Essential tremor

Potential for Intrathecal Baclofen in Treatment of Essential Tremor

INTRODUCTION

Essential tremor (ET) is the most common movement disorder of adults, affecting an estimated 7 million Americans. Symptoms of ET range from slightly noticeable to debilitating, with 1 cohort study finding 15% of patients were forced into early retirement. Additionally, depression has also been correlated with the severity of disability of ET. Treatment options include propranolol and primidone. Current treatment options are not very effective, with more than half (56.3%) of patients discontinuing medications because of no changes in symptoms.

METHODS

Unfortunately, there is a relative void and controversy in the literature explaining ET pathophysiology; however, the gamma-aminobutyric acid (GABA) hypothesis is the strongest. We conducted a PubMed search on 30 September 2015 with no time constraints using the search terms "essential tremor" and "baclofen," which resulted in a total of 5 articles.

RESULTS

Neurohistopathologic studies have demonstrated decreased GABA-A and GABA-B receptors in the cerebellar cortex of ET patients. GABA, the major inhibitory neurotransmitter in the central nervous system, is proposed to have an inhibitory effect on pacemaker output activity of the cerebello-thalamo-cortical pathway, with lower receptors resulting in decreased inhibition of baseline tremors. Tariq et al showed delayed onset and intensity of tremor with oral administration of R-baclofen in a mouse model of ET.

CONCLUSION

With a better side-effect profile and success in a physiologically related condition, we propose more clinical trials and research be carried out on intrathecal baclofen as a potential treatment option, especially drug refractory ET, so as to increase the quality of life of this patient population.

'Essential tremor' or 'the essential tremors': is this one disease or a family of diseases?

There is accumulating evidence that the entity referred to as 'essential tremor' (ET) is not a single disease. It may be a family of diseases better referred to as 'the ETs'. This review will summarize the following evidence: (1) the presence of etiological heterogeneity; (2) the heterogeneity of findings in postmortem studies, thus suggesting several diseases; (3) the recent discussion that age of onset may be an important marker of disease heterogeneity; (4) the clinical expansion of the concept of ET in recent years to include a broader range of tremor phenomenology, other motor features (gait ataxia), other involuntary movements (dystonia), and nonmotor features (cognitive problems, psychiatric problems), some of which could be primary; (5) the heterogeneity of pharmacological response profiles and clinical progression, and (6) the association of ET with Parkinson's disease, Alzheimer's disease, and possibly progressive supranuclear palsy, with the possibility that some ET patients are more predisposed to develop one of these. © 2013 S. Karger AG, Basel.

Dexterity training improves manual precision in patients affected by essential tremor

OBJECTIVE

To evaluate the effect of a short-term dexterity-training program on muscle tremor and the performance of hand precision tasks in patients with essential tremor (ET).

DESIGN

Three testing sessions: baseline, after 4 weeks without any interventions (control), and after 4 weeks of dexterity-training carried out 3 times per week.

SETTING

Biomechanics research laboratory.

PARTICIPANTS

Patients (N=8) with a diagnosis of ET.

INTERVENTION

Training program consisted of 12 dexterity training sessions where each session comprised 4 tasks involving both goal-directed manual movements and hand postural exercises.

MAIN OUTCOME MEASURES

Testing included an ET-specific quality of life questionnaire and postural and kinetic tremor assessments. Each training session was scored to evaluate the performance.

RESULTS

After training, improvements were observed in the performance of the 2 goal-directed tasks (P<.01); however, postural and kinetic tremor did not change.

CONCLUSIONS

This study suggests that dexterity training could be effective in increasing fine manual control during goal-directed movements, which are known to be the most compromised in this pathology. The absence of a decrease in tremor severity highlights the necessity for developing this novel training technique further, perhaps over a longer period of time. This study could provide guidelines for the prescription of self-directed and personalized home-based exercises and will offer clinicians a treatment that might be used as an adjuvant or an alternative to the classical pharmacotherapy.

The effects of a novel histamine-3 receptor inverse agonist on essential tremor in comparison to stable levels of alcohol

Essential tremor (ET) is a common movement disorder. Animal studies show that histaminergic modulation may affect the pathological processes involved in the generation of ET. Histamine-3 receptor inverse agonists (H3RIA) have demonstrated attenuating effects on ET in the harmaline rat model. In this double-blind, three-way cross-over, single-dose, double-dummy study the effects of 25 mg of a novel H3RIA (MK-0249) and a stable alcohol level (0.6 g L(-1)) were compared with placebo, in 18 patients with ET. Tremor was evaluated using laboratory tremorography, portable tremorography and a clinical rating scale. The Leeds Sleep Evaluation Questionnaire (LSEQ) and a choice reaction time (CRT) test were performed to evaluate potential effects on sleep and attention, respectively. A steady state of alcohol significantly diminished tremor as assessed by laboratory tremorography, portable tremorography and clinical ratings compared with placebo. A high single MK-0249 dose was not effective in reducing tremor, but caused significant effects on the LSEQ and the CRT test. These results suggest that treatment with a single dose of MK-0249 does not improve tremor in alcohol-responsive patients with ET, whereas stable levels of alcohol as a positive control reproduced the commonly reported tremor-diminishing effects of alcohol.

