Slowed saccades and increased square wave jerks in essential tremor

Oculomotor impairments in de novo Parkinson’s disease

Objective

Reliable electrophysiological indicators are urgently needed in the precise evaluation of Parkinson’s disease (PD). It is still elusive whether oculomotor performance is impaired or has clinical value in early PD. This study aims to explore oculomotor performance in newly diagnosed, drug-naïve PD and its correlation with clinical phenotype.

Methods

Seventy-five patients with de novo PD, 75 patients with essential tremor (ET), and 46 gender-and age-matched healthy controls (HCs) were included in this cross-sectional study. All subjects underwent oculomotor test via videonystagmography. Visually guided saccade latency, saccadic accuracy and gain in smooth pursuit eye movement (SPEM) at three frequencies of the horizontal axis were compared among the three groups. Patients with PD also received detailed motor and non-motor evaluation by serial scales. The association between key oculomotor parameters and clinical phenotypes were explored in PD patients.

Results

Both de novo PD and ET patients showed prolonged saccadic latency and decreased saccadic accuracy relative to HCs. SPEM gain in PD was uniformly reduced at each frequency. SPEM gain at 0.4 Hz was also decreased in ET compared with HCs. However, there was no significant difference of oculomotor parameters between de novo PD and ET patients. Furthermore, prolonged saccadic latency was correlated with long disease duration, whereas decreased SPEM gain was associated with severe motor symptoms in de novo PD patients.

Conclusion

Ocular movements are impaired in de novo, drug naïve PD patients; these changes could be indicators for disease progression in PD.

Morphological and morphometric changes in the Purkinje cells of patients with essential tremor

Essential tremor (ET) is a progressive neurological syndrome characterised by involuntary tremors of the hands or arms, head, jaw and voice. The pathophysiology of ET is not clearly understood yet. However, previous studies have reported several changes in the brain of patients with ET. One of the brain areas extensively investigated is the cerebellum. In the present study, a morphometric analysis of Purkinje cells in patients with ET and ET-plus was performed, and subsequently compared with normal controls using the Golgi silver staining method and 3D neuronal reconstruction. Substantial morphological changes were uncovered in the Purkinje cells of patients with ET compared with normal controls, including a decreased dendritic length and field density, an overall loss of terminal branches and a decreased density of dendritic spines.

Minocycline Mitigation of Tremor Syndrome and Defect of Cognitive and Balance Induced by Harmaline

Introduction:

Minocycline has anti-inflammatory, anti-apoptotic, and anti-oxidant effects. Preclinical data suggest that minocycline could be beneficial for treating common neurological disorders, including Parkinson disease and multiple sclerosis.

Methods:

In this study, the effects of minocycline on harmaline-induced motor and cognitive impairments were studied in male Wistar rats. The rats were divided into four groups of ten animals each. Harmaline was used for the induction of Essential Tremor (ET). Minocycline (90 mg/kg, IP) was administered 30 minutes before the saline or harmaline. Tremor intensity, spontaneous locomotor activity, passive avoidance memory, anxiety-related behaviors, and motor function were assessed in the rats.

Results:

The results showed that minocycline could recover tremor intensity and step width but failed to recuperate the motor balance. The memory impairments observed in harmaline-treated rats were somewhat reversed by administration of minocycline. The cerebellum and inferior olive nucleus were studied for neuronal degeneration using histochemistry and transmission electron microscopy techniques. Harmaline caused ultrastructural changes and neuronal cell loss in inferior olive and cerebellar Purkinje cells. Minocycline exhibited neuroprotective changes on cerebellar Purkinje cells and inferior olivary neurons.

Conclusion:

These results open new therapeutic perspectives for motor and memory impairments in ET. However, further studies are needed to clarify the exact mechanisms.

