Update on treatment of essential tremor

Efficacy of Cerebellar Transcranial Magnetic Stimulation in Treating Essential Tremor: A Randomized, Sham-Controlled Trial

BACKGROUND AND PURPOSE

Repetitive transcranial magnetic stimulation (rTMS) of the cerebellar hemisphere represents a new option in treating essential tremor (ET) patients. We aimed to determine the efficacy of cerebellar rTMS in treating ET using different protocols regarding the number of sessions, exposure duration, and follow-up duration.

METHODS

A randomized sham-controlled trial was conducted, in which 45 recruit patients were randomly allocated to 2 groups. The first (active group) comprised 23 patients who were exposed to 12 sessions of active rTMS with 900 pulses of 1-Hz rTMS at 90% of the resting motor threshold daily on each side of the cerebellar hemispheres over 4 weeks. The second group (sham group) comprised 22 patients who were exposed to 12 sessions of sham rTMS. Both groups were reassessed at baseline and after 1 day, 1 month, 2 months, and 3 months using the Fahn-Tolosa-Marin tremor-rating scale (FTM).

RESULTS

Demographic characteristics did no differ between the two groups. There were significant reductions both in FTM subscores A and B and in the FTM total score in the active-rTMS group during the period of assessment and after 3 months (p=0.031 and 0.011, respectively). However, subscore C did not change significantly from baseline when assessed at 2 and 3 months (p=0.073 and 0.236, respectively). Furthermore, the global assessment score was significantly higher in the active-rTMS group (p>0.001).

CONCLUSIONS

Low-frequency rTMS over the cerebellar cortex for 1 month showed relative safety and long-lasting efficacy in patients with ET. Further large-sample clinical trials are needed that include different sites of stimulation and longer follow-ups.

Phenytoin-induced cerebellar atrophy: A case for reversibility of neurological decline

This case serves as a reminder of the infrequent, yet consequential occurrence of cerebellar degeneration linked to phenytoin usage. Whilst emphasizes the importance of monitoring patients on long-term phenytoin therapy, and it further suggests considering employing bedside imaging tools such as Ultrasound fusion imaging for follow-up of patients at risk of this type of disorder. We present a case study involving a 23-year-old woman who experienced significant neurological impairment resulting in severe cerebellar atrophy while undergoing phenytoin treatment. On cessation of phenytoin, the patient exhibited improvement with enhanced cerebellar function.

Advancements in the Clinical Outcomes of Functional Neurosurgery With Deep Brain Stimulation for Movement Disorders: A Literature Review

This literature review explores recent advancements in deep brain stimulation (DBS) surgery for movement disorders. It highlights notable improvements, including closed-loop stimulation techniques, optogenetics, and improved surgical targeting. Positive clinical outcomes with low complication rates and improved motor symptoms are consistently reported. The review emphasizes the importance of minimizing risks through meticulous surgical practices and discusses potential complications associated with DBS surgery. Future prospects focus on enhancing technology, refining surgical techniques, and conducting further research. Closed-loop stimulation optimizes DBS efficacy by tailoring stimulation parameters to individual patient needs. Optogenetics offers precise modulation of neural activity with light-sensitive proteins, enabling more targeted treatments. Cybersecurity measures are essential due to the integration of wireless and digital technologies in DBS systems. DBS surgery has significantly improved the management of movement disorders with its safety and effectiveness. Ongoing research in closed-loop stimulation, optogenetics, and cybersecurity is expected to further enhance DBS technology and outcomes, benefiting patients with treatment-resistant movement disorders.

GABA-A Alpha 2/3 but Not Alpha 1 Receptor Subunit Ligand Inhibits Harmaline and Pimozide-Induced Tremor in Rats

Treatment of tremors, such as in essential tremor (ET) and Parkinson's disease (PD) is mostly ineffective. Exact tremor pathomechanisms are unknown and relevant animal models are missing. GABA-A receptor is a target for tremorolytic medications, but current non-selective drugs produce side effects and have safety liabilities. The aim of this study was a search for GABA-A subunit-specific tremorolytics using different tremor-generating mechanisms. Two selective positive allosteric modulators (PAMs) were tested. Zolpidem, targeting GABA-A α1, was not effective in models of harmaline-induced ET, pimozide- or tetrabenazine-induced tremulous jaw movements (TJMs), while the novel GABA-A α2/3 selective MP-III-024 significantly reduced both the harmaline-induced ET tremor and pimozide-induced TJMs. While zolpidem decreased the locomotor activity of the rats, MP-III-024 produced small increases. These results provide important new clues into tremor suppression mechanisms initiated by the enhancement of GABA-driven inhibition in pathways controlled by α2/3 but not α1 containing GABA-A receptors. Tremor suppression by MP-III-024 provides a compelling reason to consider selective PAMs targeting α2/3-containing GABA-A receptors as novel therapeutic drug targets for ET and PD-associated tremor. The possibility of the improved tolerability and safety of this mechanism over non-selective GABA potentiation provides an additional rationale to further pursue the selective α2/3 hypothesis.

