A new twist for stopping the shakes? Revisiting GABAergic therapy for essential tremor

Nabiximols (NBX) suppresses tremor in a rat Harmaline model of essential tremor

BACKGROUND

Essential tremor (ET) is one of the most prevalent movement disorders; despite this, there remains an unmet need for novel therapies. The treatment of rats with harmaline modulates the rhythmicity of inferior olivary neurons, resulting in generalized tremor with a frequency of 9-12 Hz in rats, comparable to that of human ET (4-12 Hz).

PURPOSE

Interestingly, cannabinoids reduce tremor, therefore we have assessed the cannabinoid nabiximols (NBX; marketed as Sativex) a complex botanical drug mixture, in the harmaline-rat model of ET.

METHOD

We tested the effects of acute (single dose) and subchronic (10 days) treatment of NBX (at 5.2, 10.4 and 20.8 mg kg-1 p.o.) administered prior to harmaline and acute NBX (20.8 mg kg-1) administered post-harmaline in male SD rats. Propranolol (20 mg kg-1 i.p.) was used as a positive control. Observed Scoring (OS) was carried out prior to placement in a tremor-monitoring apparatus for the calculation of Tremor Index (TI) and Motion Power Percentage (MPP).

RESULTS

Acute and subchronic NBX significantly attenuated harmaline-induced tremor at 10.4 and 20.8 mg kg-1, respectively, for each parameter (OS, TI, and MPP) when administered pre-harmaline as did propranolol (20 mg kg-1). NBX did not attenuate harmaline-induced tremor when administered post-harmaline.

CONCLUSIONS

These data suggest efficacy of acute and subchronic NBX to reduce tremors, based on OS, TI and MPP readouts if administered prior to harmaline. These data are the first to indicate the preclinical effects of an oral botanical cannabinoid formulation, NBX, in an animal model of ET.

A Novel KCNN2 Variant in a Family with Essential Tremor Plus: Clinical Characteristics and In Silico Analysis

BACKGROUND

Essential tremor (ET) is one of the more common movement disorders. Current diagnosis is solely based on clinical findings. ET appears to be inherited in an autosomal dominant pattern. Several loci on specific chromosomes have been studied by linkage analysis, but the causes of essential tremor are still unknown in many patients. Genetic studies described the association of several genes with familial ET. However, they were found only in distinct families, suggesting that some can be private pathogenic variants.

AIM OF THE STUDY

to characterize the phenotype of an Italian family with ET and identify the genetic variant associated.

METHODS

Clinical and genetic examinations were performed. Genetic testing was done with whole-exome sequencing (WES) using the Illumina platform. Bidirectional capillary Sanger sequencing was used to investigate the presence of variant in all affected members of the family. In silico prediction of pathogenicity was used to study the effect of gene variants on protein structure.

RESULTS

The proband was a 15-year-old boy. The patient was the first of two children of a non-consanguineous couple. Family history was remarkable for tremor in the mother line. His mother suffered from bilateral upper extremity kinetic tremors (since she was 20 years old), anxiety, and depression. Other relatives referred bilateral upper extremity tremors. In the index case, WES analysis performed supposing a dominant mode of inheritance, identified a novel heterozygous missense variant in potassium calcium-activated channel subfamily N member 2 (KCNN2) (NM_021614.3: c.1145G>A, p.Gly382Asp). In the pedigree investigation, all carriers of the gene variant had ET and showed variable expressivity, the elder symptomatic relative showing cognitive impairment and hallucinations in the last decade, in addition to tremor since a young age. The amino acid residue #382 is located in a transmembrane region and in silico analysis suggested a causative role for the variant. Modelling of the mutant protein structure showed that the variant causes a clash in the protein structure. Therefore, the variant could cause a conformational change that alters the ability of the protein in the modulation of ion channels Conclusions: The KCNN2 gene variant identified could be associated with ET. The variant could modify a voltage-independent potassium channel activated by intracellular calcium.

