochemical mechanisms of tremor in Parkinson's disease]

Tremor is one of the main motor symptoms of Parkinson's disease, and its pathophysiology remains largely unknown. The clinical and pathomorphological heterogeneity of tremor and the not always response to therapy complicate the task of researchers and clinicians. This review discusses the specific degeneration of neurotransmitter systems driving the development of tremor, and the influence of neurotransmitters on specific anatomical entities according to current models explaining tremor. It is discusses how changes in neurotransmitter systems may influence the clinical diversity of tremor and differences in response to therapy. Data from clinical trials demonstrating the effect of the dopamine receptor agonist piribedil on tremor are presented.

Pharmacological Treatment of Tremor in Parkinson's Disease Revisited

The pathophysiology of Parkinson's disease (PD) tremor remains incompletely understood and there is a lack of clinical trials specifically addressing its pharmacological treatment. Levodopa is the most efficacious drug for most patients and should be used as primary approach to control troublesome tremor. While the efficacy of oral dopamine agonists on PD tremor has been demonstrated in controlled trials, there is no evidence of greater antitremor efficacy compared to levodopa. The magnitude of the antitremor effect of anticholinergics is generally lower than that of levodopa. Due to their adverse effects, anticholinergics have a limited role in selected young and cognitively intact patients. Propranolol may improve resting and action tremor and may be considered as an adjunct in patients with insufficient tremor response to levodopa and this also applies to clozapine, despite its unfavorable adverse effect profile. Treating motor fluctuations with MAO-B and COMT inhibitors, dopamine agonists, amantadine, or on-demand treatments such as subcutaneous or sublingual apomorphine and inhaled levodopa as well as with continuous infusions of levodopa or apomorphine will improve off period tremor episodes. For patients with drug-refractory PD tremor despite levodopa optimization deep brain stimulation and focused ultrasound are first-line considerations. Surgery can also be highly effective for the treatment medication-refractory tremor in selected patients without motor fluctuations. The present review highlights the clinical essentials of parkinsonian tremor, critically examines available trial data on the effects of medication and surgical approaches and provides guidance for the choice of treatments to control PD tremor in clinical practice.

Tremor in Parkinson's Disease: From Pathophysiology to Advanced Therapies

Background

Tremor is one of the most prevalent symptoms in Parkinson's Disease (PD). The progression and management of tremor in PD can be challenging, as response to dopaminergic agents might be relatively poor, particularly in patients with tremor-dominant PD compared to the akinetic/rigid subtype. In this review, we aim to highlight recent advances in the underlying pathogenesis and treatment modalities for tremor in PD.

Methods

A structured literature search through Embase was conducted using the terms "Parkinson's Disease" AND "tremor" OR "etiology" OR "management" OR "drug resistance" OR "therapy" OR "rehabilitation" OR "surgery." After initial screening, eligible articles were selected with a focus on published literature in the last 10 years.

Discussion

The underlying pathophysiology of tremor in PD remains complex and incompletely understood. Neurodegeneration of dopaminergic neurons in the retrorubral area, in addition to high-power neural oscillations in the cerebello-thalamo-cortical circuit and the basal ganglia, play a major role. Levodopa is the first-line therapeutic option for all motor symptoms, including tremor. The addition of dopamine agonists or anticholinergics can lead to further tremor reduction. Botulinum toxin injection is an effective alternative for patients with pharmacological-resistant tremor who are not seeking advanced therapies. Deep brain stimulation is the most well-established advanced therapy owing to its long-term efficacy, reversibility, and effectiveness in other motor symptoms and fluctuations. Magnetic resonance-guided focused ultrasound is a promising modality, which has the advantage of being incisionless. Cortical and peripheral electrical stimulation are non-invasive innovatory techniques that have demonstrated good efficacy in suppressing intractable tremor.

Dopamine transporter single-photon emission computed tomography-derived radiomics signature for detecting Parkinson's disease

BACKGROUND

We hypothesised that the radiomics signature, which includes texture information of dopamine transporter single-photon emission computed tomography (DAT-SPECT) images for Parkinson's disease (PD), may assist semi-quantitative indices. Herein, we constructed a radiomics signature using DAT-SPECT-derived radiomics features that effectively discriminated PD from healthy individuals and evaluated its classification performance.