Prospective, longitudinal analysis of medication use in a cohort of elderly essential tremor cases

BACKGROUND

There are no prospective, longitudinal studies investigating patterns of medication use among essential tremor (ET) patients. Our goal was to fill this knowledge gap. We also had a unique opportunity to examine medication use patterns primarily among elders with longstanding ET. We hypothesized that by the time ET patients reach advanced ages, medication changes would be uncommon - that is, they may have reached some kind of equipoise.

METHODS

A prospective, longitudinal cohort of ET cases was evaluated across three time points. Cases were not ascertained from a treatment setting, thereby removing important selection biases. Each reported current medications and dosages of each.

RESULTS

There were 144 cases (mean baseline age = 76.1 ± 9.4 years). The mean observation period = 2.9 ± 0.2 years. Primidone and propranolol were the most commonly used medications, although almost one-half of cases (44.4%) reported using neither during this period. A third of primidone users (33.3%) and a quarter of propranolol users (24.6%) reported changes in use vs. nonuse during the observation period. The majority of our cases made some change in their daily medication dosage during the course of the study - 73.3% of primidone users and 57.9% of propranolol users.

CONCLUSION

In this prospective, longitudinal study, use vs. nonuse and daily dosage of both primidone and propranolol fluctuated across time for a sizable proportion of ET cases. Even among elders with chronic, longstanding ET, there is considerable ongoing medication adjustment, underscoring the need to improve the medication situation for ET patients.

The Pathophysiology and Treatment of Essential Tremor: The Role of Adenosine and Dopamine Receptors in Animal Models

Essential tremor (ET) is one of the most common neurological disorders that often affects people in the prime of their lives, leading to a significant reduction in their quality of life, gradually making them unable to independently perform the simplest activities. Here we show that current ET pharmacotherapy often does not sufficiently alleviate disease symptoms and is completely ineffective in more than 30% of patients. At present, deep brain stimulation of the motor thalamus is the most effective ET treatment. However, like any brain surgery, it can cause many undesirable side effects; thus, it is only performed in patients with an advanced disease who are not responsive to drugs. Therefore, it seems extremely important to look for new strategies for treating ET. The purpose of this review is to summarize the current knowledge on the pathomechanism of ET based on studies in animal models of the disease, as well as to present and discuss the results of research available to date on various substances affecting dopamine (mainly D3) or adenosine A1 receptors, which, due to their ability to modulate harmaline-induced tremor, may provide the basis for the development of new potential therapies for ET in the future.

Chronic embedded cortico-thalamic closed-loop deep brain stimulation for the treatment of essential tremor

Deep brain stimulation (DBS) is an approved therapy for the treatment of medically refractory and severe movement disorders. However, most existing neurostimulators can only apply continuous stimulation [open-loop DBS (OL-DBS)], ignoring patient behavior and environmental factors, which consequently leads to an inefficient therapy, thus limiting the therapeutic window. Here, we established the feasibility of a self-adjusting therapeutic DBS [closed-loop DBS (CL-DBS)], fully embedded in a chronic investigational neurostimulator (Activa PC + S), for three patients affected by essential tremor (ET) enrolled in a longitudinal (6 months) within-subject crossover protocol (DBS OFF, OL-DBS, and CL-DBS). Most patients with ET experience involuntary limb tremor during goal-directed movements, but not during rest. Hence, the proposed CL-DBS paradigm explored the efficacy of modulating the stimulation amplitude based on patient-specific motor behavior, suppressing the pathological tremor on-demand based on a cortical electrode detecting upper limb motor activity. Here, we demonstrated how the proposed stimulation paradigm was able to achieve clinical efficacy and tremor suppression comparable with OL-DBS in a range of movements (cup reaching, proximal and distal posture, water pouring, and writing) while having a consistent reduction in energy delivery. The proposed paradigm is an important step toward a behaviorally modulated fully embedded DBS system, capable of delivering stimulation only when needed, and potentially mitigating pitfalls of OL-DBS, such as DBS-induced side effects and premature device replacement.

Distribution of tremor among the major degrees of freedom of the upper limb in subjects with Essential Tremor

OBJECTIVE

Although Essential Tremor is one of the most common movement disorders, we do not currently know which muscles are most responsible for tremor. Determining this requires multiple steps, one of which is characterizing the distribution of tremor among the degrees of freedom (DOF) of the upper limb.

METHODS

Upper-limb motion was recorded while 22 subjects with ET performed postural and kinetic tasks involving a variety of limb configurations. We calculated the mean distribution of tremor among the seven DOF from the shoulder to the wrist, as well as the effect of limb configuration, repetition, and subject characteristics (sex, tremor onset, duration, and severity) on the distribution.

