The nature of postural tremor in Parkinson disease

Distinguishing essential tremor from Parkinson's disease: clinical and experimental tools

INTRODUCTION

Essential tremor (ET) and Parkinson's disease (PD) are the most common causes of tremor and the most prevalent movement disorders, with overlapping clinical features that can lead to diagnostic challenges, especially in the early stages.

AREAS COVERED

In the present paper, the authors review the clinical and experimental studies and emphasized the major aspects to differentiate between ET and PD, with particular attention to cardinal phenomenological features of these two conditions. Ancillary and experimental techniques, including neurophysiology, neuroimaging, fluid biomarker evaluation, and innovative methods, are also discussed for their role in differential diagnosis between ET and PD. Special attention is given to investigations and tools applicable in the early stages of the diseases, when the differential diagnosis between the two conditions is more challenging. Furthermore, the authors discuss knowledge gaps and unsolved issues in the field.

EXPERT OPINION

Distinguishing ET and PD is crucial for prognostic purposes and appropriate treatment. Additionally, accurate diagnosis is critical for optimizing clinical and experimental research on pathophysiology and innovative therapies. In a few years, integrated technologies could enable accurate, reliable diagnosis from early disease stages or prodromal stages in at-risk populations, but further research combining different techniques is needed.

Motor and non-motor outcome in tremor dominant Parkinson's disease after MR-guided focused ultrasound thalamotomy

BACKGROUND AND OBJECTIVES

Magnetic Resonance-guided Focused Ultrasound (MRgFUS) is an emerging technique for the treatment of severe, medication-refractory tremor syndromes. We here report motor and non-motor outcomes 6 and 12 months after unilateral MRgFUS thalamotomy in tremor-dominant Parkinson's disease (tdPD).

METHODS

25 patients with tdPD underwent neuropsychological evaluation including standardized questionnaires of disability, quality of life (QoL), mood, anxiety, apathy, sleep disturbances, and cognition at baseline, 6 and 12 months after MRgFUS. Motor outcome was evaluated using the Clinical Rating Scale for Tremor (CRST) and Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS). In addition, side effects and QoL of family caregivers were assessed.

RESULTS

12 months after MRgFUS significant improvements were evident in the tremor subscores. Patients with concomitant rest and postural tremor showed better tremor outcomes compared to patients with predominant rest tremor. There were no differences in the non-motor assessments. No cognitive decline was observed. Side effects were mostly transient (54%) and classified as mild (62%). No changes in the caregivers' QoL could be observed.

CONCLUSION

We found no changes in mood, anxiety, apathy, sleep, cognition or persistent worsening of gait disturbances after unilateral MRgFUS thalamotomy in tdPD. Concomitant postural tremors responded better to treatment than predominant rest tremors.

Re-emergent Tremor in Parkinson's Disease: Evidence of Pathologic β and Prokinetic γ Activity

BACKGROUND

Re-emergent tremor is characterized as a continuation of resting tremor and is often highly therapy refractory. This study examines variations in brain activity and oscillatory responses between resting and re-emergent tremors in Parkinson's disease.

METHODS

Forty patients with Parkinson's disease (25 males, mean age, 66.78 ± 5.03 years) and 40 age- and sex-matched healthy controls were included in the study. Electroencephalogram and electromyography signals were simultaneously recorded during resting and re-emergent tremors in levodopa on and off states for patients and mimicked by healthy controls. Brain activity was localized using the beamforming technique, and information flow between sources was estimated using effective connectivity. Cross-frequency coupling was used to assess neuronal oscillations between tremor frequency and canonical frequency oscillations.

RESULTS

During levodopa on, differences in brain activity were observed in the premotor cortex and cerebellum in both the patient and control groups. However, Parkinson's disease patients also exhibited additional activity in the primary sensorimotor cortex. On withdrawal of levodopa, different source patterns were observed in the supplementary motor area and basal ganglia area. Additionally, levodopa was found to suppress the strength of connectivity (P < 0.001) between the identified sources and influence the tremor frequency-related coupling, leading to a decrease in β (P < 0.001) and an increase in γ frequency coupling (P < 0.001).

CONCLUSIONS

Distinct variations in cortical-subcortical brain activity are evident in tremor phenotypes. The primary sensorimotor cortex plays a crucial role in the generation of re-emergent tremor. Moreover, oscillatory neuronal responses in pathological β and prokinetic γ activity are specific to tremor phenotypes. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Bedside clinical assessment of patients with common upper limb tremor and algorithmic approach

The diagnostic approach for patients with tremor is challenging due to the complex and overlapping phenotypes among tremor syndromes. The first step in the evaluation of tremor is to identify the tremulous movement and exclude the tremor mimics. The second step is to classify the tremor syndrome based on the characteristics of tremor from historical clues and focused examination (Axis 1). Comprehensive tremor examinations involve the assessment of tremor in different conditions (rest, action or mixed, position or task-specific), distribution of tremor (upper limb, lower limb, head, jaw), positive signs for functional tremor (FT) if suspected (distractibility, entrainment, co-contraction), and associated neurological signs including parkinsonism, dystonic posture, cerebellar/brainstem signs, neuropathy, and cognitive impairment. A pivotal feature in this step is to determine any distinct feature of a specific isolated or combined tremor syndrome. In this review, we propose an algorithm to assess upper limb tremors. Ancillary testing should be performed if clinical evaluation is unclear. The choice of investigation depends on the types of tremors considered to narrow down the spectrum of etiology (Axis 2). Laboratory blood tests are considered for acute onset and acute worsening of tremors, while structural neuroimaging is indicated in unilateral tremors with acute onset, nonclassical presentations, and a combination of neurological symptoms. Neurophysiological study is an important tool that aids in distinguishing between tremor and myoclonus, etiology of tremor and document specific signs of FT. Treatment is mainly symptomatic based depending on the etiology of the tremor and the patient's disabilities.

Cholesterol metabolism: physiological regulation and diseases

Cholesterol homeostasis is crucial for cellular and systemic function. The disorder of cholesterol metabolism not only accelerates the onset of cardiovascular disease (CVD) but is also the fundamental cause of other ailments. The regulation of cholesterol metabolism in the human is an extremely complex process. Due to the dynamic balance between cholesterol synthesis, intake, efflux and storage, cholesterol metabolism generally remains secure. Disruption of any of these links is likely to have adverse effects on the body. At present, increasing evidence suggests that abnormal cholesterol metabolism is closely related to various systemic diseases. However, the exact mechanism by which cholesterol metabolism contributes to disease pathogenesis remains unclear, and there are still unknown factors. In this review, we outline the metabolic process of cholesterol in the human body, especially reverse cholesterol transport (RCT). Then, we discuss separately the impact of abnormal cholesterol metabolism on common diseases and potential therapeutic targets for each disease, including CVD, tumors, neurological diseases, and immune system diseases. At the end of this review, we focus on the effect of cholesterol metabolism on eye diseases. In short, we hope to provide more new ideas for the pathogenesis and treatment of diseases from the perspective of cholesterol.