Association of Diet With Essential Tremor: A Narrative Review

Essential tremor is a neurological disorder categorized by the rhythmic shaking of the upper limbs, lower limbs, neck, or head. The etiology of essential tremor is believed to be genetic variations, environmental factors, lifestyle, etc. Poor lifestyle and diet are important factors contributing to the onset of various disorders. Environment and lifestyle play a significant part in the dietary habits of an individual. Some diet components may probably be associated with the etiopathogenesis or progression of the essential tremor. Dietary habits may be a key influence on the commencement of tremors in healthy individuals. Typically, the diet of essential tremor patients is not supervised. It may also intensify the tremors in essential tremor patients. Association of the diet with the essential tremor can shed light on the root of tremor aggravating aspect and aid in diet modification in essential tremor patients. The aim of the review is to establish a relation between the diet with etiopathogenesis and the progression of essential tremor. The review includes studies providing information about essential tremor and correlating essential tremor with diet, lifestyle, environment, and genetic factors. Studies that did not provide a link to the association of essential tremor were excluded. The interpretation of the research indicated that genetic variations might be triggered due to enzymatic changes triggered by dietary patterns. Dietary components showed ambiguous, weak, strong, or no association. Essential tremor may be influenced by diet. Further research must be carried out on essential tremor patients in the nutritional domain. Physicians may monitor the diet of the essential tremor patients and record the progress of the disorder on its basis to manage the patients with essential tremor and provide better services.

Is essential tremor a family of diseases or a syndrome? A syndrome

In a consensus statement, a task force of the "International Parkinson and Movement Disorder Society" (IPMDS) has recently proposed a two axes classification for tremor: axis I (clinical manifestations) and axis II (etiology). In the axis, I, the clinical features of tremor in a given patient are specified in terms of medical history, tremor characteristics, associated signs, and laboratory tests for some tremors leading to the discovery of axis 2 etiologies. Based on axis I sign and symptoms a specific clinical syndrome is diagnosed which have been categorized as isolated tremor syndrome (a syndrome consisting only of tremor) and combined tremor syndrome (consisting of tremor and other systemic or neurological signs). The IPMDS task force defined essential tremor as an isolated tremor syndrome of bilateral upper limb action tremor of at least 3years duration with or without a tremor in other locations (e.g., head, voice or lower limbs) in absence of other neurological signs, such as dystonia, ataxia, or parkinsonism. Patients with neurological signs of uncertain significance (such as impaired tandem gait, questionable dystonic posturing, or memory impairment) are classified as essential tremor plus. In this paper, the author will make the argument that essential tremor is a syndrome with multiple causes.

Is essential tremor a disorder of primary GABA dysfunction? Yes

Dysfunction in gamma-aminobutyric acid (GABA) neurotransmission has emerged as a prime suspect for the underlying neurochemical dysfunction in essential tremor (ET). This dysfunction has been termed the GABA hypothesis. We review findings to date supporting the 4 steps in this hypothesis in studies of cerebrospinal fluid, pathology, genetics, animal models, imaging, computational models, and human drugs, while not overlooking the evidence of negative studies and controversies. It remains to be elucidated whether reduced GABAergic tone is a primary contributing factor to ET pathophysiology, a consequence of altered Purkinje cell function, or even a result of Purkinje cell death. More studies are clearly needed to confirm both the neurodegenerative nature of ET and the reduction in GABA activity in the cerebellum. Also necessary is to test further therapies to enhance GABA transmission specifically focused on the cerebellar area.

Brain circuits and neurochemical systems in essential tremor: insights into current and future pharmacotherapeutic approaches

INTRODUCTION

There are few medications that are available for the treatment of essential tremor (ET) and they are only moderately effective. Areas covered: Data were obtained from a PubMed search. Original articles, review articles, and clinical guidelines were included. Two disease models for ET have been proposed: 1) the olivary model, which attributes ET to a pathological pacemaker in the inferior olivary nucleus, and 2) the cerebellar degeneration model, which postulates that ET originates in the cerebellum and could be related to deficient or abnormal Purkinje cell (PC) output. Underlying biochemical dysfunction in T-type calcium channels (T-tCaC) may loosely be linked to the first model and deficiency/abnormality in γ-aminobutyric acid (GABA) neurotransmission, to the second. Expert commentary: Human data points robustly to the role of GABA in ET. Numerous medications that target the GABA system have been tried, with variable success. Given the many different types of GABA-ergic neurons, and the multitude of GABA_A receptor subtypes, a given medication could have competing/cancelling effects. It would seem that influencing GABA receptors broadly is not as effective as targeting certain GABA_A receptor subtypes. Future research should seek to identify molecular candidates that have a more targeted effect within the GABA system.

