Reduced Purkinje cell number in essential tremor: a postmortem study

Cerebellar pathology of a dual clinical diagnosis: patients with essential tremor and dystonia

BACKGROUND

Clinical studies have implicated the cerebellum in the pathogenesis of essential tremor (ET), and recent postmortem studies have identified structural changes in the ET cerebellum. While the basal ganglia have traditionally been implicated in dystonia, cerebellar involvement has been suggested as well, and a recent study showed Purkinje cell (PC) loss. We conducted a detailed postmortem examination of the brain in four individuals with clinical diagnoses of ET and dystonia, and hypothesized that pathological changes in the cerebellum would be greater in these four ET cases than in published ET cases without dystonia.

METHODS

After a complete neuropathological assessment, a standard parasagittal neocerebellar tissue block was harvested in each brain. One 7-µm thick section was stained with luxol fast blue/hematoxylin and eosin, and one section with the Bielschowsky method. We quantified PCs, torpedoes, heterotopic PCs, PC dendritic swellings, and basket cell changes.

RESULTS

Two ET+dystonia cases had more microscopic changes in the cerebellum than published ET cases; the other two cases had similar changes to published ET cases.

DISCUSSION

This is the first report that uses human autopsy tissue to study patients with both ET and dystonia. The findings were heterogeneous. Additional studies, with larger samples, are needed.

Essential tremor is not a neurodegenerative disease

The pathophysiology of essential tremor (ET) remains unknown. Standard neuropathological studies have reported no consistent changes but a detailed study found neurodegeneration in all ET cases - 24% demonstrated lower brainstem Lewy body (LB) inclusions and 76% experienced a loss of cerebellar Purkinje cells (PCs) and its sequelae. We review the evidence on neurodegeneration in ET. The prevalence of LB inclusions in ET brains is similar to that in the asymptomatic general population. These incidental LB disease cases have evidence for reduced striatal tyrosine hydroxylase levels, as found in Parkinson's disease, but there is no evidence for reduced tyrosine hydroxylase levels in ET patients. Reduced mean PC counts in ET cases compared with the controls reported by some studies could not be replicated by others. Most ET cases have the same number of PCs as controls of a comparable age. Neither the lower brainstem LB inclusions nor the cerebellar PC loss represent the neurodegenerative basis of ET. Further studies are needed to determine the pathophysiology of ET.

Olfaction in Parkinson's disease and related disorders

Olfactory dysfunction is an early 'pre-clinical' sign of Parkinson's disease (PD). The present review is a comprehensive and up-to-date assessment of such dysfunction in PD and related disorders. The olfactory bulb is implicated in the dysfunction, since only those syndromes with olfactory bulb pathology exhibit significant smell loss. The role of dopamine in the production of olfactory system pathology is enigmatic, as overexpression of dopaminergic cells within the bulb's glomerular layer is a common feature of PD and most animal models of PD. Damage to cholinergic, serotonergic, and noradrenergic systems is likely involved, since such damage is most marked in those diseases with the most smell loss. When compromised, these systems, which regulate microglial activity, can influence the induction of localized brain inflammation, oxidative damage, and cytosolic disruption of cellular processes. In monogenetic forms of PD, olfactory dysfunction is rarely observed in asymptomatic gene carriers, but is present in many of those that exhibit the motor phenotype. This suggests that such gene-related influences on olfaction, when present, take time to develop and depend upon additional factors, such as those from aging, other genes, formation of α-synuclein- and tau-related pathology, or lowered thresholds to oxidative stress from toxic insults. The limited data available suggest that the physiological determinants of the early changes in PD-related olfactory function are likely multifactorial and may include the same determinants as those responsible for a number of other non-motor symptoms of PD, such as dysautonomia and sleep disturbances.

LINGO-1 and Neurodegeneration: Pathophysiologic Clues for Essential Tremor

Essential tremor (ET), one of the most common adult-onset movement disorders, has been associated with cerebellar Purkinje cell degeneration and formation of brainstem Lewy bodies. Recent findings suggest that genetic variants of the leucine-rich repeat and Ig domain containing 1 (LINGO-1) gene could be risk factors for ET. The LINGO-1 protein contains both leucine-rich repeat (LRR) and immunoglobulin (Ig)-like domains in its extracellular region, as well as a transmembrane domain and a short cytoplasmic tail. LINGO-1 can form a ternary complex with Nogo-66 receptor (NgR1) and p75. Binding of LINGO-1 with NgR1 can activate the NgR1 signaling pathway, leading to inhibition of oligodendrocyte differentiation and myelination in the central nervous system. LINGO-1 has also been found to bind with epidermal growth factor receptor (EGFR) and induce downregulation of the activity of EGFR-PI3K-Akt signaling, which might decrease Purkinje cell survival. Therefore, it is possible that genetic variants of LINGO-1, either alone or in combination with other genetic or environmental factors, act to increase LINGO-1 expression levels in Purkinje cells and confer a risk to Purkinje cell survival in the cerebellum.Here, we provide a concise summary of the link between LINGO-1 and neurodegeneration and discuss various hypotheses as to how this could be potentially relevant to ET pathogenesis.

