Orthostatic tremor: a cerebellar pathology?

TMS of the left primary motor cortex improves tremor intensity and postural control in primary orthostatic tremor

A ponto-cerebello-thalamo-cortical network is the pathophysiological correlate of primary orthostatic tremor. Affected patients often do not respond satisfactorily to pharmacological treatment. Consequently, the objective of the current study was to examine the effects of a non-invasive neuromodulation by theta burst repetitive transcranial magnetic stimulation (rTMS) of the left primary motor cortex (M1) and dorsal medial frontal cortex (dMFC) on tremor frequency, intensity, sway path and subjective postural stability in primary orthostatic tremor. In a cross-over design, eight patients (mean age 70.2 ± 5.4 years, 4 female) with a primary orthostatic tremor received either rTMS of the left M1 leg area or the dMFC at the first study session, followed by the other condition (dMFC or M1 respectively) at the second study session 30 days later. Tremor frequency and intensity were quantified by surface electromyography of lower leg muscles and total sway path by posturography (foam rubber with eyes open) before and after each rTMS session. Patients subjectively rated postural stability on the posturography platform following each rTMS treatment. We found that tremor frequency did not change significantly with M1- or dMFC-stimulation. However, tremor intensity was lower after M1- but not dMFC-stimulation (p = 0.033/ p = 0.339). The sway path decreased markedly after M1-stimulation (p = 0.0005) and dMFC-stimulation (p = 0.023) compared to baseline. Accordingly, patients indicated a better subjective feeling of postural stability both with M1-rTMS (p = 0.007) and dMFC-rTMS (p = 0.01). In conclusion, non-invasive neuromodulation particularly of the M1 area can improve postural control and tremor intensity in primary orthostatic tremor by interference with the tremor network.

Altered brain connectivity in hyperkinetic movement disorders: A review of resting-state fMRI

BACKGROUND

Hyperkinetic movement disorders (HMD) manifest as abnormal and uncontrollable movements. Despite reported involvement of several neural circuits, exact connectivity profiles remain elusive.

OBJECTIVES

Providing a comprehensive literature review of resting-state brain connectivity alterations using resting-state fMRI (rs-fMRI). We additionally discuss alterations from the perspective of brain networks, as well as correlations between connectivity and clinical measures.

METHODS

A systematic review was performed according to PRISMA guidelines and searching PubMed until October 2022. Rs-fMRI studies addressing ataxia, chorea, dystonia, myoclonus, tics, tremor, and functional movement disorders (FMD) were included. The standardized mean difference was used to summarize findings per region in the Automated Anatomical Labeling atlas for each phenotype. Furthermore, the activation likelihood estimation meta-analytic method was used to analyze convergence of significant between-group differences per phenotype. Finally, we conducted hierarchical cluster analysis to provide additional insights into commonalities and differences across HMD phenotypes.

RESULTS

Most articles concerned tremor (51), followed by dystonia (46), tics (19), chorea (12), myoclonus (11), FMD (11), and ataxia (8). Altered resting-state connectivity was found in several brain regions: in ataxia mainly cerebellar areas; for chorea, the caudate nucleus; for dystonia, sensorimotor and basal ganglia regions; for myoclonus, the thalamus and cingulate cortex; in tics, the basal ganglia, cerebellum, insula, and frontal cortex; for tremor, the cerebello-thalamo-cortical circuit; finally, in FMD, frontal, parietal, and cerebellar regions. Both decreased and increased connectivity were found for all HMD. Significant spatial convergence was found for dystonia, FMD, myoclonus, and tremor. Correlations between clinical measures and resting-state connectivity were frequently described.

CONCLUSION

Key brain regions contributing to functional connectivity changes across HMD often overlap. Possible increases and decreases of functional connections of a specific region emphasize that HMD should be viewed as a network disorder. Despite the complex interplay of physiological and methodological factors, this review serves to gain insight in brain connectivity profiles across HMD phenotypes.

The Phenomenology of Primary Orthostatic Tremor

Background

Objectives

Methods

Results

Conclusions

Transcranial Magnetic Stimulation in Tremor Syndromes: Pathophysiologic Insights and Therapeutic Role

Transcranial magnetic stimulation (TMS) is a painless, non-invasive, and established brain stimulation technique to investigate human brain function. Over the last three decades, TMS has shed insight into the pathophysiology of many neurological disorders. Tremor is an involuntary, rhythmic oscillatory movement disorder commonly related to pathological oscillations propagated via the cerebello-thalamo-cortical pathway. Although tremor is the most common movement disorder and recent imaging studies have enhanced our understanding of the critical pathogenic networks, the underlying pathophysiology of different tremor syndromes is complex and still not fully understood. TMS has been used as a tool to further our understanding of tremor pathophysiology. In addition, repetitive TMS (rTMS) that can modulate brain functions through plasticity effects has been targeted to the tremor network to gain potential therapeutic benefits. However, evidence is available for only a few studies that included small patient samples with limited clinical follow-up. This review aims to discuss the role of TMS in advancing the pathophysiological understanding as well as emerging applications of rTMS for treating individual tremor syndromes. The review will focus on essential tremor, Parkinson's disease tremor, dystonic tremor syndrome, orthostatic tremor, and functional tremor.

