Tremor-predominant Parkinson's disease. Approaches to treatment

[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.

Supporting Tremor Rehabilitation Using Optical See-Through Augmented Reality Technology

Tremor is a movement disorder that significantly impacts an individual's physical stability and quality of life, and conventional medication or surgery often falls short in providing a cure. Rehabilitation training is, therefore, used as an auxiliary method to mitigate the exacerbation of individual tremors. Video-based rehabilitation training is a form of therapy that allows patients to exercise at home, reducing pressure on rehabilitation institutions' resources. However, it has limitations in directly guiding and monitoring patients' rehabilitation, leading to an ineffective training effect. This study proposes a low-cost rehabilitation training system that utilizes optical see-through augmented reality (AR) technology to enable tremor patients to conduct rehabilitation training at home. The system provides one-on-one demonstration, posture guidance, and training progress monitoring to achieve an optimal training effect. To assess the system's effectiveness, we conducted experiments comparing the movement magnitudes of individuals with tremors in the proposed AR environment and video environment, while also comparing them with standard demonstrators. Participants wore a tremor simulation device during uncontrollable limb tremors, with tremor frequency and amplitude calibrated to typical tremor standards. The results showed that participants' limb movement magnitudes in the AR environment were significantly higher than those in the video environment, approaching the movement magnitudes of the standard demonstrators. Hence, it can be inferred that individuals receiving tremor rehabilitation in the AR environment experience better movement quality than those in the video environment. Furthermore, participant experience surveys revealed that the AR environment not only provided a sense of comfort, relaxation, and enjoyment but also effectively guided them throughout the rehabilitation process.

Zonisamide add-on in tremor-dominant Parkinson's disease- A randomized controlled clinical trial

INTRODUCTION

and objective: Tremor is a disabling symptom of PD that usually responds poorly to available standard pharmacological agents. This study aimed to assess the effect of Zonisamide 25 mg on tremor in tremor-dominant PD patients as compared to placebo.

METHODS

This was a randomized, placebo-controlled, double-blind study. Parkinson's disease patients were allocated either to the intervention group (standard treatment along with Zonisamide 25 mg add-on) or the placebo group (standard treatment along with placebo). Baseline Unified Parkinson's Disease Rating Scale (UPDRS) and Tremor Research Group Essential Tremor Rating Scale (TETRAS) scores, as well as accelerometric tremor analysis were done and follow-up assessments of the same were done after 12 weeks of intervention. Percentage change from baseline in the UPDRS tremor score was the primary outcome whereas percentage change from baseline of total UPDRS score, UPDRS rigidity and bradykinesia scores, TETRAS score, and accelerometric tremor analysis values were the secondary outcomes.

RESULTS

There was no significant difference in the percentage change from baseline UPDRS tremor scores between the two groups (placebo: 8.33 [-19.89-23.86] vs drug: 26.14 [-35.58 to -16.07], p-value: 0.164, CI: 0.157-0.171). Best-case analysis for missing values showed a significant improvement in the drug group, compared to the placebo group (p-value: < 0.001, CI: <0.001 - <0.001).

CONCLUSION

Zonisamide at a dose of 25 mg per day did not improve tremor in tremor-dominant PD patients, however, a positive trend was seen as compared to Placebo in the UPDRS tremor score. Larger studies are required to confirm this finding.

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.

Peripherical Electrical Stimulation for Parkinsonian Tremor: A Systematic Review

Parkinsonian tremor is one of the most common motor disorders in patients with Parkinson's disease (PD). Compared to oral medications and brain surgery, electrical stimulation approaches have emerged as effective and non-invasive methods for tremor reduction. The pathophysiology, detection and interventions of tremors have been introduced, however, a systematic review of peripherical electrical stimulation approaches, methodologies, experimental design and clinical outcomes for PD tremor suppression is still missing. Therefore, in this paper, we summarized recent studies on electrical stimulation for tremor suppression in PD patients and discussed stimulation protocols and effectiveness of different types of electrical stimulation approaches in detail. Twenty out of 528 papers published from 2010 to 2021 July were reviewed. The results show that electrical stimulation is an efficient intervention for tremor suppression. The methods fall into three main categories according to the mechanisms: namely functional electrical stimulation (FES), sensory electrical stimulation (SES) and transcutaneous electrical nerve stimulation (TENS). The outcomes of tremor suppression were varied due to various stimulation approaches, electrode locations and stimulation parameters. The FES method performed the best in tremor attenuation where the efficiency depends mainly by the control strategy and accuracy of tremor detection. However, the mechanism underlying tremor suppression with SES and TENS, is not well-known. Current electrical stimulation approaches may only work for a number of patients. The potential mechanism of tremor suppression still needs to be further explored.

Non-invasive electrical stimulation of peripheral nerves for the management of tremor

Pathological tremor in patients with essential tremor and Parkinsons disease is typically treated using medication or neurosurgical interventions. There is a widely recognized need for new treatments that avoid the side effects of current medications and do not carry the risks of surgical interventions. Building on decades of research and engineering development, non-invasive electrical stimulation of peripheral nerves has emerged as a safe and effective strategy for reducing pathologic tremor in essential tremor. This review surveys the peripheral electrical stimulation (PES) literature and summarizes effectiveness, safety, clinical translatability, and hypothesized tremor-reduction mechanisms of various PES approaches. The review also proposes guidelines for assessing tremor in the context of evaluating new therapies that combine the strengths of clinician assessments, patient evaluations, and novel motion sensing technology. The review concludes with a summary of future directions for PES, including expanding clinical access for patients with Parkinson's disease and leveraging large, at-home datasets to learn more about tremor physiology and treatment effect that will better characterize the state of tremor management and accelerate discovery of new therapies. Growing evidence suggests that non-invasive electrical stimulation of afferent neural pathways provides a viable new option for management of pathological tremor, with one specific PES therapy cleared for prescription and home use, suggesting that PES be considered along with medication and neurosurgical interventions for treatment of tremor. This article is part of the Special Issue "Tremor" edited by Daniel D. Truong, Mark Hallett, and Aasef Shaikh.

Using Machine Learning for Predicting the Best Outcomes With Electrical Muscle Stimulation for Tremors in Parkinson's Disease

Recent studies have identified that peripheral stimulation in Parkinson’s disease (PD) is effective in tremor reduction, indicating that a peripheral feedback loop plays an important role in the tremor reset mechanism. This was an open-label, quasi-experimental, pre- and post-test design, single-blind, single-group study involving 20 tremor-dominant PD patients. The objective of this study is to explore the effect of electrical muscle stimulation (EMS) as an adjunctive treatment for resting tremor during “on” period and to identify the best machine learning model to predict the suitable stimulation level that will yield the longest period of tremor reduction or tremor reset time. In this study, we used a Parkinson’s glove to evaluate, stimulate, and quantify the tremors of PD patients. This adjustable glove incorporates a 3-axis gyroscope to measure tremor signals and an EMS to provide an on-demand muscle stimulation to suppress tremors. Machine learning models were applied to identify the suitable pulse amplitude (stimulation level) in five classes that led to the longest tremor reset time. The study was registered at the www.clinicaltrials.gov under the name “The Study of Rest Tremor Suppression by Using Electrical Muscle Stimulation” (NCT02370108). Twenty tremor-dominant PD patients were recruited. After applying an average pulse amplitude of 6.25 (SD 2.84) mA and stimulation period of 440.7 (SD 560.82) seconds, the total time of tremor reduction, or tremor reset time, was 329.90 (SD 340.91) seconds. A significant reduction in tremor parameters during stimulation was demonstrated by a reduction of Unified Parkinson’s Disease Rating Scale (UPDRS) scores, and objectively, with a reduction of gyroscopic data (p < 0.05, each). None of the subjects reported any serious adverse events. We also compared gyroscopic data with five machine learning techniques: Logistic Regression, Random Forest, Support Vector Machine (SVM), Neural Network (NN), and Long-Short-Term-Memory (LSTM). The machine learning model that gave the highest accuracy was LSTM, which obtained: accuracy = 0.865 and macro-F1 = 0.736. This study confirms the efficacy of EMS in the reduction of resting tremors in PD. LSTM was identified as the most effective model for predicting pulse amplitude that would elicit the longest tremor reset time. Our study provides further insight on the tremor reset mechanism in PD.

