Population-based prospective study of cigarette smoking and risk of incident essential tremor

Association of Diet With Essential Tremor: A Narrative Review

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

Essential tremor

Essential tremor (ET) is one of the most common movement disorders, with a reported >60 million affected individuals worldwide. The definition and underlying pathophysiology of ET are contentious. Patients present primarily with motor features such as postural and action tremors, but may also have other non-motor features, including cognitive impairment and neuropsychiatric symptoms. Genetics account for most of the ET risk but environmental factors may also be involved. However, the variable penetrance and challenges in validating data make gene-environment analysis difficult. Structural changes in cerebellar Purkinje cells and neighbouring neuronal populations have been observed in post-mortem studies, and other studies have found GABAergic dysfunction and dysregulation of the cerebellar-thalamic-cortical circuitry. Commonly prescribed medications include propranolol and primidone. Deep brain stimulation and ultrasound thalamotomy are surgical options in patients with medically intractable ET. Further research in post-mortem studies, and animal and cell-based models may help identify new pathophysiological clues and therapeutic targets and, together with advances in omics and machine learning, may facilitate the development of precision medicine for patients with ET.

Expanding sexual and gender minority research in movement disorders: More than awareness and acceptance

Culturally competent and inclusive care is slowly becoming the standard throughout healthcare institutions. Awareness, acceptance, and inclusion of the sexual and gender minority (SGM) groups in medicine and neurology are progressing. Research in SGM health, although increasing, remains remarkably scant in parkinsonism and other movement disorders, a community whose patient population is on the rise. Most SGM health research in movement disorders only focuses on the symptoms associated with infection by the human immunodeficiency virus and the acquired immunodeficiency syndrome. Multiple clinical and epidemiological research questions remain unaddressed when considering the intersection of movement disorders and SGM health. In this article, we highlight gaps in the care of SGM individuals with movement disorders. First, the prevalence and phenomenology of movement disorders could be different, considering the different rates of risk factors and the use of gender-affirming hormones. Also, the effect of creating a safe environment in healthcare institutions to disclose sexual orientation and gender identity on seeking care, access to resources, and quality of services remains unknown. Moreover, many individuals with movement disorders would require services from multidisciplinary teams or long-term care facilities, which might not consider the needs of SGM patients in their models of care. Last, the effect of social isolation and self-perception (or misperceptions) in the SGM populations on the non-motor and motor symptoms of movement disorders and the treatment plans is not understood.

Etiologic links between environmental and lifestyle factors and Essential tremor

Essential tremor (ET) is one of the most common adult movement disorders, characterized by clinical tremor and other nonmotor symptoms. It is a progressive disease that shares features with other neurodegenerative diseases. ET is a complex disease with both genetic and environmental underpinnings. While genetic forms of ET are well recognized, the role of environmental and lifestyle factors in ET has been debated. Studies suggest that exposure to neurotoxic compounds such as β-carboline alkaloids and ethanol are potential risk factors for ET, while antioxidant intake may be protective. In addition, smoking acts as a protective factor in ET, parallel to its effects in other neurological diseases. New evidence points to pesticide and lead exposure as potential risk factors. There is growing evidence to suggest that environmental and lifestyle factors play a role in ET but additional research is needed in order to completely understand their cause and effect association. There is also a need for larger case-control and prospective cohort studies across different populations to further evaluate the etiological importance of these factors in ET.

Essential Tremor and Parkinson's Disease: Exploring the Relationship

Background

There is longstanding controversy surrounding the possible link between essential tremor (ET) and Parkinson's disease (PD). Inconsistent and unreliable diagnostic criteria may in part account for some of the difficulties in defining the relationship between these two common movement disorders.

Methods

References for this systematic review were identified using PubMed with the search terms "essential tremor" AND "Parkinson's disease" with articles published in English between 1960 and September 2018 included.

Results

In this review we provide evidence that some patients diagnosed with ET have an increased risk of developing PD years or decades after onset of action tremor. There are several still unresolved questions about the link between the two disorders including lack of verifiable diagnostic criteria for the two disorders and marked overlap in phenomenology. Here we review clinical, epidemiologic, imaging, pathologic, and genetic studies that address the ET-PD relationship. Several lines of evidence support the association between ET and PD, including overlapping motor and non-motor features, relatively high prevalence of rapid eye movement sleep behavior disorder (26-43%) in ET patients, increased prevalence of PD in patients with longstanding antecedent ET, increased prevalence of ET in family members of patients with PD, and the presence of Lewy bodies in the brains of some ET patients (15-24%).