Linking Essential Tremor to the Cerebellum: Neurochemical Evidence

The pathophysiology and the exact anatomy of essential tremor (ET) is not well known. One of the pillars that support the cerebellum as the main anatomical locus in ET is neurochemistry. This review examines the link between neurochemical abnormalities found in ET and cerebellum. The review is based on published data about neurochemical abnormalities described in ET both in human and in animal studies. We try to link those findings with cerebellum. γ-aminobutyric acid (GABA) is the main neurotransmitter involved in the pathophysiology of ET. There are several studies about GABA that clearly points to a main role of the cerebellum. There are few data about other neurochemical abnormalities in ET. These include studies with noradrenaline, glutamate, adenosine, proteins, and T-type calcium channels. One single study reveals high levels of noradrenaline in the cerebellar cortex. Another study about serotonin neurotransmitter results negative for cerebellum involvement. Finally, studies on T-type calcium channels yield positive results linking the rhythmicity of ET and cerebellum. Neurochemistry supports the cerebellum as the main anatomical locus in ET. The main neurotransmitter involved is GABA, and the GABA hypothesis remains the most robust pathophysiological theory of ET to date. However, this hypothesis does not rule out other mechanisms and may be seen as the main scaffold to support findings in other systems. We clearly need to perform more studies about neurochemistry in ET to better understand the relations among the diverse systems implied in ET. This is mandatory to develop more effective pharmacological therapies.

Current concepts of essential tremor

Essential tremor is clinically defined but there is increasing evidence that it is not a unique entity. Its pathophysiology has been studied with many methods but may also vary between subtypes. Neurophysiologically, there is strong evidence that a specific cerebello-thalamo-cortical loop is abnormally oscillating. The cause of its uncontrolled oscillation is not yet understood. The clear proof of a degenerative cause is still lacking and abnormal receptors or other causes of altered non-progressive functional disturbance cannot be excluded. Strong evidence supports the major involvement of the cerebellum and there is ample evidence that GABA is the main neurotransmitter involved in the pathophysiology in ET. Genetics have provided so far only a few rare subtypes which are due to specific mutations but there is no doubt that it is mostly a hereditary condition. There is evidence that the large subgroup of late onset tremor is a separate condition and this tremor is an independent risk factor for earlier mortality and comes with signs of premature aging (aging-related tremor). It will be important to improve phenotyping of patients in more detail possibly to include not only features of the tremor itself but also other clinical assessments like force measurements or cognitive testing. Based on these variables, we may be able to better understand the presumably different mechanisms underlying different variants of the disease.

Non-invasive Central and Peripheral Stimulation: New Hope for Essential Tremor?

Essential tremor (ET) is among the most frequent movement disorders. It usually manifests as a postural and kinematic tremor of the arms, but may also involve the head, voice, lower limbs, and trunk. An oscillatory network has been proposed as a neural correlate of ET, and is mainly composed of the olivocerebellar system, thalamus, and motor cortex. Since pharmacological agents have limited benefits, surgical interventions like deep brain stimulation are the last-line treatment options for the most severe cases. Non-invasive brain stimulation techniques, particularly transcranial magnetic or direct current stimulation, are used to ameliorate ET. Their non-invasiveness, along with their side effects profile, makes them an appealing treatment option. In addition, peripheral stimulation has been applied in the same perspective. Hence, the aim of the present review is to shed light on the emergent use of non-invasive central and peripheral stimulation techniques in this interesting context.

Reproducibility and effect of tissue composition on cerebellar γ-aminobutyric acid (GABA) MRS in an elderly population

MRS provides a valuable tool for the non-invasive detection of brain γ-aminobutyric acid (GABA) in vivo. GABAergic dysfunction has been observed in the aging cerebellum. The study of cerebellar GABA changes is of considerable interest in understanding certain age-related motor disorders. However, little is known about the reproducibility of GABA MRS in an aged population. Therefore, this study aimed to explore the feasibility and reproducibility of GABA MRS in the aged cerebellum at 3.0 T and to examine the effect of differing tissue composition on GABA measurements. MRI and (1)H MRS examinations were performed on 10 healthy elderly volunteers (mean age, 75.2 ± 6.5 years) using a 3.0-T Siemens Tim Trio scanner. Among them, five subjects were scanned twice to assess the short-term reproducibility. The MEGA-PRESS (Mescher-Garwood point-resolved spectroscopy) J-editing sequence was used for GABA detection in two volumes of interest (VOIs) in the left and right cerebellar dentate. MRS data processing and quantification were performed with LCModel 6.3-0L using two separate basis sets, generated from density matrix simulations using published values for chemical shifts and J couplings. Raw metabolite levels from LCModel outputs were corrected for cerebrospinal fluid contamination and relaxation. GABA-edited spectra yielded robust and stable GABA measurements with averaged intra-individual coefficients of variation for corrected GABA+ between 4.0 ± 2.8% and 13.4 ± 6.3%, and inter-individual coefficients of variation between 12.6% and 24.2%. In addition, there was a significant correlation between GABA+ obtained with the two LCModel basis sets. Overall, our results demonstrated the feasibility and reproducibility of cerebellar GABA-edited MRS at 3.0 T in an elderly population. This information might be helpful for studies using this technique to study GABA changes in normal or diseased aging brain, e.g. for power calculations and the interpretation of longitudinal observations.