Non-lesional treatment options for tremor in idiopathic Parkinson syndrome: a protocol for a systematic literature review

INTRODUCTION

Idiopathic Parkinson syndrome (iPS) is one of the most common neurodegenerative disorders characterised by the triad of bradykinesia, rigidity and tremor. Tremor at rest predominantly at one side is often perceived by patients as severely disabling and yet ranges among the most difficult symptoms to treat. In medically refractory cases, lesional approaches have proven to be effective alternatives. However, to date, there is no comprehensive analysis of non-surgical therapies to manage iPS-patients' tremor. We therefore present a detailed study protocol for a systematic literature review assessing efficacy/effectiveness and safety of non-lesional treatments for tremor in iPS.

METHODS AND ANALYSIS

We will search three electronic databases (MEDLINE, EMBASE and PsycINFO) using a combination of title/abstract keywords. Additionally, hand-searched reference and citation lists of key reviews identified through the search strategy will be screened. Eligible studies should investigate the efficacy/effectiveness and safety of therapeutic options for tremor in iPS excluding lesional interventions. Publications will be independently assessed for inclusion criteria by two investigators and study information summarised using a standardised template including quality assessment according to the QualSyst tool. We will provide a narrative synthesis of results and conduct a meta-analysis whenever possible.

ETHICS AND DISSEMINATION

We commit to present contemporary evidence on the efficacy/effectiveness and safety of non-lesional interventions for tremor in iPS in a future publication. We aim to compile rich data of published studies to inform healthcare professionals in order to ultimately improve patient outcomes.

PROSPERO REGISTRATION NUMBER

CRD42020202911).

Novel case of Parkinson's disease and schizophrenia: challenges in the management

Coexistence of idiopathic Parkinson's disease (iPD) and schizophrenia can pose great diagnostic and therapeutic challenges because of their pathophysiology. Our case highlights such challenges in management. We present a case of 73-year-old man who had parkinsonism for last several years and was also diagnosed with schizophrenia. Due to lack of collateral information about the onset of symptoms and clinical course, it was difficult to distinguish iPD from neuroleptic-induced parkinsonism. Even though, certain clinical findings may help to differentiate between the two conditions, single positron emission computerized tomography/DatScan was used to confirm the diagnosis of iPD. Treatment of coexisting iPD and schizophrenia can be challenging, and a delicate pharmacologic balance must be maintained to ensure adequate symptomatic control. Current evidence suggests that clozapine is a better choice for managing psychosis in these patients due to its unique receptor profile and better safety data.

Substantia Nigra Volume Dissociates Bradykinesia and Rigidity from Tremor in Parkinson's Disease: A 7 Tesla Imaging Study

Background:

In postmortem analysis of late stage Parkinson’s disease (PD) neuronal loss in the substantial nigra (SN) correlates with the antemortem severity of bradykinesia and rigidity, but not tremor.

Objective:

To investigate the relationship between midbrain nuclei volume as an in vivo biomarker for surviving neurons in mild-to-moderate patients using 7.0 Tesla MRI.

Methods:

We performed ultra-high resolution quantitative susceptibility mapping (QSM) on the midbrain in 32 PD participants with less than 10 years duration and 8 healthy controls. Following blinded manual segmentation, the individual volumes of the SN, subthalamic nucleus, and red nucleus were measured. We then determined the associations between the midbrain nuclei and clinical metrics (age, disease duration, MDS-UPDRS motor score, and subscores for bradykinesia/rigidity, tremor, and postural instability/gait difficulty).

Results:

We found that smaller SN correlated with longer disease duration (r = –0.49, p = 0.004), more severe MDS-UPDRS motor score (r = –0.42, p = 0.016), and more severe bradykinesia-rigidity subscore (r = –0.47, p = 0.007), but not tremor or postural instability/gait difficulty subscores. In a hemi-body analysis, bradykinesia-rigidity severity only correlated with SN contralateral to the less-affected hemi-body, and not contralateral to the more-affected hemi-body, possibly reflecting the greatest change in dopamine neuron loss early in disease. Multivariate generalized estimating equation model confirmed that bradykinesia-rigidity severity, age, and disease duration, but not tremor severity, predicted SN volume.

Conclusions:

In mild-to-moderate PD, SN volume relates to motor manifestations in a motor domain-specific and laterality-dependent manner. Non-invasive in vivo 7.0 Tesla QSM may serve as a biomarker in longitudinal studies of SN atrophy and in studies of people at risk for developing PD.

Focused Ultrasound Thalamotomy for Tremor-dominant Parkinson's Disease: A Prospective 1-year Follow-up Study

Transcranial magnetic resonance (MR)-guided focused ultrasound (FUS) therapy is an emerging and minimally invasive treatment for movement disorders. There are limited reports on its long-term outcomes for tremor-dominant Parkinson's disease (TDPD). We aimed to investigate the 1-year outcomes of ventralis intermedius (VIM) thalamotomy with FUS in patients with TDPD. Patients with medication-refractory TDPD were enrolled and underwent unilateral VIM-FUS thalamotomy. Neurologists specializing in movement disorders evaluated the tremor symptoms and disability using Parts A, B, and C of the Clinical Rating Scale for Tremor (CRST) at baseline and at 1, 3, and 12 months. In all, 11 patients (mean age: 71.6 years) were included in the analysis. Of these, five were men. The median (interquartile range) improvement from baseline in hand tremor score, the total score, and functional disability score were 87.9% (70.5-100.0), 65.3% (55.7-87.7), and 66.7% (15.5-85.1), respectively, at 12 months postoperatively. This prospective study demonstrated an improvement in the tremor and disability of patients at 12 months after unilateral VIM-FUS thalamotomy for TDPD. In addition, there were no serious persistent adverse events. Our results indicate that VIM-FUS thalamotomy can be safely and effectively used to treat patients with TDPD. A randomized controlled trial with a larger cohort and long blinded period would help investigate the recurrence, adverse effects, placebo effects, and longer efficacy of this technique.