RESULTS

On average, kinetic tremor was greatest in forearm pronation-supination and wrist flexion-extension, intermediate in shoulder internal-external rotation and wrist radial-ulnar deviation and then shoulder flexion-extension and elbow flexion-extension, and least in shoulder abduction-adduction. The average distribution of postural tremor was similar except for forearm pronation-supination, which played a smaller role than in kinetic tremor. Limb configuration and subject characteristics did significantly affect tremor, but practically only in forearm pronation-supination and wrist flexion-extension. There were no significant differences between repetitions, indicating that the distribution was consistent over the duration of the experiment.

CONCLUSIONS

This paper presents a thorough characterization of tremor distribution from the shoulder to the wrist.

SIGNIFICANCE

Understanding which DOF exhibit the most tremor may lead to more targeted peripheral tremor suppression.

Predicting high-intensity focused ultrasound thalamotomy lesions using 2D magnetic resonance thermometry and 3D Gaussian modeling

PURPOSE

To develop a method of using two-dimensional (2D) magnetic resonance thermometry, and three-dimensional (3D) Gaussian modeling to predict the volume, shape, and location of 1 day postoperative T1w high-intensity focused ultrasound lesions in medication refractory tremor patients; thereby facilitating a better comprehension of thermal damage thresholds, which can be utilized to reduce adverse events, and improve patient outcome.

METHODS

Fifteen patients underwent magnetic resonance-guided focused ultrasound (MRgFUS) thalamotomy, which was performed at our center using an InSightec ExAblate 4000 system (Haifa, Israel), and guided by magnetic resonance imaging using a 3 T Discovery 750 (General Electric Healthcare, Waukesha, WI, USA). For treatment monitoring, 2D MR thermometry (temperature sensitivity: -0.00909 ppm/°C, bandwidth: 279 Hz/pixel) was performed in multiple orthogonal planes (sagittal, coronal, and axial) intraoperatively. These images were temporally filtered using a general linear model approach to reduce noise. Temporal volumes of filtered temperature maps with a peak temperature ≥ 47°C were aligned and fitted with a 3D Gaussian to create a canonical heating model. We then fitted the filtered 2D temperature maps with a 3D Gaussian, and used the relationships derived from the 3D heating model to estimate the 3D temperature distribution. These temperature distributions were converted into thermal dose distributions and accumulated across time to create an accumulated thermal dose (ATD) profile. Thresholded ATD profiles were then correlated with manually traced T1-weighted 1 day postoperative lesion volumes across patients, and linear regression slopes were plotted against varying ATD thresholds. Additionally, the Dice-Sørensen coefficient (DSC) was calculated to quantify the volumetric overlap between predicted, and actual lesions.

RESULTS

On average, 18.1 (standard deviation (SD): ±4.6, range: 10-29) sonications were performed with an average peak temperature achieved of 62.4°C (SD: ±2.4, range: 58.2-67.7). An ATD threshold of 35.8 CEM43 was found to give a unity linear regression slope; this corresponded to an average DSC of 0.689 (SD: ±0.090, range: 0.476-0.815).

CONCLUSIONS

Using multiplanar 2D MR thermometry and 3D Gaussian modeling, we were able to achieve very good (DSC = 0.689) predictions of T1w 1 day postoperative lesion volume, shape and location at an ATD threshold of approximately 36 CEM43. Furthermore, this method has the potential to be used in clinical evaluations to further elucidate the relationship between thermal damage and clinical outcome. Accurate 3D lesion prediction will facilitate improved clinical decision making in future MRgFUS thalamotomies.

Cerebellar repetitive transcranial magnetic stimulation (rTMS) for essential tremor: A double-blind, sham-controlled, crossover, add-on clinical trial

BACKGROUND

There is controversial evidence about the effect of cerebellar low-frequency stimulation in patients with essential tremor (ET).

OBJECTIVES

In this study we assessed safety and effectiveness of 1 Hz (low-frequency) cerebellar repetitive transcranial magnetic stimulation (rTMS) on tremor severity in patients with essential tremor in a sham-controlled crossover trial.

METHODS

A total of 23 patients assigned into two groups to receive either sham (n = 10) or rTMS (n = 13) treatment, with crossing over after a two-month washout period. Intervention consisted of 900 pulses of 1 Hz rTMS at 90% resting motor threshold or the same protocol of sham stimulation over each cerebellar hemisphere for 5 consecutive days. Tremor severity was assessed by Fahn-Tolosa-Marin (FTM) scale at baseline and at days 5, 12 and 30 after intervention. The FTM consists of 3 subscales including tremor severity rating, performance of motor tasks, and functional disability. Carry-over and treatment effects were analyzed using independent samples t-test.

RESULTS

There was no significant improvement in the total FTM scores in rTMS compared to the sham stimulation on day 5 (p = 0.132), day 12 (p = 0.574), or day 30 (p = 0.382). Similarly, FTM subscales, including tremor severity rating, motor tasks, and functional disability did not improve significantly after rTMS treatment. Mild headache and local pain were the most frequent adverse events.