RESULTS

We analysed 413 cases of both normal control (NC, n = 101) and PD (n = 312) groups from the Parkinson's Progression Markers Initiative database. Data were divided into the training and two test datasets with different SPECT manufacturers. DAT-SPECT images were spatially normalised to the Montreal Neurologic Institute space. We calculated 930 radiomics features, including intensity- and texture-based features in the caudate, putamen, and pallidum volumes of interest. The striatum uptake ratios (SURs) of the caudate, putamen, and pallidum were also calculated as conventional semi-quantification indices. The least absolute shrinkage and selection operator was used for feature selection and construction of the radiomics signature. The four classification models were constructed using a radiomics signature and/or semi-quantitative indicator. Furthermore, we compared the classification performance of the semi-quantitative indicator alone and the combination with the radiomics signature for the classification models. The receiver operating characteristics (ROC) analysis was used to evaluate the classification performance. The classification performance of SUR_putamen was higher than that of other semi-quantitative indicators. The radiomics signature resulted in a slightly increased area under the ROC curve (AUC) compared to SUR_putamen in each test dataset. When combined with SUR_putamen and radiomics signature, all classification models showed slightly higher AUCs than that of SUR_putamen alone.

CONCLUSION

We constructed a DAT-SPECT image-derived radiomics signature. Performance analysis showed that the current radiomics signature would be helpful for the diagnosis of PD and has the potential to provide robust diagnostic performance.

The Role of the Cerebellum in Tremor - Evidence from Neuroimaging

Background

Neuroimaging research has played a key role in identifying which cerebral changes are associated with tremor. Here we will focus on the cerebellum, which may drive tremor oscillations, process tremor-related afferents, modulate activity in remote brain regions, or a combination.

Methods

On the 6th of October 2021, we conducted a PubMed search to select articles providing neuroimaging evidence for cerebellar involvement in essential tremor (ET), Parkinson's disease (PD) tremor, and dystonic tremor (DT).

Results

In ET, tremor-related activity is found in motor areas of the bilateral cerebellum, and altered functional connectivity within and outside the cerebellum correlates with tremor severity. Furthermore, ET is associated with cerebellar atrophy, but also with compensatory structural changes outside the cerebellum (e.g. supplementary motor area). In PD, tremor-related cerebellar activity and increased cerebello-thalamic coupling has been found. Emerging evidence suggests that the cerebellum plays a key role in dopamine-resistant rest tremor and in postural tremor. Cerebellar structural alterations have been identified in PD, but only some relate to tremor. DT is associated with more widespread cerebral networks than other tremor types.

Discussion

In ET, the cerebellum likely acts as an oscillator, potentially due to loss of inhibitory mechanisms. In contrast, in PD the cerebellum may be a modulator, which contributes to tremor oscillations by influencing the thalamo-cortical system. The precise role of the cerebellum in DT remains unclear. We recommend that future research measures tremor-related activity directly by combining electrophysiology with neuroimaging, while brain stimulation techniques may be used to establish causality.

Highlights

This review of neuroimaging studies has provided convincing evidence that the cerebellum plays a key role in the pathophysiology of ET, PD tremor, and dystonic tremor syndromes. This contribution may consist of driving tremor oscillations, processing tremor-related afferents, modulating activity in remote brain regions, or all the above.

Preserved Extrastriatal 123I-FP-CIT Binding in Scans Without Evidence of Dopaminergic Deficit (SWEDD)

PURPOSE

Scans without evidence of dopaminergic deficit (SWEDD) have been initially described in a minority of subjects with suspected Parkinson's disease (PD). Although a highly controversial entity, longitudinal studies showed that SWEDD cases mostly involve non-degenerative conditions mimicking PD or misattribution of scan images to normal status. Using the Parkinson's Progression Markers Initiative (PPMI) cohort, we undertook a case-controlled analysis of [123I]N-ω-fluoropropyl-2β-carbomethoxy-iodophenyl nortropane ([123I]FP-CIT) single photon emission computed tomography (SPECT) images to measure extrastriatal serotonergic transporter (SERT) density in SWEDD and PD.

PROCEDURES

We included 37 SWEDD cases (mean age 60 years, 33 % female) with available [123I]FP-CIT SPECT imaging and high-resolution T1-weighted magnetic resonance imaging (MRI) for coregistration. Sixty-one controls and 62 similarly aged PD subjects were included for group comparisons. Regional [123I]FP-CIT was extracted with PETPVE12 using geometric transfer matrix and partial volume effect correction.