Recent Developments in New Therapeutic Agents against Alzheimer and Parkinson Diseases: In-Silico Approaches

Neurodegenerative diseases (ND), including Alzheimer's (AD) and Parkinson's Disease (PD), are becoming increasingly more common and are recognized as a social problem in modern societies. These disorders are characterized by a progressive neurodegeneration and are considered one of the main causes of disability and mortality worldwide. Currently, there is no existing cure for AD nor PD and the clinically used drugs aim only at symptomatic relief, and are not capable of stopping neurodegeneration. Over the last years, several drug candidates reached clinical trials phases, but they were suspended, mainly because of the unsatisfactory pharmacological benefits. Recently, the number of compounds developed using in silico approaches has been increasing at a promising rate, mainly evaluating the affinity for several macromolecular targets and applying filters to exclude compounds with potentially unfavorable pharmacokinetics. Thus, in this review, an overview of the current therapeutics in use for these two ND, the main targets in drug development, and the primary studies published in the last five years that used in silico approaches to design novel drug candidates for AD and PD treatment will be presented. In addition, future perspectives for the treatment of these ND will also be briefly discussed.

All roads lead to the motor cortex: psychomotor mechanisms and their biochemical modulation in psychiatric disorders

Psychomotor abnormalities have been abundantly observed in psychiatric disorders like major depressive disorder (MDD), bipolar disorder (BD), and schizophrenia (SCH). Although early psychopathological descriptions highlighted the truly psychomotor nature of these abnormalities, more recent investigations conceive them rather in purely motor terms. This has led to an emphasis of dopamine-based abnormalities in subcortical-cortical circuits including substantia nigra, basal ganglia, thalamus, and motor cortex. Following recent findings in MDD, BD, and SCH, we suggest a concept of psychomotor symptoms in the literal sense of the term by highlighting three specifically psychomotor (rather than motor) mechanisms including their biochemical modulation. These include: (i) modulation of dopamine- and substantia nigra-based subcortical-cortical motor circuit by primarily non-motor subcortical raphe nucleus and serotonin via basal ganglia and thalamus (as well as by other neurotransmitters like glutamate and GABA); (ii) modulation of motor cortex and motor network by non-motor cortical networks like default-mode network and sensory networks; (iii) global activity in cortex may also shape regional distribution of neural activity in motor cortex. We demonstrate that these three psychomotor mechanisms and their underlying biochemical modulation are operative in both healthy subjects as well as in MDD, BD, and SCH subjects; the only difference consists in the fact that these mechanisms are abnormally balanced and thus manifest in extreme values in psychiatric disorders. We conclude that psychomotor mechanisms operate in a dimensional and cross-nosological way as their degrees of expression are related to levels of psychomotor activity (across different disorders) rather than to the diagnostic categories themselves. Psychomotor mechanisms and their biochemical modulation can be considered paradigmatic examples of a dimensional approach as suggested in RDoC and the recently introduced spatiotemporal psychopathology.

Zuranolone as an oral adjunct to treatment of Parkinsonian tremor: A phase 2, open-label study

Parkinson's disease (PD) is characterized by both motor and nonmotor deficits. Among cardinal symptoms of this disorder, tremor is the least responsive to dopamine replacement therapy and is often undertreated. Zuranolone (SAGE-217) is an investigational oral neuroactive steroid (NAS) gamma-aminobutyric acid A (GABA_A) receptor-positive allosteric modulator (PAM) that has been investigated for its safety and efficacy in patients with PD. In the current open-label study, zuranolone capsules (20 to 30 mg) were administered for 7 days in 14 patients (mean age, 65.1 years; mean time since PD diagnosis, 9 years). The primary efficacy endpoint was reduction in tremor symptoms, as assessed by change from baseline in Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) Part II/III Tremor Scores on Day 8. Additional endpoints included improvements in overall motor symptoms, and motor and nonmotor aspects of daily living. Adverse events (AEs) were also monitored. The MDS-UPDRS Part II/III Tremor Score improved by 40% (P < 0.0001) from baseline on Day 8. The motor score, and nonmotor experiences of daily living (nM-EDL), and motor experiences of daily living (m-EDL) scores (MDS-UPDRS Parts I and II, respectively), also improved on Day 8. No serious AEs were reported, and no patients discontinued treatment. The most common AEs were dizziness, sedation, and somnolence. Zuranolone was generally well tolerated and improved tremor symptoms in patients with PD who were on stable doses of concurrent dopaminergic agents. These data support the further investigation of NAS GABA_A receptor PAMs as adjunctive treatments for tremor in patients with PD.

Genetic variants of vitamin D metabolism-related DHCR7/NADSYN1 locus and CYP2R1 gene are associated with clinical features of Parkinson's disease

PURPOSE/AIM OF THE STUDY

Parkinson's disease (PD) is the second most common neurodegenerative disorder. Vitamin D deficiency is suggested to be related to PD. A genome-wide association study indicated that genes involved in vitamin D metabolism affect vitamin D levels. Among these genes, single nucleotide polymorphisms (SNPs) of the vitamin D receptor (VDR) and vitamin D binding protein (VDBP/GC) genes have also been demonstrated to be associated with PD risk. Our aim was to investigate the relevance of SNPs within the 7-dehydrocholesterol reductase/nicotinamide adenine dinucleotide synthetase 1 (DHCR7/NADSYN1) locus and vitamin D 25-hydroxylase (CYP2R1) gene, which encode important enzymes that play a role in the vitamin D synthesis pathway, with PD and its clinical features.

MATERIALS AND METHODS

Genotypes of 382 PD patients and 240 cognitively healthy individuals were evaluated by a LightSNiP assay for a total of 10 SNPs within the DHCR7/NADSYN1 locus and CYP2R1 gene.

RESULTS

There were no significant differences in the allele and genotype distributions of any of the SNPs between any patient groups and healthy subjects. However, our results indicated that all of the SNPs within the DHCR7/NADSYN1 locus and CYP2R1 gene, except rs1993116, were associated with clinical motor features of PD including initial predominant symptom, freezing of gait (FoG) and falls as well as disease stage and duration of the disease.

CONCLUSIONS

In conclusion, genetic variants of the DHCR7/NADSYN1 locus and the CYP2R1 gene might be related to the inefficient utilization of vitamin D independent from vitamin D levels, and it might result in differences in the clinical features of PD patients.

Long Term Response to Levodopa in Parkinson's Disease

BACKGROUND

Levodopa is the most efficacious medication in controlling the motor symptoms of Parkinson's disease (PD). There continues to be a controversy as to whether levodopa remains effective after years of therapy.

OBJECTIVE

To assess the long-term effectiveness of levodopa in PD patients.

METHODS

The response to levodopa in PD patients undergoing a levodopa challenge for deep brain stimulation (DBS) surgery evaluation from June 1997 through March 2017 were evaluated. The patients were broken into four groups based on disease duration (Group I: 0- 5 years, Group II: 6- 10 years, Group III: 11- 15 years, and Group IV:≥16 years). Levodopa response was calculated based on the changes in Unified Parkinson's Disease Rating Scale (UPDRS) motor and activities of daily living (ADL) scores in the medication ON and OFF states.

RESULTS

A total of 361 PD patients were included. The mean age in Group I was 59.4 years with a mean disease duration of 3.9 years (n = 29), Group II was 61 years with a mean disease duration of 8.1 years (n = 131), Group III was 64 years with a mean disease duration of 12.8 years (n = 143), and IV was 66.5 years with a mean disease duration of 18.5 years (n = 58). There was a significant improvement in UPDRS motor and ADL scores after the levodopa challenge for all groups.