Worsening essential tremor following deep brain stimulation: disease progression versus tolerance

A major concern regarding ventralis intermedius nucleus deep brain stimulation for essential tremor has been the loss of surgical efficacy over time in a minority of patients. Some experts have ascribed the worsening tremor to tolerance, while other evidence has suggested that disease progression may play a role. Suboptimal lead placement has also been reported to be a factor in worsening tremor following deep-brain stimulation; however, most authors consider this phenomenon to manifest within a few months of the actual surgery. We aimed to dissect the tolerance versus disease progression issue by analysing preoperative versus long-term post-surgical Fahn-Tolosa-Marin Tremor Rating Scale scores both on and off stimulation among 28 patients who underwent ventralis intermedius nucleus deep brain stimulation and 21 age-matched controls. Of the 28 patients in the treatment arm of the cohort, seven (25%) demonstrated evidence of tremor progression, and had a 34% increase in the tremor score off stimulation at the 36 month follow-up compared with a 32% increase among controls (P = 0.67). In one of the seven patients there was evidence of suboptimal lead placement given the lateral position of the lead, and the motor side effects during threshold testing. This patient demonstrated a loss of stimulation benefit between 24 and 36 months, which may have been more indicative of tolerance. The other six subjects (86%) maintained stimulation benefit throughout the follow-up period, despite worsening tremor off stimulation (at a comparable rate to that of controls), making disease progression the most likely explanation. The data suggest that deep brain stimulation tolerance may be over-reported in the literature, and that a tolerance versus disease progression work-up should include: examining the trend in off stimulation scores, accounting for image based lead locations, and during programming sessions checking for thresholds which may elicit clinical benefits and side effects.

Essential tremor is not dependent upon cerebellar Purkinje cell loss

The pathophysiology of essential tremor (ET) is unknown but recent studies report that the majority of ET cases has cerebellar Purkinje cell (PC) degeneration and its sequelae.

OBJECTIVE

To perform PC counts in ET, and normal and Parkinson's disease (PD) controls to determine the relationship of PC loss to ET.

METHODS

All ET cases and PD controls were followed at our clinic. Normal controls had no history of neurological disease and had normal standard neuropathological studies. The PC counts were done by a neuropathologist who was blinded to the clinical diagnosis. Three different methods were used for counting PC; section through any part of the PC, through any part of the PC nucleus, and through any part of PC nucleolus. The counts were done in five non-contiguous microscopic fields.

RESULTS

59 brains were studied. These included 12 ET, 41 PD controls, and six normal controls. The mean age at death was 82.7 in ET, 79.1 in PD, and 75.7 years in the normal controls. The mean duration of symptoms was 34 years in ET and 15.7 years in the PD cases. The mean PC counts through any part of the neuron were 64.8 in ET, 56.2 in PD, and 58.0 in normal controls. Differences were not significant.

CONCLUSION

Cerebellar PC loss does not distinguish ET from controls. It is concluded that PC loss is neither a pathological basis for, nor the distinctive feature of ET.

Treatment of Essential Tremor: Are there Issues We are Overlooking?

Background: Essential tremor (ET) is one of the most common neurological diseases. Although a large number of medications have been tested, there are only two first-line medications, primidone and propranolol, which is a situation that has not changed in approximately 30 years. Several recent reviews have summarized the current pharmacotherapeutic options for ET and the approach to the management of ET patients. Yet there remain a number of important issues, both scientific and clinical, that have not been broached in the literature and that have therapeutic implications. Objectives: To introduce several clinical and scientific issues that have not formally entered the published literature on the treatment of ET. Methods: In September 2011, materials for this article were gathered during a literature search of PubMed using the following terms: ET, clinical, clinical trial, treatment, medications, therapeutics. English-language articles were selected for further review. Results: The paper focuses on several topics that have received scant or no discussion in the published literature on ET therapeutics. These topics are as follows: the nature of the underlying disease pathophysiology, the presence of pathological heterogeneity, the complexity of cellular and neurochemical changes which may be underlying this disorder, the presence of clinical heterogeneity, the selection of treatment endpoints, the effects of diagnostic uncertainty, the presence of cognitive and psychiatric features in ET, the identification of possible modifiable risk factors, and the absence of any neuroprotective therapies. Conclusion: The author has identified several topics that have received scant or no discussion in the published literature on ET therapeutics. Further discussion of the issues raised here may lead to improvements in clinical trial methodologies as well as facilitate the development of fresh approaches to pharmacotherapy.

Increased number of Purkinje cell dendritic swellings in essential tremor

BACKGROUND AND PURPOSE

Essential Tremor (ET) is among the most prevalent neurologic disorders. Growing clinical and neuro-imaging evidence implicates cerebellar dysfunction in the pathogenesis of ET and emerging postmortem studies have identified structural changes in the cerebellum, particularly in Purkinje cells. In this study we systematically quantified focal Purkinje cell dendritic swellings (DS) in 20 ET vs. 19 control brains.

METHODS

In each brain, a standard parasagittal neocerebellar tissue block was harvested. DS were quantified in one 7-μm thick section stained with Luxol Fast Blue/Hematoxylin and Eosin (LH&E) and one section stained with Bielschowsky method.

RESULTS

The number of DS were higher in cases than controls by LH&E (1.50 ± 1.79 vs. 0.05 ± 0.23, P = 0.002) and Bielschowsky methods (2.70 ± 3.10 vs. 0.37 ± 0.50, P = 0.002). The number of DS was correlated with the number of torpedoes and marginally inversely correlated with the number of Purkinje cells.

CONCLUSION

The current study documents and quantifies an additional structural abnormality in the ET cerebellum, adding to the growing list of such changes in this disease. The mechanisms that underlie this and other structural changes observed in ET are currently unknown, and they deserve additional exploration.