The Essential Tremors: Evolving Concepts of a Family of Diseases

The past 10 years has seen a remarkable advance in our understanding of the disease traditionally referred to as “essential tremor” (ET). First, the clinical phenotype of ET has been expanded from that of a bland, unidimensional, and monosymptomatic entity to one with a host of heterogeneous features. These features include a broader and more nuanced collection of tremors, non-tremor motor features (e.g., gait abnormalities) and a range of non-motor features, including cognitive, psychiatric, sleep, and other abnormalities. The natural history of these features, as well as their relationships with one another and with disease duration and severity, are better appreciated than they were previously. Studies of disease etiology have identified a number of candidate genes as well as explored several environmental determinants of disease. In addition, the decade has seen the beginnings and expansion of rigorous postmortem studies that have identified and described the postmortem changes in the brains of patients with ET. This emerging science has given rise to a new notion that the disease, in many cases, is one of cerebellar system degeneration. Across all of these studies (clinical, etiological, and pathophysiological) is the observation that there is heterogeneity across patients and that “essential tremor” is likely not a single disease but, rather, a family of diseases. The time has come to use the more appropriate terminology, “the essential tremors,” to fully describe and encapsulate what is now apparent. In this paper, the author will review the clinical, etiological, and pathophysiological findings, referred to above, and make the argument that the terminology should evolve to reflect advances in science and that “the essential tremors” is a more scientifically appropriate term.

Essential tremor: the most common form of cerebellar degeneration?

Background

The degenerative cerebellar ataxias comprise a large and heterogeneous group of neurological diseases whose hallmark clinical feature is ataxia, and which are accompanied, to variable degrees, by other features that are attributable to cerebellar dysfunction. Essential tremor (ET) is an exceptionally common neurological disease whose primary motor feature is action tremor, although patients often manifest intention tremor, mild gait ataxia and several other features of cerebellar dysfunction.

Main Body

In this paper, we review the abundant evidence derived from clinical, neuroimaging and postmortem studies, linking ET to cerebellar dysfunction. Furthermore, we review the combination of clinical, natural history and postmortem features suggesting that ET is neurodegenerative. We then compare the prevalence of ET (400 – 900 cases per 100,000) to that of the other cerebellar degenerations (ranging from <0.5 – 9 cases per 100,000, and in composite likely to be on the order of 20 cases per 100,000) and conclude that ET is 20 to 45 times more prevalent than all other forms of cerebellar degeneration combined.

Conclusion

Given the data we present, it is logical to conclude that ET is, by far, the most common form of cerebellar degeneration.

Altered spontaneous brain activity in essential tremor with and without resting tremor: a resting-state fMRI study

OBJECTIVES

Essential tremor with resting tremor (rET) often exhibits severer clinical features and more extensive functional impairment than essential tremor without resting tremor (ETwr). However, the pathophysiology of rET is still unclear. This study aims to use resting-state functional magnetic resonance imaging (rs-fMRI) to explore the alterations of brain activity between the drug-naïve patients of rET and ETwr.

METHODS

We recruited 19 patients with rET, 31 patients with ETwr and 25 healthy controls (HCs) to undergo a 3.0-T rs-fMRI examination. The differences of regional brain spontaneous activity between the rET, ETwr and HCs, as well as between total ET (rET + ETwr) and HCs were measured by amplitude of low-frequency fluctuation (ALFF) and fractional ALFF (fALFF). The relationships between the altered brain measurements and the clinical scores were analyzed.

RESULTS

Compared with HCs, both ET subgroups showed significantly decreased ALFF or fALFF values in the basal ganglia, inferior orbitofrontal gyrus and insula. The rET group specifically showed decreased ALFF values in the hippocampus and motor cortices, while the ETwr group specifically evidenced increased ALFF and fALFF values in the cerebellum.

DISCUSSION

Regional spontaneous activity in rET and ETwr share common changes and have differences, which may suggest that the functional activities in the limbic system and cerebellum are different between the two subtypes. Improved insights into rET and ETwr subtypes and the different brain spontaneous activity will be valuable for improving our understanding of the pathophysiology of the disease.

Consensus paper: Decoding the Contributions of the Cerebellum as a Time Machine. From Neurons to Clinical Applications