Homozygous SLC6A17 mutations cause autosomal-recessive intellectual disability with progressive tremor, speech impairment, and behavioral problems

We report on Dutch and Iranian families with affected individuals who present with moderate to severe intellectual disability and additional phenotypes including progressive tremor, speech impairment, and behavioral problems in certain individuals. A combination of exome sequencing and homozygosity mapping revealed homozygous mutations c.484G>A (p.Gly162Arg) and c.1898C>G (p.Pro633Arg) in SLC6A17. SLC6A17 is predominantly expressed in the brain, encodes a synaptic vesicular transporter of neutral amino acids and glutamate, and plays an important role in the regulation of glutamatergic synapses. Prediction programs and 3D modeling suggest that the identified mutations are deleterious to protein function. To directly test the functional consequences, we investigated the neuronal subcellular localization of overexpressed wild-type and mutant variants in mouse primary hippocampal neuronal cells. Wild-type protein was present in soma, axons, dendrites, and dendritic spines. p.Pro633Arg altered SLC6A17 was found in soma and proximal dendrites but did not reach spines. p.Gly162Arg altered SLC6A17 showed a normal subcellular distribution but was associated with an abnormal neuronal morphology mainly characterized by the loss of dendritic spines. In summary, our genetic findings implicate homozygous SLC6A17 mutations in autosomal-recessive intellectual disability, and their pathogenic role is strengthened by genetic evidence and in silico and in vitro functional analyses.

Essential tremor: from bedside to bench and back to bedside

PURPOSE OF REVIEW

The last several years have witnessed a remarkable increase in research on essential tremor, with consequent advances in our understanding of this entity. An attempt to both summarize and frame this work has not been undertaken.

RECENT FINDINGS

Here, I show that observations on essential tremor arising from clinical practice/clinical studies have guided scientific studies of this disorder. In turn, the results of scientific studies are beginning to be translated back to the bedside to improve treatment. Recent essential tremor research has given rise to several novel and intriguing ideas about the disease. These include the following: essential tremor may represent a family of diseases rather than a single disease; essential tremor seems to be a disease of the cerebellum or cerebellar system; essential tremor may be neurodegenerative; low gamma aminobutyric acid tone seems to be a central feature of essential tremor. As with many emerging ideas, there is significant discussion and debate over these emerging ideas, and this fuels additional scientific studies.

SUMMARY

The flow of ideas from clinical observations about essential tremor, to their translation into scientific studies, and their translation back to the bedside, is expected to eventually lead to improvements at the patient interface.

The GABA Hypothesis in Essential Tremor: Lights and Shadows

Background

The gamma-aminobutyric acid (GABA) hypothesis in essential tremor (ET) implies a disturbance of the GABAergic system, especially involving the cerebellum. This review examines the evidence of the GABA hypothesis.

Methods

The review is based on published data about GABA dysfunction in ET, taking into account studies on cerebrospinal fluid, pathology, electrophysiology, genetics, neuroimaging, experimental animal models, and human drug therapies.

Results

Findings from several studies support the GABA hypothesis in ET. The hypothesis follows four steps: 1) cerebellar neurodegeneration with Purkinje cell loss; 2) a decrease in GABA system activity in deep cerebellar neurons; 3) disinhibition in output deep cerebellar neurons with pacemaker activity; and 4) an increase in rhythmic activity of the thalamus and thalamo-cortical circuit, contributing to the generation of tremor. Doubts have been cast on this hypothesis, however, by the fact that it is based on relatively few works, controversial post-mortem findings, and negative genetic studies on the GABA system. Furthermore, GABAergic drug efficacy is low and some GABAergic drugs do not have antitremoric efficacy.

Discussion

The GABA hypothesis continues to be the most robust pathophysiological hypothesis to explain ET. There is light in all GABA hypothesis steps, but a number of shadows cannot be overlooked. We need more studies to clarify the neurodegenerative nature of the disease, to confirm the decrease of GABA activity in the cerebellum, and to test more therapies that enhance the GABA transmission specifically in the cerebellum area.

Neuroimaging studies of essential tremor: how well do these studies support/refute the neurodegenerative hypothesis?

Background

Tissue-based research has recently led to a new patho-mechanistic model of essential tremor (ET)—the cerebellar degenerative model. We are not aware of a study that has reviewed the current neuroimaging evidence, focusing on whether the studies support or refute the neurodegenerative hypothesis of ET. This was our aim.

Methods

References for this review were identified by searches of PubMed (1966 to February 2014).

