Unawareness of head tremor in essential tremor: a study of three samples of essential tremor patients

Botulinum toxin for motor disorders

Botulinum neurotoxins are a group of biological toxins produced by the gram-negative bacteria Clostridium botulinum. After intramuscular injection, they produce dose-related muscle relaxation, which has proven useful in the treatment of a large number of motor and movement disorders. In this chapter, we discuss the utility of botulinum toxin treatment in three major and common medical conditions related to the dysfunction of the motor system, namely dystonia, tremor, and spasticity. A summary of the existing literature is provided along with different techniques of injection including those recommended by the authors.

Essential tremor

Essential tremor (ET) is a chronic and progressive neurologic disease. Its central and defining clinical feature is a 4-12Hz kinetic tremor, that is, tremor that occurs during voluntary movements such as drinking from a cup or writing. Patients may also exhibit a range of other tremors-postural, rest, intention, additional motor features (e.g., mild gait ataxia, mild dystonia), as well as nonmotor features. The disease itself seems to be a risk factor for other degenerative diseases such as Alzheimer's disease and Parkinson's disease. Both genetic and toxic environmental factors have been explored as etiologic factors. In addition to a growing appreciation of the presence of clinical, etiologic, and pathologic heterogeneity, there is some support for the notion that ET itself may not be a single disease, but may be a family of diseases whose central defining feature is kinetic tremor of the arms, and which might more accurately be referred to as "the essential tremors." Recent research has increasingly placed the seat of the disease in the cerebellum and cerebellar system and identified a host of neurodegenerative changes within the cerebellum, indicating that this progressive disorder is likely degenerative.

Essential tremor: a nuanced approach to the clinical features

Click here to listen to the Podcast Essential tremor is the most common form of tremor in humans. Given neurologists' high exposure to this condition, and its seemingly straightforward phenotype, it might seem easy to diagnose. However, 30%-50 % of patients labelled as having 'essential tremor' have other diagnoses, mostly Parkinson's disease and dystonia. The tremor of essential tremor is neither non-descript nor featureless but is multifaceted and highly patterned. This review focuses on its clinical features, beginning with a discussion of tremors and then briefly discussing its additional motor features, and presents several aids to help distinguish essential tremor from Parkinson's disease and dystonia. Careful attention to certain clinical nuances will aid the diagnosis and care of patients with essential tremor.

Early Head Tremor in Essential Tremor: A Case Series and Commentary

BACKGROUND

Classically, the onset of head tremor in essential tremor (ET) patients follows that of hand tremor, such that there is a somatotopic spread of involved areas. Here we present a series of seven self-reportedly "unaffected" relatives of ET cases. These seven were clinically asymptomatic and had normal levels of arm tremor on examination, yet each evidenced a transient head wobble on examination. We estimate the prevalence of this phenotype within the two studies from which cases were ascertained.

METHODS

ET cases and their self-reportedly affected and unaffected relatives, enrolled in two family studies, underwent a medical history and videotaped neurological examination.

RESULTS

In seven self-reportedly "unaffected" relatives, a transient and subtle head wobble was seen, always during sustained phonation, speech, or reading aloud. Total tremor score (a measure of arm tremor) ranged from 5 to 12 (i.e., mild tremor within the range of normal). The prevalence of this phenotype of early head tremor was 3.7% in one study and 23.1% in the other.

DISCUSSION

We present a series of seven individuals who had early head tremor in an evolving transition state from normal to ET. These cases raise a number of broad clinical, phenotypic, and pathophysiological issues about ET.

Agnosia for head tremor in essential tremor: prevalence and clinical correlates

BACKGROUND

Lack of awareness of involuntary movements is a curious phenomenon in patients with certain movement disorders. An interesting anecdotal observation is that patients with essential tremor (ET) often seem unaware of their own head tremor. In the current study, we asked ET patients whether they were aware of head tremor while it was occurring on examination, thereby allowing us to gauge real-time awareness of their involuntary movement.

METHODS

ET cases enrolled in an ongoing clinical research study at the Columbia University Medical Center (2009-2014). During a videotaped tremor examination, they were questioned about the presence of head tremor. True positives were cases who exhibited head tremor on examination and were aware of it; false negatives were cases who exhibited head tremor but were unaware of it.