Time perception is an essential element of conscious and subconscious experience, coordinating our perception and interaction with the surrounding environment. In recent years, major technological advances in the field of neuroscience have helped foster new insights into the processing of temporal information, including extending our knowledge of the role of the cerebellum as one of the key nodes in the brain for this function. This consensus paper provides a state-of-the-art picture from the experts in the field of the cerebellar research on a variety of crucial issues related to temporal processing, drawing on recent anatomical, neurophysiological, behavioral, and clinical research.The cerebellar granular layer appears especially well-suited for timing operations required to confer millisecond precision for cerebellar computations. This may be most evident in the manner the cerebellum controls the duration of the timing of agonist-antagonist EMG bursts associated with fast goal-directed voluntary movements. In concert with adaptive processes, interactions within the cerebellar cortex are sufficient to support sub-second timing. However, supra-second timing seems to require cortical and basal ganglia networks, perhaps operating in concert with cerebellum. Additionally, sensory information such as an unexpected stimulus can be forwarded to the cerebellum via the climbing fiber system, providing a temporally constrained mechanism to adjust ongoing behavior and modify future processing. Patients with cerebellar disorders exhibit impairments on a range of tasks that require precise timing, and recent evidence suggest that timing problems observed in other neurological conditions such as Parkinson's disease, essential tremor, and dystonia may reflect disrupted interactions between the basal ganglia and cerebellum.The complex concepts emerging from this consensus paper should provide a foundation for further discussion, helping identify basic research questions required to understand how the brain represents and utilizes time, as well as delineating ways in which this knowledge can help improve the lives of those with neurological conditions that disrupt this most elemental sense. The panel of experts agrees that timing control in the brain is a complex concept in whom cerebellar circuitry is deeply involved. The concept of a timing machine has now expanded to clinical disorders.

Heterotopic Purkinje Cells: a Comparative Postmortem Study of Essential Tremor and Spinocerebellar Ataxias 1, 2, 3, and 6

Essential tremor (ET) is among the most common neurological diseases. Postmortem studies have noted a series of pathological changes in the ET cerebellum. Heterotopic Purkinje cells (PCs) are those whose cell body is mis-localized in the molecular layer. In neurodegenerative settings, these are viewed as a marker of the progression of neuronal degeneration. We (1) quantify heterotopias in ET cases vs. controls, (2) compare ET cases to other cerebellar degenerative conditions (spinocerebellar ataxias (SCAs) 1, 2, 3, and 6), (3) compare these SCAs to one another, and (4) assess heterotopia within the context of associated PC loss in each disease. Heterotopic PCs were quantified using a standard LH&E-stained section of the neocerebellum. Counts were normalized to PC layer length (n-heterotopia count). It is also valuable to consider PC counts when assessing heterotopia, as loss of PCs extends both to normally located as well as heterotopic PCs. Therefore, we divided n-heterotopias by PC counts. There were 96 brains (43 ET, 31 SCA [12 SCA1, 7 SCA2, 7 SCA3, 5 SCA6], and 22 controls). The median number of n-heterotopias in ET cases was two times higher than that of the controls (2.6 vs. 1.2, p < 0.05). The median number of n-heterotopias in the various SCAs formed a spectrum, with counts being highest in SCA3 and SCA1. In analyses that factored in PC counts, ET had a median n-heterotopia/Purkinje cell count that was three times higher than the controls (0.35 vs. 0.13, p < 0.01), and SCA1 and SCA2 had counts that were 5.5 and 11 times higher than the controls (respective p < 0.001). The median n-heterotopia/PC count in ET was between that of the controls and the SCAs. Similarly, the median PC count in ET was between that of the controls and the SCAs; the one exception was SCA3, in which the PC population is well known to be preserved. Heterotopia is a disease-associated feature of ET. In comparison, several of the SCAs evidenced even more marked heterotopia, although a spectrum existed across the SCAs. The median n-heterotopia/PC count and median PC in ET was between that of the controls and the SCAs; hence, in this regard, ET could represent an intermediate state or a less advanced state of spinocerebellar atrophy.

Abnormal Eye Movements in Parkinsonism and Movement Disorders

Abnormal eye movements are commonly observed in movement disorders. Ocular motility examination should include bedside evaluation and laboratory recording of ocular misalignment, involuntary eye movements, including nystagmus and saccadic intrusions/oscillations, triggered nystagmus, saccades, smooth pursuit (SP), and the vestibulo-ocular reflex. Patients with Parkinson’s disease (PD) mostly show hypometric saccades, especially for the self-paced saccades, and impaired SP. Early vertical saccadic palsy is characteristic of progressive supranuclear palsy-Richardson’s syndrome. Patients with cortico-basal syndrome typically show a delayed onset of saccades. Downbeat and gaze-evoked nystagmus and hypermetric saccades are characteristic ocular motor findings in ataxic disorders due to cerebellar dysfunction. In this review, we discuss various ocular motor findings in movement disorders, including PD and related disorders, ataxic syndromes, and hyperkinetic movement disorders. Systemic evaluation of the ocular motor functions may provide valuable information for early detection and monitoring of movement disorders, despite an overlap in the abnormal eye movements among different movement disorders.