CONCLUSION

Although cerebellar rTMS seems to have acceptable safety when used in ET patients, this study could not prove any efficacy for it in reduction of tremor in these patients. Larger studies are needed to evaluate efficacy of this therapeutic intervention and to provide evidence about the optimal stimulation parameters.

Gait worsening and the microlesion effect following deep brain stimulation for essential tremor

OBJECTIVE

To investigate the effects of unilateral thalamic deep brain stimulation (DBS) on walking in persons with medication-refractory essential tremor (ET).

METHODS

We performed laboratory-based gait analyses on 24 persons with medication-refractory ET before and after unilateral thalamic DBS implantation. Normal and tandem walking parameters were analysed across sessions (PRE-DBS/DBS OFF/DBS ON) by repeated measures analyses of variance. Pearson's correlations assessed whether changes in walking after DBS were global (ie, related across gait parameters). Baseline characteristics, lead locations and stimulation parameters were analysed as possible contributors to gait effects.

RESULTS

DBS minimally affected gait at the cohort level. However, 25% of participants experienced clinically meaningful gait worsening. Walking speed decreased by >30% in two participants and by >10% in four others. Decreased walking speed correlated with increased gait variability, indicating global gait worsening in affected participants. The worsening persisted even after the stimulation was turned off. Participants with worse baseline tandem walking performance may be more likely to experience post-DBS gait worsening; the percentage of tandem missteps at baseline was nearly three times higher and tandem walking speeds were approximately 30% slower in participants who experienced gait worsening. However, these differences in tandem walking in persons with gait worsening as compared with those without worsening were not statistically significant. Lead locations and stimulation parameters were similar in participants with and without gait worsening.

CONCLUSION

Global gait worsening occurred in 25% of participants with unilateral DBS for medication-refractory ET. The effect was present on and off stimulation, likely indicating a microlesion effect.

Movement Disorders and Voice

The primary movement disorders affecting the voice are laryngeal dystonia (including spasmodic dysphonia), essential voice tremor, and Parkinson disease. Diagnosis of these conditions is clinical and based on a detailed history, voice evaluation, and physical and laryngoscopic examination. Laryngeal dystonia and essential voice tremor are hyperfunctional disorders and are treated most commonly with botulinum toxin injections. Parkinson disease is a hypofunctional disorder that may affect the voice and most commonly is treated with Lee Silverman Voice Treatment.

Cost-Effectiveness of Magnetic Resonance-Guided Focused Ultrasound for Essential Tremor

BACKGROUND

Radiofrequency thalamotomy and deep brain stimulation are current treatments for moderate to severe medication-refractory essential tremor. However, they are invasive and thus carry risks. Magnetic resonance-guided focused ultrasound is a new, less invasive surgical option. The objective of the present study was to determine the cost-effectiveness of magnetic resonance-guided focused ultrasound compared with standard treatments in Canada.

METHODS

We conducted a cost-utility analysis using a Markov cohort model. We compared magnetic resonance-guided focused ultrasound with no surgery in people ineligible for invasive neurosurgery and with radiofrequency thalamotomy and deep brain stimulation in people eligible for invasive neurosurgery. In the reference case analysis, we used a 5-year time horizon and a public payer perspective and discounted costs and benefits at 1.5% per year.

RESULTS

Compared with no surgery in people ineligible for invasive neurosurgery, magnetic resonance-guided focused ultrasound cost $21,438 more but yielded 0.47 additional quality-adjusted life years, producing an incremental cost-effectiveness ratio of $45,817 per quality-adjusted life year gained. In people eligible for invasive neurosurgery, magnetic resonance-guided focused ultrasound was slightly less effective but much less expensive compared with the current standard of care, deep brain stimulation. The results were sensitive to assumptions regarding the time horizon, cost of magnetic resonance-guided focused ultrasound, and probability of recurrence.

CONCLUSIONS

In people ineligible for invasive neurosurgery, the incremental cost-effectiveness ratio of magnetic resonance-guided focused ultrasound versus no surgery is comparable to many other tests and treatments that are widely adopted in high-income countries. In people eligible for invasive neurosurgery, magnetic resonance-guided focused ultrasound is also a reasonable option. © 2018 International Parkinson and Movement Disorder Society.