[Tremor-dominant form of Parkinson's disease]

The article is of a review nature and is devoted to tremor, one of the maladaptive and difficult-to-treat symptoms of Parkinson's disease (PD). Along with the classic rest tremor, patients with PD may experience tremor of other modalities: postural tremor, kinetic tremor, which reflects a multimodal mechanism of tremor formation involving multiple neurotransmitter systems. The unpredictable response to therapeutic options, the ambiguous response to levodopa, also reflects the role of multiple underlying pathophysiological processes. Among the drug methods of tremor correction, preference is given to dopamine receptor agonists - due to the spectrum of their pharmaceutical action, high efficiency in relation to all leading motor and a number of non-motor manifestations. The evidence for advanced neurosurgical, non-invasive modalities is mixed, and there are insufficient comparative studies to assess their efficacy in patients with tremor-dominant forms of PD.

The role of laboratory investigations in the classification of tremors

INTRODUCTION

Tremor is the most common movement disorder. Although clinical examination plays a significant role in evaluating patients with tremor, laboratory tests are useful to classify tremors according to the recent two-axis approach proposed by the International Parkinson and Movement Disorders Society.

METHODS

In the present review, we will discuss the usefulness and applicability of the various diagnostic methods in classifying and diagnosing tremors. We will evaluate a number of techniques, including laboratory and genetic tests, neurophysiology, and neuroimaging. The role of newly introduced innovative tremor assessment methods will also be discussed.

RESULTS

Neurophysiology plays a crucial role in tremor definition and classification, and it can be useful for the identification of specific tremor syndromes. Laboratory and genetic tests and neuroimaging may be of paramount importance in identifying specific etiologies. Highly promising innovative technologies are being developed for both clinical and research purposes.

CONCLUSIONS

Overall, laboratory investigations may support clinicians in the diagnostic process of tremor. Also, combining data from different techniques can help improve understanding of the pathophysiological bases underlying tremors and guide therapeutic management.

Modeling of cerebellar transcranial electrical stimulation effects on hand tremor in Parkinson's disease

Introduction

Parkinson's disease (PD) is a neurodegenerative disorder with different motor and neurocognitive symptoms. Tremor is a well-known symptom of this disease. Increasing evidence suggested that the cerebellum may substantially contribute to tremors as a clinical symptom of PD. However, the theoretical foundations behind these observations are not yet fully understood.

Methods

In this study, a computational model is proposed to consider the role of the cerebellum and to show the effectiveness of cerebellar transcranial alternating current stimulation (tACS) on the rest tremor in participants with PD. The proposed model consists of the cortex, cerebellum, spinal circuit-muscular system (SC-MS), and basal ganglia blocks as the most critical parts of the brain, which are involved in generating rest tremors. The cortex, cerebellum, and SC-MS blocks were modeled using Van der Pol oscillators that interacted through synchronization procedures. Basal ganglia are considered as a regulator of the coupling weights defined between oscillators. In order to evaluate the global behavior of the model, we applied tACS on the cerebellum of fifteen PD patients for 15 min at each patient's peak frequency of their rest tremors. A tri-axial accelerometer recorded rest tremors before, during, and after the tACS.

Results and Discussion

The simulation of the model provides a suggestion for the possible role of the cerebellum on rest tremors and how cerebellar tACS can affect these tremors. Results of human experiments also showed that the online and offline effects of cerebellar tACS could lead to the reduction of rest tremors significantly by about %76 and %68, respectively. Our findings suggest that the cerebellar tACS could serve as a reliable, therapeutic technique to suppress the PD tremor.

Parkinson's Disease Tremor Differentially Responds to Levodopa and Subthalamic Stimulation

Background

Tremor in Parkinson's disease (PD) has an inconsistent response to levodopa and subthalamic deep brain stimulation (STN-DBS).

Objectives

To identify predictive factors of PD tremor responsiveness to levodopa and STN-DBS.

Material and Methods

PD patients with upper limb tremor who underwent STN-DBS were included. The levodopa responsiveness of tremor (overall, postural, and rest sub-components), was assessed using the relevant Unified Parkinson's Disease Rating Scale-III items performed during the preoperative assessment. Post-surgical outcomes were similarly assessed ON and OFF stimulation. A score for the rest/postural tremor ratio was used to determine the influence of rest and postural tremor severity on STN-DBS outcome. Factors predictive of tremor responsiveness were determined using multiple linear regression modeling. Volume of tissue activated measurement coupled to voxel-based analysis was performed to identify anatomical clusters associated with motor symptoms improvement.

Results

One hundred and sixty five patients were included in this study. Male gender was negatively correlated with tremor responsiveness to levodopa, whereas the ratio of rest/postural tremor was positively correlated with both levodopa responsiveness and STN-DBS tremor outcome. Clusters corresponding to improvement of tremor were in the subthalamic nucleus, the zona incerta and the thalamus, whereas clusters corresponding to improvement for akinesia and rigidity were located within the subthalamic nucleus.

Conclusion

More severe postural tremor and less severe rest tremor were associated with both poorer levodopa and STN-DBS response. The different locations of clusters associated with best correction of tremor and other parkinsonian features suggest that STN-DBS effect on PD symptoms is underpinned by the modulation of different networks.

A novel MRI-based volumetric index for monitoring the motor symptoms in Parkinson's disease

BACKGROUND

Conventional MRI scans have limited usefulness in monitoring Parkinson's disease as they typically do not show any disease-specific brain abnormalities. This study aimed to identify an imaging biomarker for tracking motor symptom progression by using a multivariate statistical approach that can combine gray matter volume information from multiple brain regions into a single score specific to each PD patient.

METHODS

A cohort of 150 patients underwent MRI at baseline and had their motor symptoms tracked for up to 10 years using MDS-UPDRS-III, with motor symptoms focused on total and subscores, including rigidity, bradykinesia, postural instability, and gait disturbances, resting tremor, and postural-kinetic tremor. Gray matter volume extracted from MRI data was summarized into a patient-specific summary score using Mahalanobis distance, MGMV. MDS-UPDRS-III's progression and its association with MGMV were modeled via linear mixed-effects models over 5- and 10-year follow-up periods.

RESULTS

Over the 5-year follow-up, there was a significant increase (P < 0.05) in MDS-UPDRS-III total and subscores, except for postural-kinetic tremor. Over the 10-year follow-up, all MDS-UPDRS-III scores increased significantly (P < 0.05). A higher baseline MGMV was associated with a significant increase in MDS-UPDRS-III total, bradykinesia, postural instability and gait disturbances, and resting tremor (P < 0.05) over the 5-year follow-up, but only with total, bradykinesia, and postural instability and gait disturbances during the 10-year follow-up (P < 0.05).