RESULTS

PD subjects showed significantly lower [123I]FP-CIT binding in both striatal (caudate nucleus and putamen) and extrastriatal regions (pallidum and insula) compared with controls and SWEDD (all between-group p < 0.0001). PD group also showed lower binding in the thalamus relative to controls (p = 0.007). Receiver operating characteristics (ROC) area under the curve (AUC) did not show a significant difference when using extrastriatal region in addition to striatal ROIs for the separation of SWEDD and PD (95 % ROC-AUC for both methods, p = 0.52). In addition, striatal [123I]FP-CIT binding contralateral to the clinically more affected side was usually lower for PD (> 75 %) but not for SWEDD (< 49 %, p < 0.002). No significant difference regarding [123I]FP-CIT binding was observed between SWEDD and controls.

CONCLUSION

These findings corroborate the view that SWEDD cases represent a heterogeneous group of conditions not involving dopaminergic and serotonergic terminals. Further studies are warranted to be assessed whether using extrastriatal [123I]FP-CIT evaluation can be of help in the assessment of degenerative parkinsonism.

Item Response Theory Analysis of the MDS-UPDRS Motor Examination: Tremor vs. Nontremor Items

BACKGROUND

In PD, tremor severity behaves differently from other core motor features. However, the most commonly used assessment of overall motor severity, total MDS-UPDRS Motor Examination (Part 3) score, does not account for this distinction.

OBJECTIVES

To investigate the Motor Examination (Part 3) using Item Response Theory approaches focusing on sample-independent strategies that assess how well items measure latent models of PD motor severity.

METHODS

Data from 6,298 PD patients were analyzed with graded response model Item Response Theory approaches involving two analyses all 33 Part 3 items versus the 10 tremor items and 23 bradykinesia, rigidity, gait, and posture items considered separately. The strength of relationship between items and the latent measure of parkinsonian motor severity (discrimination parameter) and calculated thresholds (location parameters) were assessed using the mirt program implemented in R (R Foundation for Statistical Computing, Vienna, Austria).

RESULTS

Analyzing all Part 3 items together, nontremor items demonstrated good discrimination parameters (mean = 1.83 ± 0.37) and range of thresholds (-1.73 to +4.42), but tremor items had poor discrimination (mean = 0.52 ± 0.76) and thresholds (-0.69 to 14.29). Segregating nontremor from tremor items in two independent analyses provided markedly improved discrimination and location parameters for both.

CONCLUSIONS

MDS-UPDRS Part 3 tremor and nontremor items have very different relations to the construct of PD severity. Strongly improved clinimetric properties for Part 3 are obtained when tremor and nontremor items are considered separately. We suggest that evaluating PD motor severity, as an operationalized summary measure, is best attained through separate analyses with tremor and nontremor motor scores. © 2020 International Parkinson and Movement Disorder Society.

Dopamine-responsive and dopamine-resistant resting tremor in Parkinson disease

OBJECTIVE

We tested the hypothesis that there are 2 distinct phenotypes of Parkinson tremor, based on interindividual differences in the response of resting tremor to dopaminergic medication. We also investigated whether this pattern is specific to tremor by comparing interindividual differences in the dopamine response of tremor to that of bradykinesia.

METHODS

In this exploratory study, we performed a levodopa challenge in 76 tremulous patients with Parkinson tremor. Clinical scores (Movement Disorders Society-sponsored version of the Unified Parkinson's Disease Rating Scale part III) were collected "off" and "on" a standardized dopaminergic challenge (200/50 mg dispersible levodopa-benserazide). In both sessions, resting tremor intensity was quantified using accelerometry, both during rest and during cognitive coactivation. Bradykinesia was quantified using a speeded keyboard test. We calculated the distribution of dopamine-responsiveness for resting tremor and bradykinesia. In 41 patients, a double-blinded, placebo-controlled dopaminergic challenge was repeated after approximately 6 months.

RESULTS

The dopamine response of resting tremor, but not bradykinesia, significantly departed from a normal distribution. A cluster analysis on 3 clinical and electrophysiologic markers of tremor dopamine-responsiveness revealed 3 clusters: dopamine-responsive, intermediate, and dopamine-resistant tremor. A repeated levodopa challenge after 6 months confirmed this classification. Patients with dopamine-responsive tremor had greater disease severity and tended to have a higher prevalence of dyskinesia.