The Relationship between Saccades and Locomotion

Human locomotion involves a complex interplay among multiple brain regions and depends on constant feedback from the visual system. We summarize here the current understanding of the relationship among fixations, saccades, and gait as observed in studies sampling eye movements during locomotion, through a review of the literature and a synthesis of the relevant knowledge on the topic. A significant overlap in locomotor and saccadic neural circuitry exists that may support this relationship. Several animal studies have identified potential integration nodes between these overlapping circuitries. Behavioral studies that explored the relationship of saccadic and gait-related impairments in normal conditions and in various disease states are also discussed. Eye movements and locomotion share many underlying neural circuits, and further studies can leverage this interplay for diagnostic and therapeutic purposes.

Cerebellar Pathology in Familial vs. Sporadic Essential Tremor

Familial and sporadic essential tremor (ET) cases differ in several respects. Whether they differ with respect to cerebellar pathologic changes has yet to be studied. We quantified a broad range of postmortem features (Purkinje cell (PC) counts, PC axonal torpedoes, a host of associated axonal changes, heterotopic PCs, and hairy basket ratings) in 60 ET cases and 30 controls. Familial ET was defined using both liberal criteria (n = 27) and conservative criteria (n = 20). When compared with controls, ET cases had lower PC counts, more torpedoes, more heterotopic PCs, a higher hairy basket rating, an increase in PC axonal collaterals, an increase in PC thickened axonal profiles, and an increase in PC axonal branching. Familial and sporadic ET had similar postmortem changes, with few exceptions, regardless of the definition criteria. The PC counts were marginally lower in familial than sporadic ET (respective p values = 0.059 [using liberal criteria] and 0.047 [using conservative criteria]). The PC thickened axonal profile count was marginally lower in familial ET than sporadic ET (respective p values = 0.037 [using liberal criteria] and 0.17 [using conservative criteria]), and the PC axonal branching count was marginally lower in familial than sporadic ET (respective p values = 0.045 [using liberal criteria] and 0.079 [using conservative criteria]). After correction for multiple comparisons, however, there were no significant differences. Overall, familial and sporadic ET cases share very similar cerebellar postmortem features. These data indicate that pathological changes in the cerebellum are a part of the pathophysiological cascade of events in both forms of ET.

Inferior Olivary nucleus degeneration does not lessen tremor in essential tremor

BACKGROUND

In traditional models of essential tremor, the inferior olivary nucleus was posited to play a central role as the pacemaker for the tremor. However, recent data call this disease model into question.

CASE PRESENTATION

Our patient had progressive, long-standing, familial essential tremor. Upper limb tremor began at age 10 and worsened over time. It continued to worsen during the nine-year period he was enrolled in our brain donation program (age 85 - 94 years), during which time the tremor moved from the moderate to severe range on examination. On postmortem examination at age 94, there were degenerative changes in the cerebellar cortex, as have been described in the essential tremor literature. Additionally, there was marked degeneration of the inferior olivary nucleus, which was presumed to be of more recent onset. Such degeneration has not been previously described in essential tremor postmortems. Despite the presence of this degeneration, the patient's tremor not only persisted but it continued to worsen during the final decade of his life.

CONCLUSIONS

Although the pathophysiology of essential tremor is not completely understood, evidence such as this suggests that the inferior olivary nucleus does not play a critical role in the generation of tremor in these patients.

Essential tremor

Essential tremor (ET) is one of the most common neurologic disorders, and genetic factors are thought to contribute significantly to disease etiology. There has been a relative lack of progress in understanding the genetic etiology of ET. This could reflect a number of factors, including the presence of substantial phenotypic and genotypic heterogeneity. Thus, a meticulous approach to phenotyping is important for genetic research. A lack of standardized phenotyping across studies and patient centers likely has contributed to the relative lack of success of genomewide association studies in ET. To dissect the genetic architecture of ET, whole-genome sequencing will likely be of value. This will allow specific hypotheses about the mode of inheritance and genetic architecture to be tested. A number of approaches still remain unexplored in ET genetics, including the contribution of copy number variants, uncommon moderate-effect alleles, rare variant large-effect alleles (including Mendelian and complex/polygenic modes of inheritance), de novo and gonadal mosaicism, epigenetic changes, and noncoding variation.