RESULTS

The 126 ET cases had a mean age of 72.6 ± 12.4 years. Nineteen (48.7 %) of 39 cases with head tremor on examination did not report having head tremor at that moment. Even among cases with moderate or severe head tremor on examination, unawareness of head tremor was 45.5 %. We assessed the clinical correlates of unawareness of head tremor, comparing true positives to false negatives, and unawareness was correlated with older age, lower mental status test scores and several other clinical variables.

CONCLUSIONS

Nearly one-half of ET cases with head tremor on examination were acutely unaware of their tremor. Whether such agnosia for tremor may be leveraged as a diagnostic feature of ET is a question for future clinical studies.

Challenges in essential tremor genetics

The field of essential tremor (ET) genetics remains extremely challenging. The relative lack of progress in understanding the genetic etiology of ET, however, does not reflect the lack of a genetic contribution, but rather, the presence of substantial phenotypic and genotypic heterogeneity. A meticulous approach to phenotyping is important for genetic research in ET. The only tool for phenotyping is the clinical history and examination. There is currently no ET-specific serum or imaging biomarker or defining neuropathological feature (e.g., a protein aggregate specific to ET) that can be used for phenotyping, and there is considerable clinical overlap with other disorders such as Parkinson's disease (PD) and dystonia. These issues greatly complicate phenotyping; thus, in some studies, as many as 30-50% of cases labeled as "ET" have later been found to carry other diagnoses (e.g., dystonia, PD) rather than ET. A cursory approach to phenotyping (e.g., merely defining ET as an "action tremor") is likely a major issue in some family studies of ET, and this as well as lack of standardized phenotyping across studies and patient centers is likely to be a major contributor to the relative lack of success of genome wide association studies (GWAS). To dissect the genetic architecture of ET, whole genome sequencing (WGS) in carefully characterized and well-phenotyped discovery and replication datasets of large case-control and familial cohorts will likely be of value. This will allow specific hypotheses about the mode of inheritance and genetic architecture to be tested. There are a number of approaches that still remain unexplored in ET genetics, including the contribution of copy number variants (CNVs), '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 non-coding variation. Using these approaches is likely to yield new ET genes.

Are patients with limb and head tremor a clinically distinct subtype of essential tremor?

BACKGROUND

Essential tremor (ET) is the most common tremor disorder in adults. In addition to upper limbs, the tremor in ET may also involve head, jaw, voice, tongue, and trunk. Though head tremor (HT) is commonly present in patients with ET, large comparative studies of ET patients with HT (HT+) and without HT (HT-) are few.

METHODS

To determine whether ET with HT is a distinct clinical subtype by comparing ET patients with and without HT, a chart review of 234 consecutive patients with ET attending the neurology clinics of the National Institute of Mental Health and Neurosciences, India, was done. A movement disorder specialist confirmed the diagnosis of ET in all patients using the National Institutes of Health collaborative genetic criteria.

RESULTS

HT was present in 44.4% of the patients. Comparison between HT+ and HT- showed that the HT+ group patients: (1) were older, (2) had later onset of tremor, (3) had unimodal distribution of age at onset with a single peak in the fifth decade, (4) had more frequent voice tremor, and (5) were more likely to have mild cervical dystonia. HT was part of presenting symptoms in nearly two thirds of the ET patients and in the rest it was detected during clinical examination.

CONCLUSIONS

Several demographic and clinical variables suggest that ET patients with HT have a distinct clinical phenotype.

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.

Validity of a screening question for head tremor: an analysis of four essential tremor case samples

BACKGROUND

The goal of this study was to assess the validity of a screening question for head tremor in essential tremor (ET). There are no published data on this topic, and the knowledge will guide future epidemiological investigations of this disorder.

METHODS

These analyses utilized four distinct patient samples: a population-based study in northern Manhattan, a study of the environmental epidemiology of ET, a genetics study, and a brain repository. Sensitivity was the proportion of ET cases with head tremor on examination who self-reported head tremor.