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.

Brain biochemistry in autopsied patients with essential tremor

The pathology of essential tremor is increasingly being studied; however, there are limited studies of biochemical changes in this condition. We studied several candidate biochemical/anatomical systems in the brain stem, striatum, and cerebellum of 23 essential tremor subjects who came to autopsy, comparing them with a control population. Striatal tyrosine hydroxylase, a marker of dopaminergic neurons, was 91.7 ± 113.2 versus 96.4 ± 102.7 ng/mg (not significant) in cases and controls, respectively. Locus coeruleus dopamine beta-hydroxylase, a marker of noradrenergic neurons, was not significantly different between the essential tremor and control groups. Parvalbumin, a marker of GABAergic neurons, was 199.3 ± 42.0 versus 251.4 ± 74.8 ng/mg (P = .025) in the pons in the region of the locus coeruleus of essential tremor subjects versus controls, whereas there was no difference in cerebellar parvalbumin. These results are supportive of a possible role for reduced GABAergic function in the locus coeruleus in essential tremor. The hypothesis that essential tremor represents early Parkinson's disease was not supported, as striatal dopaminergic markers were not reduced compared with control subjects.

Genetic variants of α-synuclein are not associated with essential tremor

BACKGROUND

Given the overlap between Parkinson's disease and essential tremor, we examined genetic variants in α-synuclein (SNCA) as risk determinants for essential tremor.

METHODS

Samples from 661 essential tremor subjects and 1316 control subjects from 4 participating North American sites were included in this study. Parkinson's disease samples (n = 427) were compared against controls. Twenty variants were selected for association analysis within the SNCA locus. Individual logistic regression analyses against essential tremor diagnosis were run for each variant and then combined using meta-analysis.

RESULTS

Our results do not show a significant association between variants in the SNCA locus and risk of essential tremor, whereas the established association of SNCA variants with Parkinson's disease risk was observed.

CONCLUSIONS

Whereas genetic factors are likely to play a large role in essential tremor pathogenesis, our results do not support a role for common SNCA genetic variants in risk for essential tremor.

Milestones in tremor research

Tremor is one of the most frequent movement disorders and covers a wide spectrum of entities summarized in the 1998 consensus statement of the Movement Disorder Society. Essential tremor and Parkinson tremor are most common and are also the most thoroughly studied. Major progress has occurred in the clinical semiology, neuroimaging, epidemiology, and pathophysiology of tremors. Pathology and genetic research are rapidly growing fields of study. Recently described tremor entities include orthostatic tremor, dystonic tremor, cortical tremor, and thalamic tremor. Treatment research methodology has improved substantially, but few double-blind controlled trials have been published. Deep brain stimulation is the most effective treatment for most tremors but is reserved for advanced cases.

Increased number of heterotopic Purkinje cells in essential tremor

OBJECTIVE

Recent postmortem studies reveal degenerative changes, including Purkinje cell (PC) loss, in most brains from individuals with essential tremor (ET). Heterotopic PCs (HPCs) (ie, PC bodies displaced into the molecular layer) may be found in neurodegenerative diseases with PC loss. HPCs have been observed in ET but no quantitative case control analysis has been performed.

METHODS

HPCs were counted in 35 ET brains and 32 control brains (including 21 non-diseased controls and 11 diseased controls with progressive supranuclear palsy (PSP)) using a standard 20 × 25 mm cerebellar cortical section stained with a modified Bielscholwsky method.

RESULTS

The median number of HPCs per section was three times higher in 35 ET cases (median 3, mean ± SD 3.8 ± 3.6, range 0-14) versus 32 controls (median 1, mean ± SD 1.6 ± 1.7, range 0-5) (p = 0.007). The number of HPCs was similarly low in the 21 non-diseased controls and 12 PSP brains (median 1 in each group) (p = 0.04 and p = 0.01 compared with ET). In ET, the number of HPCs was inversely related to the number of PCs (Spearman's rho -0.36, p = 0.038) (ie, cases with more HPCs had fewer PCs).

CONCLUSION

PC heterotopia, which occurs in cerebellar degenerative disorders, is also a feature of ET. These findings further contribute to our understanding of the postmortem changes in this common neurological disease.

Significance of cerebellar Purkinje cell loss to pathogenesis of essential tremor

Some recent studies indicate that most essential tremor (ET) cases have cerebellar pathology characterized by Purkinje cell (PC) loss and its sequelae.

OBJECTIVE

To assess the role of PC degeneration in ET symptomatology.

METHODS

We studied seven ET, six tremor dominant Parkinson's disease controls and two normal control brains. Cerebellar PC counts were done in all cases by a neuropathologist using three different methods to identify PC.

RESULTS

There were individual differences in PC counts in all subgroups. There was no difference between ET and controls of the same age. The PC count in ET was not related to: onset site of ET, severity of symptoms, or any other clinical features that we studied but there was a trend to a reduced number of PC with age in all groups.

CONCLUSION

There is no evidence in our study or in the literature to date indicating that PC loss is the pathological basis of ET. Further studies are needed to determine the pathophysiology of ET.