Discussion

There is a substantial body of evidence supporting the association between ET and PD within at least a subset of patients, although the nature and possible pathogenic mechanisms of the relationship are not well understood.

Conditions Associated with Essential Tremor in Veterans: A Potential Role for Chronic Stress

Background

Increased depression, hearing loss, dementia, alcoholism, and mortality in essential tremor patients remain unexplained. We investigated whether conditions associated with tremor are linked to chronic stress.

Methods

The FY2013 Veterans Affairs database was queried for 38 selected dual diagnosis combinations in 5,854,223 veterans aged 21–95 years.

Results

Post-traumatic stress disorder, anxiety, and depression were the most common psychiatric diagnoses in tremor patients, with the odds ratio exceeding 2 in all 15-year cohorts. Depending on age, patients with essential tremor were more likely than those without to have obsessive–compulsive disorder, bipolar illness, schizophrenia, use tobacco and abuse alcohol, have hypertension, obesity, hyperlipidemia, diabetes, vitamin D deficiency, coronary and cerebrovascular diseases, congestive heart failure, stroke, asthma, hypothyroidism, irritable bowel syndrome, renal insufficiency, alcoholic liver disease, hearing loss, glaucoma, macular degeneration, migraine, epilepsy, idiopathic polyneuropathy, history of head trauma, and ‘Alzheimer’s dementia. In contrast, lung and colorectal cancer, amyotrophic lateral sclerosis, psychostimulant abuse, and rheumatoid arthritis were not more common.

Discussion

Post-traumatic stress disorder, anxiety, and depression, strongly associated with essential tremor, are known risk factors for poor health habits, tobacco use and alcohol abuse; collectively these are risk factors for vascular disease, with further negative health consequences for multiple organ systems. As essential tremor is associated with all these conditions, we propose that chronic stress is not only responsible for the conditions associated with tremor but in some cases itself directly and indirectly induces essential tremor, so that tremor and poor health share a common cause.

Essential tremor and the cerebellum

Essential tremor (ET) is a progressive and highly prevalent neurologic disease. Along with the tremors, mild to moderate gait ataxia and other signs of cerebellar dysfunction may occur (i.e., subtle saccadic eye movement abnormalities and abnormalities of motor timing) as well as cognitive features, some of which may be due to cerebellar dysfunction. Numerous neuroimaging studies indicate the presence of functional, metabolic, and structural abnormalities in the cerebellum of a patient with ET. In tandem with these clinical and imaging studies, which were gathering increasing support for the notion that the cerebellum and/or cerebellar systems seemed to be at the root of ET, a growing postmortem literature is for the first time beginning to identify microscopic abnormalities in the ET brain, most of which are centered on the Purkinje cells and connected neuronal populations, and are likely to be degenerative. In terms of treatment, most of these pharmacotherapeutic agents serve to enhance GABAergic neurotransmission, further bolstering the notion that ET may very well be a disorder with a primary Purkinje cell dysfunction resulting in reduced cerebellar cortical inhibition. Similarly, the interruption of presumably abnormal cerebellar outflow pathways to the thalamus is the mechanism of deep-brain stimulation surgery, which is highly effective in treating ET.

Basal Forebrain Cholinergic Circuits and Signaling in Cognition and Cognitive Decline

Recent work continues to place cholinergic circuits at center stage for normal executive and mnemonic functioning and provides compelling evidence that the loss of cholinergic signaling and cognitive decline are inextricably linked. This Review focuses on the last few years of studies on the mechanisms by which cholinergic signaling contributes to circuit activity related to cognition. We attempt to identify areas of controversy, as well as consensus, on what is and is not yet known about how cholinergic signaling in the CNS contributes to normal cognitive processes. In addition, we delineate the findings from recent work on the extent to which dysfunction of cholinergic circuits contributes to cognitive decline associated with neurodegenerative disorders.

[Essential tremor in endemic disease control agents exposed to pesticides: a case-control study]

Tremor is the most frequent movement disorder in the population and can be associated with pesticide exposure. The aim was to assess the odds of essential tremor in 442 endemic disease control agents in Rio de Janeiro State, Brazil, exposed to pesticides. Fifty-one cases and 204 controls were selected (1:4). All participants answered a questionnaire on socio-demographic, occupational, and toxicological items. The influence of pesticide exposure on the development of tremor was estimated by non-conditional logistic regression, adjusted for selected covariables. Mean age of the study population was 49 (SD = 7) years, and the difference between cases (mean = 50.8; SD = 6.9) and controls (mean = 48.5; SD = 6.9) was statistically significant (p = 0.03). Those with 16 to 16.9 years of pesticide use showed the highest odds of essential tremor (adjusted OR = 4.60; 95%CI: 1.29-16.41). Our results suggest that 16 to 16.9 years of pesticide exposure had a major impact on the development of essential tremor.