Cerebellar Atrophy in Cortical Myoclonic Tremor and Not in Hereditary Essential Tremor-a Voxel-Based Morphometry Study

Essential tremor (ET) presumably has a cerebellar origin. Imaging studies showed various cerebellar and also cortical structural changes. A number of pathology studies indicated cerebellar Purkinje cell pathology. ET is a heterogeneous disorder, possibly indicating different underlying disease mechanisms. Familial cortical myoclonic tremor with epilepsy (FCMTE), with evident Purkinje cell degeneration, can be an ET mimic. Here, we investigate whole brain and, more specifically, cerebellar morphological changes in hereditary ET, FCMTE, and healthy controls. Anatomical magnetic resonance images were preprocessed using voxel-based morphometry. Study 1 included voxel-wise comparisons of 36 familial, propranolol-sensitive ET patients, with subgroup analysis on age at onset and head tremor, and 30 healthy controls. Study 2 included voxel-wise comparisons in another nine ET patients, eight FCMTE patients, and nine healthy controls. Study 3 compared total cerebellar volume between 45 ET patients, 8 FCTME patients, and 39 controls. In our large sample of selected hereditary ET patients and ET subgroups, no local atrophy was observed compared to healthy controls or FCMTE. In ET patients with head tremor, a volume increase in cortical motor regions was observed. In FCMTE, a decrease in total cerebellar volume and in local cerebellar gray matter was observed compared to healthy controls and ET patients. The current study did not find local atrophy, specifically not in the cerebellum in hereditary ET, contrary to FCMTE. Volume increase of cortical motor areas in ET patients with head tremor might suggest cortical plasticity changes due to continuous involuntary head movements.

Cerebellar pathology in childhood-onset vs. adult-onset essential tremor

Although the incidence of ET increases with advancing age, the disease may begin at any age, including childhood. The question arises as to whether childhood-onset ET cases manifest the same sets of pathological changes in the cerebellum as those whose onset is during adult life. We quantified a broad range of postmortem features (Purkinje cell [PC] counts, PC axonal torpedoes, a host of associated axonal changes [PC axonal recurrent collateral count, PC thickened axonal profile count, PC axonal branching count], heterotopic PCs, and basket cell rating) in 60 ET cases (11 childhood-onset and 49 adult-onset) and 30 controls. Compared to controls, childhood-onset ET cases had lower PC counts, higher torpedo counts, higher heterotopic PC counts, higher basket cell plexus rating, and marginally higher PC axonal recurrent collateral counts. The median PC thickened axonal profile count and median PC axonal branching count were two to five times higher in childhood-onset ET than controls, but the differences did not reach statistical significance. Childhood-onset and adult-onset ET had similar PC counts, torpedo counts, heterotopic PC counts, basket cell plexus rating, PC axonal recurrent collateral counts, PC thickened axonal profile count and PC axonal branching count. In conclusion, we found that childhood-onset and adult-onset ET shared similar pathological changes in the cerebellum. The data suggest that pathological changes we have observed in the cerebellum in ET are a part of the pathophysiological cascade of events in both forms of the disease and that both groups seem to reach the same pathological endpoints at a similar age of death.

Essential tremor then and now: How views of the most common tremor diathesis have changed over time

BACKGROUND

Essential tremor (ET) is the most prevalent tremor diathesis. In this "then" and "now" piece, I detail how views of this disorder have changed over time.

METHODS

A PubMed search was conducted on June 15, 2017. The term "essential tremor" was crossed in sequential order with 14 s search terms (e.g., genetics, clinical).

RESULTS

The traditional view of ET was that it was monosymptomatic. An emerging view of ET is as a more clinically-complex entity with a range of possible motor and non-motor features. Traditionally, ET was viewed as autosomal dominant with complete penetrance by age 65. Current thinking is that, in addition to monogenic forms of ET, the disease is likely to be complex, with incomplete penetrance into advanced age. While non-genetic factors were traditionally presumed to exist, epidemiological studies have explored several potential environmental toxicants. The traditional olivary model of ET posited the existence of a central oscillator; an alternative is the cerebellar degenerative model, which is now under consideration.