Trans-Spinal Direct Current Stimulation for Managing Primary Orthostatic Tremor

BACKGROUND

Primary orthostatic tremor (POT) is a rare disorder, characterized by 13 to 18 Hz tremor in the legs when standing and is often refractory to medical treatment. Epidural spinal cord stimulation has been proposed as an alternative treatment. However, this approach is invasive, which limits its application.

OBJECTIVE

Trans-spinal direct current stimulation (tsDCS) is a non-invasive method to modulate spinal cord circuits. The aim of this proof-of-concept study was to investigate the potential beneficial effect of tsDCS in POT.

METHODS

We conducted a double-blind, sham-controlled study in 16 patients with POT. In two separate visits, patients received sham tsDCS first followed by active (either cathodal or anodal) tsDCS. The primary outcome was the change in time in standing position. Secondary outcomes comprised quantitative assessment of tremor, measurement of corticospinal excitability including short-latency afferent inhibition, and clinical global impression-improvement (CGI-I). Measurements were made at baseline, after sham tsDCS, 0-30 min, and 30-60 min after active conditions.

RESULTS

Cathodal-tsDCS reduced tremor amplitude and frequency and lowered corticospinal excitability whereas anodal-tsDCS reduced tremor frequency only. CGI-I scores positively correlated with the time in standing position after both active tsDCS conditions.

CONCLUSION

A single session of tsDCS can improve instability in POT. This opens a new vista for experimental treatment options using multiple sessions of spinal DC stimulation. © 2021 International Parkinson and Movement Disorder Society.

Unravelling the enigma of cortical tremor and other forms of cortical myoclonus

Cortical tremor is a fine rhythmic oscillation involving distal upper limbs, linked to increased sensorimotor cortex excitability, as seen in cortical myoclonus. Cortical tremor is the hallmark feature of autosomal dominant familial cortical myoclonic tremor and epilepsy (FCMTE), a syndrome not yet officially recognized and characterized by clinical and genetic heterogeneity. Non-coding repeat expansions in different genes have been recently recognized to play an essential role in its pathogenesis. Cortical tremor is considered a rhythmic variant of cortical myoclonus and is part of the 'spectrum of cortical myoclonus', i.e. a wide range of clinical motor phenomena, from reflex myoclonus to myoclonic epilepsy, caused by abnormal sensorimotor cortical discharges. The aim of this update is to provide a detailed analysis of the mechanisms defining cortical tremor, as seen in FCMTE. After reviewing the clinical and genetic features of FCMTE, we discuss the possible mechanisms generating the distinct elements of the cortical myoclonus spectrum, and how cortical tremor fits into it. We propose that the spectrum is due to the evolution from a spatially limited focus of excitability to recruitment of more complex mechanisms capable of sustaining repetitive activity, overcoming inhibitory mechanisms that restrict excitatory bursts, and engaging wide areas of cortex. Finally, we provide evidence for a possible common denominator of the elements of the spectrum, i.e. the cerebellum, and discuss its role in FCMTE, according to recent genetic findings.

Ataxia Prevalence in Primary Orthostatic Tremor

Background

The exact pathophysiology of primary Orthostatic Tremor (OT) is unknown. A central oscillator is assumed, and previous imaging studies show involvement of cerebellar pathways. However, the presence of ataxia on clinical exam is disputed. We set out to study ataxia in OT prospectively.

Methods

EMG-confirmed primary OT subjects and spousal controls received a neurological exam with additional semiquantitative evaluations of ataxia as part of a multinational, prospective study. These included detailed limb coordination (DLC), detailed stance and gait evaluation (DS), and the Brief Ataxia Rating Scale (BARS). Intra- and inter-rater reliability were assessed and satisfactory.

Results

34 OT subjects (mean age = 67 years, 88% female) and 21 controls (mean age = 66 years, 65% male) were enrolled. Average disease duration was 18 years (range 4-44). BARS items were abnormal in 88% of OT patients. The OT subjects were more likely to have appendicular and truncal ataxia with significant differences in DLC, DS and BARS. Ocular ataxia and dysarthria were not statistically different between the groups.

Discussion

Mild-to-moderate ataxia could be more common in OT than previously thought. This is supportive of cerebellar involvement in the pathophysiology of OT. We discuss possible implications for clinical care and future research.

Highlights

Previous studies of Primary Orthostatic Tremor (OT) have proposed pathophysiologic involvement of the cerebellar pathways.However, presence of ataxia has not been systematically studied in OT.This is a prospective comprehensive ataxia assessment in OT compared to controls. Mild-to-moderate appendiculo-truncal ataxia was found to be common in OT.

Deep brain stimulation for orthostatic tremor: A single-center case series

Background

Orthostatic tremor (OT) is a high-frequency weight-bearing tremor of the legs and trunk associated with progressive disability and is often refractory to medications. Case reports suggest that thalamic deep brain stimulation (DBS) is effective. We report 5 female patients with medication-refractory OT who underwent bilateral thalamic DBS at the Mayo Clinic and assess factors associated with a successful DBS outcome.

Methods

Demographic, clinical, electrophysiology, and DBS data were abstracted. Outcomes were change in tremor-onset latency, standing time, standing ADLs, and patient and clinician global impression of change (PGIC; CGIC).