Results

Several neuroimaging methods have been used to study ET, most of them based on magnetic resonance imaging (MRI). The methods most specific to address the question of neurodegeneration are MRI-based volumetry, magnetic resonance spectroscopy, and diffusion-weighted imaging. Studies using each of these methods provide support for the presence of cerebellar degeneration in ET, finding reduced cerebellar brain volumes, consistent decreases in cerebellar N-acetylaspartate, and increased mean diffusivity. Other neuroimaging techniques, such as functional MRI and positron emission tomography (PET) are less specific, but still sensitive to potential neurodegeneration. These techniques are used for measuring a variety of brain functions and their impairment. Studies using these modalities also largely support cerebellar neuronal impairment. In particular, changes in ¹¹C-flumazenil binding in PET studies and changes in iron deposition in an MRI study provide evidence along these lines. The composite data point to neuronal impairment and likely neuronal degeneration in ET.

Discussion

Recent years have seen a marked increase in the number of imaging studies of ET. As a whole, the combined data provide support for the presence of cerebellar neuronal degeneration in this disease.

Gaba and serotonin molecular neuroimaging in essential tremor: a clinical correlation study

BACKGROUND

Essential tremor is the most common movement disorder in adults, but its exact etiology and pathophysiology are still not fully understood. There is some consensus, however, about the involvement of the cerebellum and accumulating evidence points towards a dysfunction of the gabaergic system. We hypothesize that the serotonin neurotransmission system may also play a role as it does in tremor in Parkinson disease. This study aimed to investigate the association between the severity of tremor symptoms and the gabaergic and serotoninergic neurotransmission systems in essential tremor.

MATERIAL AND METHODS

We measured the tremor clinical rating scale score and acquired DASB and Flumazenil PET scans in 10 patients who presented with essential tremor at different stages of clinical severity. Statistically significant correlations were sought between the scale scores and parametric binding potential images.

RESULTS

The correlation analysis of cerebellar Flumazenil uptake and tremor clinical rating scale scores reached statistical significance (R2 = 0.423, p = 0.041), whereas no association was detected in the DASB scans.

CONCLUSIONS

The severity of tremor correlated with the abnormalities found in GABA receptor binding, suggesting a primary gabaergic deficiency or a functional abnormality at the level of GABA(A) receptor subtypes. These results may assist in the rational development of new pharmacological treatments for essential tremor.

The effects of TPA023, a GABAAα2,3 subtype-selective partial agonist, on essential tremor in comparison to alcohol

Essential tremor (ET) is a relatively frequent neurological disorder that responds in some patients to gamma-aminobutyric acid A (GABA(A)) agonists such as the benzodiazepines. Partial subtype-selective GABA(A) agonists may have an improved side effect profile compared to non-selective GABA(A) agonists. However, it is unknown which GABA(A) subtypes are involved in the therapeutic effects of benzodiazepines in ET. The effects of 2 mg TPA023, a GABA(A) α2,3 subtype-selective partial agonist, on ET were compared to the effects of a stable alcohol level (0.6 g/L) and placebo in nine patients with ET. Tremor evaluation included laboratory accelerometry and a performance-based scale. Additional measurements were performed to evaluate other effects on the central nervous system (CNS). Alcohol significantly diminished tremor symptoms in the postural and kinetic condition, as assessed by laboratory accelerometry, but the performance-based rating scale was unaffected. Tremor was also reduced after TPA023 treatment in the kinetic condition, albeit not significantly. Additionally, TPA023 decreased saccadic peak velocity, while alcohol decreased subjective feelings of alertness. This study showed that alcohol reduced maximum tremor power, as assessed by laboratory accelerometry, unlike TPA023, which decreased tremor symptoms to some extent but not significantly. This study showed that treatment with an α2,3 subunit-selective GABA(A) partial agonist was less effective than a stable level of alcohol in reducing ET symptoms. These results provide no support for a therapeutic role of TPA023 in the suppression of ET symptoms.

Defective dentate nucleus GABA receptors in essential tremor

The development of new treatments for essential tremor, the most frequent movement disorder, is limited by a poor understanding of its pathophysiology and the relative paucity of clinicopathological studies. Here, we report a post-mortem decrease in GABA(A) (35% reduction) and GABA(B) (22-31% reduction) receptors in the dentate nucleus of the cerebellum from individuals with essential tremor, compared with controls or individuals with Parkinson's disease, as assessed by receptor-binding autoradiography. Concentrations of GABA(B) receptors in the dentate nucleus were inversely correlated with the duration of essential tremor symptoms (r(2) = 0.44, P < 0.05), suggesting that the loss of GABA(B) receptors follows the progression of the disease. In situ hybridization experiments also revealed a diminution of GABA(B(1a+b)) receptor messenger RNA in essential tremor (↓27%). In contrast, no significant changes of GABA(A) and GABA(B) receptors (protein and messenger RNA), GluN2B receptors, cytochrome oxidase-1 or GABA concentrations were detected in molecular or granular layers of the cerebellar cortex. It is proposed that a decrease in GABA receptors in the dentate nucleus results in disinhibition of cerebellar pacemaker output activity, propagating along the cerebello-thalamo-cortical pathways to generate tremors. Correction of such defective cerebellar GABAergic drive could have a therapeutic effect in essential tremor.