CONCLUSIONS

In a subgroup of PD patients who were evaluated for DBS surgery, there was a marked improvement in UPDRS motor and ADL scores which did not decrease with disease progression.

Exploring the effects of deep brain stimulation and vision on tremor in Parkinson's disease - benefits from objective methods

Background

Tremor is a cardinal symptom of Parkinson’s disease (PD) that may cause severe disability. As such, objective methods to determine the exact characteristics of the tremor may improve the evaluation of therapy. This methodology study aims to validate the utility of two objective technical methods of recording Parkinsonian tremor and evaluate their ability to determine the effects of Deep Brain Stimulation (DBS) of the subthalamic nucleus and of vision.

Methods

We studied 10 patients with idiopathic PD, who were responsive to _L-Dopa and had more than 1 year use of bilateral subthalamic nucleus stimulation. The patients did not have to display visible tremor to be included in the study. Tremor was recorded with two objective methods, a force platform and a 3 dimensional (3D) motion capture system that tracked movements in four key proximal sections of the body (knee, hip, shoulder and head). They were assessed after an overnight withdrawal of anti-PD medications with DBS ON and OFF and with eyes open and closed during unperturbed and perturbed stance with randomized calf vibration, using a randomized test order design.

Results

Tremor was detected with the Unified Parkinson’s Disease Rating Scale (UPDRS) in 6 of 10 patients but only distally (hands and feet) with DBS OFF. With the force platform and the 3D motion capture system, tremor was detected in 6 of 10 and 7 of 10 patients respectively, mostly in DBS OFF but also with DBS ON in some patients. The 3D motion capture system revealed that more than one body section was usually affected by tremor and that the tremor amplitude was non-uniform, but the frequency almost identical, across sites. DBS reduced tremor amplitude non-uniformly across the body. Visual input mostly reduced tremor amplitude with DBS ON.

Conclusions

Technical recording methods offer objective and sensitive detection of tremor that provide detailed characteristics such as peak amplitude, frequency and distribution pattern, and thus, provide information that can guide the optimization of treatments. Both methods detected the effects of DBS and visual input but the 3D motion system was more versatile in that it could detail the presence and properties of tremor at individual body sections.

Parkinson's Disease Motor Subtypes Show Different Responses to Long-Term Subthalamic Nucleus Stimulation

Background and purpose: Subthalamic nucleus deep brain stimulation (STN DBS) is well established for the treatment of advanced Parkinson's disease (PD), substantially improving motor symptoms, quality of life, and reducing the long-term need for dopaminergic medication. However, whether chronic STN DBS produces different effects on PD motor subtypes is unknown. This retrospective study aimed to evaluate the long-term effects of STN DBS on the PD motor subtypes. Methods: Eighty patients undergoing STN DBS were included. The Unified Parkinson's Disease Rating Scale (UPDRS) analysis was performed in "On" and "Off" medication/"On" and "Off" stimulation conditions. The patients were classified as akinetic-rigid type (ART), tremor-dominant type (TDT), and mixed type (MT) based on the preoperative UPDRS III subscores in the "Off" medication state. Preoperative and postoperative comparisons were performed. Results: After 4.9 years, STN DBS produced significant improvement in the UPDRS III total scores and subscores of tremor, rigidity, and bradykinesia in the "Off" medication state in the ART group, less improvement in the MT group, and the least improvement in the TDT group. The UPDRS II and III total scores and other subscores failed to improve during the "On" medication state. However, all groups improved substantially, and the improvement in tremor was sustained for both the "On" and "Off" medication states after years. Long-term STN DBS failed to improve swallowing and speech in all the subtypes. Conclusion: The data confirms that PD is heterogeneous. Long-term STN DBS produced the best effects on bradykinesia/rigidity in the "Off" medication state and on tremor in the "On" and "Off" medication states. There were differences in the response by each group, but some of the differences could be explained by the fact that more severe symptoms at baseline tend to have greater improvement. The findings support the idea that ART mainly involves the basal ganglia-thalamo-cortical pathway, whereas TDT involves a different circuit, likely the cerebellar-thalamo-cortical pathway.

Impact of Tremor on Patients With Early Stage Parkinson's Disease

Tremor is one of the most visible features of Parkinson's disease (PD), and the majority of PD patients experience tremor during the course of the disease. However, the distress caused by this cardinal motor feature for patients early in the course of their PD is commonly underappreciated. People living with early stage PD often experience intense embarrassment and difficulties due to their tremor that limit social interactions, and tremor frequently interferes with the ability to perform activities of daily living and simple tasks at home and work. Although tremor is primarily managed with medications, both tremor response and satisfaction with medical therapy are highly variable. This review offers an overview of reports of the patient experience of tremor in early stage PD and current management options for this cardinal motor feature.

Schizophrenia with Comorbid Idiopathic Parkinson's Disease: A Difficult Clinical Management Scenario

Comorbidity of idiopathic Parkinson's disease (IPD) and schizophrenia is an uncommon and rare scenario, which often poses a difficult and challenging situation for management. Both the disorders have completely opposite pathophysiology and treatment of one disorder with available pharmacological agents can pose a threat to the other disorder. The situation becomes graver and risk of adverse side effects increases when an individual presents at a later age with both these disorders along with compromised physical and mental health. Of all the available psychopharmacological agents, clozapine has been found to be quite helpful for the management of psychosis without deterioration of existing movement problems of Parkinson's disease. In this case report, we present the case of a 60-year-old female with long-standing paranoid schizophrenia for the last 30 years, who later developed IPD and discuss the various management issues encountered during her treatment.

Distinct alterations in Parkinson's medication-state and disease-state connectivity

Altered brain connectivity has been described in people with Parkinson's disease and in response to dopaminergic medications. However, it is unclear whether dopaminergic medications primarily 'normalize' disease related connectivity changes or if they induce unique alterations in brain connectivity. Further, it is unclear how these disease- and medication-associated changes in brain connectivity relate differently to specific motor manifestations of disease, such as bradykinesia/rigidity and tremor. In this study, we applied a novel covariance projection approach in combination with a bootstrapped permutation test to resting state functional MRI data from 57 Parkinson's disease and 20 healthy control participants to determine the Parkinson's medication-state and disease-state connectivity changes associated with different motor manifestations of disease. First, we identified brain connections that best classified Parkinson's disease ON versus OFF dopamine and Parkinson's disease versus healthy controls, achieving 96.9 ± 5.9% and 72.7 ± 12.4% classification accuracy, respectively. Second, we investigated the connections that significantly contribute to the classifications. We found that the connections greater in Parkinson's disease OFF compared to ON dopamine are primarily between motor (cerebellum and putamen) and posterior cortical regions, such as the posterior cingulate cortex. By contrast, connections that are greater in ON compared to OFF dopamine are between the right and left medial prefrontal cortex. We also identified the connections that are greater in healthy control compared to Parkinson's disease and found the most significant connections are associated with primary motor regions, such as the striatum and the supplementary motor area. Notably, these are different connections than those identified in Parkinson's disease OFF compared to ON. Third, we determined which of the Parkinson's medication-state and disease-state connections are associated with the severity of different motor symptoms. We found two connections correlate with both bradykinesia/rigidity severity and tremor severity, whereas four connections correlate with only bradykinesia/rigidity severity, and five connections correlate with only tremor severity. Connections that correlate with only tremor severity are anchored by the cerebellum and the supplemental motor area, but only those connections that include the supplemental motor area predict dopaminergic improvement in tremor. Our results suggest that dopaminergic medications do not simply 'normalize' abnormal brain connectivity associated with Parkinson's disease, but rather dopamine drives distinct connectivity changes, only some of which are associated with improved motor symptoms. In addition, the dissociation between of connections related to severity of bradykinesia/rigidity versus tremor highlights the distinct abnormalities in brain circuitry underlying these specific motor symptoms.