Results

All 5 patients had improved standing time (72 vs 408 seconds, p ≤ 0.001) and improved standing ADLs after surgery, without change in tremor-onset latency (16 vs 75 seconds, p = 0.14). Maximal benefit was reached up to 3 years after surgery and sustained for up to 6 years. CGIC was "much improved" in all; PGIC was "much improved" in 4 and "minimally improved" in 1. There were no major complications. Postoperative electrophysiology (n = 1) showed lower tremor amplitude and slower tremor ramp-up on vs off stimulation.

Conclusions

Bilateral thalamic DBS improved OT symptoms with benefit lasting up to 6 years. A modest increase in standing time of several minutes was associated with meaningful improvement in standing ADLs. Microlesional effect and bilateral stimulation are likely favorable features, while baseline standing time of several minutes may be unfavorable. These findings may inform clinician and patient counseling and require confirmation in larger studies.

The gait disorder in primary orthostatic tremor

OBJECTIVE

To uncover possible impairments of walking and dynamic postural stability in patients with primary orthostatic tremor (OT).

METHODS

Spatiotemporal gait characteristics were quantified in 18 patients with primary OT (mean age 70.5 ± 5.9 years, 10 females) and 18 age-matched healthy controls. One-third of patients reported disease-related fall events. Walking performance was assessed on a pressure-sensitive carpet under seven conditions: walking at preferred, slow, and maximal speed, with head reclination or eyes closed, and while performing a cognitive or motor dual-task paradigm.

RESULTS

Patients exhibited a significant gait impairment characterized by a broadened base of support (p = 0.018) with increased spatiotemporal gait variability (p = 0.010). Walking speed was moderately reduced (p = 0.026) with shortened stride length (p = 0.001) and increased periods of double support (p = 0.001). Gait dysfunction became more pronounced during slow walking (p < 0.001); this was not present during fast walking. Walking with eyes closed aggravated gait disability as did walking during cognitive dual task (p < 0.001).

CONCLUSION

OT is associated with a specific gait disorder with a staggering wide-based walking pattern indicative of a sensory and/or a cerebellar ataxic gait. The aggravation of gait instability during visual withdrawal and the normalization of walking with faster speeds further suggest a proprioceptive or vestibulo-cerebellar deficit as the primary source of gait disturbance in OT. In addition, the gait decline during cognitive dual task may imply cognitive processing deficits. In the end, OT is presumably a complex network disorder resulting in a specific spino-cerebello-frontocortical gait disorder that goes beyond mere tremor networks.

Associated co-morbidities in a retrospective cohort of orthostatic tremor

BACKGROUND

Orthostatic tremor (OT) is characterized by tremor in orthostatism. Primary OT is characterized by a high-frequency tremor at surface EMG recording and assumed to be idiopathic, whereas slow-frequency OT is classically associated with neurological pathologies. We report here a retrospective monocentric cohort study of primary (fast OT) and pseudo-OT (slow OT) patients to describe associated neurological and non-neurological co-morbidities.

METHODS

Between November 2014 and October 2019, 27 patients with OT were selected from the EMG database of the Department of Clinical Physiology in Lariboisière' s hospital. Patients were classified in primary OT if tremor frequency was ≥ 13 Hz and in pseudo-OT if tremor frequency was < 13 Hz.

RESULTS

Leg tremor on standing represented 10.2% of all tremor recordings. Ten patients were included in the primary and 17 in the pseudo-OT group. Females were predominant (62.9%) (p = 0.04). Mean age at diagnosis was 64.8 ± 1.1 years. At the first visit, a movement disorder was associated with 30% of primary OT, among them one CADASIL patient, whereas extrapyramidal or cerebellar disorders were reported in 100% of pseudo-OT, among them three Wilson's disease patients. These pathologies all preceded primary OT and occurred concomitantly with pseudo-OT. Frequency remained unchanged during evolution, except pseudo-OT in two patients that completely resolved following the introduction of antiParkinsonian drugs. Treatment of primary OT was partially effective in 28% and in 50% of pseudo-OT patients.

CONCLUSION

In this monocentric study, movement disorders were present in 30% of primary OT patients. This result questions the term "idiopathic" or "primary" OT, but the small number of patients does not allow answering this issue.

Gait characterization for patients with orthostatic tremor

INTRODUCTION

Orthostatic tremor (OT) patients frequently report gait unsteadiness with the advancement of disease; however, there is little understanding of its physiology. We sought to examine in OT, the spatial and temporal characteristics of gait, and the relationship with tremor physiology.

METHODS

Gait parameters for OT (n = 16) were recorded with an instrumented Zeno walkway system. All participants complained of gait unsteadiness, especially during slow walking. In a subset of OT, recordings were synchronized with a wireless EMG system for tremor assessment and feet pressure recording. Gait assessments were performed at self-selected habitual, fast, and slow speeds.

RESULTS

Compared to data available for an age- and sex-matched healthy controls, OT patients had a significantly reduced step length, increased step width, and increased gait variability (p < 0.0001). Tremor discharges related to OT were consistently recorded across three different speeds of walking. These discharges persisted through all phases of the gait cycle, including the swing phase when the limb was not weight-bearing. The highest tremor amplitude was recorded in the single support phase, followed by double support, and least during the swing phase.