CONCLUSIONS

For ET, there is clearly a "then" and "now" when one assesses changes in our understanding of the disease with time. Indeed, concepts relating to the clinical features, disease etiology and pathogenesis have all changed substantially.

The evolving definition of essential tremor: What are we dealing with?

BACKGROUND

Although essential tremor (ET) is commonly encountered in clinical practice, historically, there has been considerable disagreement as how to best define it, and now with a growing sense of its clinical complexity, how to best encapsulate it. Here, I draw attention to five issues of current uncertainty.

METHODS

A PubMed search conducted on June 19, 2017 crossed "essential tremor" with 9 second search terms (e.g., definition, diagnosis).

RESULTS

There are several major issues of clinical and diagnostic uncertainty. Underlying each issue is a larger question about the nature of the underlying pathophysiology of ET. Does age of onset of ET matter? How much dystonia is acceptable in ET? How much in the way of "cerebellar signs" are acceptable? Are non-motor features due to the underlying disease or merely secondary to the clinical features? Is ET a single disease entity or something else?

CONCLUSIONS

We are learning more about ET and, as a by-product of these efforts, are struggling with its definition. Further understanding the nature of the underlying disease pathogenesis as well as the role the cerebellum and cerebellar relays play in this process will likely provide important clues to enable us to bring order to areas of uncertainty.

Ocular Tremor in Parkinson's Disease: Discussion, Debate, and Controversy

The identification of ocular tremor in a small cohort of patients with Parkinson’s disease (PD) had lay somewhat dormant until the recent report of a pervasive ocular tremor as a universal finding in a large PD cohort that was, however, generally absent from a cohort of age-matched healthy subjects. The reported tremor had frequency characteristics similar to those of PD limb tremor, but the amplitude and frequency of the tremor did not correlate with clinical tremor ratings. Much controversy ensued as to the origin of such a tremor, and specifically as to whether a pervasive ocular tremor was a fundamental feature of PD, or rather a compensatory eye oscillation secondary to a transmitted head tremor, and thus a measure of a normal vestibulo-ocular reflex. In this mini review, we summarize some of the evidence for and against the case for a pervasive ocular tremor in PD and suggest future experiments that may help resolve these conflicting opinions.

Linking Essential Tremor to the Cerebellum: Neuropathological Evidence

A fundamental question about essential tremor (ET) is whether its associated pathological changes and disease mechanisms are linkable to a specific brain region. To that end, recent tissue-based studies have made significant strides in elucidating changes in the ET brain. Emerging from these studies is increasing neuropathological evidence linking ET to the cerebellum. These studies have systematically identified a broad range of structural, degenerative changes in the ET cerebellum, spanning across all Purkinje cell compartments. These include the dendritic compartment (where there is an increase in number of Purkinje cell dendritic swellings, a pruning of the dendritic arbor, and a reduction in spine density), the cell body (where, aside from reductions in Purkinje cell linear density in some studies, there is an increase in the number of heterotopic Purkinje cell soma), and the axonal compartment (where a plethora of changes in axonal morphology have been observed, including an increase in the number of thickened axonal profiles, torpedoes, axonal recurrent collaterals, axonal branching, and terminal axonal sprouting). Additional changes, possibly due to secondary remodeling, have been observed in neighboring neuronal populations. These include a hypertrophy of basket cell axonal processes and changes in the distribution of climbing fiber-Purkinje cell synapses. These changes all distinguish ET from normal control brains. Initial studies further indicate that the profile (i.e., constellation) of these changes may separate ET from other diseases of the cerebellum, thereby serving as a disease signature. With the discovery of these changes, a new model of ET has arisen, which posits that it may be a neurodegenerative disorder centered in the cerebellar cortex. These newly emerging neuropathological studies pave the way for anatomically focused, hypothesis-driven, molecular mechanistic studies of disease pathogenesis.