Purkinje cell loss is a characteristic of essential tremor

This paper began as a letter to the editor, commenting on several methodological and conceptual problems with the paper by Rajput et al. [1]. We were asked by the editors to expand the paper to include a more general discussion of the role of the cerebellum in essential tremor (ET). The study of the neuropathological underpinnings of essential tremor (ET) is a relatively new undertaking. The purpose of this paper is three-fold. The first is to comment on methodological problems in a recently-published paper by Rajput et al., the major one being the small sample size of that study, which resulted in a Type II statistical error. Hence, one cannot conclude based on their data that there is no Purkinje cell (PC) loss in ET. Secondly, we comment on conceptual problems with that study, which suggested that PC loss might not be a featured characteristic of ET because it is also found in other disease states. We discuss why this is an erroneous conclusion. Our third purpose is to more broadly discuss the role of the cerebellum in ET, giving consideration to the wealth of clinical and postmortem data that have accumulated over recent years. In this discussion, we make the following points: (1) it is now generally recognized that ET is a disease of cerebellar systems dysfunction, (2) given the nature of the postmortem work, revealing the presence of several types of structural-anatomical changes within the cerebellum and absence of detectable changes in other brain regions, the most empirically-based explanation is that the primary problem in ET is in the cerebellum itself, (3) that the collection of cellular changes in the cerebellum in ET are also present in other cerebellar degenerations should add to rather than detract from the notion that ET is a disease of cerebellar degeneration.

Wine drinking and essential tremor: a possible protective role

The purpose of this study was to evaluate the possible association of cigarette smoking, coffee drinking, and wine consumption with essential tremor using a matched case-control design. Cases and controls were enrolled from 6 Movement Disorder centers in central-southern Italy. Essential tremor was diagnosed according to Bain's criteria. Three unrelated healthy controls (not affected by neurological disorders) per each enrolled case, matched by sex and age (± 5 years), were selected. A standardized questionnaire was administered to record demographic, epidemiological, and clinical data. All cases and controls underwent a standard neurological examination. Adjusted odds ratios and 95% confidence intervals were estimated using conditional logistic regression for the matched cases and controls. Eighty-three patients with essential tremor (38 men and 45 women; mean age, 68.2 ± 8.6 years) and 245 matched control subjects (113 men and 132 women; mean age, 68.4 ± 9.7 years) were enrolled in the study. Multivariate analysis showed a significant negative association between essential tremor and wine consumption preceding the onset of disease (adjusted odds ratio, 0.23; 95% confidence interval, 0.08-0.64; P = .0005) with a significant dose effect (1-2 glass of wine per day: odds ratio, 0.32; 95% confidence interval, 0.10-0.95; P = .04; more than 3 glass of wine per day: odds ratio, 0.14; 95% confidence interval, 0.03-0.62; P = .01). In our sample no association between essential tremor and cigarette smoking or coffee drinking was found. Our data suggest a negative association between wine drinking and essential tremor, which could be explained by the long-term neuroprotective effect of its antioxidant components.

Heterotopic Purkinje cells in ataxia-telangiectasia

Ataxia-telangiectasia (A-T) is a heritable disorder of cerebellar ataxia and oculocutaneous telangiectasias caused by mutation of the ATM gene. The most prominent and consistent neuropathologic finding in the disorder is cerebellar cortical degeneration involving significant loss of granule and Purkinje cells. Several past autopsy studies of A-T patients have also noted large-bodied cells located within the molecular layer of the cerebellar cortex and, noting similarities in morphology between these cells and Purkinje cells, hypothesized that the cells were heterotopic Purkinje cells. This study aimed to test this hypothesis using an antibody that labels Purkinje cells, and also to investigate other cell types in the degenerating cerebellar cortex in A-T. Using the anti-calbindin D-28K antibody to label Purkinje cells in cerebellar tissue from five A-T patients and five age- and sex-matched controls, the study found calbindin-positive heterotopic Purkinje cells in the molecular layer occurring at a significantly higher rate in A-T patients than in controls (P = 0.012). Further immunohistochemistry with the anti-Iba-1 and anti-parvalbumin antibodies showed, respectively, an increase in microglial activity (P = 0.14) and stellate-cell density (P = 0.0048) in the cerebellar cortex of A-T patients versus controls. These data add to the as yet unresolved debate over the origin and significance of heterotopic Purkinje cells in A-T.

3D Winding Number: Theory and Application to Medical Imaging

We develop a new formulation, mathematically elegant, to detect critical points of 3D scalar images. It is based on a topological number, which is the generalization to three dimensions of the 2D winding number. We illustrate our method by considering three different biomedical applications, namely, detection and counting of ovarian follicles and neuronal cells and estimation of cardiac motion from tagged MR images. Qualitative and quantitative evaluation emphasizes the reliability of the results.

Comparison of mibefradil and derivative NNC 55-0396 effects on behavior, cytochrome P450 activity, and tremor in mouse models of essential tremor