CONCLUSION

OT patients have distinct gait abnormalities similar to cerebellar disorders. Tremor discharges from the non-weight bearing leg in the swing phase suggests that muscle contractions, even when occurring without resistance, contribute to OT generation.

Contralesional homotopic functional plasticity in patients with temporal glioma

OBJECTIVE

This study aimed to explore the contralesional homotopic functional plasticity in the brain of patients with unilateral temporal glioma.

METHODS

Demographic, neurocognitive, and resting-state functional MRI data were collected from 17 patients with temporal glioma (10 in the right lobe and 7 in the left lobe), along with 14 age- and sex-matched healthy controls. The amplitude of low-frequency fluctuation (ALFF) of the contralesional homotopic region and 2 control regions was examined. The region-of-interest-based analysis was used to determine the altered functional connectivity (FC) of the contralesional homotopic region, showing significantly different intrinsic regional brain activity between patients and controls. Partial correlation analysis was conducted to determine the association between the altered neural activity and behavioral characteristics.

RESULTS

Compared with controls, patients with right temporal glioma exhibited significantly increased ALFF in the contralesional homotopic hippocampus and parahippocampal region. In addition, the intrinsic regional activity in these regions was negatively correlated with the visuospatial score (r = -0.718, p = 0.045). Whole-brain FC analysis revealed significantly increased FC between the left hippocampus and parahippocampal regions and the left inferior temporal gyrus, and decreased FC between the left hippocampus and parahippocampal regions and the left inferior frontal gyrus. No significant changes were found in the 2 control regions.

CONCLUSIONS

Contralesional homotopic regions are instrumental in the process of neural plasticity and functional compensation observed in patients with unilateral temporal glioma. The observed findings might be used to help preoperative evaluation or rehabilitation of postsurgical patients.

A data mining approach for classification of orthostatic and essential tremor based on MRI-derived brain volume and cortical thickness

Objective

Orthostatic tremor (OT) is an extremely rare, misdiagnosed, and underdiagnosed disorder affecting adults in midlife. There is debate as to whether it is a different condition or a variant of essential tremor (ET), or even, if both conditions coexist. Our objective was to use data mining classification methods, using magnetic resonance imaging (MRI)‐derived brain volume and cortical thickness data, to identify morphometric measures that help to discriminate OT patients from those with ET.

Methods

MRI‐derived brain volume and cortical thickness were obtained from 14 OT patients and 15 age‐, sex‐, and education‐matched ET patients. Feature selection and machine learning methods were subsequently applied.

Results

Four MRI features alone distinguished the two, OT from ET, with 100% diagnostic accuracy. More specifically, left thalamus proper volume (normalized by the total intracranial volume), right superior parietal volume, right superior parietal thickness, and right inferior parietal roughness (i.e., the standard deviation of cortical thickness) were shown to play a key role in OT and ET characterization. Finally, the left caudal anterior cingulate thickness and the left caudal middle frontal roughness allowed us to separate with 100% diagnostic accuracy subgroups of OT patients (primary and those with mild parkinsonian signs).

Conclusions

A data mining approach applied to MRI‐derived brain volume and cortical thickness data may differentiate between these two types of tremor with an accuracy of 100%. Our results suggest that OT and ET are distinct conditions.

Diffusion tensor imaging in orthostatic tremor: a tract-based spatial statistics study

Objective

The pathogenesis of orthostatic tremor (OT) is unknown. We investigated OT‐related white matter changes and their correlations with scores from a neuropsychological testing battery.

Methods

Diffusion tensor imaging measures were compared between 14 OT patients and 14 age‐ and education‐matched healthy controls, using whole‐brain tract‐based spatial statistics analysis. Correlations between altered diffusion metrics and cognitive performance in OT group were assessed.

Results

In all cognitive domains (attention, executive function, visuospatial ability, verbal memory, visual memory, and language), OT patients’ cognitive performance was significantly worse than that of healthy controls. OT patients demonstrated altered diffusivity metrics not only in the posterior lobe of the cerebellum (left cerebellar lobule VI) and in its efferent cerebellar fibers (left superior cerebellar peduncle), but also in medial lemniscus bilaterally (pontine tegmentum), anterior limb of the internal capsule bilaterally, right posterior limb of the internal capsule, left anterior corona radiata, right insula, and the splenium of corpus callosum. No relationship was found between diffusion measures and disease duration in OT patients. Diffusion white matter changes, mainly those located in right anterior limb of the internal capsule, were correlated with poor performance on tests of executive function, visuospatial ability, verbal memory, and visual memory in OT patients.

Interpretation

White matter changes were preferentially located in the cerebellum, its efferent pathways, as well as in the pontine tegmentum and key components of the frontal–thalamic–cerebellar circuit. Further work needs to be done to understand the evolution of these white matter changes and their functional consequences.

Grey matter changes in patients with vestibular migraine

AIM

To identify structural changes in the brain regions of patients with vestibular migraine (VM) so as to better understand its pathophysiology.