Management of essential tremor, including medical and surgical approaches

Essential tremor (ET) is one of the most common neurological disorders among adults. For many years, ET was viewed as a benign monosymptomatic condition, characterized by a kinetic arm tremor, yet over the last 10 years, a growing body of evidence suggests that this disorder is a progressive condition that is heterogeneous. Tremor may have a negative impact on health-related quality of life in some patients. Pharmacotherapy is initiated when the tremor interferes with the patient's ability to perform daily activities or when the tremor becomes embarrassing or affects health-related quality of life. For severe tremor, deep-brain stimulation of the thalamus may improve function.

GABAergic dysfunction in essential tremor: an 11C-flumazenil PET study

Essential tremor is the most common movement disorder, but the underlying pathophysiology is not well understood. A primary overactivity of cerebellothalamic output pathways is the most conspicuous finding, as indicated by animal and human studies. It has been argued that this overactivity may be due to impaired central inhibition, and converging evidence points toward a potential role of gamma-aminobutyric acid (GABA) dysfunction in tremor generation.

METHODS

Using (11)C-flumazenil and PET, we calculated the distribution volume, an index of availability of benzodiazepine receptor sites of the GABA(A) complex, in a group of 8 patients with bilateral essential tremor, as compared with 11 healthy controls.

RESULTS

Significant increases in binding of (11)C-flumazenil at the benzodiazepine receptor site of the GABA(A) receptor in the cerebellum, the ventrolateral thalamus, and the lateral premotor cortex were identified in the essential tremor group.

CONCLUSION

Essential tremor is associated with reduced GABAergic function and increased availability of benzodiazepine receptor sites in brain regions implicated specifically in tremor genesis. This finding is thought to reflect overactivity of cerebellothalamic circuits and, hence, lends support to the "GABA hypothesis" of essential tremor.

Essential tremor: evolving clinicopathological concepts in an era of intensive post-mortem enquiry

Essential tremor (ET) is one of the most common neurological disorders. In recent years, as a result of systematic post-mortem examinations, our knowledge of the pathophysiology of this disease has grown substantially. Clearly identifiable structural changes (ie, Purkinje cell loss, Lewy bodies) have been observed in the brains of individuals with ET. These changes are not uniform and seem to follow several patterns, localising to the cerebellum itself or to a collection of brainstem neurons that synapse directly with Purkinje cells. Furthermore, these changes are similar to those seen in degenerative diseases. A wealth of clinical, epidemiological, and now post-mortem data indicate that this disease, or perhaps this family of diseases, is likely to be neurodegenerative. The molecular mechanisms that underlie these structural changes in ET are unknown. However, with more controlled, tissue-based studies being done, it is hoped that these mechanisms will be elucidated, thereby laying the foundation for the development of more targeted, effective pharmacotherapeutic interventions.

Transient improvement of essential tremor during electroconvulsive therapy

We present a patient who demonstrated transient yet significant improvement of essential tremor (ET) during electroconvulsive therapy. To our knowledge, this is the first such report. The improvement lasted during the course of electroconvulsive therapy and was of a similar magnitude to that which she had experienced on a first-line medication for ET. We discuss the potential pathophysiological implications of this observation in light of recent histopathologic findings in patients with ET.

Essential tremor: emerging views of a common disorder

Essential tremor (ET) is the most prevalent tremor disorder. ET has traditionally been viewed as a monosymptomatic disorder characterized by a kinetic arm tremor, but this definition is gradually being replaced. The clinical spectrum has come to include several motor features, including tremor and ataxia, and several non-motor features, including possible cognitive impairment and personality disturbances. Postmortem studies are revealing several different patterns of pathology. The emerging view is that ET might be a family of diseases, unified by the presence of kinetic tremor, but further characterized by etiological, clinical and pathological heterogeneity. Effective pharmacological treatments for the disorder remain limited, although new insights into disease mechanisms might result in more-effective therapies. In addition, recent investigations of environmental toxicants that might be linked to ET open the way towards primary disease prevention through a reduction in exposure to these factors.