CONCLUSION

Parkinson resting tremor can be divided into 3 partially overlapping phenotypes, based on the dopamine response. These tremor phenotypes may be associated with different underlying pathophysiologic mechanisms, requiring a different therapeutic approach.

Extrastriatal 123I-FP-CIT SPECT impairment in Parkinson's disease - the PPMI cohort

Background

Neuropathological data and nuclear medicine imaging show extensive serotonergic impairment in Parkinson’s disease (PD). We undertook a case-controlled analysis of ¹²³I-FP-CIT SPECT images to measure extrastriatal serotonergic transporters (SERT) in PD using the Parkinson’s Progression Markers Initiative (PPMI) cohort.

Methods

We included all PD (n = 154) and Control subjects (n = 62) with available ¹²³I-FP-CIT SPECT imaging and high-resolution T1-weighted MRI for coregistration (PD: mean age 61.6 years, 62% male, disease duration 26 months, MDS-UPDRS III score 22). ¹²³I-FP-CIT SPECT images were processed with PETPVE12 using an exploratory voxel-wise analysis including partial-volume effect correction. Linear regressions were performed in the PD group to assess correlations between region of interest ¹²³I-FP-CIT uptake and clinical motor and non-motor impairment.

Results

Compared to Controls, PD exhibited an uptake reduction in bilateral caudate nucleus, putamen, insula, amygdala and right pallidum (family-wise error (FWE)-corrected p <  0.05). While lower putaminal uptake on the contralateral side to clinically more affected side was associated with higher MDS-UPDRS III score (p = 0.022), we found a trend association between higher geriatric depression scale and lower pallidum uptake (p = 0.09). Higher SCOPA-AUT gastrointestinal subscore was associated with lower uptake in mean putamen and caudate nucleus (p = 0.01 to 0.03), whereas urological subscore was inversely correlated with mean caudate nucleus, putamen, and pallidum uptake (p = 0.002 to 0.03). REM sleep behaviour disorder screening questionnaire was associated with lower ¹²³I-FP-CIT binding in caudate nucleus, putamen and pallidum (all p <  0.05). No significant association was found for Montreal Cognitive Assessment (all p > 0.45) or excessive daytime sleepiness (all p > 0.29).

Conclusions

In addition to the well-established striatal deficit, this study provides evidence of a major extrastriatal ¹²³I-FP-CIT impairment, and therefore of an altered serotonergic transmission in early PD.

Effects of deep brain stimulation on rest tremor progression in early stage Parkinson disease

OBJECTIVE

To evaluate whether the progression of individual motor features was influenced by early deep brain stimulation (DBS), a post hoc analysis of Unified Parkinson's Disease Rating Scale-III (UPDRS-III) score (after a 7-day washout) was conducted from the 2-year DBS in early Parkinson disease (PD) pilot trial dataset.

METHODS

The prospective pilot trial enrolled patients with PD aged 50-75 years, treated with PD medications for 6 months-4 years, and no history of dyskinesia or other motor fluctuations, who were randomized to receive optimal drug therapy (ODT) or DBS plus ODT (DBS + ODT). At baseline and 6, 12, 18, and 24 months, all patients stopped all PD therapy for 1 week (medication and stimulation, if applicable). UPDRS-III "off" item scores were compared between the ODT and DBS + ODT groups (n = 28); items with significant between-group differences were analyzed further.

RESULTS

UPDRS-III "off" rest tremor score change from baseline to 24 months was worse in patients receiving ODT vs DBS + ODT (p = 0.002). Rest tremor slopes from baseline to 24 months favored DBS + ODT both "off" and "on" therapy (p < 0.001, p = 0.003, respectively). More ODT patients developed new rest tremor in previously unaffected limbs than those receiving DBS + ODT (p = 0.001).

CONCLUSIONS

These results suggest the possibility that DBS in early PD may slow rest tremor progression. Future investigation in a larger cohort is needed, and these findings will be tested in the Food and Drug Administration-approved, phase III, pivotal, multicenter clinical trial evaluating DBS in early PD.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that for patients with early PD, DBS may slow the progression of rest tremor.