NNC 55-0396 [(1S,2S)-2-(2-(N-[(3-benzimidazol-2-yl)propyl]-N-methylamino)ethyl)-6-fluoro-1,2, 3,4-tetrahydro-1-isopropyl-2-naphtyl cyclopropanecarboxylate dihydrochloride], is a mibefradil derivative that retains potent in vitro T-type calcium channel antagonist efficacy. We compared the two compounds for behavioral toxicity, effects on cytochrome P450 activity, and efficacy against tremor in the γ-aminobutyric acid type A (GABAA) receptor subunit α1-null mouse, and the harmaline tremor model of essential tremor in wild-type mice. NNC 55-0396 was better tolerated than mibefradil in the horizontal wire test of sedation/motor function, with 3/6 failing at 300 and 30mg/kg respectively. To assess for a potential interaction with harmaline, mice were given the drugs, followed by harmaline or vehicle, and tested 30min later in the inverted wire grid test. Mibefradil exacerbated, whereas NNC 55-0396 ameliorated harmaline-induced test deficits. In mouse liver microsomes, NNC 55-0396 was a less potent inhibitor of harmaline O-demethylation than mibefradil (Ki: 0.95 and 0.29μM respectively), and also less potent at inhibiting testosterone 6-β-hydroxylation (Ki: 0.71 and 0.12μM respectively). In the GABAA α1-null model, NNC 55-0396 but not mibefradil, (each at 20mg/kg), suppressed tremor while NNC 55-0396 at 12.5mg/kg suppressed harmaline-induced tremor by half by 20-100min, whereas mibefradil at the same dose did not significantly affect tremor. In contrast to mibefradil, NNC 55-0396 is well tolerated and suppresses tremor, and exerts less cytochrome P450 inhibition. These results suggest potential clinical utility for NNC 55-0396 or similar derivatives as a T-type calcium antagonist.

Essential tremor

Essential tremor (ET) is among the most common neurological disorders. This chapter reviews the epidemiology, clinical features, and pathophysiology of ET. The defining feature is a kinetic tremor of the arms. Patients often have a postural tremor as well. Other body regions may also be involved (especially the head). The severity of tremor may range from mild cases in population settings to more severe cases in treatment settings. Motor features aside from tremor have been described in ET, including tandem gait difficulty. Mild cognitive changes (especially executive dysfunction) have been documented in many studies as well. Despite being regarded as one of the most common hyperkinetic movement disorders, establishing a precise prevalence has been difficult, yet the prevalence among persons aged 40 and older seems to be 4% or higher. There are numerous examples of families in which the disease appears to be inherited yet genetic studies have not progressed to the point where ET genes have been identified. There is also a growing understanding that environmental factors are likely to contribute to the etiology of ET. More recent postmortem studies have helped localize the possible source of ET to structural alterations in the cerebellum and its connecting pathways.

Beta-carboline alkaloids and essential tremor: exploring the environmental determinants of one of the most prevalent neurological diseases

Essential tremor (ET) is among the most prevalent neurological diseases, yet its etiology is not well understood. Susceptibility genotypes undoubtedly underlie many ET cases, although no genes have been identified thus far. Environmental factors are also likely to contribute to the etiology of ET. Harmane (1-methyl-9H-pyrido[3,4-beta]indole) is a potent, tremor-producing beta-carboline alkaloid, and emerging literature has provided initial links between this neurotoxin and ET. In this report, we review this literature. Two studies, both in New York, have demonstrated higher blood harmane levels in ET cases than controls and, in one study, especially high levels in familial ET cases. Replication studies of populations outside of New York and studies of brain harmane levels in ET have yet to be undertaken. A small number of studies have explored several of the biological correlates of exposure to harmane in ET patients. Studies of the mechanisms of this putative elevation of harmane in ET have explored the role of increased dietary consumption, finding weak evidence of increased exogenous intake in male ET cases, and other studies have found initial evidence that the elevated harmane in ET might be due to a hereditarily reduced capacity to metabolize harmane to harmine (7-methoxy-1-methyl-9H-pyrido[3,4-beta]-indole). Studies of harmane and its possible association with ET have been intriguing. Additional studies are needed to establish more definitively whether these toxic exposures are associated with ET and are of etiological importance.

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.

T-type calcium channel antagonists suppress tremor in two mouse models of essential tremor

Essential tremor is a common disorder that lacks molecular targets for therapeutic development. T-type calcium channel activation has been postulated to underlie rhythmicity in the olivo-cerebellar system that is implicated in essential tremor. We therefore tested whether compounds that antagonize T-type calcium channel currents suppress tremor in two mouse models that possess an essential tremor-like pharmacological response profile. Tremor was measured using digitized spectral motion power analysis with harmaline-induced tremor and in the GABA(A) receptor α1 subunit-null model. Mice were given ethosuximide, zonisamide, the neuroactive steroid (3β,5α,17β)-17-hydroxyestrane-3-carbonitrile (ECN), the 3,4-dihydroquinazoline derivative KYS05064, the mibefradil derivative NNC 55-0396, or vehicle. In non-sedating doses, each compound reduced harmaline-induced tremor by at least 50% (range of maximal suppression: 53-81%), and in the GABA(A) α1-null model by at least 70% (range 70-93%). Because the T-type calcium channel Cav3.1 is the dominant subtype expressed in the inferior olive, we assessed the tremor response of Cav3.1-deficient mice to harmaline, and found that null and heterozygote mice exhibit as much tremor as wild-type mice. In addition, ECN and NNC 55-0396 suppressed harmaline tremor as well in Cav3.1-null mice as in wild-type mice. The finding that five T-type calcium antagonists suppress tremor in two animal tremor models suggests that T-type calcium channels may be an appropriate target for essential tremor therapy development. It is uncertain whether medications developed to block only the Cav3.1 subtype would exhibit efficacy.

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.