CONCLUSIONS

Higher MGMV scores were linked to faster motor symptom progression, suggesting it could be a valuable marker for clinicians monitoring Parkinson's disease over time.

Subtle changes in central dopaminergic tone underlie bradykinesia in essential tremor

INTRODUCTION

In this research, our primary objective was to explore the correlation between basal ganglia dopaminergic neurotransmission, assessed using 123I-FP-CIT (DAT-SPECT), and finger movements abnormalities in patients with essential tremor (ET) and Parkinson's disease (PD).

METHODS

We enrolled 16 patients with ET, 17 with PD, and 18 healthy controls (HC). Each participant underwent comprehensive clinical evaluations, kinematic assessments of finger tapping. ET and PD patients underwent DAT-SPECT imaging. The DAT-SPECT scans were subjected to both visual and semi-quantitative analysis using DaTQUANT®. We then investigated the correlations between the clinical, kinematic, and DAT-SPECT data, in patients.

RESULTS

Our findings confirm that individuals with ET exhibited slower finger tapping than HC. Visual evaluation of radiotracer uptake in both striata demonstrated normal levels within the ET patient cohort, while PD patients displayed reduced uptake. However, there was notable heterogeneity in the quantification of uptake within the striata among ET patients. Additionally, we found a correlation between the amount of radiotracer uptake in the striatum and movement velocity during finger tapping in patients. Specifically, lower radioligand uptake corresponded to decreased movement velocity (ET: coef. = 0.53, p-adj = 0.03; PD: coef. = 0.59, p-adj = 0.01).

CONCLUSION

The study's findings suggest a potential link between subtle changes in central dopaminergic tone and altered voluntary movement execution, in ET. These results provide further insights into the pathophysiology of ET. However, longitudinal studies are essential to determine whether the slight reduction in dopaminergic tone observed in ET patients represents a distinct subtype of the disease or could serve as a predictor for the clinical progression into PD.

The Clinical Profile of Tremor in Parkinson's Disease

Background

Tremor is one of the most troublesome manifestations of Parkinson's Disease (PD) and its response to dopaminergic medication is variable; an evidence-based framework of PD tremor is lacking yet needed to inform future investigations.

Objective

To perform a comprehensive longitudinal analysis on the clinical characteristics, course and response to dopaminergic medication of tremor in de-novo PD.

Methods

Three hundred ninety-seven participants were recruited in the Parkinson Progressive Markers Initiative, a prospective observational cohort study in early de-novo PD. Rest, postural and kinetic tremor scores were extracted from the Movement Disorders Society-Unified Parkinson's Disease Rating Scale. Progression from baseline to 7-year follow-up of rest, postural and kinetic tremor scores, and their response to in-clinic dopaminergic medication were analyzed through linear mixed-effects models adjusted for age, sex and disease duration at enrollment. A sensitivity analysis was conducted through subgroup and imputation analyses.

Results

382 (96.2%) participants showed tremor and 346 (87.2%) showed rest tremor in at least one assessment over 7 years. Off-state rest, postural and kinetic tremor scores increased significantly over time, coupled with a significant effect of dopaminergic medication in reducing tremor scores. However, at each assessment, tremor was unresponsive to in-clinic dopaminergic medication in at least 20% of participants for rest, 30% for postural and 38% for kinetic tremor.

Conclusions

PD tremor is a troublesome manifestation, with increasing severity and variable response to medications. This analysis details the current clinical natural history of tremor in early-to-mid stage PD, outlining an evidence-based framework for future pathophysiological and interventional studies.

Detecting Minor Symptoms of Parkinson's Disease in the Wild Using Bi-LSTM with Attention Mechanism

Parkinson's disease (PD) is a neurodegenerative disorder characterized by motor and nonmotor impairment with various implications on patients' quality of life. Since currently available therapies are only symptomatic, identifying individuals with prodromal, preclinical, or early-stage PD is crucial, as they would be ideal candidates for future disease-modifying therapies. Our analysis aims to develop a robust model for accurate PD detection using accelerometer data collected from PD and non-PD individuals with mild or no tremor during phone conversations. An open-access dataset comprising accelerometer recordings from 22 PD patients and 11 healthy controls (HCs) was utilized. The data were preprocessed to extract relevant time-, frequency-, and energy-related features, and a bidirectional long short-term memory (Bi-LSTM) model with attention mechanism was employed for classification. The performance of the model was evaluated using fivefold cross-validation, and metrics of accuracy, precision, recall, specificity, and f1-score were computed. The proposed model demonstrated high accuracy (98%), precision (99%), recall (98%), specificity (96%), and f1-score (98%) in accurately distinguishing PD patients from HCs. Our findings indicate that the proposed model outperforms existing approaches and holds promise for detection of PD with subtle symptoms, like tremor, in the wild. Such symptoms can present in the early or even prodromal stage of the disease, and appropriate mobile-based applications may be a practical tool in real-life settings to alert individuals at risk to seek medical assistance or give patients feedback in monitoring their symptoms.

Distal Upper Limb Tremor during Walking in Parkinson's Disease

Background

Distal upper limb tremor during walking (TW) is frequently observed in Parkinson's disease (PD) but its clinical features are unknown.

Objective

To characterize the occurrence and the clinical features of TW in comparison to the other types of tremors in PD.

Methods

Fifty-one PD patients with rest tremor were evaluated off- and on-treatment. Occurrence, body distribution, severity and latency of TW and of other tremor types were assessed.

Results

TW was present in 78% of the PD patients examined. TW body distribution and severity were similar to those of rest and re-emergent tremor but different from the postural tremor presented by the same patients. TW latency, observed in 85% of patients, was on average 5.8 s. Dopaminergic treatment significantly improved TW, rest, and re-emergent tremor severity but left TW latency unaffected.

Conclusions

TW is a frequent motor sign in PD and is likely a clinical variant of rest tremor.

Clinical Heterogeneity of Essential Tremor: Understanding Neural Substrates of Action Tremor Subtypes

Essential tremor (ET) is a common movement disorder affecting millions of people. Studies of ET patients and perturbations in animal models have provided a foundation for the neural networks involved in its pathophysiology. However, ET encompasses a wide variability of phenotypic expression, and this may be the consequence of dysfunction in distinct subcircuits in the brain. The cerebello-thalamo-cortical circuit is a common substrate for the multiple subtypes of action tremor. Within the cerebellum, three sets of cerebellar cortex-deep cerebellar nuclei connections are important for tremor. The lateral hemispheres and dentate nuclei may be involved in intention, postural and isometric tremor. The intermediate zone and interposed nuclei could be involved in intention tremor. The vermis and fastigial nuclei could be involved in head and proximal upper extremity tremor. Studying distinct cerebellar circuitry will provide important framework for understanding the clinical heterogeneity of ET.