Motor subtype changes in early Parkinson's disease

INTRODUCTION

Distinct motor subtypes of Parkinson's disease (PD) have been described through both clinical observation and through data-driven approaches. However, the extent to which motor subtypes change during disease progression remains unknown. Our objective was to determine motor subtypes of PD using an unsupervised clustering methodology and evaluate subtype changes with disease duration.

METHODS

The Parkinson's Progression Markers Initiative database of 423 newly diagnosed PD patients was utilized to retrospectively identify unique motor subtypes through a data-driven, hierarchical correlational clustering approach. For each patient, we assigned a subtype to each motor assessment at each follow-up visit (time points) and by using published criteria. We examined changes in PD subtype with disease duration using both qualitative and quantitative methods.

RESULTS

Five distinct motor subtypes were identified based on the motor assessment items and these included: Tremor Dominant (TD), Axial Dominant, Appendicular Dominant, Rigidity Dominant, and Postural and Instability Gait Disorder Dominant. About half of the patients had consistent subtypes at all time points. Most patients met criteria for TD subtype soon after diagnosis. For patients with inconsistent subtypes, there was an overall trend to shift away from a TD phenotype with disease duration, as shown by chi-squared test, p < 0.001, and linear regression analysis, p < 0.05.

CONCLUSION

These results strongly suggest that classification of motor subtypes in PD can shift with increasing disease duration. Shifting subtypes is a factor that should be accounted for in clinical practice or in clinical trials.

Structural connectivity differences in motor network between tremor-dominant and nontremor Parkinson's disease

Motor phenotypes of Parkinson's disease (PD) are recognized to have different prognosis and therapeutic response, but the neural basis for this clinical heterogeneity remains largely unknown. The main aim of this study was to compare differences in structural connectivity metrics of the main motor network between tremor-dominant and nontremor PD phenotypes (TD-PD and NT-PD, respectively) using probabilistic tractography-based network analysis. A total of 63 PD patients (35 TD-PD patients and 28 NT-PD patients) and 30 healthy controls underwent a 3 T MRI. Next, probabilistic tractography-based network analysis was performed to assess structural connectivity in cerebello-thalamo-basal ganglia-cortical circuits, by measuring the connectivity indices of each tract and the efficiency of each node. Furthermore, dopamine transporter single-photon emission computed tomography (DAT-SPECT) with ¹²³ I-ioflupane was used to assess dopaminergic striatal depletion in all PD patients. Both PD phenotypes showed nodal abnormalities in the substantia nigra, in agreement with DAT-SPECT evaluation. In addition, NT-PD patients displayed connectivity alterations in nigro-pallidal and fronto-striatal pathways, compared with both controls and TD-PD patients, in which the same motor connections seemed to be relatively spared. Of note, in NT-PD group, rigidity-bradykinesia score correlated with fronto-striatal connectivity abnormalities. These findings demonstrate that structural connectivity alterations occur in the cortico-basal ganglia circuit of NT-PD patients, but not in TD-PD patients, suggesting that these anatomical differences may underlie different motor phenotypes of PD. Hum Brain Mapp 38:4716-4729, 2017. © 2017 Wiley Periodicals, Inc.

Molecular mechanisms underlying protective effects of quercetin against mitochondrial dysfunction and progressive dopaminergic neurodegeneration in cell culture and MitoPark transgenic mouse models of Parkinson's Disease

Quercetin, one of the major flavonoids in plants, has been recently reported to have neuroprotective effects against neurodegenerative processes. However, since the molecular signaling mechanisms governing these effects are not well clarified, we evaluated quercetin's effect on the neuroprotective signaling events in dopaminergic neuronal models and further tested its efficacy in the MitoPark transgenic mouse model of Parkinson's disease (PD). Western blot analysis revealed that quercetin significantly induced the activation of two major cell survival kinases, protein kinase D1 (PKD1) and Akt in MN9D dopaminergic neuronal cells. Furthermore, pharmacological inhibition or siRNA knockdown of PKD1 blocked the activation of Akt, suggesting that PKD1 acts as an upstream regulator of Akt in quercetin-mediated neuroprotective signaling. Quercetin also enhanced cAMP response-element binding protein phosphorylation and expression of the cAMP response-element binding protein target gene brain-derived neurotrophic factor. Results from qRT-PCR, Western blot analysis, mtDNA content analysis, and MitoTracker assay experiments revealed that quercetin augmented mitochondrial biogenesis. Quercetin also increased mitochondrial bioenergetics capacity and protected MN9D cells against 6-hydroxydopamine-induced neurotoxicity. To further evaluate the neuroprotective efficacy of quercetin against the mitochondrial dysfunction underlying PD, we used the progressive dopaminergic neurodegenerative MitoPark transgenic mouse model of PD. Oral administration of quercetin significantly reversed behavioral deficits, striatal dopamine depletion, and TH neuronal cell loss in MitoPark mice. Together, our findings demonstrate that quercetin activates the PKD1-Akt cell survival signaling axis and suggest that further exploration of quercetin as a promising neuroprotective agent for treating PD may offer clinical benefits.

White matter microstructure damage in tremor-dominant Parkinson's disease patients

PURPOSE

Resting tremor is one of the cardinal motor features of Parkinson's disease (PD). Several lines of evidence suggest resting tremor may have different underlying pathophysiological processes from those of bradykinesia and rigidity. The current study aims to identify white matter microstructural abnormalities associated with resting tremor in PD.

METHODS

We recruited 60 patients with PD (30 with tremor-dominant PD and 30 with nontremor-dominant PD) and 26 normal controls. All participants underwent clinical assessment and diffusion tensor MRI. We used tract-based spatial statistics to investigate white matter integrity across the entire white matter tract skeleton.

RESULTS

Compared with both healthy controls and the nontremor-dominant PD patients, the tremor-dominant PD patients were characterized by increased mean diffusivity (MD) and axial diffusivity (AD) along multiple white matter tracts, mainly involving the cerebello-thalamo-cortical (CTC) pathway. The mean AD value in clusters with significant difference was correlated with resting tremor score in the tremor-dominant PD patients. There was no significant difference between the nontremor-dominant PD patients and controls.

CONCLUSION

Our results support the notion that resting tremor in PD is a distinct condition in which significant microstructural white matter changes exist and provide evidence for the involvement of the CTC in tremor genesis of PD.

Default mode network differences between rigidity- and tremor-predominant Parkinson's disease

BACKGROUND

Parkinson's disease (PD) traditionally is characterized by tremor, rigidity, and bradykinesia, although cognitive impairment also is a common symptom. The clinical presentation of PD is heterogeneous and associated with different risk factors for developing cognitive impairment. PD patients with primary akinetic/rigidity (PDAR) are more likely to develop cognitive deficits compared to those with tremor-predominant symptoms (PDT). Because cognitive impairment in PD appears to be related to changes in the default mode network (DMN), this study tested the hypothesis that DMN integrity is different between PDAR and PDT subtypes.