Familial Aggregation of the Cerebellar Signs in Familial Essential Tremor

Background

Although the hallmark feature of essential tremor (ET) is kinetic tremor, patients may exhibit additional motor features (e.g., intention tremor and mild gait ataxia) that are markers of an underlying abnormality of cerebellar function. ET is also a highly familial disorder, but we do not know whether the presence and expression of cerebellar signs are similar across family members. There are simply no published data. The alternative possibility is that these features are not heritable. We tested the specific hypothesis that the presence of cerebellar signs (i.e., intention tremor, tandem gait difficulty) ran in ET families.

Methods

ET probands and relatives enrolled in a genetic study at Yale and Columbia universities underwent a detailed videotaped neurological examination.

Results

There were 187 enrollees (59 probands, 128 affected relatives). In a bivariate logistic regression model, the presence of intention tremor in the proband was not a predictor of the presence of intention tremor in the relatives (odds ratio [OR] = 0.60, 95% confidence interval [CI] = 0.28–1.27, p = 0.18). In a similar model, the presence of greater tandem gait difficulty (i.e., a tandem gait score in the upper quartile) in the proband was not a predictor of the presence of such difficulty in the relatives (OR = 1.22, 95% CI = 0.41–3.66, p = 0.73).

Discussion

The presence of cerebellar signs did not aggregate in families with ET. In the current dataset, these did not seem to be disease features that were heritable.

Eye movement abnormalities in essential tremor

Essential tremor (ET) is the most prevalent movement disorder, characterized mainly by an action tremor of the arms. Only a few studies published as yet have assessed oculomotor abnormalities in ET and their results are unequivocal. The aim of this study was to assess the oculomotor abnormalities in ET patients compared with the control group and to find the relationship between oculomotor abnormalities and clinical features of ET patients. We studied 50 ET patients and 42 matched by age and gender healthy controls. Saccadometer Advanced (Ober Consulting, Poland) was used to investigate reflexive, pace-induced and cued saccades and conventional electrooculography for evaluation of smooth pursuit and fixation. The severity of the tremor was assessed by the Clinical Rating Scale for Tremor. Significant differences between ET patients and controls were found for the incidence of reflexive saccades dysmetria and deficit of smooth pursuit. Reflexive saccades dysmetria was more frequent in patients in the second and third phase of ET compared to the first phase. The reflexive saccades latency increase was correlated with severity of the tremor. In conclusion, oculomotor abnormalities were significantly more common in ET patients than in healthy subjects. The most common oculomotor disturbances in ET were reflexive saccades dysmetria and slowing of smooth pursuit. The frequency of reflexive saccades dysmetria increased with progression of ET. The reflexive saccades latency increase was related to the severity of tremor.

Essential Tremor: A Common Disorder of Purkinje Neurons?

Essential tremor (ET) is one of the most common neurological diseases, with an estimated 7 million affected individuals in the United States. Postmortem studies in the past few years have resulted in new knowledge as well as a new formulation of disease pathophysiology. This new formulation centers on the notion that ET might be a disease of the cerebellum and, more specifically, the Purkinje cell (PC) population. Indeed, several investigators have proposed that ET may be a "Purkinjopathy." Supporting this formulation are data from controlled postmortem studies demonstrating (1) a range of morphological changes in the PC axon, (2) abnormalities in the position and orientation of PC bodies, (3) reduction in the number of PCs in some studies, (4) morphological changes in and pruning of the PC dendritic arbor with loss of dendritic spines, and (5) alterations in both the PC-basket cell interface and the PC-climbing fiber interface in ET cases. This new formulation has engendered some controversy and raised additional questions. Whether the constellation of changes observed in ET differs from that seen in other degenerative disorders of the cerebellum remains to be determined, although initial studies suggest the likely presence of a distinct profile of changes in ET.

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.

Tandem gait performance in essential tremor patients correlates with cognitive function

Background

Emerging yet separate literatures have highlighted gait/balance impairments (i.e., mild ataxia) and cognitive problems in patients with essential tremor (ET). However, the relationship between the two has not been studied. The goal of these analyses was to study the relationship between gait/balance impairments and cognitive problems in ET. One-hundred-twenty ET cases were enrolled in an epidemiological study at Columbia University Medical Center. A Telephone Interview for Cognitive Status (TICS, range = 0–41 [no deficits]) was administered and a videotaped assessment of tandem gait was performed, during which the number of missteps during 10-steps was counted.