Essential Tremor Treated with Topiramate: A Case Series

Objective

The authors evaluated a series of essential tremor (ET) patients treated with topiramate in a university-based movement disorders clinic.

Design

A retrospective clinical review of patient cases in a naturalistic setting was employed.

Subjects and Setting

Patients who were prescribed topiramate for ET were identified from clinic records. Patients were contacted by telephone to determine subjective improvement of tremor. Patients reporting improvement were invited to return for clinical evaluation.

Outcome Measures

Patients drew the Archimedes Spiral and were asked about performance of activities of daily living at each office visit. These activities were evaluated using a 5-point Essential Tremor Scale (ETS).

Results

Fourteen ET patients had been prescribed topiramate. The average age was 58 years and the average tremor duration was 17 years. The mean final topiramate dose was 105 mg/day (range: 25 to 400 mg/day). Eight of the 14 patients reported subjective tremor improvement with a mean dose of 128 mg/day (50 to 400 mg/day). Five of the patients were available for further evaluation. The average topiramate dose for the five patients was 175 mg/day (50 to 400 mg/day). The mean initial ETS score was 3.02 (2.5 to 3.5) for the patients; the final mean ETS score was 2.3 (1.75 to 3). The mean dose for the six patients who stated they did not respond to topiramate treatment was 75 mg/day (25 to 100 mg/day). One patient discontinued topiramate due to increased nervousness.

Conclusions

Based on the 57% subjective response rate seen in our case series, topiramate may be a useful treatment for some patients with ET in a clinical practice.

Semiquantitative study of current coffee, caffeine, and ethanol intake in essential tremor cases and controls

There are several reasons to study caffeine, coffee, and ethanol intake in essential tremor (ET) patients. ET patients also might modify their use of these beverages because of their effects on tremor. Intake of caffeine, coffee, and ethanol has not been quantified in a group of ET patients. Our objective is to use a semiquantitative food frequency questionnaire to compare current daily intake of coffee, caffeine, and ethanol in ET patients and controls. A total of 130 ET cases were patients at the Neurological Institute of New York, and 175 controls were ascertained by random digit dialing. Caffeine (in milligrams) and ethanol (in grams) intake were calculated from a semiquantitative food-frequency questionnaire. Mean daily caffeine intake in patients was 138.4 versus 246.6 mg in controls; medians were 101.1 versus 175.5 mg (P < 0.001). Mean daily ethanol intake in patients was 8.2 versus 6.2 gm in controls; medians were 2.4 versus 1.9 gm (P = 0.89). Cases drank less coffee than controls, but drank similar amounts of tea, soft drinks, fruit juices, and milk. Daily caffeine intake was not correlated with tremor severity or duration. ET patients consumed less caffeine than did controls, which is likely to be a dietary modification in response to tremor. The observation that caffeine consumption was not correlated with tremor severity raises the additional possibility that lower caffeine consumption in ET patients may not exclusively be a response to tremor. A prospective study is needed to explore whether decreased caffeine consumption is a risk factor for ET.

Gabapentin for the treatment of tremor

OBJECTIVE

To review the use of the antiepileptic drug gabapentin for the treatment of various types of tremor.

DATA SOURCES

A search of biomedical literature was completed through MEDLINE and EMBASE (1993-May 2002) to identify all clinical trials pertaining to the use of gabapentin for the treatment of tremor in humans.

DATA SYNTHESIS

Outcome data from the few published studies have varied widely. Patient groups have been small, and conclusions have been based largely on subjective patient and investigator ratings.

CONCLUSIONS

A trial of gabapentin is warranted in patients who fail therapy with traditional agents. Improvement should be measured by a patient's perceived functional ability.

2-deoxy-D-glucose attenuates harmaline induced tremors in rats

Neuronal hyperactivity in essential tremor is accompanied by high energy demand in cerebellum, medulla and the thalamus. It has been suggested that brain regions that have increased metabolic demands are highly vulnerable to interruptions in glucose metabolism. In the present investigation attempt was made to study the effect of 2-deoxyglucose (2DG) a glycolytic pathway inhibitor on harmaline induced tremor in rats. Wistar rats of either sex weighing 100+/-3 g were given harmaline (10 mg/kg, i.p.) alone or along with 2DG (15 min before harmaline) in doses of 300, 600 and 900 mg/kg, respectively. The latency of onset, intensity and duration of tremor following harmaline administration were recorded. Neurobehavioral responses, electromyography (EMG) and levels of blood glucose and cerebellar serotonin (5HT) were determined after 40 min of harmaline administration. 2DG significantly and dose dependently attenuated severity of harmaline induced tremors and amplitude of EMG. Treatment of rats with 2DG alone reduced the locomotor activity, however, no significant change was observed in grip strength, landing foot splay, air righting reflex and response to tactile stimuli. Harmaline alone and along with 2DG had no effect on behavioral parameters except a decrease in landing foot splay. 2DG produced a dose-dependent hyperglycemia and attenuated harmaline induced increase in cerebellar 5HT levels. Our results clearly suggest the protective effect of 2DG in harmaline induced tremor. Further studies are warranted to assess the role of glucoprivation in the suppression of neuronal excitability in tremors.