The effect of standing posture on amplitude and variability of postural tremor in Parkinson’s disease

INTRODUCTION

This study examined whether altering body position (i.e., sitting or standing) affected the dynamics of physiological tremor for healthy older adults and persons with Parkinson's disease (PD). It was also of interest to determine how consistent the tremor was for both groups as determined by examining changes in within-subject variability of tremor amplitude, regularity and frequency.

METHODS

Ten Parkinsonian participants (65.1±3.2 yrs.) and twelve elderly persons (71.2±2.6 yrs.) participated in this study. Tremor was collected from the index finger and hand segments using lightweight accelerometers during the performance of a bilateral pointing task. Persons performed the pointing task in a standing or sitting position.

RESULTS

As expected, the tremor for the PD persons was greater in magnitude (mean RMS, peak power), more regular (lower SampEn), and more inconsistent from trial-to-trial (increased intra-individual variability, IIV) than the tremor recorded for the elderly. Further, when assessed during standing, the magnitude of the tremor for all individuals (elderly and PD) was greater, more variable, and less complex compared to the tremor when assessed during the sitting posture. The only measure which did not change within each group was the frequency of the major tremor peak which remained consistent, showing no significant change between limbs or as a function of the posture adopted.

CONCLUSION

The findings revealed that tremor increased in amplitude and decreased in regularity for all individuals was assessed when standing compared to sitting. It is likely that these increases were task-related, reflecting the increased physical demands of performing the task when standing rather than being driven by specific age- or disease-related changes in the mechanisms underlying tremorgenesis. Further, the tremor for the PD individuals tended to be more variable from trial-by-trial in terms of both amplitude and regularity as compared to the elderly persons. Interestingly, the only tremor metric which showed no change within each group was the frequency of the major tremor peak which was consistent within both groups irrespective of the posture adopted.

Diagnostic Uncertainties in Tremor

The approach and diagnosis of patients with tremor may be challenging for clinicians. According to the most recent consensus statement by the Task Force on Tremor of the International Parkinson Movement Disorder Society, the differentiation between action (i.e., kinetic, postural, intention), resting, and other task- and position-specific tremors is crucial to this goal. In addition, patients with tremor must be carefully examined for other relevant features, including the topography of the tremor, since it can involve different body areas and possibly associate with neurological signs of uncertain significance. Following the characterization of major clinical features, it may be useful to define, whenever possible, a particular tremor syndrome and to narrow down the spectrum of possible etiologies. First, it is important to distinguish between physiological and pathological tremor, and, in the latter case, to differentiate between the underlying pathological conditions. A correct approach to tremor is particularly relevant for appropriate referral, counseling, prognosis definition, and therapeutic management of patients. The purpose of this review is to outline the possible diagnostic uncertainties that may be encountered in clinical practice in the approach to patients with tremor. In addition to an emphasis on a clinical approach, this review discusses the important ancillary role of neurophysiology and innovative technologies, neuroimaging, and genetics in the diagnostic process.

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.

Writing tremor in Parkinson's disease: frequency and associated clinical features

Action tremor in Parkinson's disease may present in up to 46% of patients, either as postural or kinetic tremor. How action tremor may affect handwriting has been the object of some investigations; however, clinical features of writing tremor in Parkinson's disease are still not well-characterised. One hundred consecutive patients with idiopathic Parkinson's disease were included in the study. Demographic and clinical data were collected through a standardized questionnaire. Patients were assessed for the presence of rest, action and writing tremor in on condition. The effect of a standardised sensory trick (gently touching the wrist of the upper limb manifesting tremor with the contralateral hand) was also investigated in all patients with action tremor. Writing tremor was found in 10% of patients (26% of patients with postural/kinetic tremor, either alone or in combination with rest tremor). Severity of writing tremor did not correlated with that of the other tremor variants and to the other clinical variables. Writing tremor was task-specific in 4/10 patients, no task-specific in 6/10. Sensory trick was effective on writing tremor in two patients but did not improve action tremor in any of the study patients. Results showed that writing tremor in Parkinson's disease is less common than other tremor variants, may be associated with other forms of action tremor, and may sometimes have dystonic features, including task-specificity and sensitivity to sensory trick.

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.

Lower serum triglyceride levels linked to more severe motor performance in Parkinson’s disease

Introduction

Emerging evidence has suggested that lipid metabolism is correlated with Parkinson’s disease (PD) onset and progression. However, the effect of lipid metabolism on motor performance in PD patients is still unknown. This study estimated the association between lipid profiles and the severity of motor performance in PD.

Methods

This cross-sectional study enrolled 279 idiopathic PD patients from the Department of Neurology of Beijing Tiantan Hospital from May 2016 to August 2018. Serum triglyceride (TG), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), apolipoprotein A1 (Apo-A1), and apolipoprotein B (Apo-B) levels were detected in fast serum samples. Motor performance was assessed by Movement Disorder Society-Unified Parkinson’s Disease Rating Scale part III (MDS-UPDRS III) total scores and subscores in these patients. The associations of lipid profiles with motor performance were analyzed using multivariable linear regression models.

Results

Compared to males, females with PD exhibited significantly higher serum TC, LDL-C, HDL-C, Apo-A1, and Apo-B levels. When accounting for covariates, lower serum TG levels were significantly associated with higher MDS-UPDRS III total scores and gait/postural instability subscores. Additionally, the univariate linear regression model showed that in males with PD, serum HDL-C or Apo-A1 levels were significantly associated with tremor subscores.

Conclusion

Lower serum TG levels were associated with more severe motor performance in patients with PD and TG may be a potential predictive biomarker for motor performance in PD patients.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10072-022-06113-9.

Clinical neurophysiology of Parkinson's disease and parkinsonism

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This review is part of the series on the clinical neurophysiology of movement disorders and focuses on Parkinson’s disease and parkinsonism.

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The pathophysiology of cardinal parkinsonian motor symptoms and myoclonus are reviewed.

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The recordings from microelectrode and deep brain stimulation electrodes are reported in detail.

This review is part of the series on the clinical neurophysiology of movement disorders. It focuses on Parkinson’s disease and parkinsonism. The topics covered include the pathophysiology of tremor, rigidity and bradykinesia, balance and gait disturbance and myoclonus in Parkinson’s disease. The use of electroencephalography, electromyography, long latency reflexes, cutaneous silent period, studies of cortical excitability with single and paired transcranial magnetic stimulation, studies of plasticity, intraoperative microelectrode recordings and recording of local field potentials from deep brain stimulation, and electrocorticography are also reviewed. In addition to advancing knowledge of pathophysiology, neurophysiological studies can be useful in refining the diagnosis, localization of surgical targets, and help to develop novel therapies for Parkinson’s disease.