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.

Statin Use and Its Association with Essential Tremor and Parkinson's Disease

BACKGROUND

Statins have potent anti-inflammatory and immunomodulating effects, and may have neuroprotective properties in patients with Parkinson's disease (PD). There are no studies about the use of statins in the related tremor disorder, essential tremor (ET). We determined whether statin use differed in ET cases vs. controls and PD cases vs.

METHODS

One hundred and thirty nine ET cases, 108 PD cases, and 124 controls participated in a research study of the epidemiology of movement disorders. They were frequency matched based on age and gender. Statin use was assessed by self-report.

RESULTS

In adjusted logistic regression analyses, statin use (current or ever) was inversely associated with PD (ORs 0.56-0.63), with marginal values (p values = 0.07-0.187). In similar adjusted models, ET was not associated with statin use (p values = 0.45-0.50). However, ET was inversely associated with longer-term statin use (adjusted OR 0.27, p values = 0.04-0.048).

CONCLUSIONS

We observed a marginally significant inverse association between PD and statin use. Although in primary analyses we found no evidence that statin use was protective in ET, there was an inverse association in analyses that assessed longer term use of statins. Further observational studies are warranted.

Serious head trauma preceding essential tremor: A population-based study (NEDICES)

BACKGROUND

An association between head trauma and essential tremor (ET) has not been formally assessed. Our purpose was to assess the association between serious head trauma and ET.

METHODS

History of head trauma was assessed in 274 ET cases and 3201 controls in the Neurological Disorders in Central Spain (NEDICES) study, a population-based study in central Spain. Head trauma was defined as serious only if the subject reported that the trauma resulted in loss of consciousness, hospitalization, or a visit to the emergency department.

RESULTS

Thirty-two (11.7%) of 274 ET cases vs. 260 (8.1%) of 3201 controls reported a history of serious head trauma (p=0.04). In an adjusted logistic regression analysis, participants who reported serious head trauma were 52% more likely to have ET (odds ratio [OR] 1.52; 95% confidence interval [CI] 1.02-2.27, p=0.04). The odds of ET increased with increasing age of head trauma: adjusted ORs=1.23 (95% CI 0.43-3.46, p = 0.70) for serious head trauma that occurred before age 18 years, adjusted OR=1.49 (95% CI 0.62-3.55, p = 0.37) for serious head trauma between ages 18 to 39 years, and adjusted OR=1.61 (95% CI 1.00-2.57, p = 0.04) for serious head trauma at age 40 years or older.

CONCLUSIONS

Our study suggests that serious head trauma, especially when it occurs after 40 years, is associated with increased odds of ET. Additional studies are needed to reproduce this novel finding.

Human α4β2 nicotinic acetylcholine receptor as a novel target of oligomeric α-synuclein

Cigarette smoking is associated with a decreased incidence of Parkinson disease (PD) through unknown mechanisms. Interestingly, a decrease in the numbers of α4β2 nicotinic acetylcholine receptors (α4β2-nAChRs) in PD patients suggests an α4β2-nAChR-mediated cholinergic deficit in PD. Although oligomeric forms of α-synuclein have been recognized to be toxic and involved in the pathogenesis of PD, their direct effects on nAChR-mediated cholinergic signaling remains undefined. Here, we report for the first time that oligomeric α-synuclein selectively inhibits human α4β2-nAChR-mediated currents in a dose-dependent, non-competitive and use-independent manner. We show that pre-loading cells with guanyl-5'-yl thiophosphate fails to prevent this inhibition, suggesting that the α-synuclein-induced inhibition of α4β2-nAChR function is not mediated by nAChR internalization. By using a pharmacological approach and cultures expressing transfected human nAChRs, we have shown a clear effect of oligomeric α-synuclein on α4β2-nAChRs, but not on α4β4- or α7-nAChRs, suggesting nAChR subunit selectivity of oligomeric α-synuclein-induced inhibition. In addition, by combining the size exclusion chromatography and atomic force microscopy (AFM) analyses, we find that only large (>4 nm) oligomeric α-synuclein aggregates (but not monomeric, small oligomeric or fibrillar α-synuclein aggregates) exhibit the inhibitory effect on human α4β2-nAChRs. Collectively, we have provided direct evidence that α4β2-nAChR is a sensitive target to mediate oligomeric α-synuclein-induced modulation of cholinergic signaling, and our data imply that therapeutic strategies targeted toward α4β2-nAChRs may have potential for developing new treatments for PD.