MATERIAL AND METHODS

The differences in grey matter (GM) in patients with VM, patients with migraine without aura (MWoA), and healthy controls (HC) were investigated. Using a GE Signa 3 T magnetic resonance imaging (MRI) system, 3D structural images were acquired from 18 VM, 21 MWoA, and 21 age-, gender-, and education level-matched HC using a T1-weighted magnetization-prepared rapid acquisition gradient-echo (MPRAGE) sequence. The volumetric abnormalities of GM were estimated by voxel-based morphometry. Analysis of variance and Bonferroni multiple comparisons were applied.

RESULTS

Compared with HC, patients with VM had significantly increased GM volume of the right medial superior frontal gyrus (p=0.008) and the right angular gyrus (p=0.009). Compared to patients with MWoA, patients with VM also had significantly increased volume of the right medial superior frontal gyrus (p=0.001), the right angular gyrus (p=0.008), and the left middle frontal gyrus (p=0.001).

CONCLUSIONS

The GM volume of some brain regions of patients with VM is significantly larger than the other two groups. The increased GM volume in these brain regions in patients with VM may be related to self-adaptation of the nervous system, leading to an abnormal brain sensitization. Some of the brain regions with increased GM volume identified in this study were involved in assessment, integration, and expectations of pain and were strongly related to mood and anxiety.

Towards computerized diagnosis of neurological stance disorders: data mining and machine learning of posturography and sway

We perform classification, ranking and mapping of body sway parameters from static posturography data of patients using recent machine-learning and data-mining techniques. Body sway is measured in 293 individuals with the clinical diagnoses of acute unilateral vestibulopathy (AVS, n = 49), distal sensory polyneuropathy (PNP, n = 12), anterior lobe cerebellar atrophy (CA, n = 48), downbeat nystagmus syndrome (DN, n = 16), primary orthostatic tremor (OT, n = 25), Parkinson's disease (PD, n = 27), phobic postural vertigo (PPV n = 59) and healthy controls (HC, n = 57). We classify disorders and rank sway features using supervised machine learning. We compute a continuous, human-interpretable 2D map of stance disorders using t-stochastic neighborhood embedding (t-SNE). Classification of eight diagnoses yielded 82.7% accuracy [95% CI (80.9%, 84.5%)]. Five (CA, PPV, AVS, HC, OT) were classified with a mean sensitivity and specificity of 88.4% and 97.1%, while three (PD, PNP, and DN) achieved a mean sensitivity of 53.7%. The most discriminative stance condition was ranked as "standing on foam-rubber, eyes closed". Mapping of sway path features into 2D space revealed clear clusters among CA, PPV, AVS, HC and OT subjects. We confirm previous claims that machine learning can aid in classification of clinical sway patterns measured with static posturography. Given a standardized, long-term acquisition of quantitative patient databases, modern machine learning and data analysis techniques help in visualizing, understanding and utilizing high-dimensional sensor data from clinical routine.

Fully automated leg tracking of Drosophila neurodegeneration models reveals distinct conserved movement signatures

Some neurodegenerative diseases, like Parkinsons Disease (PD) and Spinocerebellar ataxia 3 (SCA3), are associated with distinct, altered gait and tremor movements that are reflective of the underlying disease etiology. Drosophila melanogaster models of neurodegeneration have illuminated our understanding of the molecular mechanisms of disease. However, it is unknown whether specific gait and tremor dysfunctions also occur in fly disease mutants. To answer this question, we developed a machine-learning image-analysis program, Feature Learning-based LImb segmentation and Tracking (FLLIT), that automatically tracks leg claw positions of freely moving flies recorded on high-speed video, producing a series of gait measurements. Notably, unlike other machine-learning methods, FLLIT generates its own training sets and does not require user-annotated images for learning. Using FLLIT, we carried out high-throughput and high-resolution analysis of gait and tremor features in Drosophila neurodegeneration mutants for the first time. We found that fly models of PD and SCA3 exhibited markedly different walking gait and tremor signatures, which recapitulated characteristics of the respective human diseases. Selective expression of mutant SCA3 in dopaminergic neurons led to a gait signature that more closely resembled those of PD flies. This suggests that the behavioral phenotype depends on the neurons affected rather than the specific nature of the mutation. Different mutations produced tremors in distinct leg pairs, indicating that different motor circuits were affected. Using this approach, fly models can be used to dissect the neurogenetic mechanisms that underlie movement disorders.

This study uses automated leg tracking to characterise gait and tremor features in fruit fly models of Parkinson’s disease and spinocerebellar ataxia 3, finding movement features that resemble characteristics of the respective human diseases.

Walking in orthostatic tremor modulates tremor features and is characterized by impaired gait stability

Primary orthostatic tremor (OT) is characterized by high-frequency lower-limb muscle contractions and a disabling sense of unsteadiness while standing. Patients consistently report a relief of symptoms when starting to ambulate. Here, we systematically examined and linked tremor and gait characteristics in patients with OT. Tremor and gait features were examined in nine OT patients and controls on a pressure-sensitive treadmill for one minute of walking framed by two one-minute periods of standing. Tremor characteristics were assessed by time-frequency analysis of surface EMG-recordings from four leg muscles. High-frequency tremor during standing (15.29 ± 0.17 Hz) persisted while walking but was consistently reset to higher frequencies (16.34 ± 0.25 Hz; p < 0.001). Tremor intensity was phase-dependently modulated, being predominantly observable during stance phases (p < 0.001). Tremor intensity scaled with the force applied during stepping (p < 0.001) and was linked to specific gait alterations, i.e., wide base walking (p = 0.019) and increased stride-to-stride fluctuations (p = 0.002). OT during walking persists but is reset to higher frequencies, indicating the involvement of supraspinal locomotor centers in the generation of OT rhythm. Tremor intensity is modulated during the gait cycle, pointing at specific pathways mediating the peripheral manifestation of OT. Finally, OT during walking is linked to gait alterations resembling a cerebellar and/or sensory ataxic gait disorder.