Opicapone, a Novel Catechol-O-methyl Transferase Inhibitor, for Treatment of Parkinson's Disease "Off" Episodes

Parkinson's Disease (PD) is a common neurodegenerative disorder and the leading cause of disability. It causes significant morbidity and disability through a plethora of symptoms, including movement disorders, sleep disturbances, and cognitive and psychiatric symptoms. The traditional pathogenesis theory of PD involves the loss of dopaminergic neurons in the substantia nigra (SN). Classically, treatment is pursued with an assortment of medications that are directed at overcoming this deficiency with levodopa being central to most treatment plans. Patients taking levodopa tend to experience "off episodes" with decreasing medication levels, causing large fluctuations in their symptoms. These off episodes are disturbing and a source of morbidity for these patients. Opicapone is a novel, peripherally acting Catechol-O-methyl transferase (COMT) inhibitor that is used as adjunctive therapy to carbidopa/levodopa for treatment and prevention of "off episodes." It has been approved for use as an adjunct to levodopa since 2016 in Europe and has recently (April 2020) gained FDA approval for use in the USA. By inhibiting COMT, opicapone slows levodopa metabolism and increases its availability. Several clinical studies demonstrated significant improvement in treatment efficacy and reduction in duration of "off episodes." The main side effect demonstrated was dyskinesia, mostly with the 100mg dose, which is higher than the approved, effective dose of 50mg. Post-marketing surveillance and analysis are required to further elucidate its safety profile and contribute to patient selection. This paper reviews the seminal and latest evidence in the treatment of PD "off episodes" with the novel drug Opicapone, including efficacy, safety, and clinical indications.

Virtual exam for Parkinson's disease enables frequent and reliable remote measurements of motor function

Sensor-based remote monitoring could help better track Parkinson's disease (PD) progression, and measure patients' response to putative disease-modifying therapeutic interventions. To be useful, the remotely-collected measurements should be valid, reliable, and sensitive to change, and people with PD must engage with the technology. We developed a smartwatch-based active assessment that enables unsupervised measurement of motor signs of PD. Participants with early-stage PD (N = 388, 64% men, average age 63) wore a smartwatch for a median of 390 days. Participants performed unsupervised motor tasks both in-clinic (once) and remotely (twice weekly for one year). Dropout rate was 5.4%. Median wear-time was 21.1 h/day, and 59% of per-protocol remote assessments were completed. Analytical validation was established for in-clinic measurements, which showed moderate-to-strong correlations with consensus MDS-UPDRS Part III ratings for rest tremor (⍴ = 0.70), bradykinesia (⍴ = -0.62), and gait (⍴ = -0.46). Test-retest reliability of remote measurements, aggregated monthly, was good-to-excellent (ICC = 0.75-0.96). Remote measurements were sensitive to the known effects of dopaminergic medication (on vs off Cohen's d = 0.19-0.54). Of note, in-clinic assessments often did not reflect the patients' typical status at home. This demonstrates the feasibility of smartwatch-based unsupervised active tests, and establishes the analytical validity of associated digital measurements. Weekly measurements provide a real-life distribution of disease severity, as it fluctuates longitudinally. Sensitivity to medication-induced change and improved reliability imply that these methods could help reduce sample sizes needed to demonstrate a response to therapeutic interventions or disease progression.

Deep brain stimulation for arm tremor: A randomized trial comparing two targets

OBJECTIVE

Deep brain stimulation (DBS) of the thalamic ventral intermediate nucleus (VIM) effectively suppresses arm tremor. Uncontrolled studies suggest the posterior subthalamic area (PSA) may be superior. We compared the intra-individual efficacy of VIM- versus PSA-DBS on tremor suppression and arm function.

METHODS

We performed a randomized, double-blind, crossover trial at Oslo University Hospital in patients (18-80 years) with isolated or combined action tremor affecting at least one arm. Four-contact DBS leads were implanted (bi- or unilaterally) with a trajectory to cover the VIM (upper two contacts) and PSA (lower two contacts). Patients were randomized (1:1 ratio) post-surgery to: Group 1, VIM-stimulation months 0-3 (period 1), then PSA-stimulation months 4-6 (period 2); Group 2, PSA-stimulation first, then VIM-stimulation. Primary endpoint was the difference in improvement from baseline to the end of the VIM- versus PSA-period in the sum of the dominant arm tremor scores of the Fahn-Tolosa-Marin Tremor Rating Scale (FTMTRS), items 5/6 + 10-14.

RESULTS

Forty-five patients were randomized to Group 1 (n = 23) or 2 (n = 22). In the primary endpoint per-protocol analysis (mixed model, n = 40), mean difference in the sum FTMTRS score improvement for the dominant arm was -2.65 points (95% CI -4.33 to -0.97; p = 0.002). The difference in favour of PSA stimulation was highly significant in period 2, but not period 1.

INTERPRETATION

Our randomized trial demonstrated that PSA stimulation provided superior tremor suppression compared with VIM stimulation. A period effect reducing tremor for up to three months in both groups was most likely attributed to a post-surgery stun effect. This article is protected by copyright. All rights reserved.

Essential tremor: Clinical perspectives and pathophysiology

Essential tremor (ET) is one of the most common neurological disorders and can be highly disabling. In recent years, studies on the clinical perspectives and pathophysiology have advanced our understanding of ET. Specifically, clinical heterogeneity of ET, with co-existence of tremor and other neurological features such as dystonia, ataxia, and cognitive dysfunction, has been identified. The cerebellum has been found to be the key brain region for tremor generation, and structural alterations of the cerebellum have been extensively studied in ET. Finally, four main ET pathophysiologies have been proposed: 1) environmental exposures to β-carboline alkaloids and the consequent olivocerebellar hyper-excitation, 2) cerebellar GABA deficiency, 3) climbing fiber synaptic pathology with related cerebellar oscillatory activity, 4) extra-cerebellar oscillatory activity. While these four theories are not mutually exclusive, they can represent distinctive ET subtypes, indicating multiple types of abnormal brain circuitry can lead to action tremor. This article is part of the Special Issue "Tremor" edited by Daniel D. Truong, Mark Hallett, and Aasef Shaikh.

Tremor and Rigidity in Patients with Parkinson's Disease: Emphasis on Epidemiology, Pathophysiology and Contributing Factors

Parkinson's disease (PD) is the second most prominent neurodegenerative movement disorder after Alzheimer's disease, involving 2-3% of the population aged above 65 years. This is mainly triggered by the depletion of dopaminergic neurons located in substantia nigra pars compacta (SNpc) in the region of basal ganglia. At present, diagnosis for symptoms of PD is clinical, contextual, unspecified and therapeutically incomprehensive. Analysis of various causes of PD is essential for an accurate examination of the disease. Among the different causes, such as tremors and rigidity, unresponsiveness to the current treatment approach contributes to mortality. In the present review article, we describe various key factors of pathogenesis and physiology associated with tremors and rigidity necessary for the treatment of PI (postural instability) in patients with PD. Additionally, several reports showing early tremor and rigidity causes, particularly age, cortex lesions, basal ganglia lesions, genetic abnormalities, weakened reflexes, nutrition, fear of fall, and altered biomechanics, have been explored. By summarizing the factors that contribute to the disease, histopathological studies can assess rigidity and tremor in PD. With a clear understanding of the contributing factors, various prospective studies can be done to assess the incidence of rigidity and tremors.