Botulinum Toxin Treatment of Movement Disorders

Botulinum neurotoxins (BoNTs) are now among the most widely used therapeutic agents in clinical medicine with indications applied to the fields of movement disorders, pain disorders, and autonomic dysfunction. In this literature review, the efficacy and utility of BoNTs in the field of movement disorders are assessed using the criteria of the Guideline Development Subcommittee of the American Academy of Neurology. The literature supports a level A efficacy (established) for BoNT therapy in cervical dystonia and a level B efficacy (probably effective) for blepharospasm, hemifacial spasm, laryngeal dystonia (spasmodic dysphonia), task-specific dystonias, essential tremor, and Parkinson rest tremor. It is the view of movement disorder experts, however, that despite the level B efficacy, BoNTs should be considered treatment of first choice for blepharospasm, hemifacial spasm, laryngeal, and task-specific dystonias. The emerging data on motor and vocal tics of Tourette syndrome and oromandibular dystonias are encouraging but the current level of efficacy is U (undetermined) due to lack of published high-quality studies.

Botulinum Toxin Type A Injections as Monotherapy for Upper Limb Essential Tremor Using Kinematics

Background:There is a significant need for a targeted therapy for essential tremor (ET), as medications have not been developed specifically for ET, and the ones prescribed are often not well-tolerated, so that many patients remain untreated. Recent work has shown that, unlike previous experience, kinematically guided individualized botulinum toxin type A (BoNT-A) injections provide benefit along with minimal weakness. Ours is the first long-term (96-week) safety and efficacy study of BoNT-A as monotherapy for ET using kinematically driven injection parameters.Methods:Ten ET patients were administered six serial BoNT-A treatments every 16 weeks and were assessed at 6 weeks following treatment. During each study visit, the Fahn–Tolosa–Marin (FTM) scale, the Unified Parkinson’s Disease Rating Scale, and the Quality of Life for Essential Tremor Questionnaire (QUEST) were administered along with kinematic assessment of the treated limb. Participants performed scripted tasks with motion sensors placed over each arm joint. Dosing patterns were determined using the movement disorder neurologist’s interpretation of muscles contributing to the kinematically analyzed upper limb tremor biomechanics.Results:There was a 33.8% (p<0.05) functional improvement (FTM part C) and a 39.8% (p<0.0005) improvement in QUEST score at week 96 compared to pretreatment scores at week 0. Although there was a 44.6% (p<0.0005) non-dose-dependent reduction in maximal grip strength, only 2 participants complained of mild weakness. Following the fourth serial treatment, mean action tremor score was reduced by 62.9% (p=0.001) in the treated and by 44.4% (p=0.03) in the untreated arm at week 96 compared to week 48.Conclusions:Individualized BoNT-A dosing patterns to each individual’s tremor biomechanics provided an effective monotherapy for ET as function improved without functionally limiting muscle weakness.

Botulinum Toxin in Management of Limb Tremor

Essential tremor is characterized by persistent, usually bilateral and symmetric, postural or kinetic activation of agonist and antagonist muscles involving either the distal or proximal upper extremity. Quality of life is often affected and one's ability to perform daily tasks becomes impaired. Oral therapies, including propranolol and primidone, can be effective in the management of essential tremor, although adverse effects can limit their use and about 50% of individuals lack response to oral pharmacotherapy. Locally administered botulinum toxin injection has become increasingly useful in the management of essential tremor. Targeting of select muscles with botulinum toxin is an area of active research, and muscle selection has important implications for toxin dosing and functional outcomes. The use of anatomical landmarks with palpation, EMG guidance, electrical stimulation, and ultrasound has been studied as a technique for muscle localization in toxin injection. Earlier studies implemented a standard protocol for the injection of (predominantly) wrist flexors and extensors using palpation and EMG guidance. Targeting of muscles by selection of specific activators of tremor (tailored to each patient) using kinematic analysis might allow for improvement in efficacy, including functional outcomes. It is this individualized muscle selection and toxin dosing (requiring injection within various sites of a single muscle) that has allowed for success in the management of tremors.

Eligibility Criteria for Deep Brain Stimulation in Parkinson’s Disease, Tremor, and Dystonia

In this review, the available evidence to guide clinicians regarding eligibility for deep brain stimulation (DBS) in the main conditions in which these forms of therapy are generally indicated—Parkinson’s disease (PD), tremor, and dystonia—is presented. In general, the literature shows that DBS is effective for PD, essential tremor, and idiopathic dystonia. In these cases, key points in patient selection must include the level of disability and inability to manage symptoms using the best available medical therapy. Results are, however, still not optimal when dealing with other aetiologies, such as secondary tremors and symptomatic dystonia. Also, in PD, issues such as age and neuropsychiatric profile are still debatable parameters. Overall, currently available literature is able to guide physicians on basic aspects of patient selection and indications for DBS; however, a few points are still debatable and controversial. These issues should be refined and clarified in future studies.

Functional Ability Improved in Essential Tremor by IncobotulinumtoxinA Injections Using Kinematically Determined Biomechanical Patterns - A New Future

Objective

Effective treatment for functional disability caused by essential tremor is a significant unmet need faced by many clinicians today. Current literature regarding focal therapy by botulinum toxin type A (BoNT-A) injections uses fixed dosing regimens, which cannot be individualized, provides only limited functional benefit and unacceptable muscle weakness commonly occurs. This 38-week open label study, the longest to-date, demonstrates how kinematic technology addressed all these issues by guiding muscle selection.