"Hairy baskets" associated with degenerative Purkinje cell changes in essential tremor

Essential tremor (ET) is one of the most common neurologic diseases. Increased numbers of torpedoes and Purkinje cell (PC) loss have been documented in the brains of patients with ET. We recently observed a dense and tangled appearance ("hairiness") of the basket cell axonal plexuses that surround PC soma in Bielschowsky preparations of cerebellar cortex in ET brains. Here, we assessed basket cell "hairiness" in 37 ET (32 cerebellar ET; 5 Lewy body variant ET), 21 nondisease control, and 48 disease control brains using a semiquantitative scale. In 8 cerebellar ET cases (25%), there were high basket scores (rating = 3), whereas no Lewy body variant ET, 1 nondisease control (4.8%), and 2 diseased controls (4.2%) had high basket scores (p = 0.001). The hairy basket scores correlated with numbers of torpedoes (p < 0.001) and inversely with numbers of PCs (p = 0.06). Axonal plexus density obtained by image analysis of basket cell processes traced from digitized images was higher in ET than in nondiseased control cases (p = 0.016). Closely spaced sites of synaptic contact between basket cell processes and PCs were identified by electron microscopy in ET cases. These data indicate that structural changes are not restricted to PCs in ET, and that other neurons within their functional network may be involved in its pathogenesis.

Older onset essential tremor: More rapid progression and more degenerative pathology

There are few data on rate of progression in essential tremor (ET). To quantify the rate of tremor progression in a cross-sectional sample of 348 ET cases in an epidemiological study; characterize the relationship between age of tremor onset and rate of tremor progression in that sample; and characterize the relationship between age of tremor onset, rate of tremor progression, and severity of underlying brain changes in 9 cases from a brain repository. Rate of tremor progression was defined as tremor severity / duration. The degeneration index = number of torpedoes per section / Purkinje cell linear density. In the epidemiological study, older age of tremor onset was associated with faster rate of tremor progression (P < 0.001). In the brain repository, older age of tremor onset was associated with higher degeneration index (P = 0.037), and higher degeneration index was associated with faster rate of tremor progression (P = 0.018). In a large clinical sample, older age of onset was associated with more rapid tremor progression. In a brain bank, older age of onset was associated with more degenerative pathology in the cerebellum. As in several neurodegenerative disorders, in older onset cases, it is possible that the disease advances more rapidly.

Spiral analysis in Niemann-Pick disease type C

Spiral analysis is a computerized method of analyzing upper limb motor physiology through the quantification of spiral drawing. The objective of this study was to determine whether spirals drawn by patients with Niemann-Pick disease type C (NPC) could be distinguished from those of controls, and to physiologically characterize movement abnormalities in NPC. Spiral data consisting of position, pressure, and time were collected from 14 NPC patients and 14 age-matched controls, and were analyzed by the Mann-Whitney U test. NPC spirals were characterized by: lower speed (2.67 vs. 9.56 cm/s, P < 0.001) and acceleration (0.10 vs. 2.04 cm/s(2), P < 0.001), higher loop width variability (0.88 vs. 0.28, P < 0.001), tremor (5/10 vs. 0/10 trials in the dominant hand, P < 0.001), and poor overall spiral rating (2.53 vs. 0.70, P < 0.005). NPC spirals also exhibited sustained drawing pressure profiles that were abnormally invariant with time. Other features, such as the tightness of loop widths, were normal. Our findings reveal that differing aspects of tremor, Parkinsonism, ataxia, and dystonia are quantifiable in NPC patients.

Essential tremors: a family of neurodegenerative disorders?

Essential tremor (ET) is the most common pathologic tremor in humans. The traditional view of ET, as a monosymptomatic condition, is being replaced by an appreciation of the spectrum of clinical features, with both motor and nonmotor elements. These features are not distributed homogeneously across patients. In addition, postmortem studies are now demonstrating distinct structural changes in ET. There is growing evidence that ET may be a family of diseases rather than a single entity. Furthermore, this aging-associated, progressive disorder is associated with neuronal loss and postmortem changes that occur in traditional neurodegenerative disorders.

Essential tremor as a neuropsychiatric disorder

The traditional view of essential (ET) tremor is as a mono-symptomatic condition characterized by action tremor. Over the past decade, researchers have learned that this picture is an over-simplification. First, it is clear that many patients also have other motor manifestations (e.g., ataxic gait). Second, the presence of a variety of non-motor features, both cognitive and psychiatric, is now appreciated. Mild cognitive changes (esp. executive dysfunction) have been documented in several studies. More recently, two population-based studies have demonstrated an association between ET and dementia. Clinically, while most of these cases developed Alzheimer's disease, the neuropathological underpinnings of this dementia have not been fully explored. Psychiatric manifestations include specific personality traits, anxiety, social phobia, and depressive symptoms. Depression may be a primary manifestation of the illness rather than a secondary response to disability. The emerging view of ET is that it is a disease whose central feature is action tremor but in which both motor and non-motor features occur. As in other neurodegenerative conditions, ET appears to be more than a disease of the motor system. Further study of these non-motor phenomena will advance our understanding of disease mechanisms and enhance the quality of clinical interactions with patients.