The Role of the Motor Cortex in Tremor Suppression in Parkinson's Disease

BACKGROUND

Patients with Parkinson's disease (PD) and rest tremor may also have tremor during posture holding, with tremor being transiently suppressed during the transition between resting and posture holding. Other PD patients show no tremor suppression between resting and posture holding. The mechanisms responsible for tremor suppression in PD are unknown. Understanding the mechanisms of tremor suppression would expand our knowledge of tremor pathophysiology in PD.

OBJECTIVE

To investigate whether tremor suppression reflects the activity of the primary motor cortex (M1) and assess whether tremor features are different in patients with and without tremor suppression.

METHODS

We compared corticomuscular coherence (CMC) at tremor frequency and transcranial magnetic stimulation tremor resetting between 10 PD patients with tremor suppression and 10 patients without suppression. We also compared tremor spectral features between the two groups.

RESULTS

Patients with tremor suppression had higher CMC at tremor frequency during both rest tremor and postural tremor, and a higher postural tremor resetting index and stability when compared with patients without tremor suppression. Rest tremor frequency was similar between the two groups, but postural tremor frequency was lower in patients with tremor suppression as compared to patients without.

CONCLUSION

M1 plays a major role in tremor suppression in PD, and the mechanisms of postural tremor may differ between patients with and without tremor suppression.

Approach to Tremor Disorders

Tremor disorders are diverse and complex. Historical clues and examination features play a major role in diagnosing these disorders, but diagnosis can be challenging due to phenotypic overlap. Ancillary testing, such as neuroimaging or laboratory testing, is driven by the history and examination, and should be performed particularly when there are other neurological or systemic manifestations. The pathophysiology of tremor is not entirely understood, but likely involves multiple networks along with the cerebello-thalamo-cortical pathways. Treatment options include medications, botulinum toxin, surgery, and nonpharmacologic interventions utilizing physical and occupational therapies and assistive devices. Further work is needed in developing accurate diagnostic tests and better treatment options for tremor disorders.

The Molecular Neuroimaging of Tremor

Purpose of Review

Tremor is a hyperkinetic movement disorder most commonly encountered in essential tremor (ET) and Parkinson’s disease (PD). The purpose of this review is to summarize molecular neuroimaging studies with major implications on pathophysiological and clinical features of tremor.

Recent Findings

Oscillatory brain activity responsible for tremor manifestation is thought to originate in a cerebello-thalamo-cortical network. Molecular neuroimaging has helped clarify metabolic aspects and neurotransmitter influences on the main tremor network. In ET, recent positron emission tomography (PET) studies are built on previous knowledge and highlighted the possibility of investigating metabolic brain changes after treatments, in the attempt to establish therapeutic biomarkers. In PD, molecular neuroimaging has advanced the knowledge of non-dopaminergic determinants of tremor, providing insights into serotonergic and noradrenergic contributions.

Summary

Recent advances have greatly extended the knowledge of tremor pathophysiology and it is now necessary to translate such knowledge in more efficacious treatments for this symptom.

Subthalamic-Cortical Network Reorganization during Parkinson's Tremor

Tremor, a common and often primary symptom of Parkinson's disease, has been modeled with distinct onset and maintenance dynamics. To identify the neurophysiologic correlates of each state, we acquired intraoperative cortical and subthalamic nucleus recordings from 10 patients (9 male, 1 female) performing a naturalistic visual-motor task. From this task, we isolated short epochs of tremor onset and sustained tremor. Comparing these epochs, we found that the subthalamic nucleus was central to tremor onset, as it drove both motor cortical activity and tremor output. Once tremor became sustained, control of tremor shifted to cortex. At the same time, changes in directed functional connectivity across sensorimotor cortex further distinguished the sustained tremor state.SIGNIFICANCE STATEMENT Tremor is a common symptom of Parkinson's disease (PD). While tremor pathophysiology is thought to involve both basal ganglia and cerebello-thalamic-cortical circuits, it is unknown how these structures functionally interact to produce tremor. In this article, we analyzed intracranial recordings from the subthalamic nucleus and sensorimotor cortex in patients with PD undergoing deep brain stimulation surgery. Using an intraoperative task, we examined tremor in two separate dynamic contexts: when tremor first emerged, and when tremor was sustained. We believe that these findings reconcile several models of Parkinson's tremor, while describing the short-timescale dynamics of subcortical-cortical interactions during tremor for the first time. These findings may describe a framework for developing proactive and responsive neurostimulation models for specifically treating tremor.

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.

Parkinsonism and tremor syndromes

Tremor, the most common movement disorder, may occur in isolation or may co-exist with a variety of other neurologic and movement disorders including parkinsonism, dystonia, and ataxia. When associated with Parkinson's disease, tremor may be present at rest or as an action tremor overlapping in phenomenology with essential tremor. Essential tremor may be associated not only with parkinsonism but other neurological disorders, suggesting the possibility of essential tremor subtypes. Besides Parkinson's disease, tremor can be an important feature of other parkinsonian disorders, such as atypical parkinsonism and drug-induced parkinsonism. In addition, tremor can be a prominent feature in patients with other movement disorders such as fragile X-associated tremor/ataxia syndrome, and Wilson's disease in which parkinsonian features may be present. This article is part of the Special Issue "Parkinsonism across the spectrum of movement disorders and beyond" edited by Joseph Jankovic, Daniel D. Truong and Matteo Bologna.

[Effects of switching from dopamine agonists to zonisamide on psychiatric and motor symptoms in patients with Parkinson's disease]

In 11 patients with Parkinson's disease (PD) who were using levodopa and had hallucinations and/or delusions considered to be attributed to use of dopamine agonists (DAs), we reduced or discontinued DAs and added zonisamide, and we then evaluated the effects of this treatment on psychiatric and motor symptoms. As a result, changes in the Movement Disorder Society-sponsored revision of the Unified Parkinson's Disease Rating Scale Part 1.2 (Hallucinations and Psychosis) and Part 3 (Motor Examination) scores 12 weeks from baseline were -2.4 ± 0.2 and -5.1 ± 0.9 (least-squares mean ± standard error), respectively, with the score reductions being statistically significant. These results indicated that zonisamide switching therapy is a useful strategy for managing psychiatric and motor symptoms in patients with PD when DAs are reduced or discontinued to avoid the onset or exacerbation of hallucinations and delusions.

Tremor Syndromes: An Updated Review

Tremor is the most commonly encountered movement disorder in clinical practice. A wide range of pathologies may manifest with tremor either as a presenting or predominant symptom. Considering the marked etiological and phenomenological heterogeneity, it would be desirable to develop a classification of tremors that reflects their underlying pathophysiology. The tremor task force of the International Parkinson Disease and Movement Disorders Society has worked toward this goal and proposed a new classification system. This system has remained a prime topic of scientific communications on tremor in recent times. The new classification is based on two axes: 1. based on the clinical features, history, and tremor characteristics and 2. based on the etiology of tremor. In this article, we discuss the key aspects of the new classification, review various tremor syndromes, highlight some of the controversies in the field of tremor, and share the potential future perspectives.