Effect of acute caffeine on severity of harmaline induced tremor in rats

Recent studies suggest an association between caffeine consumption and tremor. However, the available literature is scanty and inconclusive. The present study was undertaken to investigate the effect of acute caffeine treatment on harmaline induced tremors in the rat. Four groups of male Sprague-Dawley rats (six animals in each group) weighing 88+/-2 g were administered harmaline (10 mg/kg, intraperitoneally (i.p.)) for inducing experimental tremors. The rats in group 1 served as controls and received normal saline, whereas the animals in groups 2, 3 and 4 were given caffeine (i.p.) at doses of 50, 100 and 150 mg/kg, respectively 60 min after harmaline administration. The latency of onset, intensity and duration of tremor and electromyographic (EMG) responses were recorded. Treatment of rats with caffeine resulted in a significant increase in the intensity and duration of harmaline induced tremors. Caffeine also enhanced the EMG amplitude in harmaline treated animals. In conclusion, the results of this study suggest that acute treatment with caffeine significantly potentiates the severity of harmaline induced tremors in rats.

Clinical predictors of response to lamotrigine and gabapentin monotherapy in refractory affective disorders

BACKGROUND

The objective of the current study was to examine possible clinical predictors of positive response to lamotrigine or gabapentin monotherapy in treatment-refractory affectively ill patients.

METHODS

Forty-five patients with treatment refractory bipolar (n = 35) or unipolar (n = 10) affective disorder participated in a clinical study evaluating six weeks of treatment with lamotrigine, gabapentin, or placebo monotherapy given in a double-blind, randomized fashion with two subsequent cross-overs to the other agents. Patients received daily mood ratings and weekly cross-sectional scales. Much or very much improved on the Clinical Global Impression scale modified for bipolar illness was considered a positive response. Degree of response was correlated with a number of baseline demographic and course of illness variables in a univariate analysis and then by linear regression.

RESULTS

Response rates to lamotrigine (51%) exceeded those to gabapentin (28%) and placebo (21%). A positive response to lamotrigine monotherapy was associated with a bipolar diagnosis; fewer hospitalizations; fewer prior medication trials; and male gender (of which the latter two variables survived logistic regression). For gabapentin, degree of response correlated with shorter duration of illness; younger age; and lower baseline weight (with the latter two surviving linear regression).

CONCLUSIONS

In this highly treatment-refractory population, lamotrigine appeared most effective for male patients with fewer prior medication trials. Gabapentin monotherapy, although not better than placebo, appeared most effective in those with younger age and lower baseline weight. These preliminary data in a treatment refractory subgroup may help in the further definition of the range of clinical utility of these widely used anticonvulsants.

Baclofen attenuates harmaline induced tremors in rats

Recent experimental and clinical studies clearly suggest the role of gamma-aminobutyric acid (GABA) in the pathogenesis of tremors. The present study was undertaken to investigate the effect of baclofen, a GABA B receptor agonist on harmaline induced tremors. Four groups of female Wistar rats weighing 100+/-15 g were injected with harmaline (10 mg/kg, intraperitoneally) for inducing experimental tremors. The animals in groups 2, 3 and 4 were given baclofen by gavage at doses of 2.5, 5 and 10 mg/kg, respectively, half an hour before harmaline administration, whereas, the rats in group 1 served as control and received water. The latency of onset, intensity and duration of tremor and electromyographic (EMG) responses were recorded. Treatment with baclofen resulted in a dose dependent decrease in the intensity of tremor. Our EMG study also revealed a significant decrease in the amplitude of tremors in baclofen treated rats. A highly significant increase in latency of onset of tremor was observed in the rats treated with high dose (10 mg/kg) of baclofen only. This study clearly suggests beneficial effects of baclofen in harmaline induced tremors.

Tremor

Tremor research during the past year has focused on clinical differential diagnosis, and a new clinical classification has been developed. The origin of tremor is thought to depend on unstable central loops, and new coherence data suggest that these often involve the motor cortex. Gabapentine has been assessed for efficacy in some tremors, and deep brain stimulation of the ventrolateral thalamus has been shown to be safer and more effective for severe essential and parkinsonian tremor than thalamotomy.