Harmaline tremor: underlying mechanisms in a potential animal model of essential tremor

BACKGROUND

Harmaline and harmine are tremorigenic β-carbolines that, on administration to experimental animals, induce an acute postural and kinetic tremor of axial and truncal musculature. This drug-induced action tremor has been proposed as a model of essential tremor. Here we review what is known about harmaline tremor.

METHODS

Using the terms harmaline and harmine on PubMed, we searched for papers describing the effects of these β-carbolines on mammalian tissue, animals, or humans.

RESULTS

Investigations over four decades have shown that harmaline induces rhythmic burst-firing activity in the medial and dorsal accessory inferior olivary nuclei that is transmitted via climbing fibers to Purkinje cells and to the deep cerebellar nuclei, then to brainstem and spinal cord motoneurons. The critical structures required for tremor expression are the inferior olive, climbing fibers, and the deep cerebellar nuclei; Purkinje cells are not required. Enhanced synaptic norepinephrine or blockade of ionic glutamate receptors suppresses tremor, whereas enhanced synaptic serotonin exacerbates tremor. Benzodiazepines and muscimol suppress tremor. Alcohol suppresses harmaline tremor but exacerbates harmaline-associated neural damage. Recent investigations on the mechanism of harmaline tremor have focused on the T-type calcium channel.

DISCUSSION

Like essential tremor, harmaline tremor involves the cerebellum, and classic medications for essential tremor have been found to suppress harmaline tremor, leading to utilization of the harmaline model for preclinical testing of antitremor drugs. Limitations are that the model is acute, unlike essential tremor, and only approximately half of the drugs reported to suppress harmaline tremor are subsequently found to suppress tremor in clinical trials.

The NEDICES Study: Recent Advances in the Understanding of the Epidemiology of Essential Tremor

BACKGROUND

Essential tremor (ET) is the most common tremor disorder. ET has classically been viewed as a benign monosymptomatic condition. Yet over the past 10 years, a growing body of evidence indicates that this is a progressive condition that is clinically heterogeneous, and may be associated with a variety of different features. Large epidemiological studies such as the Neurological Disorders of Central Spain (NEDICES), a longitudinal, population-based survey, have contributed significantly to the changing view of the disease. Our aim is to review some of the main results of NEDICES within the larger framework of the epidemiology of ET.

METHODS

Data for this review were gathered from all our articles published up to October 2011 regarding NEDICES study and "Essential Tremor".

RESULTS

We have published 18 articles up to October 2011. The prevalence, incidence, and mortality of ET were analyzed in this cohort. In addition, ET was found to be associated with increased frailty and low morale, as well as with a series of non-motor manifestations, including cognitive deficits, mild cognitive impairment, dementia, depressive symptoms, and hearing impairment. Finally, the link between ET and Parkinson's disease (PD) was formally quantified in the NEDICES study, which demonstrated that the risk of developing incident PD was 4.3 times higher in prevalent ET cases than in age-matched controls without ET.

CONCLUSIONS

This review highlights the contributions of NEDICES towards the advancement of current knowledge of the epidemiology and clinical features of ET, and emphasizes the importance of population-based studies towards the understanding of complex, ageing-related diseases.

Screening for action tremor in epidemiological field surveys: assessing the reliability of a semi-quantitative, visual, template-based scale for rating hand-drawn spirals

BACKGROUND

Population-based epidemiological studies of essential and other tremors have need of a rapid yet accurate means to assess tremor, especially mild tremors. Handwriting is often affected by tremor, and a hand-drawn spiral can provide investigators with objective rather than self-reported data. We present a semi-quantitative, ordinal scale to rate hand-drawn spirals. The scale, which includes values for mild tremor, is accompanied by photographic examples of spirals of each rating, providing a visual template for guidance.

METHODS

This study, conducted within the framework of a population-based epidemiological study of 5,000 individuals aged 60 and older in Shanghai, asked enrollees to draw an Archimedes spiral with each hand. Spirals were rated using an ordinal scale (0, 0.5, 1, 1.5, 2, and 3). Three raters rated an initial set of 548 spirals. Four raters rated a subsequent set of 200 spirals using a visual template for guidance.

RESULTS

Initial agreement (548 spirals) was good (r values ranged from 0.49 to 0.62, all p<0.001). Subsequent agreement (200 spirals and using visual template) improved (r values ranged from 0.67 to -0.91, all p<0.001).