Effects of DBS on precision grip abnormalities in essential tremor

Deep brain stimulation (DBS) of the ventrolateral thalamus is a highly effective procedure for the treatment of essential tremor (ET). The regularity of repetitive, self-paced finger tapping is known to be abnormal in patients with ET and improved following DBS. However, the more complex timing that underlies force development in the hands in ET and after DBS has not been evaluated. In this pilot study, we assessed precision grip performance in seven ET subjects before and after 5 months of DBS. Ten healthy controls were also studied. ET subjects showed a significant increase in preload duration (235 +/- 145 vs. 82 +/- 49 ms) and peak negative load (-0.524 +/- 0.35 vs. -0.174 +/- 0.14 N) during grip-lift compared with healthy subjects. No difference in load duration was observed between the groups. Following DBS, the magnitude of the peak negative load was significantly reduced (P = 0.03). In contrast, the duration of the load phase was worsened (non-significant) after DBS. We conclude that defects in the control of distal musculature necessary for establishing a stable grip exist in ET, whereas proximal muscles necessary for object lift-off remain relatively intact. Further, synergy paradigms governing grip-lift coordination may also be impaired. Although DBS is successful in alleviating tremor in ET, it produces only a partial restoration of normal precision grip.

Histamine N-methyltransferase Thr105Ile is not associated with Parkinson's disease or essential tremor

A functional variant in the Histamine N-Methyltransferase gene (HNMT - rs11558538) resulting in a threonine to isoleucine substitution (Thr105Ile) has been shown to impair histamine degradation. Two recent studies reported that the threonine allele of this polymorphism might be a risk factor for Parkinson disease (PD) and essential tremor (ET) development. Although PD and ET are considered different entities, they share some clinical and pathological features, suggesting a possible joint etiology. In this study we assess the role of the Thr105Ile variant in PD and ET development, genotyping the variant in a North American Caucasian PD and ET case-control series. Statistical analysis did not identify any significant association between this variant and PD or ET; therefore, our findings do not support the HNMT Thr105Ile variant as a factor in disease development or a genetic link between the disorders.

DRD3 Ser9Gly and HS1BP3 Ala265Gly are not associated with Parkinson disease

Variants in the dopamine receptor D3 (DRD3) and HCLS1 binding protein 3 (HS1BP3) have been nominated as risk factors for essential tremor (ET). Although ET and Parkinson disease (PD) are considered different entities, they have many overlapping clinical and pathological features. We aim to evaluate the role of the Ser9Gly variant in DRD3 and Ala265Gly in HS1BP3 in PD development. To this end, we genotyped these two variants in a PD matched case-control series from the United States. Statistical analysis failed to identify significant differences in the frequency of these variants between the case and control groups; therefore our results do not support a role for these DRD3 and HS1BP3 variants in PD.

The pattern of cognitive-functional decline in elderly essential tremor patients: an exploratory-comparative study with Parkinson's and Alzheimer's disease patients

OBJECTIVE

Essential tremor (ET) is a neurological disorder that produces motor, cognitive, and functional disability. However, there has been no investigation linking cognitive impairment with functional disability in ET. Therefore, we examine the similarities and differences between ET, Alzheimer's disease (AD), and Parkinson's disease (PD) in terms of the linkage between cognitive and functional impairment.

DESIGN

Thirty-four ET, 26 PD, and 31 AD subjects were tested for cognition (Mini-Mental State Examination [MMSE]), motor disability (United Parkinson's Disease Rating Scale part III [UPDRS-III]), and functional disability (Minimum Data Set-Activities of Daily Living Section [MDS-ADL]).

RESULTS

As expected, in PD and AD subjects, MDS-ADL scores significantly correlated with UPDRS-III and MMSE scores. The ET subjects showed a different pattern of functional disability with MDS-ADL scores significantly correlating only with MMSE scores, and with the orientation MMSE modalities.

CONCLUSIONS

Our findings highlight the need to be more cognizant of the nonmotor aspects of ET, which in some patients may be more functionally disabling than the motor features themselves.