Reorganization of cerebro-cerebellar circuit in patients with left hemispheric gliomas involving language network: A combined structural and resting-state functional MRI study

The role of cerebellum and cerebro-cerebellar system in neural plasticity induced by cerebral gliomas involving language network has long been ignored. Moreover, whether or not the process of reorganization is different in glioma patients with different growth kinetics remains largely unknown. To address this issue, we utilized preoperative structural and resting-state functional MRI data of 78 patients with left cerebral gliomas involving language network areas, including 46 patients with low-grade glioma (LGG, WHO grade II), 32 with high-grade glioma (HGG, WHO grade III/IV), and 44 healthy controls. Spontaneous brain activity, resting-state functional connectivity and gray matter volume alterations of the cerebellum were examined. We found that both LGG and HGG patients exhibited bidirectional alteration of brain activity in language-related cerebellar areas. Brain activity in areas with increased alteration was significantly correlated with the language and MMSE scores. Structurally, LGG patients exhibited greater gray matter volume in regions with increased brain activity, suggesting a structure-function coupled alteration in cerebellum. Furthermore, we observed that cerebellar regions with decreased brain activity exhibited increased functional connectivity with contralesional cerebro-cerebellar system in LGG patients. Together, our findings provide empirical evidence for a vital role of cerebellum and cerebro-cerebellar circuit in neural plasticity following lesional damage to cerebral language network. Moreover, we highlight the possible different reorganizational mechanisms of brain functional connectivity underlying different levels of behavioral impairments in LGG and HGG patients.

Deep brain stimulation in uncommon tremor disorders: indications, targets, and programming

BACKGROUND

In uncommon tremor disorders, clinical efficacy and optimal anatomical targets for deep brain stimulation (DBS) remain inadequately studied and insufficiently quantified.

METHODS

We performed a systematic review of PubMed.gov and ClinicalTrials.gov. Relevant articles were identified using the following keywords: "tremor", "Holmes tremor", "orthostatic tremor", "multiple sclerosis", "multiple sclerosis tremor", "neuropathy", "neuropathic tremor", "fragile X-associated tremor/ataxia syndrome", and "fragile X."

RESULTS

We identified a total of 263 cases treated with DBS for uncommon tremor disorders. Of these, 44 had Holmes tremor (HT), 18 orthostatic tremor (OT), 177 multiple sclerosis (MS)-associated tremor, 14 neuropathy-associated tremor, and 10 fragile X-associated tremor/ataxia syndrome (FXTAS). DBS resulted in favorable, albeit partial, clinical improvements in HT cases receiving Vim-DBS alone or in combination with additional targets. A sustained improvement was reported in OT cases treated with bilateral Vim-DBS, while the two cases treated with unilateral Vim-DBS demonstrated only a transient effect. MS-associated tremor responded to dual-target Vim-/VO-DBS, but the inability to account for the progression of MS-associated disability impeded the assessment of its long-term clinical efficacy. Neuropathy-associated tremor substantially improved with Vim-DBS. In FXTAS patients, while Vim-DBS was effective in improving tremor, equivocal results were observed in those with ataxia.

CONCLUSIONS

DBS of select targets may represent an effective therapeutic strategy for uncommon tremor disorders, although the level of evidence is currently in its incipient form and based on single cases or limited case series. An international registry is, therefore, warranted to clarify selection criteria, long-term results, and optimal surgical targets.

Health-Related Quality of Life Is Severely Affected in Primary Orthostatic Tremor

Background

Primary orthostatic tremor (POT) is a movement disorder characterized by unsteadiness upon standing still due to a tremor affecting the legs. It is a gradually progressive condition with limited treatment options. Impairments in health-related quality of life (HQoL) seem to far exceed the physical disability associated with the condition.

Methods

A multi-center, mixed-methodology study was undertaken to investigate 40 consecutive patients presenting with POT to four movement disorder centers in France. HQoL was investigated using eight quantitative scales and a qualitative study which employed semi-structured interviews. Qualitative data were analyzed with a combination of grounded-theory approach.

Results

Our results confirm that HQoL in POT is severely affected. Fear of falling was identified as the main predictor of HQoL. The qualitative arm of our study explored our initial results in greater depth and uncovered themes not identified by the quantitative approach.

Conclusion

Our results illustrate the huge potential of mixed methodology in identifying issues influencing HQoL in POT. Our work paves the way for enhanced patient care and improved HQoL in POT and is paradigmatic of this modern approach for investigating HQoL issues in chronic neurological disorders.