METHOD

Resting state fMRI (rs-fMRI) and whole brain volumetric data were obtained from 17 PDAR, 15 PDT and 24 healthy controls (HCs) using a 3T scanner. PD patients were matched closely to HCs for demographic and cognitive variables, and showed no symptoms of dementia. Voxel-based morphometry (VBM) was used to examine brain gray matter (GM) volume changes between groups. Independent component analysis (ICA) interrogated differences in the DMN among PDAR, PDT, and HC.

RESULTS

There was decreased activity in the left inferior parietal cortex (IPC) and the left posterior cingulate cortex (PCC) within the DMN between PDAR and both HC and PDT subjects, even after controlling for multiple comparisons, but not between PDT and HC. GM volume differences between groups were detected at a lower threshold (p < 0.001, uncorrected). Resting state activity in IPC and PCC were correlated with some measures of cognitive performance in PD but not in HC.

CONCLUSION

This is the first study to demonstrate DMN differences between cognitively comparable PDAR and PDT subtypes. The DMN differences between PD and HC appear to be driven by the PDAR subtype. Further studies are warranted to understand the underlying neural mechanisms and their relevance to clinical and cognitive outcomes in PDAR and PDT subtypes.

The external globus pallidus: progress and perspectives

The external globus pallidus (GPe) of the basal ganglia is in a unique and powerful position to influence processing of motor information by virtue of its widespread projections to all basal ganglia nuclei. Despite the clinical importance of the GPe in common motor disorders such as Parkinson's disease, there is only limited information about its cellular composition and organizational principles. In this review, recent advances in the understanding of the diversity in the molecular profile, anatomy, physiology and corresponding behaviour during movement of GPe neurons are described. Importantly, this study attempts to build consensus and highlight commonalities of the cellular classification based on existing but contentious literature. Additionally, an analysis of the literature concerning the intricate reciprocal loops formed between the GPe and major synaptic partners, including both the striatum and the subthalamic nucleus, is provided. In conclusion, the GPe has emerged as a crucial node in the basal ganglia macrocircuit. While subtleties in the cellular makeup and synaptic connection of the GPe create new challenges, modern research tools have shown promise in untangling such complexity, and will provide better understanding of the roles of the GPe in encoding movements and their associated pathologies.

Exploring the effect of electrical muscle stimulation as a novel treatment of intractable tremor in Parkinson's disease

BACKGROUND

As the pathophysiology of tremor in Parkinson disease (PD) involves a complex interaction between central and peripheral mechanisms, we propose that modulation of peripheral reflex mechanism by electrical muscle stimulation (EMS) may improve tremor temporarily.

OBJECTIVES

To determine the efficacy of EMS as a treatment for drug resistant tremor in PD patients.

METHODS

This study was a single-blinded, quasi-experimental study involving 34 PD patients with classic resting tremor as confirmed by tremor analysis. The EMS was given at 50Hz over the abductor pollicis brevis and interrosseus muscles for 10s with identified tremor parameters before and during stimulation as primary outcomes.

RESULTS

Compared to before stimulation, we observed a significant reduction in the root mean square (RMS) of the angular velocity (p<0.001) and peak magnitude (p<0.001) of resting tremor while tremor frequency (p=0.126) and dispersion (p=0.284) remained unchanged during stimulation. The UPDRS tremor score decreased from 10.59 (SD=1.74) before stimulation to 8.85 (SD=2.19) during stimulation (p<0.001). The average percentage of improvement of the peak magnitude and RMS angular velocity was 49.57% (SD=38.89) and 43.81% (SD=33.15) respectively. 70.6% and 61.8% of patients experienced at least 30% tremor attenuation as calculated from the peak magnitude and RMS angular velocity respectively.

CONCLUSIONS

Our study demonstrated the efficacy of EMS in temporarily improving resting tremor in medically intractable PD patients. Although tremor severity decreased, they were not completely eliminated and continued with a similar frequency, thus demonstrating the role of peripheral reflex mechanism in the modulation of tremor, but not as a generator. EMS should be further explored as a possible therapeutic intervention for tremor in PD.

Cannabinoids: new promising agents in the treatment of neurological diseases

Nowadays, Cannabis sativa is considered the most extensively used narcotic. Nevertheless, this fame obscures its traditional employ in native medicine of South Africa, South America, Turkey, Egypt and in many regions of Asia as a therapeutic drug. In fact, the use of compounds containing Cannabis and their introduction in clinical practice is still controversial and strongly limited by unavoidable psychotropic effects. So, overcoming these adverse effects represents the main open question on the utilization of cannabinoids as new drugs for treatment of several pathologies. To date, therapeutic use of cannabinoid extracts is prescribed in patients with glaucoma, in the control of chemotherapy-related vomiting and nausea, for appetite stimulation in patients with anorexia-cachexia syndrome by HIV, and for the treatment of multiple sclerosis symptoms. Recently, researcher efforts are aimed to employ the therapeutic potentials of Cannabis sativa in the modulation of cannabinoid receptor activity within the central nervous system, particularly for the treatment of neurodegenerative diseases, as well as psychiatric and non-psychiatric disorders. This review evaluates the most recent available data on cannabinoids utilization in experimental and clinical studies, and highlights their beneficial effects in the prevention of the main neurological diseases and for the clinical treatment of symptoms with them correlated.

Development and evaluation of buccal films impregnated with selegiline-loaded nanospheres

Poor peroral therapeutic efficiency of selegiline is primarily due to the extensive hepatic metabolism and hence the need for an alternative route of administration. The present study is based on evaluation of a buccal film which is impregnated with selegiline nanospheres to enhance the systemic bioavailability. Selegiline-loaded nanospheres prepared using poly(lactide-co-glycolide) was embedded into buccal films (F₁-F₄) with varying polymer composition [hydroxypropyl methylcellulose and eudragit]. The developed films were evaluated for their physicomechanical properties, hydration, mucoadhesive strength, in vitro drug release and ex vivo permeation in order to identify the ideal system suitable for further development. In vivo studies were carried out on rabbits to assess the comparative pharmacokinetics profile of the selected buccal film with oral solution. Preliminary studies indicated that the prepared films exhibited excellent physical properties, adequate mucoadhesive strength and moderate hydration. In vitro drug release data of the buccal films (F₁, F₂ and F₃) showed distinct profiles. Permeation studies indicated higher steady-state flux from film F₃ (p < 0.0001) when compared to film F₂. In-vivo results of film (F₃) demonstrated significant increase in absorption (p < 0.0001), C_max (∼1.6-fold), T_max, AUC_0-α (∼3-fold, p < 0.0001) and improved bioavailability, when compared to control. This study concludes that the buccal delivery of selegiline using the developed buccal film (F₃) would be a promising alternative approach for the treatment of Parkinson's disease.

Treatment of advanced Parkinson’s disease

Parkinson's disease is a progressive neurological disorder characterized by tremor, bradykinesia, rigidity, gait and postural instability and a variety of nonmotor symptoms. While these and other motor signs typically improve with levodopa, the so-called axial signs, such as dysarthria, dysphagia, postural instability and freezing, and most nonmotor signs, such as depression, cognitive decline and dysautonomia, usually do not respond satisfactorily to levodopa. Furthermore, the use of levodopa may be limited by the development of motor fluctuations, dyskinesias and other adverse effects. This manuscript reviews the medical management of advanced Parkinson's disease, focusing on the treatment of motor fluctuations and dyskinesias and of nonmotor and nonlevodopa responsive symptoms.