RESULTS

The sensitivity of the screening question for head tremor was lowest in the population-based study (31.6%), and higher as well as somewhat similar across the remaining studies (46.7 to 62.2%). Higher sensitivity was associated with tremor of longer duration, presence of voice tremor on examination, female gender, and lower education. The use of the screening question would have increased case ascertainment during the screening phase of these four studies by 1.9, 4.1, 10.2, and 20.3%.

CONCLUSIONS

A screening question for head tremor had low-to-moderate sensitivity in ET. The use of such a screening questionnaire, however, has the potential to increase case ascertainment by as much as 20% in some screening settings.

Twelve clinical pearls to help distinguish essential tremor from other tremors

The features of the tremor in essential tremor are often not fully appreciated, and essential tremor is frequently mis-diagnosed. Close inspection indicates that the tremor is characterized by a specific and definable pattern of features. Recognizing these features will aid in the diagnosis. The features are as follows: (1) kinetic tremor is greater than postural tremor, for postural tremor, (2) wrist tremor is greater than metacarpal joint tremor and wrist flexion-extension tremor is greater than wrist rotation tremor, (3) tremor is regularly recurrent and without directionality, (4) arm tremor is generally mildly asymmetric, (5) postural tremors (right, left) are out of phase, (6) on spiral drawing, a single tremor orientation axis is often identifiable, (7) intention tremor (finger-nose-finger) occurs in 50% of cases, (8) rest tremor (in the arms but not the legs) can occur as a late feature, (9) arm tremor precedes head tremor, and head tremor occurs mainly in women, (10) head tremor, unless severe, resolves while supine, (11) patients are often unaware of head tremor, (12) tremor is progressive.

Distinguishing essential tremor from Parkinson's disease: bedside tests and laboratory evaluations

Distinguishing essential tremor from Parkinson's disease can be challenging, both in the early stages of these diseases and as these diseases progress. Various tremor types (rest, postural, kinetic and intention) may be seen in both essential tremor and Parkinson's disease. Furthermore, with time, the two diseases may coexist within a single patient. Detailed clinical examination with attention to specific features of tremor (frequency, amplitude, pattern and distribution) and associated neurological findings may help distinguish patients with the two diseases. Laboratory testing may provide information that further aids in differentiating the two diseases. These tests include accelerometry and surface electromyography, spiral analysis, dopamine transporter imaging, olfactory testing and, eventually, postmortem histopathology. These tests have limitations and their diagnostic utility requires additional study.

Essential tremor, the cerebellum, and motor timing: towards integrating them into one complex entity

Essential tremor (ET) is the most common movement disorder in humans. It is characterized by a postural and kinetic tremor most commonly affecting the forearms and hands. Isolated head tremor has been found in 1-10% of patients, suggesting that ET may be a composite of several phenotypes. The exact pathophysiology of ET is still unknown. ET has been repeatedly shown as a disorder of mild cerebellar degeneration, particularly in postmortem studies. Clinical observations, electrophysiological, volumetric and functional imaging studies all reinforce the fact that the cerebellum is involved in the generation of ET. However, crucial debate exists as to whether ET is a neurodegenerative disease. Data suggesting that it is neurodegenerative include postmortem findings of pathological abnormalities in the brainstem and cerebellum, white matter changes on diffusion tensor imaging, and clinical studies demonstrating an association with cognitive and gait changes. There is also conflicting evidence against ET as a neurodegenerative disease: the improvement of gait abnormalities with ethanol administration, lack of gray matter volume loss on voxel-based morphometry, failure to confirm the prominent presence of Lewy bodies in the locus ceruleus, and other pathological findings. To clarify this issue, future research is needed to describe the mechanism of cellular changes in the ET brain and to understand the order in which they occur. The cerebellum has been shown to be involved in the timing of movement and sensation, acting as an internal timing system that provides the temporal representation of salient events spanning hundreds of milliseconds. It has been reported that cerebellar timing function is altered in patients with ET, showing an increased variability of rhythmic hand movements as well as diminished performance during predictive motor timing task. Based on current knowledge and observations, we argue that ET is essentially linked with cerebellar degeneration, or at least cerebellar dysfunction, together with disturbance of motor timing. We explain the context of our current understanding on this topic, highlighting possible clinical consequences for patients suffering from ET and future research directions.

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.