Tremor

Tremor is a phenomenon observed in a broad spectrum of diseases with different pathophysiologies. While patients with tremor may not complain in the clinic of symptoms of imbalance, gait difficulties, or falls, laboratory research studies using quantitative analysis of gait and posture and neurophysiologic techniques have demonstrated impaired gait and balance across a variety of tremor etiologies. These findings have been supported by careful epidemiologic studies assessing symptoms of imbalance. Imaging and neurophysiologic studies have identified cerebellar networks as important mediators of tremor, and therefore a likely common site of dysfunction to explain the phenomenologic overlap between impaired postural and gait control with tremor. Further understanding of these mechanisms and networks is of crucial importance in the development of new treatments, particularly surgical or minimally invasive lesional therapies.

Pathogenesis of Primary Orthostatic Tremor: Current Concepts and Controversies

Background

Orthostatic tremor (OT), a rare and complex movement disorder, is characterized by rapid tremor of both legs and the trunk while standing. These disappear while the patient is either lying down or walking. OT may be idiopathic/primary or it may coexist with several neurological conditions (secondary OT/OT plus). Primary OT remains an enigmatic movement disorder and its pathogenesis and neural correlates are not fully understood.

Methods

A PubMed search was conducted in July 2017 to identify articles for this review.

Results

Structural and functional neuroimaging studies of OT suggest possible alterations in the cerebello-thalamo-cortical network. As with essential tremor, the presence of a central oscillator has been postulated for OT; however, the location of the oscillator within the tremor network remains elusive. Studies have speculated a possible dopaminergic deficit in the pathogenesis of primary OT; however, the evidence in favor of this concept is not particularly robust. There is also limited evidence favoring the concept that primary OT is a neurodegenerative disorder, as a magnetic resonance spectroscopic imaging study revealed significant reduction in cerebral and cerebellar N-acetyl aspartate (NAA) levels, a marker of neuronal compromise or loss.

Discussion

Based on the above, it is clear that the pathogenesis of primary OT still remains unclear. However, the available evidence most strongly favors the existence of a central oscillatory network, and involvement of the cerebellum and its connections.

Pathological ponto-cerebello-thalamo-cortical activations in primary orthostatic tremor during lying and stance

Primary orthostatic tremor is a rare neurological disease characterized mainly by a high frequency tremor of the legs while standing. The aim of this study was to identify the common core structures of the oscillatory circuit in orthostatic tremor and how it is modulated by changes of body position. Ten patients with orthostatic tremor and 10 healthy age-matched control subjects underwent a standardized neurological and neuro-ophthalmological examination including electromyographic and posturographic recordings. Task-dependent changes of cerebral glucose metabolism during lying and standing were measured in all subjects by sequential ¹⁸F-fluorodeoxyglucose-positron emission tomography on separate days. Results were compared between groups and conditions. All the orthostatic tremor patients, but no control subject, showed the characteristic 13-18 Hz tremor in coherent muscles during standing, which ceased in the supine position. While lying, patients had a significantly increased regional cerebral glucose metabolism in the pontine tegmentum, the posterior cerebellum (including the dentate nuclei), the ventral intermediate and ventral posterolateral nucleus of the thalamus, and the primary motor cortex bilaterally compared to controls. Similar glucose metabolism changes occurred with clinical manifestation of the tremor during standing. The glucose metabolism was relatively decreased in mesiofrontal cortical areas (i.e. the medial prefrontal cortex, supplementary motor area and anterior cingulate cortex) and the bilateral anterior insula in orthostatic tremor patients while lying and standing. The mesiofrontal hypometabolism correlated with increased body sway in posturography. This study confirms and further elucidates ponto-cerebello-thalamo-primary motor cortical activations underlying primary orthostatic tremor, which presented consistently in a group of patients. Compared to other tremor disorders one characteristic feature in orthostatic tremor seems to be the involvement of the pontine tegmentum in the pathophysiology of tremor generation. High frequency oscillatory properties of pontine tegmental neurons have been reported in pathological oscillatory eye movements. It is remarkable that the characteristic activation and deactivation pattern in orthostatic tremor is already present in the supine position without tremor presentation. Multilevel changes of neuronal excitability during upright stance may trigger activation of the orthostatic tremor network. Based on the functional imaging data described in this study, it is hypothesized that a mesiofrontal deactivation is another characteristic feature of orthostatic tremor and plays a pivotal role in development of postural unsteadiness during prolonged standing.

Subperceptional Burst Versus Perceptional Tonic Spinal Cord Stimulation Waveforms for Drug-resistant Orthostatic Tremor: Comparative Data of 2 Cases

Background

Spinal cord stimulation (SCS) and deep-brain stimulation reportedly improve refractory orthostatic tremor (OT). No comparative data exist assessing subperceptional versus perceptional SCS with sham stimulation in patients with OT.

Methods

Two patients who had refractory OT were assessed at baseline and 3 months after SCS implantation using 3 different SCS modes: paraesthesia-free burst SCS (40 Hz), sham SCS, and paraesthesia-evoking tonic SCS (100-130 Hz). Surface electromyography, standing time, stimulation parameters, and any adverse events were prospectively recorded.

Results

Improved standing time was observed under burst and tonic mode versus stimulation off and compared with baseline in both patients (patient 1: baseline = 22-second; burst SCS [subperceptional]/ standing time = 2.8 minutes; stimulation off/ standing time = 28 seconds; and tonic SCS [perceptional]/ standing time = 1.2 minutes; patient 2: baseline = 47-second; burst SCS [subperceptional]/ standing time = 3.1 minutes; stimulation off/ standing time = 48 seconds; and tonic SCS [perceptional]/ standing time = 1.1 minute). The electromyography frequency demonstrated a decline in tremor frequency.