Parkinson's Disease Patient Monitoring: A Real-Time Tracking and Tremor Detection System Based on Magnetic Measurements

Reliable diagnosis of early-stage Parkinson’s disease is an important task, since it permits the administration of a timely treatment, slowing the progression of the disease. Together with non-motor symptoms, other important signs of disease can be retrieved from the measurement of the movement trajectory and from tremor appearances. To measure these signs, the paper proposes a magnetic tracking system able to collect information about translational and vibrational movements in a spatial cubic domain, using a low-cost, low-power and highly accurate solution. These features allow the usage of the proposed technology to realize a portable monitoring system, that may be operated at home or in general practices, enabling telemedicine and preventing saturation of large neurological centers. Validation is based on three tests: movement trajectory tracking, a rest tremor test and a finger tapping test. These tests are considered in the Unified Parkinson’s Disease Rating Scale and are provided as case studies to prove the system’s capabilities to track and detect tremor frequencies. In the case of the tapping test, a preliminary classification scheme is also proposed to discriminate between healthy and ill patients. No human patients are involved in the tests, and most cases are emulated by means of a robotic arm, suitably driven to perform required tasks. Tapping test results show a classification accuracy of about 93% using a k-NN classification algorithm, while imposed tremor frequencies have been correctly detected by the system in the other two tests.

Developing a Consistent, Reproducible Botulinum Toxin Type A Dosing Method for Upper Limb Tremor by Kinematic Analysis

Botulinum toxin type A (BoNT-A) injection patterns customized to each patient’s unique tremor characteristics produce better efficacy and lower adverse effects compared to the fixed-muscle-fixed-dose approach for Essential Tremor (ET) and Parkinson’s disease (PD) tremor therapy. This article outlined how a kinematic-based dosing method to standardize and customize BoNT-A injections for tremors was developed. Seven ET and eight PD participants with significant tremor reduction and minimal perceived weakness using optimized BoNT-A injections determined by clinical and kinematic guidance were retrospectively selected to develop the kinematic-based dosing method. BoNT-A dosages allocated per joint were paired to baseline tremor amplitudes per joint. The final kinematic-based dosing method was prospectively utilized to validate BoNT-A injection pattern selection without clinical/visual assessments in 31 ET and 47 PD participants with debilitating arm tremors (totaling 122 unique tremor patterns). Whole-arm kinematic tremor analysis was performed at baseline and 6-weeks post-injection. Correlation and linear regression analyses between baseline tremor amplitudes and the change in tremor amplitude 6-weeks post-injection, with BoNT-A dosages per joint, were performed. Injection patterns determined using clinical assessment and interpretation of kinematics produced significant associations between baseline tremor amplitudes and optimized BoNT-A dosages in all joints. The change in elbow tremor was only significantly associated with the elbow total dose as the change in the wrist and shoulder tremor amplitudes were not significantly associated with the wrist and shoulder dosages from the selected 15 ET and PD participants. Using the kinematic-based dosing method, significant associations between baseline tremor amplitudes and the change (6-weeks post-first treatment) in tremor at each joint with BoNT-A dosages for all joints was observed in all 78 ET and PD participants. The kinematic-based dosing method provided consistency in dose selection and subsequent tremor reduction and can be used to standardize tremor assessments for whole-arm tremor treatment planning.

Rest tremor correlates with reduced contralateral striatal dopamine transporter binding in Parkinson's disease

INTRODUCTION

In vivo dopamine transporter imaging is a useful tool for distinguishing nigrostriatal pathologies (e.g. Parkinson's disease) from other causes of tremor. However, while many of the motoric features of Parkinson's disease (e.g. bradykinesia, rigidity, hypomimia) correlate well with reduced striatal dopamine transporter binding, the same relationship has not been demonstrated for tremor. We investigated the relationship between striatal dopamine transporter binding and quantitative measures of tremor.

METHODS

23 participants with Parkinson's disease underwent standardised clinical assessment including structured, videotaped clinical examination, tremor neurophysiology study of both upper limbs using accelerometry and surface EMG, and Technitium-99 m TRODAT-1 brain SPECT imaging. Normalised striatal uptake values were calculated. Tremor EMG and accelerometry time series were processed with Fourier transformation to identify peak tremor power within a window of 3-10Hz and to calculate the tremor stability index (TSI).

RESULTS

Spearman correlation analyses revealed an association between tremor power and contralaterally reduced striatal uptake in a number of recording conditions. This association was strongest for rest tremor, followed by postural tremor, with the weakest association observed for kinetic tremor. Lower TSI was also associated with lower contralateral striatal uptake in a number of rest and postural conditions.

CONCLUSION

These data suggest a relationship between Parkinsonian rest tremor and contralateral reduction in striatal dopamine binding. Use of quantitative neurophysiology techniques may allow the demonstration of clinico-pathophysiological relationships in tremor that have remained occult to previous studies.

Non-motor symptoms in essential tremor, akinetic rigid and tremor-dominant subtypes of Parkinson's disease

Objectives

To compare non-motor symptoms (NMSs) among patients with essential tremor (ET), Parkinson’s disease (PD) subtypes (akinetic-rigid type (ART) and tremor-dominant type (TDT)), and healthy controls.

Patients and methods

This retrospective study included 129 participants, 72 PD (33 PD-ART, 33 PD-TDT, and 6 Mixed), 29 ET patients, and 28 controls. PD patients were assessed by the unified Parkinson’s disease rating scale (UPDRS), Hoehn, and Yahr scale (H&Y), while ET patients were evaluated by the Fahn Tolosa Marin Tremor Rating Scale. All subjects were evaluated by non-motor symptoms scale (NMSS) for NMSs and Beck depression inventory (BDI) for depression.

Results

PD subtypes groups, ET, and controls were age and gender-matched. Compared to controls, all PD, PD subtypes, and ET showed significantly worse most of NMSs (p<0.001) and depression. Compared to ET, all PD and PD-ART had significantly worse gastrointestinal (p = 0.002), urinary symptoms (p = 0.001, p = 0.003) and depression (p = 0.002) and PD-TDT worse depression, while ET patients showed worse memory/attention than PD subtypes. Total NMSS of ET is highly correlated to depression and moderately to tremor severity and age of onset, while total of NMSS is highly correlated to depression, disease severity, and disability.

Conclusion

The current study demonstrated several comparable domains of NMSs of PD subtypes and ET, except worse gastrointestinal and urinary symptoms among PD-ART. Identifying different NMSs profiles is important for predicting, better assessing, and tailoring management of ET and PD subtypes.