Method

Participants (n = 24) were assessed at weeks 0, 6, 16, 22, 32, and 38 and injected with incobotulinumtoxinA at weeks 0, 16, and 32. Clinical assessments including UPDRS tremor items, Fahn-Tolosa-Marin (FTM) tremor rating scale assessing tremor severity, writing and functional ability, quality of life questionnaire (QUEST) and objective kinematic assessments were completed at every visit. Participants performed two postural and two weight-bearing scripted tasks with motion sensors placed over the wrist, elbow and shoulder joints. These sensors captured angular tremor amplitude (RMS units) and acceleration joint motion that was segmented into directional components: flexion-extension (F/E), pronation-supination and radial-ulnar at the wrist, F/E at the elbow, and F/E and adduction-abduction at the shoulder. Injection parameters were determined using kinematics, followed by the clinician’s determination of which muscles would contribute to the specific upper limb tremor biomechanics and dosing per participant.

Results

Multi-joint biomechanical recordings allowed individualized muscle selection and showed significant improvement in whole-arm function, FTM parts A-C scores, at week 6 which continued throughout the study. By week 38, the total FTM score statistically significantly reduced from 16.2±4.6 at week 0 to 9.5±6.3 (p<0.0005). UPDRS item 21 score rating action tremor was significantly reduced from 2.6±0.5 at week 0 to 1.6±1.1 (p = 0.01) at week 32. Quality of life (QUEST) significantly improved from 40.3±15.8 at week 0 to 31.1±15.3 (p = 0.035) at week 32 and to 27.8±15.3 (p = 0.028) at week 38. Kinematics provided an objective, secondary outcome measure, which showed a significant decrease in tremor amplitude in the wrist and shoulder joints (p<0.05). Eight participants (40%) self-reported mild weakness in injected muscles but had no interference in arm function.

Conclusion

Kinematic tremor assessments provide the injector unique insight to objectively individualize and personalize injection parameters demonstrating BoNT-A effectively alleviates functional disability caused by essential tremor. Kinematic technology is a promising method for standardizing assessments and for focal upper limb tremor treatment.

Trial Registration

ClinicalTrials.gov NCT02427646

Memory Similarities Between Essential Tremor and Parkinson's Disease: A Final Common Pathway?

OBJECTIVE

A growing body of literature supports the view that essential tremor (ET) involves alteration of cerebellar-thalamo-cortical networks which can result in working memory and executive deficits. In this study, we tested the hypothesis that individuals with ET would exhibit worse performance on memory tasks requiring more intrinsic organization and structuring (i.e., word lists) relative to those with fewer 'executive' demands (i.e., stories), similar to that previously observed in individuals with Parkinson's disease (PD).

METHOD

Participants included a convenience sample of 68 ET patients and 68 idiopathic PD patients, retrospectively matched based on age, education, and sex. All patients underwent routine neuropsychological evaluation assessing recent memory, auditory attention/working memory, language, and executive function. Memory measures included the Hopkins Verbal Learning Test-R and WMS-III Logical Memory.

RESULTS

Both ET and PD patients performed significantly worse on word list than story memory recall tasks. The magnitude of the difference between these two memory tasks was similar for ET and PD patients. In both patient groups, performance on measures of executive function and auditory attention/working memory was not distinctly correlated with word list vs. story recall.

CONCLUSIONS

These findings suggest that frontal-executive dysfunction in both ET and PD may negatively influence performance on memory tests that are not inherently organized. Although the pathophysiology of these two 'movement disorders' are quite distinct, both have downstream effects on thalamo-frontal circuitry which may provide a common pathway for a similar memory phenotype. Findings are discussed in terms of neuroimaging evidence, conceptual models, and best practice.

Comparative effectiveness of propranolol and botulinum for the treatment of essential voice tremor

OBJECTIVES/HYPOTHESIS

To assess the comparative effectiveness of botulinum toxin and propranolol in patients with essential vocal tremor (EVT).

STUDY DESIGN

Individual prospective cohort study.

METHODS

Study patients were recruited at the Emory Voice Center from patients seeking treatment for EVT. Exclusion criteria included current β-blocker treatment, spasmodic dysphonia, or other disease that prevented the use of propranolol therapy. A 10-week washout period from prior botulinum toxin treatment occurred before enrollment. Patients were assessed via the Voice-Related Quality-Of-Life (VRQOL) questionnaire, Quality of life in Essential Tremor questionnaire, and blinded perceptual voice assessment. These assessments were made at baseline voice 2 weeks after propranolol therapy and 4 weeks after botulinum toxin injection.