Torpedoes in Parkinson's disease, Alzheimer's disease, essential tremor, and control brains

Purkinje cell axonal swellings ("torpedoes"), described in several cerebellar disorders as well as essential tremor (ET), have not been quantified in common neurodegenerative conditions. The aim of this study was to quantify torpedoes Parkinson's disease (PD) and Alzheimer's disease (AD) compared with ET and control brains. Brains included 40 ET cases (34 cerebellar ET, 6 Lewy body variant of ET) and age-matched comparison brains (21 AD, 14 PD/diffuse Lewy body disease, 25 controls). Torpedoes were counted in 20 x 25 mm cerebellar cortical sections stained with Luxol Fast Blue/Hematoxylin and Eosin. The median number of torpedoes in cerebellar ET (12) was 12x higher than that of controls (1) and nearly 2.5x higher than in AD (5) or PD/DLBD (5) (all P < or = 0.005). Furthermore, in a logistic regression model that adjusted for age and Alzheimer's-type changes, each torpedo more than doubled the odds of having cerebellar ET (Odds ratio(cerebellar ET vs. control) = 2.57, P = 0.006), indicating that the association between increased torpedoes and cerebellar ET was independent of these Alzheimer's-type changes. Although torpedoes are increased in AD and PD, as well as cerebellar ET, the magnitude of increase in cerebellar ET is greater, and cannot be accounted for by concomitant AD or PD pathology.

The cerebellum, cerebellar disorders, and cerebellar research--two centuries of discoveries

Research on the cerebellum is evolving rapidly. The exquisiteness of the cerebellar circuitry with a unique geometric arrangement has fascinated researchers from numerous disciplines. The painstaking works of pioneers of these last two centuries, such as Rolando, Flourens, Luciani, Babinski, Holmes, Cajal, Larsell, or Eccles, still exert a strong influence in the way we approach cerebellar functions. Advances in genetic studies, detailed molecular and cellular analyses, profusion of brain imaging techniques, emergence of behavioral assessments, and reshaping of models of cerebellar function are generating an immense amount of knowledge. Simultaneously, a better definition of cerebellar disorders encountered in the clinic is emerging. The essentials of a trans-disciplinary blending are expanding. The analysis of the literature published these last two decades indicates that the gaps between domains of research are vanishing. The launch of the society for research on the cerebellum (SRC) illustrates how cerebellar research is burgeoning. This special issue gathers the contributions of the inaugural conference of the SRC dedicated to the mechanisms of cerebellar function. Contributions were brought together around five themes: (1) cerebellar development, death, and regeneration; (2) cerebellar circuitry: processing and function; (3) mechanisms of cerebellar plasticity and learning; (4) cerebellar function: timing, prediction, and/or coordination?; (5) anatomical and disease perspectives on cerebellar function.

Population-based study of baseline ethanol consumption and risk of incident essential tremor

BACKGROUND

Recent postmortem studies have demonstrated pathological changes, including Purkinje cell loss, in the cerebellum in essential tremor (ET). Toxic exposures that compromise cerebellar tissue could lower the threshold for developing ET. Ethanol is a well-established cerebellar toxin, resulting in Purkinje cell loss.

OBJECTIVE

To test whether higher baseline ethanol consumption is a risk factor for the subsequent development of incident ET.

METHODS

Lifetime ethanol consumption was assessed at baseline (1994-1995) in a prospective, population-based study in central Spain of 3285 elderly participants, 76 of whom developed incident ET by follow-up (1997-1998).

RESULTS

In a Cox proportional hazards model adjusting for cigarette pack-years, depressive symptoms and community, the baseline number of drink-years was marginally associated with a higher risk of incident ET (relative risk, RR = 1.003, p = 0.059). In an adjusted Cox model, the highest baseline drink-year quartile doubled the risk of incident ET (RR = 2.29, p = 0.018), while other quartiles were associated with more modest elevations in risk (RR(3rd quartile) = 1.82 (p = 0.10), RR(2nd quartile) = 1.75 (p = 0.10), RR(1st quartile) = 1.43 (p = 0.34) vs non-drinkers (RR = 1.00)). With each higher drink-year quartile, the risk of incident ET increased an average of 23% (p = 0.01, test for trend).

CONCLUSIONS

Higher levels of chronic ethanol consumption increased the risk of developing ET. Ethanol is often used for symptomatic relief; studies should explore whether higher consumption levels are a continued source of underlying cerebellar neurotoxicity in patients who already manifest this disease.

Prevalence of essential tremor in a multiethnic, community-based study in northern Manhattan, New York, N.Y

BACKGROUND

Our aims were to: (1) estimate the prevalence of essential tremor (ET) in a community-based study in northern Manhattan, New York, N.Y., USA; (2) compare prevalence across ethnic groups, and (3) provide prevalence estimates for the oldest old.

METHODS

This study did not rely on a screening questionnaire. Rather, as part of an in-person neurological evaluation, each participant produced several handwriting samples, from which ET diagnoses were assigned.

RESULTS

There were 1,965 participants (76.7 +/- 6.9 years, range = 66-102 years); 108 had ET [5.5%, 95% confidence interval (CI) = 4.5-6.5%]. Odds of ET were robustly associated with Hispanic ethnicity versus white ethnicity [odds ratio (OR) = 2.19, 95% CI = 1.03-4.64, p = 0.04] and age (OR = 1.14, 95% CI = 1.03-1.26, p = 0.01), i.e. with every 1 year advance in age, the odds of ET increased by 14%. Prevalence reached 21.7% among the oldest old (age > or = 95 years).

CONCLUSIONS

This study reports a significant ethnic difference in the prevalence of ET. The prevalence of ET was high overall (5.5%) and rose markedly with age so that in the oldest old, more than 1 in 5 individuals had this disease.