DISCUSSION

This tool will be useful to researchers who are attempting to rapidly assess action tremor in their field surveys.

[Neuropsychiatric disturbances in essential tremor]

This review focuses on the neuropsychiatric manifestations (personality disturbances, depressive symptoms, cognitive impairment and dementia), which have been described in this last decade in patients with essential tremor. We compared the data derived from the Neurologic Disorders in Central Spain (NEDICES) study, a prospective population-based survey, with those derived from the literature. The traditional view of essential tremor as a mono-symptomatic condition characterized by action tremor is now changing. First, it is known that many patients also have other motor manifestations apart from tremor (e.g., ataxic gait). Second, in the last years, the presence of a variety of non-motor neuropsychiatric features has been described. Mild cognitive changes (especially executive dysfunction) have been documented in several independent studies. Further, two population-based studies have demonstrated an association between essential tremor with mild cognitive impairment and dementia. Psychiatric manifestations include specific personality traits, anxiety, social phobia, and depressive symptoms. Taking together, the neuropsychiatric dysfunction pattern and the new data on neuropathology of essential tremor suggest that this disease is a neurodegenerative cerebellar disorder and let us to question the classical concept of essential tremor as a benign mono-symptomatic disorder.

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.

Methods and design of the baseline survey of the neurological disorders in Salamanca (NEDISA) cohort: a population-based study in Central-Western Spain

BACKGROUND

To describe the design of the baseline assessment of an epidemiological study of elderly persons living in Salamanca, central-western Spain: the Neurological Diseases in Salamanca (NEDISA) study. We assessed the epidemiology of stroke, cognitive disorders, essential tremor (ET), Parkinson's disease (PD) and restless legs syndrome.

METHODS

In phase 1 (February 1 to May 31, 2007), 4 neurologists and 2 trained general physicians examined and performed phlebotomy on all participants. In phase 2 (June 1, 2007, to June 1, 2008), the participants were reexamined and had a complete neuropsychological assessment. Neuroimaging was performed in participants with cognitive disorders, ET and PD.

RESULTS

The registered study population consisted of 1,077 individuals, but 45 people were ineligible (address change, refusals or death), leaving a final sample of 1,032 (95.8%). The main demographic data on the 1,032 participants (408 men, 624 women) are provided.

CONCLUSIONS

Most of the registered study population was enrolled, and this may have been due to the close relationship between NEDISA researchers and the general physicians in the area of study. The NEDISA study will likely improve our knowledge of prevalence rates of the neurological diseases chosen for study as well as the set of risk factors that predispose individuals in Spain to these disorders.

Epidemiology and management of essential tremor in children

Essential tremor (ET) is a common, often familial, movement disorder characterized by tremor of the limbs, head, and voice. Epidemiological surveys indicate that up to 5% of the adult population has ET, and 5-30% of adults with ET report symptom onset during childhood. There is, however, little published regarding ET in the pediatric population, and no prospective studies targeted specifically to children. Retrospective studies from subspecialty movement disorder clinics indicate that childhood-onset ET is usually hereditary, begins at a mean age of 6 years, and affects boys three times as often as girls. While ET occasionally results in disability during childhood, only one-quarter of children seeing a neurologist for ET require pharmacotherapy. Small case series suggest that propranolol is effective in approximately 50% of children with ET, but controlled treatment trials are lacking.

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.

Apolipoprotein E polymorphism interacts with cigarette smoking in progression of multiple sclerosis

BACKGROUND AND PURPOSE

The influence of apolipoprotein E (ApoE) polymorphism on clinical severity of multiple sclerosis (MS) is still controversial. Cigarette smoking has been suggested to influence the progression of disability in these patients. In this study, we aimed to investigate whether an interaction of smoking with the ApoE polymorphism influences the progression of disability in MS patients.

METHODS

Smoking history from 205 female patients with MS was obtained. Clinical data collected include age at onset, disease duration, annual relapse rate, the Expanded Disability Status Scale (EDSS) and the Multiple Sclerosis Severity Score (MSSS). ApoE polymorphism was examined in all patients and stratified according to smoking status and associations with the clinical data investigated.

RESULTS

There were no significant associations between cigarette smoking and any of the clinical characteristics in the whole group of patients. In women carrying the ApoE E4 isoform, smokers had a lower EDSS (P = 0.033) and MSSS (P = 0.023) in comparison with non-smokers.

CONCLUSION

Our data suggest that in women with MS carrying the ApoE E4 isoform, cigarette smoking may have a protective influence on disease progression and accumulation of disability. These findings need to be confirmed by future large longitudinal studies.

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.