RESULTS

Eighteen patients were enrolled. After 2 to 4 weeks of propranolol therapy (with a maximum dosage of 60 mg to 90 mg per day), patients report an average ΔVRQOL of 9.31. Six patients report significant VRQOL improvement >10, with the rest reporting changes between -7.5 and 7.5. Fifteen patients were followed for at least 4 weeks after botulinum toxin injection, reporting an average improvement in scaled VRQOL of 22.00. Blinded perceptual voice assessment demonstrates an improvement in overall severity of tremor with botulinum toxin.

CONCLUSIONS

In some patients with EVT, propranolol led to significant vocal improvement with no major side effects. Although botulinum toxin remains the gold-standard therapy for patients with EVT, propranolol represents a possible alternative or adjuvant therapy for certain patients.

Electrical stimuli in the central nervous system microenvironment

Electrical stimulation to manipulate the central nervous system (CNS) has been applied as early as the 1750s to produce visual sensations of light. Deep brain stimulation (DBS), cochlear implants, visual prosthetics, and functional electrical stimulation (FES) are being applied in the clinic to treat a wide array of neurological diseases, disorders, and injuries. This review describes the history of electrical stimulation of the CNS microenvironment; recent advances in electrical stimulation of the CNS, including DBS to treat essential tremor, Parkinson's disease, and depression; FES for the treatment of spinal cord injuries; and alternative electrical devices to restore vision and hearing via neuroprosthetics (retinal and cochlear implants). It also discusses the role of electrical cues during development and following injury and, importantly, manipulation of these endogenous cues to support regeneration of neural tissue.

Resetting tremor by single and paired transcranial magnetic stimulation in Parkinson's disease and essential tremor

OBJECTIVE

The pathogenesis of tremor in Parkinson's disease (PD) and essential tremor (ET) is not fully understood. This study tested the role of primary motor cortex (M1), supplementary motor area (SMA) and cerebellar cortex on PD and ET tremor by single- and paired-pulse transcranial magnetic stimulation (TMS).

METHODS

Ten PD patients with resting tremor, six of them also with postural tremor, and ten ET patients with postural tremor were studied. Randomized single- and paired-pulse TMS with an interstimulus interval of 100 ms were delivered over M1, SMA and cerebellum. TMS effects were evaluated by calculating a tremor-resetting index (RI).

RESULTS

Single- vs. paired-pulse TMS showed no difference. M1-TMS and SMA-TMS but not by cerebellar TMS induced a significant RI in PD and ET. M1-TMS resulted in a significantly higher RI in PD than ET. Furthermore, M1-TMS in PD but not in ET resulted in a significantly higher RI than SMA-TMS.

CONCLUSIONS

Findings suggest a stronger involvement of M1 in resting and postural tremor in PD than postural tremor in ET.

SIGNIFICANCE

RI provides a useful marker to explore the differential functional role of M1, SMA and cerebellum in PD vs. ET tremor.

Noradrenaline transmission reducing drugs may protect against a broad range of diseases

1 A growing body of evidence suggests that the signalling molecule, noradrenaline (NA), plays a pathophysiological role in a broad range of psychiatric, neurological and peripheral disorders. Both preclinical and clinical data suggest that elevated NA signalling may be involved in the aetiology of major diseases such as depression, Alzheimer's disease and diabetes mellitus. 2 The molecular pathways by which NA may cause the manifestation of disease remain poorly understood, although they may include G protein-coupled receptor modulation of the Ras/MAP kinase, Stat3 and PI3K pathways, among others. In both individual animals and humans, NA tone may be elevated largely due to genetics, but also because of the exposure to marked psychological stress or trauma, or other environmental factors. 3 As NA is involved in the 'fight or flight' response by the sympathetic nervous system, this transmitter may be elevated in a large number of organisms due to evolutionary selection of enhancing responses to immediate environmental dangers. Likewise, acetylcholine signalling by the parasympathetic ('rest and digest') nervous system may be relatively diminished. This putative autonomic imbalance may result in diminished engagement in homeostatic processes, resulting in the emergence and progression of a number of diseases throughout the body. 4 In this scenario, a large number of individuals may benefit from chronic use of pharmacological agents - such as clonidine, guanfacine, propranolol or prazosin - that diminish NA signalling throughout the body. If so, NA transmission lowering drugs may protect against a wide range of diseases.

The variability of atlas-based targets in relation to surrounding major fibre tracts in thalamic deep brain stimulation

BACKGROUND

In essential tremor (ET), the main target for deep brain stimulation (DBS) is the thalamic ventralis intermedius nucleus (Vim). This target cannot be identified on conventional magnetic resonance imaging (MRI). Therefore, targeting depends on probabilistic coordinates derived from stereotactic atlases. The goal of our study was to investigate the variability of atlas-based Vim targets in relation to surrounding major fibre tracts.