Results

The mean TICS score was 35.7 (range 25–39), and mean number of tandem mis-steps was 2.9 (range 0–10). The number of tandem mis-steps was correlated with the TICS score (Spearman’s r = −0.245, p = 0.011, i.e., individuals who had more tandem gait difficulty also had more cognitive difficulty). In a multivariate analysis, tandem mis-steps were associated with TICS score (p = 0.04) independent of age and other factors.

Conclusions

More cognitive difficulty was associated with more tandem gait difficulty in ET. Ambulation often requires the concurrent use of both cognitive and motor neural systems; hence it is possible that the cognitive and gait problems in ET reflect an underlying pervasive disorder affecting both cognitive and motor circuits.

Morphometric and functional MRI changes in essential tremor with and without resting tremor

The etiopathogenesis of essential tremor (ET) is still debated, since the predominant role of circuit dysfunction or brain degenerative changes has not been clearly established. The relationship with Parkinson's Disease (PD) is also controversial and resting tremor occurs in up to 20 % of ET. We investigated the morphological and functional changes associated with ET and we assessed potential differences related to the presence (ET+R) or absence (ET-R) of resting tremor. 32 ET patients (18 ET+R; 14 ET-R) and 12 healthy controls (HC) underwent 3T-MRI protocol including Spoiled Gradient T1-weighted sequence for Voxel-Based Morphometry (VBM) analysis and functional MRI during continuous writing of "8" with right dominant hand. VBM analysis revealed no gray and white matter atrophy comparing ET patients to HC and ET+R to ET-R patients. HC showed a higher BOLD response with respect to ET patients in cerebellum and other brain areas pertaining to cerebello-thalamo-cortical circuit. Between-group activation maps showed higher activation in precentral gyrus bilaterally, right superior and inferior frontal gyri, left postcentral gyrus, superior and inferior parietal gyri, mid temporal and supramarginal gyri, cerebellum and internal globus pallidus in ET-R compared to ET+R patients. Our findings support that the dysfunction of cerebello-thalamo-cortical network is associated with ET in absence of any morphometric changes. The dysfunction of GPi in ET+R patients, consistently with data reported in PD resting tremor, might suggest a potential role of this structure in this type of tremor.

From neurons to neuron neighborhoods: the rewiring of the cerebellar cortex in essential tremor

Remarkably little has been written on the biology of essential tremor (ET), despite its high prevalence. The olivary model, first proposed in the 1970s, is the traditional disease model for ET; however, the model is problematic for a number of reasons. Recently, intensive tissue-based studies have identified a series of structural changes in the brains of most ET cases, and nearly all of the observed changes are located in the cerebellar cortex. These studies suggest that Purkinje cells are central to the pathogenesis of ET and may thus provide a focus for the development of novel therapeutic strategies. Arising from these studies, a new model of ET proposes that the population of Purkinje cells represents the site of the initial molecular/cellular events leading to ET. Furthermore, a number of secondary changes/remodeling observed in the molecular and granular layers (i.e., in the Purkinje cell "neighborhood") are likely to be of additional mechanistic importance. On a physiological level, the presence of remodeling indicates the likely formation of aberrant synapses and the creation of new/abnormal cortical circuits in ET. Specific efforts need to be devoted to understanding the cascade of biochemical and cellular events occurring in the Purkinje cell layer in ET and its neuron neighborhood, as well as the physiological effects of secondary remodeling/rewiring that are likely to be occurring in this brain region in ET.

Understanding essential tremor: progress on the biological front

For many years, little was written about the underlying biology of ET, despite its high prevalence. Discussions of disease mechanisms were dominated by a focus on tremor physiology. The traditional model of ET, the olivary model, was proposed in the 1970s. The model suffers from several critical problems, and its relevance to ET has been questioned. Recent mechanistic research has focused on the cerebellum. Clinical and neuroimaging studies strongly implicate the importance of this brain region in ET. Recent mechanistic research has been grounded more in tissue-based changes (i.e., postmortem studies of the brain). These studies have collectively and systematically identified a sizable number of changes in the ET cerebellum, and have led to a new model of ET, referred to as the cerebellar degenerative model. Hence, there is a renewed interest in the science behind the biology of ET. How the new understanding of ET will translate into treatment changes is an open question.

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.