Clinical utility of dopamine transporter single photon emission CT (DaT-SPECT) with (123I) ioflupane in diagnosis of parkinsonian syndromes

The diagnosis of movement disorders including Parkinson's disease (PD) and essential tremor is determined through clinical assessment. The difficulty with diagnosis of early PD has been highlighted in several recent clinical trials. Studies have suggested relatively high clinical diagnostic error rates for PD and essential tremor. This review was undertaken to clarify the utility of DaT-SPECT imaging with ((123)I)ioflupane (DaTSCAN or DaTscan or ((123)I)FP-CIT) in assisting practitioners in their clinical decision making by visualising the dopamine transporter in parkinsonian cases. In some patients with suspected parkinsonian syndromes, SPECT imaging with ((123)I)ioflupane is useful to assist in the diagnosis and to help guide prognosis and treatment decisions, including avoiding medications that are unlikely to provide benefit. Clinicians ordering ((123)I)ioflupane SPECT should be aware of its limitations and pitfalls and should order scans when there is diagnostic uncertainty or when the scan will be helpful in clinical decision making.

The relationship between the phenotype of Parkinson's disease and levodopa-induced dyskinesia

Levodopa has been demonstrated to be an effective medication for Parkinson's disease (PD), but its long-term use is complicated by the subsequent development of dyskinesias. Few studies have distinguished distinct PD subtypes associated with the occurrence of Levodopa-Induced Dyskinesia (LID). Therefore, we performed a retrospective analysis to determine if the specific phenotype of PD and other epidemiological factors are associated with the development of LID. Of 367 PD patients taking levodopa, 101 of them developed LID. Multivariate logistic regression analysis demonstrated that initial tremor-dominant manifestation was associated with a reduced risk of LID, independent of other risk factors, such as age at the onset of PD, the duration and dose of levodopa.

The relationship between clinical phenotype and early staged bilateral deep brain stimulation in Parkinson disease

OBJECT

While many centers place bilateral deep brain stimulation (DBS) systems simultaneously, unilateral subthalamic nucleus (STN) DBS followed by a staged contralateral procedure has emerged as a treatment option for many patients. However, little is known about whether the preoperative phenotype predicts when staged placement of a DBS electrode in the opposite STN will be required. The authors aimed to determine whether preoperative clinical phenotype predicts early staged placement of a second STN DBS electrode in patients who undergo unilateral STN DBS for Parkinson disease (PD).

METHODS

Eighty-two consecutive patients with advanced PD underwent unilateral STN DBS contralateral to the most affected hemibody and had at least 2 years of follow-up. Multivariate logistic regression analysis determined preoperative characteristics that predicted staged placement of a second electrode in the opposite STN. Preoperative measurements included aspects of the Unified Parkinson's Disease Rating Scale (UPDRS), motor asymmetry index, and body weight.

RESULTS

At 2-year follow-up, 28 (34%) of the 82 patients had undergone staged placement of a contralateral electrode while the remainder chose to continue with unilateral stimulation. Statistically significant improvements in UPDRS total and Part 3 scores were retained at the end of the 2-year follow-up period in both subsets of patients. Multivariate logistic regression analysis showed that the most important predictors for early staged placement of a second subthalamic stimulator were low asymmetry index (OR 13.4, 95% CI 2.8-64.9), high tremor subscore (OR 7.2, CI 1.5-35.0), and low body weight (OR 5.5, 95% CI 1.4-22.3).

CONCLUSIONS

This single-center study provides evidence that elements of the preoperative PD phenotype predict whether patients will require early staged bilateral STN DBS. These data may aid in the management of patients with advanced PD who undergo STN DBS.

Mini Review: linkages between essential tremor and Parkinson's disease?

Essential tremor (ET) and Parkinson’s disease (PD) are two of the most common movement disorders. Tremors are the primary symptoms of ET and of some PD patients, the two are often mistaken for each other. Especially since there are no available differentiate tests for the tremor of ET or PD, the early diagnoses mainly based on clinical assessments of medical symptoms, family and medication history, and examination by physicians. There is increasing evidence suggesting an association between ET and PD, such as a similar tremor frequency, overlapping resting tremors (a typical PD tremor), postural tremors (mainly in ET patients) in both ET and PD patients, and many ET patients develop PD later in life. Although it is difficult to make a differential diagnosis of ET and tremor-dominant PD based on clinical assessment, recent developments of objective measurements, such as brain imaging, neuropathology, and genetic analysis, has opened a helpful window for distinguishing ET from PD. In this mini review, we included literatures of ET and PD studies and discussed various advanced methods for differential diagnosis between ET and PD such as neuroimaging, genetic markers, tremor intensity and frequency, and drug-responses.

The role of the cerebellum in the pathophysiology of Parkinson's disease

Parkinson's disease (PD), the most common neurodegenerative movement disorder, has traditionally been considered a "classic" basal ganglia disease, as the most obvious pathology is seen in the dopaminergic cells in the substantia nigra pars compacta. Nevertheless recent discoveries in anatomical connections linking the basal ganglia and the cerebellum have led to a re-examination of the role of the cerebellum in the pathophysiology of PD. This review summarizes the role of the cerebellum in explaining many curious features of PD: the significant variation in disease progression between individuals; why severity of dopaminergic deficit correlates with many features of PD such as bradykinesia, but not tremor; and why PD subjects with a tremor-predominant presentation tend to have a more benign prognosis. It is clear that the cerebellum participates in compensatory mechanisms associated with the disease and must be considered an essential contributor to the overall pathophysiology of PD.

Both coordination and symmetry of arm swing are reduced in Parkinson's disease

OBJECTIVE

A recent study reporting significantly reduced symmetry in arm swing amplitude in early Parkinson's disease (PD), as measured during single strides in a gait laboratory, led to this investigation of arm swing symmetry and coordination over many strides using wearable accelerometers in PD.

METHODS

Forearm accelerations were recorded while eight early PD subjects and eight Controls performed 8-min walking trials. Arm swing asymmetry (ASA), maximal cross-correlation (MXC), and instantaneous relative phase (IRP) of bilateral arm swing were compared between PD and Controls. Correlations between arm swing measurements (ASA and MXC) and Unified PD Rating Scale (UPDRS) scores were estimated.

RESULTS

PD subjects demonstrated significantly higher ASA (p=0.002) and lower MXC (p<0.001) than Controls. The IRP probability distribution for PD was significantly different than Controls (p<0.001), with an angular standard deviation of 67.2° for PD and 50.6° for Controls. Among PD subjects, ASA was significantly correlated with the UPDRS score for the limbs (R(2)=0.58, p=0.049), whereas MXC was significantly correlated with the tremor subscore of the limbs (R(2)=0.64, p=0.031).

DISCUSSION

The study confirms previously reported higher arm swing asymmetry in PD but also shows there is significantly lower MXC and greater IRP variability, suggesting that reduction in bilateral arm coordination may contribute to clinically observed asymmetry in PD. The differential correlation of clinical measures of motor disability with measurements of arm swing during gait is intriguing and deserves further investigation.