METHODS

With the MRI and computed tomography (CT) scan data of ten patients who underwent DBS, we planned atlas based Vim targets in both hemispheres. We also performed deterministic fibre-tracking with diffusion tensor imaging (DTI) of the dentato-rubro-thalamic tract (DRTT), pyramidal tract (PT) and lemniscus medialis (LM) in all 20 hemispheres. Subsequently, we measured the distance from the atlas-based Vim target to each tract along the medial/lateral (x-coordinate), anterior/posterior (y-coordinate) and superior/inferior axis (z-coordinate).

RESULTS

Seventeen out of 20 DRTTs could be depicted with our standardised DTI/fibre-tracking parameters. The PT and the LM could be displayed in all 20 hemispheres. The atlas-based Vim target was found inside the DRTT in 11 (concerning the x-coordinate) and 10 hemispheres (concerning the z-coordinate). Regarding the anterior/posterior direction, the target was posterior to the DRTT in 11 cases. In 19 hemispheres the Vim target was located medial and superior to the PT and in 17 hemispheres posterior to it. Concerning the LM, the Vim target was found inside the LM in 16 (regarding the x-coordinate) and in 14 cases (regarding the z-coordinate). In eight cases it was located inside and in 12 cases anterior to the LM concerning the y-coordinate.

CONCLUSIONS

We found a considerable variability of the location of atlas-based target points of the ventralis intermedius nucleus in relation to neighbouring major fibre tracts in individual patients. These results suggest that individualised targeting to structures not directly visible on conventional MRI is necessary.

Deep brain stimulation for movement disorders

Deep brain stimulation (DBS) is an implanted electrical device that modulates specific targets in the brain resulting in symptomatic improvement in a particular neurologic disease, most commonly a movement disorder. It is preferred over previously used lesioning procedures due to its reversibility, adjustability, and ability to be used bilaterally with a good safety profile. Risks of DBS include intracranial bleeding, infection, malposition, and hardware issues, such migration, disconnection, or malfunction, but the risk of each of these complications is low--generally ≤ 5% at experienced, large-volume centers. It has been used widely in essential tremor, Parkinson's disease, and dystonia when medical treatment becomes ineffective, intolerable owing to side effects, or causes motor complications. Brain targets implanted include the thalamus (most commonly for essential tremor), subthalamic nucleus (most commonly for Parkinson's disease), and globus pallidus (Parkinson's disease and dystonia), although new targets are currently being explored. Future developments include brain electrodes that can steer current directionally and systems capable of "closed loop" stimulation, with systems that can record and interpret regional brain activity and modify stimulation parameters in a clinically meaningful way. New, image-guided implantation techniques may have advantages over traditional DBS surgery.

Structural and vibrational study of primidone based on monomer and dimer calculations

Primidone (Mysoline), with the chemical formula 5-ethyl-5-phenyl-hexahydropyrimidine- 4,6-dione (C12H14N2O2), has been a valuable drug in the treatment of epilepsy. In the present work, the experimental IR and Raman spectra of solid phase primidone were recorded, and the results were compared with theoretical wavenumber values of monomer and dimer forms of the title molecule. Vibrational spectral simulations in the dimer form were carried out to improve the assignment of the bands in the solid phase experimental spectra. The possible stable conformers of free molecule were searched by means of torsion potential energy surfaces scan studies through two dihedral angles. The molecular geometries of the monomer and dimer forms of title molecule were optimized using DFT method at B3LYP/6-31++G(d,p) level of theory. Using PEDs determined the contributions of internal (stretching, bending, etc.) coordinates to each normal mode of vibration. Further, HOMO-LUMO energy gap and NBO properties of the investigated molecule in monomer and dimer forms were also calculated.

Differential diagnosis of psychiatric symptoms after deep brain stimulation for movement disorders

OBJECTIVES

The presence of a deep brain stimulator (DBS) in a patient with a movement disorder who develops psychiatric symptoms poses unique diagnostic and therapeutic challenges for the treating clinician. Few sources discuss approaches to diagnosing and treating these symptoms.

MATERIALS AND METHODS

The authors review the literature on psychiatric complications in DBS for movement disorders and propose a heuristic for categorizing symptoms according to their temporal relationship with the DBS implantation process.

RESULTS

Psychiatric symptoms after DBS can be categorized as preimplantation, intra-operative/perioperative, stimulation related, device malfunction, medication related, and chronic stimulation related/long term. Once determined, the specific etiology of a symptom guides the practitioner in treatment.

CONCLUSIONS

A structured approach to psychiatric symptoms in DBS patients allows practitioners to effectively diagnose and treat them when they arise.

Pharmacotherapy of essential tremor

Essential tremor (ET) is a common movement disorder but its pathogenesis remains poorly understood. This has limited the development of effective pharmacotherapy. The current therapeutic armamentaria for ET represent the product of careful clinical observation rather than targeted molecular modeling. Here we review their pharmacokinetics, metabolism, dosing, and adverse effect profiles and propose a treatment algorithm. We also discuss the concept of medically refractory tremor, as therapeutic trials should be limited unless invasive therapy is contraindicated or not desired by patients.