Prevalence and Relationship of Rest Tremor and Action Tremor in Parkinson's Disease

Background:

Despite the significance of tremor in Parkinson’s disease (PD) diagnosis, classification, and patient’s quality of life, there is a relative lack of data on prevalence and relationship of different tremor types in PD.

Methods:

The presence of rest tremor (RT) and action tremor (AT; defined as combination of both postural and kinetic tremor) was determined and RT severity was defined using the Movement Disorders Society Unified Parkinson’s Disease Rating Scale (MDS-UPDRS) at baseline in the Progression Marker Initiative (PPMI, n = 423), the Fox Investigation for New Discovery of Biomarkers (BioFIND, n = 118) and the Parkinson’s Disease Biomarkers Program (PDBP, n = 873) cohorts.

Results:

Across baseline data of all three cohorts, RT prevalence (58.2%) was higher than AT prevalence (39.0%). Patients with RT had significantly higher (Chi-square test, p < 0.05) prevalence of AT compared to patients without RT in the PPMI (40.0% versus 30.1%), BioFIND (48.0% versus 40.0%) and PDBP (49.9% versus 21.0%) cohorts. Furthermore, patients with AT had significantly (Student t-test, p < 0.05) higher RT severity that those without AT in PPMI (5.7 ± 5.4 versus 3.9 ± 3.3), BioFIND, 6.4 ± 6.3 versus 3.8 ± 4.4) and PDBP (6.4 ± 6.6 versus 3.7 ± 4.4) cohorts. In the BioFIND cohort, the prevalence of all types of tremor and their combinations significantly decreased from the off-state to on-state.

Discussion:

The RT is the most frequent tremor type and present in more than half of the PD patients. However, AT is also present in nearly one-third of the PD patients. Our results also indicate that RT and AT may have cross-interactions in PD, and that dopaminergic treatment influences both RT and AT.

Effects of dopamine on reinforcement learning in Parkinson's disease depend on motor phenotype

Parkinson's disease is clinically defined by bradykinesia, along with rigidity and tremor. However, the severity of these motor signs is greatly variable between individuals, particularly the presence or absence of tremor. This variability in tremor relates to variation in cognitive/motivational impairment, as well as the spatial distribution of neurodegeneration in the midbrain and dopamine depletion in the striatum. Here we ask whether interindividual heterogeneity in tremor symptoms could account for the puzzlingly large variability in the effects of dopaminergic medication on reinforcement learning, a fundamental cognitive function known to rely on dopamine. Given that tremor-dominant and non-tremor Parkinson's disease patients have different dopaminergic phenotypes, we hypothesized that effects of dopaminergic medication on reinforcement learning differ between tremor-dominant and non-tremor patients. Forty-three tremor-dominant and 20 non-tremor patients with Parkinson's disease were recruited to be tested both OFF and ON dopaminergic medication (200/50 mg levodopa-benserazide), while 22 age-matched control subjects were recruited to be tested twice OFF medication. Participants performed a reinforcement learning task designed to dissociate effects on learning rate from effects on motivational choice (i.e. the tendency to 'Go/NoGo' in the face of reward/threat of punishment). In non-tremor patients, dopaminergic medication improved reward-based choice, replicating previous studies. In contrast, in tremor-dominant patients, dopaminergic medication improved learning from punishment. Formal modelling showed divergent computational effects of dopaminergic medication as a function of Parkinson's disease motor phenotype, with a modulation of motivational choice bias and learning rate in non-tremor and tremor patients, respectively. This finding establishes a novel cognitive/motivational difference between tremor and non-tremor Parkinson's disease patients, and highlights the importance of considering motor phenotype in future work.

STN Versus GPi Deep Brain Stimulation for Action and Rest Tremor in Parkinson's Disease

Objective

To investigate the effects of subthalamic nucleus (STN) and globus pallidus internus (GPi), deep brain stimulation (DBS) on individual action tremor/postural tremor (AT) and rest tremor (RT) in Parkinson’s disease (PD). Randomized DBS studies have reported marked benefit in tremor with both GPi and STN and DBS, however, there is a paucity of information available on AT vs RT when separated by the surgical target.

Methods

We retrospectively reviewed the 1-year clinical outcome of PD patients treated with STN and GPi DBS at the University of Florida. We specifically selected patients with moderate to severe AT. Eighty-eight patients (57 STN and 31 GPi) were evaluated at 6 and 12 months for changes in AT and RT in the OFF-medication/ON stimulation state. A comparison of “response” was performed and defined as greater than or equal to a 2-point decrease in tremor score.

Results

STN and GPi DBS both improved AT at 6- and 12-months post-implantation (p < 0.001 and p < 0.001). The STN DBS group experienced a greater improvement in AT at 6 months compared to the GPi group (p = 0.005) but not at the 12 months follow-up (p = 0.301). Both STN and GPi DBS also improved RT at 6- and 12-months post-implantation (p < 0.001 and p < 0.001). There was no difference in RT scores between the two groups at 6 months (p = 0.23) or 12 months (p = 0.74). The STN group had a larger proportion of patients who achieved a “response” in AT at 6 months (p < 0.01), however, this finding was not present at 12 months (p = 0.23). A sub-analysis revealed that in RT, the STN group had a larger percentage of “responders” when followed through 12 months (p < 0.01).

Conclusion

Both STN and GPi DBS reduced PD associated AT and RT at 12 months follow-up. There was no advantage of either brain target in the management of RT or AT. One nuance of the study was that STN DBS was more effective in suppressing AT in the early postoperative period, however, this effect diminished over time. Clinicians should be aware that it may take longer to achieve a similar tremor outcome when utilizing the GPi target.

Impaired Hand Dexterity Function in a Non-human Primate Model with Chronic Parkinson's Disease

Symptoms of Parkinson’s disease (PD) caused by loss of dopaminergic neurons are accompanied by movement disorders, including tremors, rigidity, bradykinesia, and akinesia. Non-human primate (NHP) models with PD play an essential role in the analysis of PD pathophysiology and behavior symptoms. As impairments of hand dexterity function can affect activities of daily living in patients with PD, research on hand dexterity function in NHP models with chronic PD is essential. Traditional rating scales previously used in the evaluation of animal spontaneous behavior were insufficient due to factors related to subjectivity and passivity. Thus, experimentally designed applications for an appropriate apparatus are necessary. In this study, we aimed to longitudinally assess hand dexterity function using hand dexterity task (HDT) in NHP-PD models. To validate this assessment, we analyzed the alteration in Parkinsonian tremor signs and the functionality of presynaptic dopaminergic neuron using positron emission tomography imaging of dopamine transporters in these models. In addition, a significant inverse correlation between HDT and DAT level was identified, but no local bias was found. The correlation with intention tremor signs was lower than the resting tremor. In conclusion, the evaluation of HDT may reflect behavioral symptoms of NHP-PD models. Furthermore, HDT was effectively used to experimentally distinguish intention tremors from other tremors.