Conclusion

Burst as a novel SCS paradigm may be co-considered in patients with refractory OT before more invasive deep-brain stimulation.

Orthostatic Tremor and Orthostatic Myoclonus: Weight-bearing Hyperkinetic Disorders: A Systematic Review, New Insights, and Unresolved Questions

BACKGROUND

Orthostatic tremor (OT) and orthostatic myoclonus (OM) are weight-bearing hyperkinetic movement disorders most commonly affecting older people that induce "shaky legs" upon standing. OT is divided into "classical" and "slow" forms based on tremor frequency. In this paper, the first joint review of OT and OM, we review the literature and compare and contrast their demographic, clinical, electrophysiological, neuroimaging, pathophysiological, and treatment characteristics.

METHODS

A PubMed search up to July 2016 using the phrases "orthostatic tremor," "orthostatic myoclonus," "shaky legs," and "shaky legs syndrome" was performed.

RESULTS

OT and OM should be suspected in older patients reporting unsteadiness with prolonged standing and/or who exhibit cautious, wide-based gaits. Surface electromyography (SEMG) is necessary to verify the diagnoses. Functional neuroimaging and electrophysiology suggest the generator of classical OT lies within the cerebellothalamocortical network. For OM, and possibly slow OT, the frontal, subcortical cerebrum is the most likely origin. Clonazepam is the most useful medication for classical OT, and levetiracetam for OM, although results are often disappointing. Deep brain stimulation appears promising for classical OT. Rolling walkers reliably improve gait affected by these disorders, as both OT and OM attenuate when weight is transferred from the legs to the arms.

DISCUSSION

Orthostatic hyperkinesias are likely underdiagnosed, as SEMG is often unavailable in clinical practice, and thus may be more frequent than currently recognized. The shared weight-bearing induction of OT and OM may indicate a common pathophysiology. Further research, including use of animal models, is necessary to better define the prevalence and pathophysiology of OT and OM, in order to improve their treatment, and provide additional insights into basic balance and gait mechanisms.

Lessons I have learned from my patients: everyday life with primary orthostatic tremor

Background

Primary orthostatic tremor is a rare disorder that is still under-diagnosed or misdiagnosed. Motor symptoms are fairly characteristics but the real impact on the patient’s every day life and quality of life is under-estimated. The ”how my patients taught me” format describes the impact on the patients’ every day life with their own words, which is rarely done.

Case presentation

A 46 year old lady was diagnosed primary orthostatic tremor (POT) based on the cardinal symptoms: feelings of instability, leg tremor and fear of falling in the standing position, improvement with walking and disappearance while sitting, frequency of Tremor in the 13–18Hz range, normal neurological examination. She gives illustrative examples of her disability in every day life activity (shower, public transportation, shopping). She reports how she felt stigmatized by her “invisible disorder”. As a consequence, she developed anxiety depression and social phobia. All these troubles are unknown or under recognized by doctors and family.

Conclusions

We review the clinical signs of POT that may help to increase the awareness of doctors and improve the diagnosis accuracy, based on the motor symptoms and description of the every day life disability, as reported by the patient. Non-motor symptoms (including somatic concerns, anxiety, depression, and social phobia) should be better considered in POT as they have a major impact on quality of life. Pharmacological treatments (clonazepam, gabapentin) may be helpful but have a limited effect over the years as the patients experience a worsening of their condition. On the long term follow-up, there are still unmet needs in POT, and new therapeutic avenues may be based on the pathophysiology by modulating the cerebello-thalamo-cortical network.

Electronic supplementary material

The online version of this article (doi:10.1186/s40734-016-0048-5) contains supplementary material, which is available to authorized users.

Orthostatic Tremor: An Update on a Rare Entity

Background

Orthostatic tremor (OT) remains among the most intriguing and poorly understood of movement disorders. Compared to Parkinson’s disease or even essential tremor, there are very few articles addressing more basic science issues. In this review, we will discuss the findings of main case series on OT, including data on etiology, pathophysiology, diagnostic approach, treatment strategies, and outcome.

Methods

Data for this review were identified by searching PUBMED (January 1966 to August 2016) for the terms “orthostatic tremor” or “shaky leg syndrome,” which yielded 219 entries. We did not exclude papers on the basis of language, country, or publication date. The electronic database searches were supplemented by articles in the authors’ files that pertained to this topic.

Results

Owing to its rarity, the current understanding of OT is limited and is mostly based on small case series or case reports. Despite this, a growing body of evidence indicates that OT might be a progressive condition that is clinically heterogeneous (primary vs. secondary cases) with a broader spectrum of clinical features, mainly cerebellar signs, and possible cognitive impairment and personality disturbances. Along with this, advanced neuroimaging techniques are now demonstrating distinct anatomical and functional changes, some of which are consistent with neuronal loss.

Discussion

OT might be a family of diseases, unified by the presence of leg tremor, but further characterized by etiological and clinical heterogeneity. More work is needed to understand the pathogenesis of this condition.