Revisiting the relationship between essential tremor and Parkinson's disease

BACKGROUND

The relationship between essential tremor and Parkinson's disease has been a subject of reviews and debates for long time, but there is now growing evidence that the two common movement disorders are pathogenically related, at least in some patient populations.

METHODS

PubMed as well as authors' own files were searched for relevant keywords regarding overlap between the disorders in clinical features as well as on epidemiologic, genetic, imaging, and pathological studies.

RESULTS

New findings in each of these categories are critically reviewed and placed in the context of previously published data.

DISCUSSION

Although we believe that there is compelling evidence for the notion that some patients with "pure" ET evolve into PD, the biologic nature of the association is not well understood. Furthermore, it is not clear what factors predict which ET patients later develop PD and whether patients with PD are more likely to develop ET. Further epidemiologic, clinical, genetic, imaging, and pathological studies are needed to better understand this mixed, ET-PD phenotype.

Differential involvement of striato- and cerebello-thalamo-cortical pathways in tremor- and akinetic/rigid-predominant Parkinson's disease

Parkinson's disease (PD) presents clinically with varying degrees of resting tremor, rigidity, and bradykinesia. For decades, striatal-thalamo-cortical (STC) dysfunction has been implied in bradykinesia and rigidity, but does not explain resting tremor in PD. To understand the roles of cerebello-thalamo-cortical (CTC) and STC circuits in the pathophysiology of the heterogeneous clinical presentation of PD, we collected functional magnetic resonance imaging (fMRI) data from 17 right-handed PD patients [nine tremor predominant (PDT) and eight akinetic-rigidity predominant (PDAR)] and 14 right-handed controls while they performed internally-guided (IG) sequential finger tapping tasks. The percentage of voxels activated in regions constituting the STC and CTC [divided as cerebellar hemisphere-thalamo-cortical (CHTC) and vermis-thalamo-cortical (CVTC)] circuits was calculated. Multivariate analysis of variance compared the activation patterns of these circuits between study groups. Compared to controls, both PDAR and PDT subjects displayed an overall increase in the percentage of voxels activated in both STC and CTC circuits. These increases reached statistical significance in contralateral STC and CTC circuits for PDT subjects, and in contralateral CTC pathways for PDAR subjects. Comparison of PDAR and PDT subjects revealed significant differences in ipsilateral STC (P=0.005) and CTC (P=0.043 for CHTC and P=0.003 for CVTC) circuits. These data support the differential involvement of STC and CTC circuits in PD subtypes, and help explain the heterogeneous presentation of PD symptoms. These findings underscore the importance of integrating CTC circuits in understanding PD and other disorders of the basal ganglia.

GABAergic circuits in the basal ganglia and movement disorders

GABA is the major inhibitory neurotransmitter in the basal ganglia, and GABAergic pathways dominate information processing in most areas of these structures. It is therefore not surprising that abnormalities of GABAergic transmission are key elements in pathophysiologic models of movement disorders involving the basal ganglia. These include hypokinetic diseases such as Parkinson's disease, and hyperkinetic diseases, such as Huntington's disease or hemiballism. In this chapter, we will briefly review the major anatomic features of the GABAergic pathways in the basal ganglia, and then describe in greater detail the changes of GABAergic transmission, which are known to occur in movement disorders.

Modulation of L-DOPA-induced abnormal involuntary movements by clinically tested compounds: further validation of the rat dyskinesia model

L-DOPA-induced dyskinesia (LID) is a major complication of the pharmacotherapy of Parkinson's Disease. A model of LID has recently been described in rats with unilateral 6-hydroxydopamine (6-OHDA) lesions. In the present study, the model was used in order to compare the efficacies of some clinically available compounds that have shown antidyskinetic effects in nonhuman primate models of LID and/or in patients, namely, amantadine (20 and 40 mg/kg), buspirone (1, 2 and 4 mg/kg), clonidine (0.01, 0.1 and 1 mg/kg), clozapine (4 and 8 mg/kg), fluoxetine (2.5 and 5 mg/kg), propranolol (5, 10 and 20mg/kg), riluzole (2 and 4 mg/kg), and yohimbine (2 and 10 mg/kg). Rats were treated for 3 weeks with L-DOPA for an induction and monitoring of abnormal involuntary movements (AIMs) prior to the drug screening experiments. The antidyskinetic drugs or their vehicles were administered together with L-DOPA, and their effects were evaluated according to a randomized cross-over design both on the AIM rating scale and on the rotarod test. Most of the compounds under investigation attenuated the L-DOPA-induced axial, limb and orolingual AIM scores. However, the highest doses of many of these substances (but for amantadine and riluzole) had also detrimental motor effects, producing a reduction in rotarod performance and locomotor scores. Since the present results correspond well to existing clinical and experimental data, this study indicates that axial, limb and orolingual AIMs possess predictive validity for the preclinical screening of novel antidyskinetic treatments. Combining tests of general motor performance with AIMs ratings in the same experiment allows for selecting drugs that specifically reduce dyskinesia without diminishing the anti-akinetic effect of L-DOPA.

Atlas-based identification of targets for functional radiosurgery

Functional disorders of the brain, such as Parkinson's disease, dystonia, epilepsy, and neuropathic pain, may exhibit poor response to medical therapy. In such cases, surgical intervention may become necessary. Modern surgical approaches to such disorders include radio-frequency lesioning and deep brain stimulation (DBS). The subthalamic nucleus (STN) is one of the most useful stereotactic targets available: STN DBS is known to induce substantial improvement in patients with end-stage Parkinson's disease. Other targets include the Globus Pallidus pars interna (GPi) for dystonia and Parkinson's disease, and the centromedian nucleus of the thalamus (CMN) for neuropathic pain. Radiosurgery is an attractive noninvasive alternative to treat some functional brain disorders. The main technical limitation to radiosurgery is that the target can be selected only on the basis of magnetic resonance anatomy without electrophysiological confirmation. The aim of this work is to provide a method for the correct atlas-based identification of the target to be used in functional neurosurgery treatment planning. The coordinates of STN, CMN, and GPi were identified in the Talairach and Tournoux atlas and transformed to the corresponding regions of the Montreal Neurological Institute (MNI) electronic atlas. Binary masks describing the target nuclei were created. The MNI electronic atlas was deformed onto the patient magnetic resonance imaging-T1 scan by applying an affine transformation followed by a local nonrigid registration. The first transformation was based on normalized cross correlation and the second on optimization of a two-part objective function consisting of similarity criteria and weighted regularization. The obtained deformation field was then applied to the target masks. The minimum distance between the surface of an implanted electrode and the surface of the deformed mask was calculated. The validation of the method consisted of comparing the electrode-mask distance to the clinical outcome of the treatments in ten cases of bilateral DBS implants. Electrode placement may have an effect within a radius of stimulation equal to 2 mm, therefore the registration process is considered successful if error is less than 2 mm. The registrations of the MNI atlas onto the patient space succeeded in all cases. The comparison of the distance to the clinical outcome revealed good agreement: where the distance was high (at least in one implant), the clinical outcome was poor; where there was a close correlation between the structures, clinical outcome revealed an improvement of the pathological condition. In conclusion, the proposed method seems to provide a useful tool for the identification of the target nuclei for functional radiosurgery. Also, the method is applicable to other types of functional treatment.