Structural study of Purkinje cell axonal torpedoes in essential tremor

Essential tremor (ET) is one of the most common neurological diseases. A basic understanding of its neuropathology is now emerging. Aside from Purkinje cell loss, a prominent finding is an abundance of torpedoes (rounded swellings of Purkinje cell axons). Such swellings often result from the mis-accumulation of cell constituents. Identifying the basic nature of these accumulations is an important step in understanding the underlying disease process. Torpedoes, only recently identified in ET, have not yet been characterized ultrastructurally. Light and electron microscopy were used to characterize the structural constituents of torpedoes in ET. Formalin-fixed cerebellar cortical tissue from four prospectively collected ET brains was sectioned and immunostained with a monoclonal phosphorylated neurofilament antibody (SMI-31, Covance, Emeryville, CA). Using additional sections from three ET brains, torpedoes were assessed using electron microscopy. Immunoreactivity for phosphorylated neurofilament protein revealed clear labeling of torpedoes in each case. Torpedoes were strongly immunoreactive; in many instances, two or more torpedoes were noted in close proximity to one another. On electron microscopy, torpedoes were packed with randomly arranged 10-12nm neurofilaments. Mitochondria and smooth endoplasmic reticulum were abundant as well, particularly at the periphery of the torpedo. We demonstrated that the torpedoes in ET represent the mis-accumulation of disorganized neurofilaments and other organelles. It is not known where in the pathogenic cascade these accumulations occur (i.e., whether these accumulations are the primary event or a secondary/downstream event) and this deserves further study.

Hypothetical membrane mechanisms in essential tremor

Background

Essential tremor (ET) is the most common movement disorder and its pathophysiology is unknown. We hypothesize that increased membrane excitability in motor circuits has a key role in the pathogenesis of ET. Specifically, we propose that neural circuits controlling ballistic movements are inherently unstable due to their underlying reciprocal innervation. Such instability is enhanced by increased neural membrane excitability and the circuit begins to oscillate. These oscillations manifest as tremor.

Methods

Postural limb tremor was recorded in 22 ET patients and then the phenotype was simulated with a conductance-based neuromimetic model of ballistic movements. The model neuron was Hodgkin-Huxley type with added hyperpolarization activated cation current (I_h), low threshold calcium current (I_T), and GABA and glycine mediated chloride currents. The neurons also featured the neurophysiological property of rebound excitation after release from sustained inhibition (post-inhibitory rebound). The model featured a reciprocally innervated circuit of neurons that project to agonist and antagonist muscle pairs.

Results

Neural excitability was modulated by changing I_h and/or I_T. Increasing I_h and/or I_T further depolarized the membrane and thus increased excitability. The characteristics of the tremor from all ET patients were simulated when I_h was increased to ~10× the range of physiological values. In contrast, increasing other membrane conductances, while keeping I_h at a physiological value, did not simulate the tremor. Increases in I_h and I_T determined the frequency and amplitude of the simulated oscillations.

Conclusion

These simulations support the hypothesis that increased membrane excitability in potentially unstable, reciprocally innervated circuits can produce oscillations that resemble ET. Neural excitability could be increased in a number of ways. In this study membrane excitability was increased by up-regulating I_h and I_T. This approach suggests new experimental and clinical ways to understand and treat common tremor disorders.

Environmental epidemiology of essential tremor

BACKGROUND

Essential tremor (ET) is one of the most common neurological disorders. Despite this, the disease mechanisms and etiology are not well understood. While susceptibility genotypes undoubtedly underlie many ET cases, no ET genes have been identified thus far. As with many other progressive, degenerative neurological disorders, it is likely that environmental factors contribute to the etiology of ET. Environmental epidemiology is the study in specific populations or communities of the effect on human health of physical, biologic and chemical factors in the external environment. The purpose of this article is to review current knowledge with regards to the environmental epidemiology of ET.

RESULTS

As will be discussed, a series of preliminary case-control studies in recent years has begun to explore several candidate toxins/exposures, including harmane (1-methyl-9H-pyrido[3,4-b]indole), lead and agricultural exposures/pesticides.

CONCLUSIONS

While several initial results are promising, as will be discussed, additional studies are needed to more definitively establish whether these exposures are associated with ET and if they are of etiological importance.

A novel approach to non-biased systematic random sampling: a stereologic estimate of Purkinje cells in the human cerebellum

Non-biased systematic sampling using the principles of stereology provides accurate quantitative estimates of objects within neuroanatomic structures. However, the basic principles of stereology are not optimally suited for counting objects that selectively exist within a limited but complex and convoluted portion of the sample, such as occurs when counting cerebellar Purkinje cells. In an effort to quantify Purkinje cells in association with certain neurodegenerative disorders, we developed a new method for stereologic sampling of the cerebellar cortex, involving calculating the volume of the cerebellar tissues, identifying and isolating the Purkinje cell layer and using this information to extrapolate non-biased systematic sampling data to estimate the total number of Purkinje cells in the tissues. Using this approach, we counted Purkinje cells in the right cerebella of four human male control specimens, aged 41, 67, 70 and 84 years, and estimated the total Purkinje cell number for the four entire cerebella to be 27.03, 19.74, 20.44 and 22.03 million cells, respectively. The precision of the method is seen when comparing the density of the cells within the tissue: 266,274, 173,166, 167,603 and 183,575 cells/cm3, respectively. Prior literature documents Purkinje cell counts ranging from 14.8 to 30.5 million cells. These data demonstrate the accuracy of our approach. Our novel approach, which offers an improvement over previous methodologies, is of value for quantitative work of this nature. This approach could be applied to morphometric studies of other similarly complex tissues as well.